I built a solar powered off grid office from a Tuff-Shed.

[Syonyk]

I moved recently, and as part of this move, I'll be working from home.

I can't work from "home" - I have a hard time separating work from not-work.

So, I built a remote office to use from a Tuff-Shed Pro Studio.

However, due to the nature of our land (a lot of lava rock/basalt), trenching power out there is a "Haha, you want me to what?  Well, I guess if you pay me enough..." type thing.  I cannot trench through basalt.  Lots of other people can't either, so it usually involves explosives.

... and I kind of want an off grid solar system to play with.

As such, it's an off grid shed! :D

It starts with this (a pre-assembled Tuff-Shed I got for 40% off):


I had to dig a level foundation for it, since they can't block it as they're building it like they normally do.  Two days with a shovel, and I made this:



It showed up on a truck:


And got delivered to my foundation:


It being an off grid shed, insulation is really, really important.  I have a very limited energy budget to work with.

So, I foamed around the windows/doors to seal them and reduce drafts (as well as reducing the amount of cold metal surface facing the interior air).





Interior insulation is several layers.  I have 3.5" of rock wool in the walls (less-awful to work with than fiberglass).



And 5.5" above.



Additionally, I put 2" of foam insulation inside that, and taped all the seams with aluminum tape to help keep things draft-free.  There's no electrical in the walls, so I don't have to mess with insulating around junction boxes and such.

I have (nominally) R25 walls, R35 ceiling, and R0 floor.  :/  I may get someone to come put some closed cell foam under it if it's a problem.  Due to how the shed was delivered in one piece, there was no way to insulate under it.





Inside that, I installed 1/2" plywood for the interior.  I don't like working with drywall, and it's easier to mount stuff to plywood.  Plus, it's more robust against dents and dings.



HVAC is a through-wall mounted heat pump.  Yes, a proper reverse cycle unit instead of just an air conditioner with electric coils.  It also has electric coils, but most of the year it's running it's compressor.

This required cutting a hole in the wall, which is remarkably harder than one might expect.



And installing the air conditioner.



You can get an idea of my wall construction from the plug removed.



Solar panels are on a ground mount frame built of pressure treated lumber.



I have 4 up now, but 10 total, for 2850W nameplate capacity.  Overkill for an office, perhaps, but I do run some significant computing equipment on occasion, and I want to avoid generator use in the winter as much as possible.

Power storage is 8x Trojan T105RE cells, for 12kWh nameplate capacity at 48v.



Inside, I've got a nice workbench and shelves on one side.



And my desk and a lot of shelves on the other side.



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

Beyond the shed, I've done all the work myself.  It's been about three weeks of full time work to go from "bare dirt" to a usable solar office.

I've got a Midnite Classic 200 MPPT charge controller (going to run 2 strings of 4 panels), and I've got a cheap PWM controller on order for some "east wall" panels (morning power, and a set of panels to mess with cheap controllers on).  The inverter is a 2kW unit that can run up to 6kW for short periods - important for some of my activities like spot welding battery packs (very, very abusive to power supplies).

Build cost up to now is about $15k.  It's a bit higher than I was hoping for, but that includes all 10 panels, and I'm likely to spend about another $1k on finishing touches - more panel mounts, vent fans, lighting, etc.

This office is going to be used year round for full time work - both tech work and bench work (teardowns/analysis, pack rebuilding, ebike design, etc).

Interior space is just over 7' x 11' (after insulation/plywood), so I've got about 80 square feet of my own space to work in, crank music in, and generally do whatever I want with. :)

==========

Blog posts are going up with radically more details on each of the steps weekly, and I'll add them to this post as they show up.

Part 1: Overview ("Why I'm doing this"): https://syonyk.blogspot.com/2016/05/solar-shed-part-1-overview.html
Part 2: Foundation ("Lots of digging"): https://syonyk.blogspot.com/2016/05/solar-shed-part-2-foundations.html

[Smokystache]

That is sweet. I've always loved the idea of a "writer's cottage" or similar retreat. I'll be curious to hear how the solar & batteries work for your need. Very sweet.

[ShoulderThingThatGoesUp]

This is very, very cool. I am having a porch finished into an office shortly for the same reasons you wanted a separate office; it should cost about $7k. Your budget confirms that in my case this is the right move - we had considered putting a garage with an office above back there but estimates started getting into the $40k, $50k range.

