Author Topic: Off Grid Solar Systems  (Read 4698 times)

FI Curious

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Off Grid Solar Systems
« on: January 20, 2018, 08:07:28 AM »
I recently discovered that the Tesla Powerwall is not available for off-grid installation.  This seems completely counter intuitive to me since it seems like the Powerwall would be a nice solution for storage for off-grid systems.  So now I'm considering battery back up options.  Does anyone have information about where to start looking and what the best options might be?

Syonyk

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Re: Off Grid Solar Systems
« Reply #1 on: January 20, 2018, 08:59:52 AM »
Let's rewind a bit.

What is your current power setup, and what are you looking to actually do, with what specifications?

Are you currently grid tied and looking for backup power for power outages?  The right answer is an automatic transfer switch and a generator, ideally one tied to your home's natural gas line.

Are you building a new off grid structure and looking at batteries?  In that case, the Powerwall is certainly the wrong answer, for a variety of reasons.

If you're grid tied and want instant power switchover to backup in the event of a power outage, I don't believe the Powerwall can even do that, either, though I'm not certain because there are no specs available for the switchover time and how it interfaces with transfer switches.  The right answer for something like that would be the Outback Radian, in UPS mode, with a large chunk of your home post-inverter as a critical load.  I believe that particular configuration can charge from a generator as well for indefinite grid down runtime (as long as you have generator fuel or solar panels feeding the system).

The Powerwall is, from my (solar powered office) point of view, a gimmick.  It was Tesla's way of saying, "Look, there's a ton of demand for this other battery gizmo, we promise we can find some way to sell all the batteries you build even if car sales flop, will you please invest in building out this factory???" to Panasonic.  It's not a useful product, it's a corporate backstop.

The Powerwall is very useful to people with lots of money who want to "be on the list for a Powerwall" for their local social circle green cred.  It's a fairly small down payment with no guarantees at all of delivery, so there's no chance you might have to actually get one and deal with their limitations (which you won't know about until you buy it, mostly).

I'd be able to say more about it if there were detailed specifications and operator's manuals out for it, but, lol.  It's Tesla.  Pay your money and you get something.  Eventually.  Maybe.

Here's what passes for technical documentation on the Powerwall: https://www.tesla.com/sites/default/files/pdfs/powerwall/Powerwall%202_AC_Datasheet_en_northamerica.pdf

Here's what passes for technical documentation on the Outback Radian I mentioned earlier: http://www.outbackpower.com/outback-products/make-the-power/radian-series-inverter-chargers/item/radian-series-gs8048a-gs4048a?category_id=529 - it's the whole right side of the page.  There are hundreds of pages of PDF I can go through to find out if it will work for my particular use cases and how to configure it.

============

Now, minor rant finished, you are asking about batteries.  And they're a bit of a hobby of mine.

For a daily cycled off grid system (which is what I have for my office), I highly recommend flooded lead acid.  They're a good fit for the nature of off grid usage, especially with solar (you won't be cycling them very deeply in the summer), and you can keep them outside because they don't care about temperature, though if it gets extremely cold you may want to shelter them somewhat as they can freeze if it's cold enough and they're discharged enough.  Plus you get less power out of them in the winter, which is a bit annoying.

For standby use (where a battery is mostly sitting charged and waiting around to be used), flooded doesn't work as well.  AGM is the way to go.  They tolerate sitting around like that a lot better - you don't have acid stratification issues.  And they're sealed, which means no offgassing to deal with under normal operation (they should still be vented, but they don't normally offgas hydrogen).

Gel batteries are best avoided for any use cases, and this includes marketing names such as "lead silicone" and "silica crystal" and "lead crystal" and anything like that.  They're new age woo applied to battery marketing.

Now, if you want lithium, which does have advantages (but not as strong of advantages as most people seem to think), the best way to go off grid is LiFePO4 packs.  That's an older, lower energy density chemistry that's quite safe in operation (it's quite tightly chemically bound, which is useful), and it has a very flat discharge voltage curve.  A group of 4 LiFePO4 cells is almost identical, voltage-wise, to a standard 6S lead acid configuration (12V), so you can use lead acid designed inverters and chargers easily enough.  For a typical house configuration, 48V is the way to go.  You will need some balancing interface, which isn't a common part, but otherwise LiFePO4 is awesome.  Longer cycle life, very good power density, and doesn't gas.  However, you have to keep them warm.  They can't get cold and charge safely, so you'll need space inside for them.

If you really want a plug and play lithium pack, look at some of LG's offerings.  They've got a high voltage (~400V) pack that's comparable in how it interacts with the system to the PowerWall Gen 1, and a lower voltage pack (~48V) that interfaces like a big lead acid string, more or less.  However, I don't know much about those, and it's hard to find good information - I believe you need a compatible inverter.

Also, in the context of this forum, it's worth noting that the moment you say "battery," your power system is now super expensive and will never beat grid power in terms of operating cost.  It just won't.  So you'd better value backup capacity a lot.

I plan to do this on my house, mostly because it's an interesting system and I value reliable power for a few reasons, but I also plan to install a lot of my system myself (and am in a part of the country where I can likely find an electrician to sign off on my work).  Solar on the roof, a Radian unit with most of the house as a critical load subpanel, and a moderately sized battery bank in the crawlspace (either LiFePO4 or AGM, though probably AGM because I'm going to be stretching the limits of what local electricians are used to already, so AGM will probably be easier to get approved).  I expect long conversations with the power company about what I'm doing as well, because it's not the usual grid tied system.

Cork

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Re: Off Grid Solar Systems
« Reply #2 on: January 20, 2018, 10:36:18 AM »

This is the type of content  that keeps me coming back to this forum.  Thanks for the detailed post, Syonyk.  I really enjoy learning about off grid battery tech.

Syonyk

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Re: Off Grid Solar Systems
« Reply #3 on: January 20, 2018, 11:03:49 AM »
That's a short summary. :/

I've got some far longer posts in the works on the care and feeding of lead acid batteries coming on my blog.

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Re: Off Grid Solar Systems
« Reply #4 on: January 20, 2018, 11:24:53 AM »
Let's rewind a bit.

What is your current power setup, and what are you looking to actually do, with what specifications?

