Various comments/thoughts. My office is purely off grid solar (2850W nameplate of panel, 12kWh nameplate of flooded lead acid, 2000W inverter, and a small generator for winter extra power). My house is grid tied and fully electric - I plan to eventually get solar on it with off grid capabilities, but I simply don't have the money for that right now.
Part of my plan to achieve FIRE is to eliminate/reduce my utility costs.
This is definitely part of my path as well. My goal is to spend the next few years doing "productive property improvements" that lead to either long term cost savings, or long term insulation from varying costs. This looks (for me) like solar (likely both thermal and PV), some battery capacity, gardens/greenhouses, water storage for rainwater, shop space, etc. My goal is to be able to provide for a lot of our own energy and food needs, with surplus to share. That includes storage for such things (I intend to dig in a root cellar at some point, with walls built of basalt).
About 2 years ago I acquired an electric car out of environmental, safety, and financial concerns.
I've been eyeing used Leafs - they're down to around $6500 on the coast, but I'm hoping the Model 3 will push them down a bit further, and then I'll pick one up for transportation. I'm rural enough that biking is iffy (I can do it part of the year on an electric, but I really don't care for biking on the roads around me), motorcycling... heh. Yeah. My shoulder is not in good shape right now from a crash. I normally ride on three wheels (sidecar rig), took the two wheeler today, and I have a few parts to replace and a week or so of some nice pain coming up. Didn't drop it, but... yeah. Would have preferred a lot of metal around me.
I think the used Leafs are a good secondary car at this point, at least for me. My wife and daughter regularly do 30-40 mile days, so the range is perfect, and our power is cheap. I'm not going to replace the gas burners/diesel burners, because rural property and such (I haul a 10k lb trailer a few times a month), but we can divert an awful lot of miles onto a cheap electric beater.
I use about 400KWH per month plus another 150KWH per month on my car. I have an electric air conditioner (which I don't often use) and an electric spa. I have several NG appliances such as a water heater, clothes dryer, and range/oven. As those appliances break down I plan on replacing them with electric versions. Here in San Diego we pay about 22 - 40 cents per KWH so my electric bill was often over $100 per month.
As you replace those thermal appliances with electric, expect your electric use to go up a
lot. I use somewhere between 700 and 2100 kWh/mo with my house. We've got a heat pump for heating/cooling, but it gets cold and the backup coils burn a lot. If you value low energy use, consider a heat pump - I expect it would work wonderfully in your climate. You can also get heat pumping hot water heaters that are more efficient than a resistive setup, though if you have the space going to a dual heater setup and solar thermal is a better option (preheat with solar thermal, the resistive heater makes up the extra in the winter). I also pay to pump my water (well pump), and it's about a 250' water level, so a good bit of power goes that way as well. Plus, eventually, electric car miles (estimated at 150-200kWh/mo).
7.6KW hybrid grid tie inverter that uses "DC Optimizers" on each panel to regulate and monitor
Presumably the SolarEdge unit? That's the only one I've found that meets those specs, and it sure runs at high enough DC voltages to need the boost converters/optimizers. What optimizer wattage did you go with? Generally, panels produce below rated power
most of the time, so you can get away with a slightly smaller optimizer/microinverter and save some money. I almost never see nameplate on my panels, though a sunny day in the dead of winter with snow reflection can push them well beyond rated output.
10 KWH wall mounted DC coupled lithium battery
Which unit? The Sonnon? Or did you find someone with a PowerWall in stock?
Today's PV panel tech allows for upwards of 360 watts per equivalent sized panel, however in my case it was a much lower cost to have more lower wattage panels than fewer higher wattage panels for an equal power output.
Quite true, and if you have enough area for the power, "installed cost per nameplate watt" is the way to go. The higher wattage panels are great for area limited homes (or RVs, if you go that way), but they're a lot more expensive.
I SERIOUSLY considered going off grid. However now that residential grid tied batteries are available, it is possible to get the best of both worlds.