[nereo]

That's a really cool project.
Curious why you didn't mount any of the panels to the roof - just cheaper that way?
Also - do you need/want any source of water for your off-grid office?

[brute]

Pretty cool man. In the days of yore, my dad and I built a shed about that size and put an old cast iron wood stove in it for heat in the winter.

Nice work on the separate work space. I worked from home for 4 years and still do some consulting on the side, and I have to make sure I close the office door at the end of the day, and even then it never really feels like I left work.

[forummm]

Nice setup. Are the solar panels so far away from the house that you can't use them for the house or to feed into the grid? It seems like a lot of power for such a small shed.

[Syonyk]

I'll be curious to hear how the solar & batteries work for your need. Very sweet.

Ask me in a year. :)

It's going to be seriously overpowered in the summer, but I'm concerned about winter production because I don't want to run a generator that often.  And we get inversion layers where it can be cloudy for a month - so I may need a generator anyway.  But I'm hoping I can get enough light through to create 300-500W, which is enough to run me in a low power state and keep the batteries topped off.  In the summer, I'll be generating more power than my inverter can actually sustain, so... uh.  No idea.  Charge the bikes, and if I buy a Leaf, charge it too.

This is very, very cool. I am having a porch finished into an office shortly for the same reasons you wanted a separate office; it should cost about $7k. Your budget confirms that in my case this is the right move...

$7k sounds sane.  My shed would probably be around $7k if I didn't go solar - not only would I not need the panels/batteries/etc, I wouldn't have insulated it quite as aggressively.  Doesn't matter as much on grid power.

Curious why you didn't mount any of the panels to the roof - just cheaper that way?

The roof faces north.  So either I'd have to go with seriously raised mounts (not cheap), or have seriously suboptimal panel placement, and they'd be essentially worthless all winter long.

My panel mounts can swing for winter angles, and I'll be doing that.  The roof will be shaded or nearly shaded a lot of the winter months.

Also - do you need/want any source of water for your off-grid office?

Totally rocking the gallon jug I fill before I head out there each day. :)  I may get a 5 gallon water dispenser, but there's really not much space in there right now.

Nice setup. Are the solar panels so far away from the house that you can't use them for the house or to feed into the grid? It seems like a lot of power for such a small shed.

Sadly, "getting power to the house" requires the same type of trenching (to be legal) as trenching power from the house to the office.  So, no.  There's no real way I can feed them into the grid.

If summer production is utterly absurd, I might be able to eventually trench the long way around, but I'm talking several hundred feet of UF cable and conduit (or a 2' trench).  That's damned expensive to do, and even feeding 3-4kWh/day into the house, it'd be decades to pay for the trenching.

My plan is to charge my electric bikes down there, and if we end up with an electric car, I'll charge it down there in the summer.

It is a lot of power for an office, but I do a lot of work with fairly high powered computing, so I'll be using it when it's available.  Sunny summer afternoon?  Crank up the servers.  Cloudy winter day?  Laptop time (or Raspberry Pi, or iPad).

Mostly, by the time I paid freight, it didn't make sense to get fewer than about 10 panels.  I tried to sell a few locally on Craigslist, but nobody is interested, so I'll just use them.

[ShoulderThingThatGoesUp]

Is the roof metal? Could you collect water from it and filter it for drinking? I know it's Idaho so the rainfall might not be huge.

I wonder if you could collect rainwater to feed a deciduous tree that would shade the shed in summer so you don't need as much air conditioning...might be hard with the rock, I guess.

[HipGnosis]

It's going to be seriously overpowered in the summer, but I'm concerned about winter production because I don't want to run a generator that often.  And we get inversion layers where it can be cloudy for a month - so I may need a generator anyway.  But I'm hoping I can get enough light through to create 300-500W, which is enough to run me in a low power state and keep the batteries topped off.  In the summer, I'll be generating more power than my inverter can actually sustain, so... uh.  No idea.  Charge the bikes, and if I buy a Leaf, charge it too.

Are your panels at the optimum angle for winter?  That will reduce your summer 'overpower' and increase your winter power.
I'm pretty sure it's a 'bad thing' to have more power than your inverter can handle.

[Syonyk]

Is the roof metal? Could you collect water from it and filter it for drinking? I know it's Idaho so the rainfall might not be huge.

Roof is just plain shingle.  That was one downside to the prebuilt unit I got, but at 40% off, I can deal with it...

I wonder if you could collect rainwater to feed a deciduous tree that would shade the shed in summer so you don't need as much air conditioning...might be hard with the rock, I guess.