Are you currently grid tied and looking for backup power for power outages?  The right answer is an automatic transfer switch and a generator, ideally one tied to your home's natural gas line.

Are you building a new off grid structure and looking at batteries?  In that case, the Powerwall is certainly the wrong answer, for a variety of reasons.

If you're grid tied and want instant power switchover to backup in the event of a power outage, I don't believe the Powerwall can even do that, either, though I'm not certain because there are no specs available for the switchover time and how it interfaces with transfer switches.  The right answer for something like that would be the Outback Radian, in UPS mode, with a large chunk of your home post-inverter as a critical load.  I believe that particular configuration can charge from a generator as well for indefinite grid down runtime (as long as you have generator fuel or solar panels feeding the system).

The Powerwall is, from my (solar powered office) point of view, a gimmick.  It was Tesla's way of saying, "Look, there's a ton of demand for this other battery gizmo, we promise we can find some way to sell all the batteries you build even if car sales flop, will you please invest in building out this factory???" to Panasonic.  It's not a useful product, it's a corporate backstop.

The Powerwall is very useful to people with lots of money who want to "be on the list for a Powerwall" for their local social circle green cred.  It's a fairly small down payment with no guarantees at all of delivery, so there's no chance you might have to actually get one and deal with their limitations (which you won't know about until you buy it, mostly).

I'd be able to say more about it if there were detailed specifications and operator's manuals out for it, but, lol.  It's Tesla.  Pay your money and you get something.  Eventually.  Maybe.

Here's what passes for technical documentation on the Powerwall: https://www.tesla.com/sites/default/files/pdfs/powerwall/Powerwall%202_AC_Datasheet_en_northamerica.pdf

Here's what passes for technical documentation on the Outback Radian I mentioned earlier: http://www.outbackpower.com/outback-products/make-the-power/radian-series-inverter-chargers/item/radian-series-gs8048a-gs4048a?category_id=529 - it's the whole right side of the page.  There are hundreds of pages of PDF I can go through to find out if it will work for my particular use cases and how to configure it.

============

Now, minor rant finished, you are asking about batteries.  And they're a bit of a hobby of mine.

For a daily cycled off grid system (which is what I have for my office), I highly recommend flooded lead acid.  They're a good fit for the nature of off grid usage, especially with solar (you won't be cycling them very deeply in the summer), and you can keep them outside because they don't care about temperature, though if it gets extremely cold you may want to shelter them somewhat as they can freeze if it's cold enough and they're discharged enough.  Plus you get less power out of them in the winter, which is a bit annoying.

For standby use (where a battery is mostly sitting charged and waiting around to be used), flooded doesn't work as well.  AGM is the way to go.  They tolerate sitting around like that a lot better - you don't have acid stratification issues.  And they're sealed, which means no offgassing to deal with under normal operation (they should still be vented, but they don't normally offgas hydrogen).

Gel batteries are best avoided for any use cases, and this includes marketing names such as "lead silicone" and "silica crystal" and "lead crystal" and anything like that.  They're new age woo applied to battery marketing.

Now, if you want lithium, which does have advantages (but not as strong of advantages as most people seem to think), the best way to go off grid is LiFePO4 packs.  That's an older, lower energy density chemistry that's quite safe in operation (it's quite tightly chemically bound, which is useful), and it has a very flat discharge voltage curve.  A group of 4 LiFePO4 cells is almost identical, voltage-wise, to a standard 6S lead acid configuration (12V), so you can use lead acid designed inverters and chargers easily enough.  For a typical house configuration, 48V is the way to go.  You will need some balancing interface, which isn't a common part, but otherwise LiFePO4 is awesome.  Longer cycle life, very good power density, and doesn't gas.  However, you have to keep them warm.  They can't get cold and charge safely, so you'll need space inside for them.

If you really want a plug and play lithium pack, look at some of LG's offerings.  They've got a high voltage (~400V) pack that's comparable in how it interacts with the system to the PowerWall Gen 1, and a lower voltage pack (~48V) that interfaces like a big lead acid string, more or less.  However, I don't know much about those, and it's hard to find good information - I believe you need a compatible inverter.

Also, in the context of this forum, it's worth noting that the moment you say "battery," your power system is now super expensive and will never beat grid power in terms of operating cost.  It just won't.  So you'd better value backup capacity a lot.

I plan to do this on my house, mostly because it's an interesting system and I value reliable power for a few reasons, but I also plan to install a lot of my system myself (and am in a part of the country where I can likely find an electrician to sign off on my work).  Solar on the roof, a Radian unit with most of the house as a critical load subpanel, and a moderately sized battery bank in the crawlspace (either LiFePO4 or AGM, though probably AGM because I'm going to be stretching the limits of what local electricians are used to already, so AGM will probably be easier to get approved).  I expect long conversations with the power company about what I'm doing as well, because it's not the usual grid tied system.
seriously one of best posts on this forum. Thank you for taking the time to give us such a clear and concise summary.

Syonyk

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Re: Off Grid Solar Systems
« Reply #5 on: January 20, 2018, 12:14:48 PM »
seriously one of best posts on this forum. Thank you for taking the time to give us such a clear and concise summary.

Thanks.  My viewpoints aren't particularly popular a lot of places because I don't think Elon Musk is the second coming, I think the Powerwall is a gimmick instead of the future of energy independence (their industrial Powerpacks, on the other hand, seem to be excellent products), and I have a realistic view of the costs and capabilities of off grid energy instead of casually expressing that "one of these days I'll kick the power company to the curb with a SolarCity setup and a few Powerwalls."  That I actually live within the energy constraints (mostly) of a small solar setup for my office helps with that realism - I have those weeks when I barely see 100W out of nearly 3000W of panels and am running on a blend of generator for power and propane for heat, because I've got no sun, no wind, and don't have a battery bank sized for those once a year type events.

And I still think properly maintained (which is a bit tricker than it seems) flooded lead acid is a really good battery technology, especially with the recent work on adding carbon to help reduce the impact of negative plate sulfation. :)

I'm happy to help clarify any questions people have!

Bicycle_B

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Re: Off Grid Solar Systems
« Reply #6 on: January 20, 2018, 12:23:20 PM »
Just adding to the chorus "wow, great answer."  Came for the curiosity, wondering if anyone would say something that helped me understand - just didn't think it would be a one punch deal.  Thanks, Syonyk.