Here's where I'll disagree, strongly. Taking a standard home off grid is damned near impossible unless you either have a comically huge battery bank, a comically oversized solar array, or you're fine with an awful lot of generator use. You're in a region where it might be possible, but standard homes simply are not designed to work with renewable energy in limited quantities. Go check out a few issues of Home Power for what a pure off grid home looks like - they're not much like a standard home. Usually earth coupled, insanely insulated, and even those typically rely on biomass for heat in the winter (or propane, but biomass is a better option, and thermal mass rocket stoves and the like are super efficient at turning biomass into heat - far more efficient than a standard wood stove).
If you have the data, do the math on your system once you've had it in place for a year. Pair your daily usage and daily production, and see how large of a battery bank you'd have needed or how much generator you need. On a bad day, my 2280W primary array will be generating 200-300W - and there are plenty of winter days when I've seen less than half a kWh on that array. Given that my office, idle, pulls about 1.5kWh/day (inverter idle draw, network gear and radios for the property, etc), that's a problem when I'm working in there. I need about 3-3.5kWh/day to break even on a workday, and that doesn't do a good job of charging my batteries - if I can pull that, great, but typically in the winter I have an hour or so of generator during the depths. And I heat with propane in the winter if I don't have good sun (I can heat on electric, but "converting gasoline into electricity at 10-12% efficiency to then heat with that" isn't a good trade, and I haven't worked out a micro-CHP setup for my generator - it's on my list of things to do, but will also never pay off with how little propane I use in the winter).
Also, off grid power is still very expensive. Even though your power is expensive, the LCOE for a pure off grid system is a good bit higher than what you're paying. Pick your way of approaching it, it gets more expensive. And you have to live within your energy budget. My office is off grid partly because trenching power out to it would be very expensive, partly because it makes it a good bit more convenient as it's legally a "storage shed" (no power connection to the grid), and partly because I've wanted hands on experience with an off grid system for a long while, and this lets me only annoy myself if something is acting up or if I can barely use any energy on a crappy winter day because my generator needs maintenance again.
The grid tied battery will store extra power generated by the panels during the day and provide energy for the house at night while the grid will fill in the gaps when the battery drains or when the panels generate more than what the battery can hold.
It should give you limited power outage ridethrough. How much control do you have over when the battery is charged/discharged? I've not been able to find the algorithms they use to charge or discharge the battery, and most of that stuff is depressingly proprietary (I'm not a fan of that). But you don't even have a typical day's use in your battery.
The inverter is a much higher output than my current system needs, however it was the only grid tie inverter I could find that could integrate a DC coupled battery. The DC optimizers I mentioned aren't really necessary for me. They come in handy if you have something shading the panels, or for detecting when a specific panel isn't working properly. They can also come in handy if later you replace some panels and end up with mismatched panels.
For the high voltage DC coupled stuff, yes. There are some grid tie inverters that work on lower voltage battery banks (the Radian series work off a 48V bank), but that type of system ends up being a lot more expensive (the 8kW Radian unit is a $4k inverter, plus a few grand in charge controllers to go from the battery bank). However, for my style of system, it's a good bit more useful. It also has a ton of useful outputs (DC diversion, AC diversion, generator start, etc). I can either use those to directly control diversion loads (hot water is a good place to store energy, as long as you don't exceed the limits of the tank), or as inputs to a microcontroller that handles various other loads and interfaces with other devices.
I'll be grid tied with net metering (assuming that's still an option), but I intend to design the system such that it can run standalone indefinitely if needed. I'm one hell of a pessimist about some things, and power systems are one such thing...
Technically speaking, DC coupled systems are simpler overall. However during a power outage, my battery can only power 2 "critical load" circuits.
... ah. Well. That's definitely where our system designs differ. I intend to put "the house" as the critical loads subpanel, and only route a few things to the utility side of the system. I'll probably put the stove and heat pump backup coils outside the critical loads panel, but an awful lot of other stuff (including some car charging outlets) will be post-inverter. I should be able to get away with the 8kW unit, though if I mount enough panels, a paired 4kW slave unit might be needed to make use of all the output. I'll see. The advantage of some DC diversion loads is that I can make use of the battery bank voltage directly, and resistive loads (say, one element of a hot water heater) are agreeable to pulse width modulated operation.