The view lines up with the sun, so... *shrug*

Not like summer power is a concern for me.  It's really going to be absurd how much excess I'll have.

Are your panels at the optimum angle for winter?  That will reduce your summer 'overpower' and increase your winter power.
I'm pretty sure it's a 'bad thing' to have more power than your inverter can handle.

They're on swings.  So I can angle them for summer/winter.  I'll change them a few times a year.

It's not really a bad thing to have more power than my inverter can handle.  The charge controller won't pull power out of the panels if the pack doesn't need them.

If the pack is full (at float voltage) and I'm using 150W, it'll pull 150W from the panels, even if it's a sunny day with 900+W available.

What "more power than my inverter can deal with" means is that there's just no way to use all the power I can potentially generate on a summer afternoon with AC.  That's fine - I plan to use DC power as well (I'm working on how to run my whole office on DC, but that's a long term project).  The reason for all the panels is to try and generate enough energy during winter.  I'll "waste" panel generation potential during the summer, and I really don't care that much.  I'll use what I can, but the panels are there for winter.

And there will be gobs of energy available to charge battery packs and such.  I'll do what I can with DC conversion straight off the main pack terminals.

[Syonyk]

Excellent. :D  *tents fingers*

My DC wattmeter arrived and actually works!

[nereo]

I've always kinda wondered what would happen with non-grid tied PVs when the generate an excess of power but have no place to send it.  It doesn't 'hurt' the panel any?

[Rural]

Very cool, and now I know one other person with through-the-wall heat pumps. We have two on the house as our only non solar heat source and only AC.

[Syonyk]

I've always kinda wondered what would happen with non-grid tied PVs when the generate an excess of power but have no place to send it.  It doesn't 'hurt' the panel any?

No, you just don't pull any power out of it.

If you put a panel in the sun with nothing connected to it, it'll sit at open circuit voltage - so just under 40v on my panels.  It's generating voltage, but no current.  They're perfectly happy to do that, but not exactly useful.  There's no power being produced, and nothing being dissipated.

At the other end, if you short circuit my panels, they'll provide just under 10A at almost 0v, so again, almost no power, but this isn't a great thing to do to panels.

Maximum power in perfectly sunny conditions comes on around 31v and just over 9A.  This varies based on the sun conditions, but if I'm pulling full power from my strings, I'll be seeing around 120v and 9A.  Maybe a bit lower on the voltage, but somewhere around there.

Once the batteries are charged, the charge controller (I have a nice MPPT unit) pulls less current and lets the voltage float up to wherever it feels like.  So, right now, my batteries are full, there's wonderful evening sun, but the charge controller is only pulling 75W out of the panels (running itsself, the inverter, a Raspberry Pi, holding an iMac asleep, and running a few other power bricks).  It's got the panels at 132v, and is pulling about 0.6A from them.  The rest of the potential power is just not being generated.

I wish I had something useful to do with the power.  I'm going to have over 2kW of panels hung (mostly for winter use - heavy clouds and inversion layers mean I need a lot of panel to pull even a couple hundred watts out), and nothing to do with it.  I can charge my ebikes down there, but that's about it.  I may pick up a Leaf or something and use the power to drive for free, but we've got a perfectly good set of vehicles for our needs already.

Very cool, and now I know one other person with through-the-wall heat pumps. We have two on the house as our only non solar heat source and only AC.

Have you had any issues with condensation or air leakage during the winter?  I foamed around it, but it's still a large hole in the wall with a bunch of metal in it.

[Rural]

Very cool, and now I know one other person with through-the-wall heat pumps. We have two on the house as our only non solar heat source and only AC.

Have you had any issues with condensation or air leakage during the winter?  I foamed around it, but it's still a large hole in the wall with a bunch of metal in it.

No inside condensation at all. I assume yours has an external drain? It will put out a good bit of water unless your climate is much dryer than ours (quite possible) - the evaporative function just doesn't work here, and we have to manage the overflow.


I have never noticed a draft - like you, we foamed around the outside. The ones here in the house are up quite high and so I might not notice, but we heated the mobile home we lived in while building the house with these, too, and while there were plenty of drafts, none seemed to be coming from the heat pumps.