FI Curious

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Re: Off Grid Solar Systems
« Reply #7 on: January 20, 2018, 12:51:57 PM »
Thank you for the responses.  We are building a small energy efficient home on a piece of land we purchased.  We are considering our options, but the utility company wants 40k to bring electric to our property.  At that price, it seems like it would make sense to go with an off-grid solar system since we have optimum solar orientation at our property anyway.  The cost of the whole system would be less than 40k and we would not have monthly electric bills. 

I'm just beginning to try to figure out how to configure a system that will work for us.  I appreciate the comments regarding the Powerwall. :)  It just seemed like an easy clean solution, but maybe it isn't the best option anyway.

Poeirenta

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Re: Off Grid Solar Systems
« Reply #8 on: January 20, 2018, 01:44:30 PM »
Hi OP,

We built a small (925 sq. ft), passive solar, earth bermed house on our property. Our power company wanted $50k, so we knew from the outset we would be off grid and were able to design the house with that in mind. Our system cost $26k but we got a chunk of that back from state and federal incentives.

We went with the sealed AGM batteries so we wouldn't have to worry about watering them. Luckily for us, my coworker had a side business doing solar setups. We were actually his last project before he retired. Between him, Backwoods Solar (such helpful people, a number of whom are also off grid), and our own research, we feel we have a solid system that is right-sized.

So far this winter season (starting in mid November), we have had to run the generator to charge batteries 13.5 hours and have gotten enough sun to charge to 100% 17 days so far. We purchased 19 gallons of propane which may or may not get us quite to the end of winter. Whenever possible, we try to charge when there is sun in the forecast-that way we don't have to run the genny as long but will still get up to 100% the following day. Unless the forecast fails of course! By mid-February there is usually enough sun here in far northern WA to keep us charged enough that we don't have to run the generator anymore. Several of my neighbors are off grid and our running joke in winter is "it's sunny! time to vacuum!".

We actually wound up standing behind a guy who works for Tesla as we were waiting to board a plane last year, so we quizzed him about the powerwall and found out it's wired completely differently and at some astronomically large amps/watts/volts (i forgot which it was but in any case, not gonna work when it comes time to replace our batteries).

Order the Backwoods Solar catalog and start calculating your loads, especially the big ones like microwave, vacuum, and well pump. If you really want to dig in, order the textbook from the Solar Energy International in Colorado that trains solar installers like my coworker.

Syonyk

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Re: Off Grid Solar Systems
« Reply #9 on: January 20, 2018, 02:09:21 PM »
Thank you for the responses.  We are building a small energy efficient home on a piece of land we purchased.  We are considering our options, but the utility company wants 40k to bring electric to our property.  At that price, it seems like it would make sense to go with an off-grid solar system since we have optimum solar orientation at our property anyway.  The cost of the whole system would be less than 40k and we would not have monthly electric bills.

My first advice, if you've not done this: Subscribe to Home Power Magazine, with the digital backlog option.  Start reading backwards (stuff from the 80s is not as relevant currently).  A good sized tablet makes this easier.  Specifically focus on the off grid homes and how they live.  If you're OK with those sort of restrictions on your lifestyle and thermals (mostly, heating with propane ($$$) or biomass (labor intensive)), great.  Carry on.

If you or other people who will live in the house read that and have no interest in that, pay for the power company to bring power in.  $40k is sort of on the border where you could go either way, but if you want reliable power with low maintenance, that's the way to go.

Off grid power can be roughly translated as "generator and battery maintenance."  You do a lot of it.  And you are pretty well forced to live within the power budget coming from the sky - 9 months of the year, not a big deal, the other 3 (usually 2 in winter and one in late summer fire season), heavily restricted.

It's certainly doable, but it's not the lifestyle to which we've become accustomed.  However, LED bulbs and such make your life a good bit easier.

Quote
I'm just beginning to try to figure out how to configure a system that will work for us.  I appreciate the comments regarding the Powerwall. :)  It just seemed like an easy clean solution, but maybe it isn't the best option anyway.

The Powerwall is marketed with all the ethics of a used car salesman.  It's everything, to everyone, at least long enough to get you to sign on the preorder form.  It's battery storage for your solar.  It's backup power.  It's your ticket to kick the utility company to the curb.  It slices!  It dices!  It even cores plums!  And I'll say more if I have to!  You can trust me, I'm Tesla!

What it actually does/is rated to do?  Uh... well... you know... um... sign up for the preorder, someone will contact you eventually... um... professional installers only... limited inverter selection... well... you know, you're saving the planet with this product!

Beyond the technical black hole, when would you like to be living in your house?  Sometime in the next 5 years, maybe?  If nothing else comes up?  Great, sign up.

Sorry, I really don't like the Powerwall, if it's not obvious.  I'd perhaps change my opinion if I could find out what it can actually do and what the real limits are, but until then, it's just this side of vaporware.

We built a small (925 sq. ft), passive solar, earth bermed house on our property. Our power company wanted $50k, so we knew from the outset we would be off grid and were able to design the house with that in mind. Our system cost $26k but we got a chunk of that back from state and federal incentives.

That's definitely how you have to do it.  If it'll be off grid, you can design for that, and build something that doesn't suck a ton of energy.  But taking "standard grid tied construction" off grid is somewhere between comically expensive and mostly impossible, because they're not built for it.

Quote
We went with the sealed AGM batteries so we wouldn't have to worry about watering them. Luckily for us, my coworker had a side business doing solar setups. We were actually his last project before he retired. Between him, Backwoods Solar (such helpful people, a number of whom are also off grid), and our own research, we feel we have a solid system that is right-sized.

If you don't mind sharing, what are the nameplate specs on your system?  Panel wattage, battery bank configuration and capacity, inverter, any DC power systems?

Quote
We actually wound up standing behind a guy who works for Tesla as we were waiting to board a plane last year, so we quizzed him about the powerwall and found out it's wired completely differently and at some astronomically large amps/watts/volts (i forgot which it was but in any case, not gonna work when it comes time to replace our batteries).

The Powerwall 1 is a 400VDC system designed for hanging on the high voltage side of high voltage inverters.