I'm not sure how many panels my utility will let me use - I'm going to get the electric car first, because they generally won't allow systems that exceed annual use, so I'll hog power for a year with the EV to get my average up and get approved for more panels.
An AC coupled battery would have been able to power all the circuits in my house during grid outage.
So will a DC coupled system designed for that. ;)
...and guaranteeing yourself that all your energy comes from solar.
A kWh is a kWh. And if you're grid tied, there's no guarantee about where a particular electron is being energized from.
It is expected to be at 80% capacity after 10 years.
What sort of cycling is that rated at? Daily cycling? Weekly cycling? And what depth of discharge? Battery lifespan is hugely, hugely dependent on use conditions. Also, does your pack have active thermal management? If so, what's the expected energy use on that?
It is also possible to greatly reduce the cost of a system by purchasing 2nd hand batteries from old electric cars as well as using inverters that are not grid tied.
Maybe. Self built or recycled lithium batteries are certainly cheaper, though lead acid is also cheaper. You can get them set up to grid tie, or to run a separate set of circuits, but good luck if you ever have a house fire insurance claim with a self designed battery pack. The "DIY Powerwall" folks scare the hell out of me with their builds. Electric car batteries are a better option, but still may cause an insurance investigator to ask an awful lot of questions, since they're not a standard setup, and you don't know the history of them.
From a cost standpoint, this is just like a battery.
Typically the grid is being your free battery under those conditions. I expect those agreements to go away eventually. The newer inverter specifications/requirements (1741SA) will improve the ability of grid tie inverters to offer grid support services, but utilities really don't like net metering, for solid technical reasons. Using their infrastructure, offsetting rotating generation (which inherently provides inertia and phase balancing), and pretty much requiring that they take what you generate with no limits on ramp rate... eh. There's a good reason utilities don't like current inverters.
Has anybody else taken it more to the extreme? Self installed, off grid, self designed recycled battery, crazy low consumption?
Well, my office is off grid, but I'm using pretty boring flooded lead acid cells. Lithium makes limited sense for a self installed system, because the costs of lead are so low for the capacity, and it works well with the 9 months of good production typically found in most areas.
Most places, a properly designed system will be producing a surplus of energy in the summer - so the batteries will be regularly full. Lead is super happy to be charged daily, or to sit at a float charge. AGM is lower maintenance, at the cost of a designed in life limit (it's inherent to how you have to create a lead battery to not require watering) - typically 5-7 years, or a bit less if cycled. Flooded is awesome, but requires the occasional watering, and a good vent for hydrogen buildup. Another plus of lead is that you don't have to thermally manage it. If you can keep it cooler, it'll enhance the life, but it can sit outside year round and be perfectly fine.
While regular deep discharges are bad for lead (you can't cycle it to 80% DoD and expect a long life), a few deeper cycles a year isn't a big deal, as long as the pack is kept from getting
too cold while deeply discharged. Fully charged lead acid freezes at about -92F (depending slightly on design specific gravity), whereas a 20% charged one freezes around 19F. Underground storage is good for a large lead bank (crawlspace or such), if you can water them and vent them down there.
But what you can do with a lead bank is to size it such that you get occasional deep discharges, but mostly cycle it at the top of the capacity. My 12kWh bank can run me for a day or two if I really need it to, but I generally don't pull more than 1-2kWh out of it overnight. For a house bank, you could have a 100kWh bank, normally only pull 5-10kWh out during the sunny 9 months, but still pull 80kWh out of it on occasion during the winter if you need to. That doesn't impact longevity that much, as long as you have proper charge profiles (and don't, say, discharge it that far and then leave it). But you can pull a few days use out of a bank like that if you have biomass heating and be fine.
With lithium, a huge bank like that is both stunningly expensive, and generally not made good use of (using a small fraction of a lead bank during the summer keeps them happy, keeping lithium charged like that is actually hard on the cells).
... anyway, thoughts on your system. :)