The Powerwall 2 is an AC coupled system that... somehow does something.  See previous rants.  There was supposedly a DC Powerwall 2, but that seems to have been canceled, or rumors are that it's canceled, or something like that.

In any case, not useful at all for an off grid system.

Quote
Order the Backwoods Solar catalog and start calculating your loads, especially the big ones like microwave, vacuum, and well pump. If you really want to dig in, order the textbook from the Solar Energy International in Colorado that trains solar installers like my coworker.

The good news on that front is that things like a microwave use a lot of power, but not that much energy - and larger inverters are more and more common.  I could comfortably run a microwave in my office if I wanted, since I've got a 2000W inverter that peaks to 6000W.  And that's a small setup for a modern off grid home.

FI Curious

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Re: Off Grid Solar Systems
« Reply #10 on: January 20, 2018, 02:45:28 PM »
That's definitely how you have to do it.  If it'll be off grid, you can design for that, and build something that doesn't suck a ton of energy.  But taking "standard grid tied construction" off grid is somewhere between comically expensive and mostly impossible, because they're not built for it.

We are planning to build to PassivHaus standards, or as close to it as we can.  These homes use 80-90% less energy than a typical house mainly because of the fact that the building envelope is so tight.  Living in California, we may not need a heater at all since the building will retain the heat produced by our appliances and bodies as well as solar gain through the windows.

FI Curious

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Re: Off Grid Solar Systems
« Reply #11 on: January 20, 2018, 02:48:59 PM »
Hi OP,

We built a small (925 sq. ft), passive solar, earth bermed house on our property. Our power company wanted $50k, so we knew from the outset we would be off grid and were able to design the house with that in mind. Our system cost $26k but we got a chunk of that back from state and federal incentives.

We went with the sealed AGM batteries so we wouldn't have to worry about watering them. Luckily for us, my coworker had a side business doing solar setups. We were actually his last project before he retired. Between him, Backwoods Solar (such helpful people, a number of whom are also off grid), and our own research, we feel we have a solid system that is right-sized.

So far this winter season (starting in mid November), we have had to run the generator to charge batteries 13.5 hours and have gotten enough sun to charge to 100% 17 days so far. We purchased 19 gallons of propane which may or may not get us quite to the end of winter. Whenever possible, we try to charge when there is sun in the forecast-that way we don't have to run the genny as long but will still get up to 100% the following day. Unless the forecast fails of course! By mid-February there is usually enough sun here in far northern WA to keep us charged enough that we don't have to run the generator anymore. Several of my neighbors are off grid and our running joke in winter is "it's sunny! time to vacuum!".

We actually wound up standing behind a guy who works for Tesla as we were waiting to board a plane last year, so we quizzed him about the powerwall and found out it's wired completely differently and at some astronomically large amps/watts/volts (i forgot which it was but in any case, not gonna work when it comes time to replace our batteries).

Order the Backwoods Solar catalog and start calculating your loads, especially the big ones like microwave, vacuum, and well pump. If you really want to dig in, order the textbook from the Solar Energy International in Colorado that trains solar installers like my coworker.

  It is interesting to hear how this works in real life!  It is funny to think that you need to consider the time to vacuum but it makes sense. 

Syonyk

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Re: Off Grid Solar Systems
« Reply #12 on: January 20, 2018, 02:57:21 PM »
We are planning to build to PassivHaus standards, or as close to it as we can.  These homes use 80-90% less energy than a typical house mainly because of the fact that the building envelope is so tight.  Living in California, we may not need a heater at all since the building will retain the heat produced by our appliances and bodies as well as solar gain through the windows.

Ok.  In that case, you should be fine with off grid power.

I still suggest flooded lead acid, and I highly suggest overpaneling your system - put in 20% more panels than you think you need, because that helps get the batteries fully charged on a regular basis and gives you more power on cloudy days (when it's cloudy, where the panels point doesn't matter, but the panel area does).

Definitely go with a renewable energy/solar battery.  I'm happy with my Trojans.  And make sure it has the Smart Carbon or whatever your preferred battery company calls their carbon blend in the negative electrode.

TomTX

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Re: Off Grid Solar Systems
« Reply #13 on: January 20, 2018, 03:06:46 PM »
My only comment about this (and I know Syonyk has done this) - when overpaneling, strongly consider aiming extra panels more East and West for more even output through the day.

Syonyk

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Re: Off Grid Solar Systems
« Reply #14 on: January 20, 2018, 03:18:14 PM »
My only comment about this (and I know Syonyk has done this) - when overpaneling, strongly consider aiming extra panels more East and West for more even output through the day.

Yeah, good point - I do forget that my east facing "morning panels" are unusual.  They start the recharge process far earlier than my main array, and are outproducing the main array (2 panels vs 8) in raw power for the first hour or two of the morning.

West facing panels are likely to be less useful on a properly designed system, because the battery pack should be full by evening, so there's a bit less benefit of having the west panels.  But some east, southeast, and southwest arrays would work nicely to help even power throughout the day without that hard solar noon peak.

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Re: Off Grid Solar Systems
« Reply #15 on: January 20, 2018, 03:59:31 PM »

I built a stand-alone system 10 years ago,  using gel batteries and -sign of the times-  ridiculously expensive solar panels. Because the power supply is/was notoriously unreliable, and because I liked the idea.   

I think the most important aspect has so far been neglected in this thread:  these systems require your attention, daily.
It's become my hobby to check the voltage, load, amount of charging, etc. Anything abnormal gets noticed immediately. And fixed if need be. 

And it's become my experience that all other people don't care.  Until the lights go out and alarms go off on lots of appliances,  then they intensely care,  but have no clue.  Regardless of the number of times you explain it.

So I changed it some years ago in a hybrid system,  with battery back-up.   This reduced the number of incidents.

Over the years things have become a lot easier, thanks to more energy efficient appliances, notable LED lighting.
This reduced load surely extended the lifetime of the batteries by a few years.
I also like the much lower price of the more efficient panels today. The replacement of my system will cost far less than I could imagine ten years ago.
 

The second important aspect is : don't forget solar water heating. It's more efficient and saves a lot of energy.

 




 

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Re: Off Grid Solar Systems
« Reply #16 on: January 20, 2018, 04:04:49 PM »
Syonyk, here is our schematic. https://imgur.com/a/UeB4h

For the record, we use a microwave, just very judiciously when the sun is in short supply. Today is was unexpectedly sunny so I happily nuked the butter for my popcorn instead of melting it on the stove. :-)

We are also remarkably entertained by checking our remote control frequently to see what we're making or using at any given time.


Syonyk

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Re: Off Grid Solar Systems
« Reply #17 on: January 20, 2018, 04:42:21 PM »
Interesting.  Very similar to my system in a lot of ways, just designed for home use (you apparently have something that needs 240V).

Comparable total panel capacity (2850 vs 3100) - you have higher output panels.  I opted to go with 2 strings of 4 and then the spare 2 on a PWM controller into my bank (my max power point is similar enough to my bank voltage range that I don't lose much by going with a PWM unit, and the cost delta is huge for PWM vs MPPT).  I went with the Midnite Classic 200 for my winter open circuit concerns - any reason you didn't go with two strings of 5 and a Classic 250?  I'd expect the copper savings would be significant in the run from the panels to the charge controller.  Carrying 18A vs 45A is a substantial difference.

Battery bank is similar, though yours is a bit larger (as is reasonable for a home vs a mostly day occupied office) - I'm 48V/225Ah/flooded, you're 48V/405Ah/AGM.  Presumably temperature compensated and such properly.  How often do you equalize?

And then your inverter is a beast.  I'm just running an Aims Power 2000W inverter/charger, single phase, since nothing I run needs 240V (though that doesn't mean I haven't considered it, since some of the spot welders I'd like to use are better served by 240V).

What's your generator rating?  Your charger is 3-4x what mine will do - I can charge my bank at about 17A off my charger, while running the office off the generator output (a little inverter generator).  It looks like you need a 240V beast of a generator for that unit.

One of the things I've been working on is a low voltage DC bus (around 40VDC) to run various DC loads.  I haven't gotten around to doing it yet, but my inverter idle is a good chunk of my idle draw.  I wouldn't be surprised if your inverter is actually more efficient than mine at no load (25W rated, and I haven't fully unloaded mine recently to measure idle draw, but idle in my office is 55W per one meter and a bit higher per the other).

Do you have the WhizBang Jr on your Classic?  I see you've got the DC shunt, but I can't tell if it's wired up to the Classic or to something else.  If you don't have one, you should consider it.  Doing current based charge termination is a good bit easier on the cells than timed termination (especially in the summer), and it gets you a good estimate of amp-hour capacity remaining.  Not sure if the other equipment in there offers that capability or not, but if you don't have it, it's really, really nice.  It's a ton better than relying on under load voltage, especially in the winter.

Nice system!

Abe

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Re: Off Grid Solar Systems
« Reply #18 on: January 20, 2018, 04:43:29 PM »
This is all really interesting. I'm currently renting in southern California, but plan to buy a house in the next 1-2 years. We'd like to use solar power as much as is practical, and seems based on our usage online calculators suggest a 2.5 - 3 kW system. Would anyone be interested in looking at our energy usage and see if that's accurate or if we need more power? We plan to be grid-tied.  Also, anyone have a recommendation on a good solar water heater for 2 people? Thanks!

Power usage:
https://docs.google.com/spreadsheets/d/1wMbO4k_jcfqfOzWTC1qe33geTWRRg9b1Kl7cVJph8o0/edit?usp=sharing

Poeirenta

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Re: Off Grid Solar Systems
« Reply #19 on: January 20, 2018, 06:31:54 PM »
Interesting.  Very similar to my system in a lot of ways, just designed for home use (you apparently have something that needs 240V).

We have a 420' deep well and no good option for gravity feed, hence the 240V for the soft start Grundfos pump.

Comparable total panel capacity (2850 vs 3100) - you have higher output panels.  I opted to go with 2 strings of 4 and then the spare 2 on a PWM controller into my bank (my max power point is similar enough to my bank voltage range that I don't lose much by going with a PWM unit, and the cost delta is huge for PWM vs MPPT).  I went with the Midnite Classic 200 for my winter open circuit concerns - any reason you didn't go with two strings of 5 and a Classic 250?  I'd expect the copper savings would be significant in the run from the panels to the charge controller.  Carrying 18A vs 45A is a substantial difference.

That's a question for the company that built the system. They didn't get into this level of detail with us.

Battery bank is similar, though yours is a bit larger (as is reasonable for a home vs a mostly day occupied office) - I'm 48V/225Ah/flooded, you're 48V/405Ah/AGM.  Presumably temperature compensated and such properly.  How often do you equalize?

We have a power room off the mud room-unheated but in the bermed part of the house so it stays fairly constant temp. We've only equalized once in the 4 years we've had the system and that was during the first year when we hadn't quite figured out how to best manage the system. The batteries were resisting a full charge then and that hasn't happened since we made adjustments. DH knows this stuff better than I.

And then your inverter is a beast.  I'm just running an Aims Power 2000W inverter/charger, single phase, since nothing I run needs 240V (though that doesn't mean I haven't considered it, since some of the spot welders I'd like to use are better served by 240V).

What's your generator rating?  Your charger is 3-4x what mine will do - I can charge my bank at about 17A off my charger, while running the office off the generator output (a little inverter generator).  It looks like you need a 240V beast of a generator for that unit.

We have a 10K watt generator...probably could have gotten a 7K but went with what was recommended. It's a honda converted to run on propane by Central Maine Diesel.

One of the things I've been working on is a low voltage DC bus (around 40VDC) to run various DC loads.  I haven't gotten around to doing it yet, but my inverter idle is a good chunk of my idle draw.  I wouldn't be surprised if your inverter is actually more efficient than mine at no load (25W rated, and I haven't fully unloaded mine recently to measure idle draw, but idle in my office is 55W per one meter and a bit higher per the other).

Do you have the WhizBang Jr on your Classic?  I see you've got the DC shunt, but I can't tell if it's wired up to the Classic or to something else.  If you don't have one, you should consider it.  Doing current based charge termination is a good bit easier on the cells than timed termination (especially in the summer), and it gets you a good estimate of amp-hour capacity remaining.  Not sure if the other equipment in there offers that capability or not, but if you don't have it, it's really, really nice.  It's a ton better than relying on under load voltage, especially in the winter.

Yes, we have a whizbang jr on the classic.

Nice system!

Thanks, so far so good. The power goes out pretty regularly for our on-grid neighbors, so we're pretty happy to have our own power plant.

FI Curious

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Re: Off Grid Solar Systems
« Reply #20 on: January 20, 2018, 07:23:14 PM »
We do plan to install a separate solar water heating system with storage.  Thanks for the suggestion regarding East facing panels. We have Southern all day exposure with no trees or interference of any kind.  We purchased 20 panels so far.  How many would I face East and West?  I don't know if it would be necessary in my area to do this.

I just checked http://pvwatts.nrel.gov/index.php and the 20 panels we purchased would produce 10k kwh in my location facing South at 20 degrees but only 386 in January (the month where we could expect the lowest output). But if we tilted some of the panels up to 30 degrees or more we would get slightly more power in the winter.  We might purchase more in order to overpanel and get more power in the winter.
« Last Edit: January 20, 2018, 08:47:10 PM by FI Curious »

Syonyk

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Re: Off Grid Solar Systems
« Reply #21 on: January 20, 2018, 09:07:47 PM »
We have a 420' deep well and no good option for gravity feed, hence the 240V for the soft start Grundfos pump.

That would definitely do it!  I plan to put a 240V split phase inverter on the house, mostly because our well pump is 240V as well and I don't like not being able to run that. 

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We have a power room off the mud room-unheated but in the bermed part of the house so it stays fairly constant temp. We've only equalized once in the 4 years we've had the system and that was during the first year when we hadn't quite figured out how to best manage the system. The batteries were resisting a full charge then and that hasn't happened since we made adjustments. DH knows this stuff better than I.

Constant, cool temperatures are definitely good for batteries.  My bank gets warmer than I'd like in the summer, and it's super saggy in the winter, because it's outside in a deck box.  Not buried.  I've considered building some sort of buried box for them to help stabilize the temperature, but keeping water out would be tricky, and my property is basalt covered in cheatgrass, so digging is always a challenge.

It's definitely good that you've worked out how to maintain the system without equalizing.  That's one of those bits of folk knowledge about batteries that mostly solves problems created with incorrect charging settings in the first place.  The problem with an awful lot of off grid systems (up until surprisingly recently) was that everyone was using the "grid tied charger" voltages - which work, if you've got 18 or 24 hours to charge a battery.  They don't cram enough current in during a typical solar day to fully charge the battery bank, and so people were getting chronically undercharged cells.  Equalizing helps with that, though not perfectly.  If you've got the charge voltages adjusted up (which it sounds like you do) and current based termination (with evidence that you're dropping into float regularly), there's often no reason to equalize because the cells don't get degraded such that it helps.

For those unfamiliar, equalizing is the fine art of thrashing a lead acid bank with high voltage to shove current through an already "full" bank.  It accomplishes several things.

First and most commonly, it helps drive sulfation out of the plates (mostly the negative plate).  As the battery bank discharges, the lead (and lead oxide) change to lead sulfate.  This is fine when it's the soft sulfate and reverses with recharging, but if a battery sits undercharged for long periods of time, that hardens and becomes harder to get rid of.  That hard lead sulfate blocks the plate area and removes sulfuric acid permanently from the electrolyte, reducing the battery capacity (it'll seem full, but not actually be full).  Beating on the battery helps drive this out and reverse it, though it can't help a badly sulfated battery.  Proper charging, with the proper voltages, should prevent this from being an issue most of the year, and the carbon inclusions help with the winter time when you can't charge fully.  The carbon magic somehow helps prevent sulfation from being as hard to remove.

The second feature of equalization is that it helps mix the electrolyte to resolve stratification.  If you don't have enough charging current or time to properly charge the batteries (or to charge them fast enough), you'll end up with stratification, in which the heavy (more concentrated) acid is at the bottom, and the lighter (less concentrated) acid is at the top.  This is no good, because it's really, really hard on the plates.  AGMs don't suffer from this, only flooded lead acid.  Equalizing drives the cells well into the gassing region of voltage, and the gas bubbles (from the water in the electrolyte being split) help stir the solution.  Again, with a proper sized charging system, properly set, this shouldn't be an issue.  This is one reason that lead needs to be overcharged (especially flooded) - the sustained bubbling helps mix things up.  Somewhere in the 8-10% overcharge is where everything is properly mixed, per some charts I've seen.

Sorry about all the brain dump here, I've actually been working on a blog post about lead acid maintenance, so this is all on the top of my brain.

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We have a 10K watt generator...probably could have gotten a 7K but went with what was recommended. It's a honda converted to run on propane by Central Maine Diesel.

Jealous.  Not that my bank could really use that (10kW is about a 0.8C charge rate for me - not that my charger will do that).  How happy are you with the propane conversion?  Mine is still gas, and I've built an extended run tank for it, but I'm seriously considering doing a propane conversion.  I'd need to bring a larger tank down by my office, and the cost of the conversion kit is close to what I paid for my generator, but it should work on other similar generators as well.  The ease of starting in the winter would be nice - my generator does not start particularly well when it's below 0F out.  Lots of pulling and then I have to let it sit for a while before it will start.  On the plus side, it always starts, and I'm nice and warm when it lights off...

I've considered designing a micro-CHP system - combined heating and power.  Generally, if I need the generator, I need heat as well, and the generator heating the outside and me burning propane to heat the inside seems a waste.  I've considered putting together some heat exchangers to suck heat out of the cooling air and exhaust (this would require building a custom enclosure for my generator) and dumping them in my office.  However, the cost to accomplish this would radically exceed any savings I'd ever get in fuel use (I burn 5-10 gallons of gas a winter and 4-7 gallons of propane), so it's one of those "Because I can..." type projects.  I'd likely be far better off investing in some thermal storage - a 55 gallon drum of stratified thermal storage, perhaps (useful stratification, in which the top part is always hot and the bottom is always cold).  Even then, it's firmly into the realm of "This is an interesting project to reduce my fossil fuel consumption in the winter," and is unlikely to pay off ever.  But it'd be neat.  And that's often enough for me.

We do plan to install a separate solar water heating system with storage.  Thanks for the suggestion regarding East facing panels but we have Southern all day exposure with no trees or interference of any kind.  Wouldn't it be best to face them South?

It depends on what you're optimizing for.  For maximum raw energy production (kWh/day), yes, facing true south is ideal (in the northern hemisphere, of course).  However, for off grid use, raw energy production is seldom useful.  A system sized for winter use will overproduce so comically in the summer that you can't use all the energy - or a system designed for the summer will basically be a pure generator system in the winter.  For an off grid system, "morning panels" reduce by an hour or two the time you're sucking power out of the battery bank, which helps with longevity of lead - depth of discharge and time of discharge both impact longevity.

Another issue (again, mostly with lead) is that it takes quite a while to fully charge them.  You dump as much current as you can into them until you get up to the absorb voltage setpoint (temperature compensated - I cannot stress enough how important this is for longevity), then you hold that voltage and the current into the pack tapers off as the pack charges.  Once you hit your termination current (1-3% of C/20 capacity in amps, though mine is set to 1% for winter - I plan to bump that up to 2% or so in the spring), you drop back to the float voltage.  This takes time.  Today, my bank took ~5.4 hours to hit that 1% charge rate, though it's quicker if it's fully charged every day (and I was pretty hard on it this morning - I heat with electrons if I expect sun).  Starting that recovery 1-2 hours earlier is worth a lot in an off grid system, since it gives you the hours to fully charge it before sundown.

If you're using a lithium pack, it doesn't matter quite as much, so pointing everything south works fine.  You can hammer a ton of current into lithium compared to lead, so you can make use of that solar peak and store it.  On a sunny day, by solar peak, my bank is full and tapering off.

I literally can't use all the power I generate with my system on a good sunny day, so it's worth it (again, for an off grid system) to spend some panel area to start the recovery earlier.  Off grid is different from grid tied in many ways.  You don't get to use the grid as your free, ideal battery.

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I just checked http://pvwatts.nrel.gov/index.php and the 20 panels we purchased would produce 10k kwh in my location but only 386 in January (the month where we could expect the lowest output). But if we tilted some of the panels up to 30 degrees or more we would get slightly more power in the winter.  We might purchase more in order to overpanel and get more power in the winter.

That sounds about right.  Solar really is feast or famine.  It's rarely balanced.  In a reasonable system, you either have a ton of energy you can't use (off grid), or are running the generator.  There's very little in between, and what in between you have is mostly "It's cloudy, and I'm choosing not to use much energy today."  Finding uses for that summer feast is interesting.  I run Folding@Home and BOINC on some spare hardware, because tossing some excess energy at climate simulation and such seems useful (trying to pay back for my filthy power - anyone who tells you off grid power is clean is either clueless or has an agenda, because generators are stupid-inefficient and batteries are pretty bad too).

One thing those simulations don't make clear is just how little panel angle matters on a cloudy day.  I can swing my morning panels from east to southwest, and with heavy clouds, where I point them doesn't matter.  Not one bit.  I might see 0.1A difference between east and southwest as I swing them around (and generally, peak production has nothing to do with where the sun is, but where the clouds are slightly thinner).  It just doesn't matter.  Panel area is king.

I've actually been running my upper panel bank nearly vertical this winter.  It's less optimal from a power production perspective, but it's better from a snow shedding perspective.  Vertical panels shed snow.  Angled panels don't.  If I have a sunny winter day, I have enough panel that I don't care about optimizing production, if I have a cloudy day, it doesn't matter either, but the vertical angle sheds snow a lot better.  My lower bank is mutter mumble summer angle I really should change that soon.  Being able to tilt a bank or two of panels for the winter clearing is nice.  If you don't get snow, it matters less.

What I'd suggest, if you have movable panels, is to set them at your latitude for spring/summer/fall (basically, optimize year round production - you'll get more power in the spring and fall when the sun lines up, and the days in the summer are so long that it just doesn't matter), and then set them nearly vertical for winter.  You'll get pretty good angle on the winer sun, and the snow clearing is far better than at other angles.

When in doubt, for lead, opt for more panels.  You want to fully charge the bank regularly for longevity.  If you trust your charge controller at 100% rated power, you can even attach more panels than your controller can deal with - it'll just clip.  But that area will help you in the spring/fall/winter when you don't have as much power.

Another quirk of off grid, especially if you have air conditioning: Spring and fall are the feast times, moreso than summer.  Nobody really has a feel for how the heat impacts panel production until they live with it.  The panel power rating is at STC conditions - panels at 77F.  When are the panels at 77F?  Well, in the winter, maybe...  As solar panels get hotter, they produce less power.

So, with a standard temperature coefficient of around -0.4%/C, what does summer look like?  Well, it's 105F out (40C), but the panels are black and in the sun.  Let's call them too darn hot to touch, at maybe 65C.  What's production?  They're 40C hotter than reference, so production is down by 16%.  Those 310W panels won't produce more than 260W.  Worse, the sky is hazy from the summer humidity - or, if you're in a dry climate, the wildfires.  And there hasn't been rain for a month, so the panels are dusty.  You might be lucky to see 200W peak out of them in the depths of summer.

Spring and fall, with frequent rain, and clear skies?  Cold, happy panels.

And then there's winter.  Which mostly sucks.  And then you have a vertical panel, snow on the ground, a super cold panel, and bright sun.  Wowie powerie!  My panels are rated for 9A.  My PWM controller is rated at 10A, and will cut off over 11A.  How do I know this?  Because in those conditions, my morning panels were producing somewhere north of 11A.  I don't know how much, because my charge controller wouldn't deal with them and I moved them off-angle pretty far to avoid repeatedly overloading my controller.

So... living within your solar power budget is rather non-intuitive unless you've been doing it for a while.

It's fun, but occasionally frustrating.  And you really do need a good generator.

hernandz

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Re: Off Grid Solar Systems
« Reply #22 on: January 20, 2018, 10:09:29 PM »
Really useful thread folks. If I can ask two semi-related questions:

We have a manual transfer switch and a portable generator that until this year was a reliable backup system for us.  This past spring, DH really wanted solar panels and we went with a grid-tied system.I wasn't sure if the portable generator is just coming to replacement age or if we had shortened the life of the generator with the new panels.   From this thread, but it sounds like our backup generator problems aren't related to our solar.  We will replace the battery on the portable generator (2nd in 5 years), but I suspect that we've been lax in routine maintenance because of our recent health issues.

Are there any special considerations for the next backup generator? I don't have the specs handy, but it was appropriately sized at the time of purchase (10 years ago). We haven't increased our conscious usage but I know we have a lot more vampire/standby appliances (FACEPUNCH!!).  Because our area is subject to frequent outages, our current generator powers our house about 3 times a year for a day or two (at these times we don't care about "normal" consumption except for the well pump, the fridge and the 2nd freezer. Stove, heat and hot water are not electric-based). 

The other question is does anyone have tips for brushing snow off our panels (we are just north of NYC). Single story house with not very steep pitch for the majority of our panels. 


Syonyk

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Re: Off Grid Solar Systems
« Reply #23 on: January 20, 2018, 10:20:57 PM »
We have a manual transfer switch and a portable generator that until this year was a reliable backup system for us.  This past spring, DH really wanted solar panels and we went with a grid-tied system.I wasn't sure if the portable generator is just coming to replacement age or if we had shortened the life of the generator with the new panels.   From this thread, but it sounds like our backup generator problems aren't related to our solar.  We will replace the battery on the portable generator (2nd in 5 years), but I suspect that we've been lax in routine maintenance because of our recent health issues.

The grid tied solar should have absolutely nothing to do with the condition of your backup generator.  A typical grid tied system won't sync to a backup generator.  If it does... well, yeah, that could destroy a generator in short order by backfeeding power into a generator.  I'd guess the transfer switch handles isolating the solar from the generator, but you might want to check that.  If the generator is running, your solar circuit should be isolated from the rest of the system somehow.

A few years per battery isn't that unusual.  You might consider a small Harbor Freight solar panel for your generator battery - all you really have to do is outrun the self discharge, which isn't hard.

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Are there any special considerations for the next backup generator? I don't have the specs handy, but it was appropriately sized at the time of purchase (10 years ago).

How is your generator fueled?  Propane or natural gas is a lot easier to deal with than a gas or diesel generator, in that the fuel is either infinitely available (natural gas, to a first order approximation), or highly storable (50 year old propane is still just fine).

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We haven't increased our conscious usage but I know we have a lot more vampire/standby appliances (FACEPUNCH!!).

Modern energy efficiency requirements mean that most "vampire draw" is reduced, dramatically.  The old "wall wart" chargers were warm to the touch - that's wasted energy.  Modern switching power supplies are cold, always.  If you can't tell that it's warm, it's not wasting enough power to really worry about.  IMO.  A typical USB charger has a standby draw of milliwatts.  Someone tested an Apple USB charger and determined the draw was below 0.05W.  Run that for a year, vampire consumption is less than $0.03.  It's just not a big deal anymore.

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The other question is does anyone have tips for brushing snow off our panels (we are just north of NYC). Single story house with not very steep pitch for the majority of our panels.

You can get "roof rakes" for snow removal that will help.  They're not particular easy to use, though.

Poeirenta

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Re: Off Grid Solar Systems
« Reply #24 on: January 21, 2018, 12:00:35 PM »
@ syonyk, we have been happy with the propane generator...but we've never had a gas one since I really don't like keeping gas around. Initially we had issues with the valve freezing on the big generator, but once we went to a 100# tank it's been fine.

hernandz

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Re: Off Grid Solar Systems
« Reply #25 on: January 21, 2018, 05:17:14 PM »
Thanks for all the thoughts. 

You might consider a small Harbor Freight solar panel for your generator battery - all you really have to do is outrun the self discharge, which isn't hard.

Interesting thought. Hubby probably will jump at the chance to add more solar. 

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How is your generator fueled?  Propane or natural gas is a lot easier to deal with than a gas or diesel generator, in that the fuel is either infinitely available (natural gas, to a first order approximation), or highly storable (50 year old propane is still just fine).

It's a gasoline generator.  it may well be worth changing to propane, which we use for hot water and indoor heat if we choose to go with a permanent backup generator.

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Modern energy efficiency requirements mean that most "vampire draw" is reduced, dramatically.  The old "wall wart" chargers were warm to the touch - that's wasted energy.  Modern switching power supplies are cold, always.  If you can't tell that it's warm, it's not wasting enough power to really worry about.  IMO.  A typical USB charger has a standby draw of milliwatts.  Someone tested an Apple USB charger and determined the draw was below 0.05W.  Run that for a year, vampire consumption is less than $0.03.  It's just not a big deal anymore.

Yeah, it might be that hubby is now home all day, and I'm more aware of luxury gadgets we now own.  Our home was built in 1940 and not a lot of outlets..  He really likes cordless power tools for home and lawn and my side gig involves computers and mobile devices, so our wall warts and chargers are in very plain view

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  You can get "roof rakes" for snow removal that will help.  They're not particular easy to use, though.

Oh well.  I'm really looking forward to the day iRobot comes up with a drone or similar. 

Syonyk

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Re: Off Grid Solar Systems
« Reply #26 on: January 21, 2018, 05:46:47 PM »
Interesting thought. Hubby probably will jump at the chance to add more solar.

Alternately, could you schedule a generator run?  You should run it every month or so anyway... not that I run mine much in the summer.  That'll keep the battery charged and also keep the fuel in it fresher (in the carburetor).  Unless you have a fancy fuel injected generator, then it probably doesn't matter.

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It's a gasoline generator.  it may well be worth changing to propane, which we use for hot water and indoor heat if we choose to go with a permanent backup generator.

There's benefits to both ways.  Propane is a lot more storable, and a large propane tank, when full, contains quite a bit of energy.  Plus, it doesn't go bad like gasoline does.

On the downside, you're now totally dependent on one fuel and one storage tank (well, either way, I'd keep a few spares of propane around - maybe a few 9 gallon containers).  So if something happens to that feed, you have no heat and no power.  A gas generator is separate fuel.

In general, I think the propane conversion is probably worth it.

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Yeah, it might be that hubby is now home all day, and I'm more aware of luxury gadgets we now own.  Our home was built in 1940 and not a lot of outlets..  He really likes cordless power tools for home and lawn and my side gig involves computers and mobile devices, so our wall warts and chargers are in very plain view

That would make a difference...

If you're really curious, pick up a Kill-a-Watt unit and measure the idle draw of your electronics.  It's likely to be very low, though.