I've lived seven years now with the heat pumps as our only hvac, and I'm still quite happy with them. We are more insulated than you are, and earth sheltered besides, but then you're much more insulated than that old mobile home was. Winter will tell you for sure if you have enough power production. It'll likely depend on how much your temps go low enough to kick on the backup heat - that electric resistance uses a lot more power (but this is true of any air heat pump, not just the through the wall sort).

[Syonyk]

No inside condensation at all. I assume yours has an external drain? It will put out a good bit of water unless your climate is much dryer than ours (quite possible) - the evaporative function just doesn't work here, and we have to manage the overflow.

I think it does.  There's a hole in the bottom, though I should probably pull the guts and make sure it's draining properly.  I installed it with the proper down angle according to the directions, but it's stupidly dry here most of the time.

I've lived seven years now with the heat pumps as our only hvac, and I'm still quite happy with them. We are more insulated than you are, and earth sheltered besides, but then you're much more insulated than that old mobile home was. Winter will tell you for sure if you have enough power production. It'll likely depend on how much your temps go low enough to kick on the backup heat - that electric resistance uses a lot more power (but this is true of any air heat pump, not just the through the wall sort).

I'm sure the temps will hit backup heat temperature, but I'm considering an earth tube fed shroud to warm it's outside.  And propane backup heat.  I don't think I can power the backup coils for long. :/  But I'll see.

[Rural]

No inside condensation at all. I assume yours has an external drain? It will put out a good bit of water unless your climate is much dryer than ours (quite possible) - the evaporative function just doesn't work here, and we have to manage the overflow.

I think it does.  There's a hole in the bottom, though I should probably pull the guts and make sure it's draining properly.  I installed it with the proper down angle according to the directions, but it's stupidly dry here most of the time.

 Probably not an issue then, but in the packaging with your heat pump, you probably got a little plastic or rubber nipple-looking deal. Hang onto that – it's to fit through the hole in the housing and let you attach a drain tube if you need to.


 Good luck with the heating – the backup will kick on at 40 or 45° F, depending on your model. Your manual should tell you.  Sheltering the unit would probably help some; just be sure it has enough air circulation.

[Syonyk]

New panels are up, and I've seen 2164W coming in today.  I tried a different approach to this panel mount based on suggestions by someone, and these were much easier to hang - especially since I borrowed a neighbor, and traded for helping pour 7 yards of concrete this afternoon.

I now have 8 285W panels hung - so 2280W nameplate capacity.  Today was very cloudy - the nice smooth curve is "estimated power" based on my location and panel config, and the green curve is actual generation.



The panels can swing up to 90 degrees.  They can't face north.  I don't really care. :)



Panels, in position.  I apparently forgot the 1/2" carriage bolts for the adjuster arms, so they're just screwed in for now.  I'll fix it when I need to swing them down in a few months.  The panels swing easily - I can move them with one hand if I need to, which is a huge improvement over the other setup.

Exposed wire is ground.  Still need to ground the frames.



From the rear:



I ran the BOINC PC hard all afternoon and was fine - 1.85kW peak DC output from my pack with that and the AC on.  So, I don't think I'll be needing any more racks of hardware to soak power.

It's 5PM and I still have 1300W coming in from the panels. :)  This is exciting.  Means I'll be able to run mostly in float if I let it get there.

And I may rebuild the front panel mount to match this one, assuming it holds up.  So much nicer to work with.

I've settled on BOINC as my "waste diversion load" - I could just let the panels idle and not run, but that's no fun.  So I'll be doing some charity computing on my spare power as it's available.

[GuitarBrian]

This is really cool. Thanks for sharing.

[Syonyk]

I've been actually using this space for about a month now for some web development and battery pack rebuilds.

It's doing exactly what I want!  I'm incredibly happy with it.

I've got two strings of panels up (so 8 panels), with around 2kW peak output.  I'm demand-limited in production during the summer (I can't use all the power I generate), so my peak production is around 15.5kWh.  I could generate more, if I could use more, but this is me, in the shed, all the computers lit up, AC set to 65 (so about 70F interior temperature) on a 100F day.

Before winter, I'm going to toss up another two panels on a hinged mount, so they catch the morning sun and can swing around to be a "manual tracker" if I'm really hard up for power.

This is my workstation corner:



My charge controller is kind of awesome looking.



And my battery bank, which is working great.

[CowboyAndIndian]

Syonyk, awesome build.

I plan to use DC power as well (I'm working on how to run my whole office on DC, but that's a long term project).

You could look into marine equipment since they are usually DC.  Since they are lower volume products, they may be more costly.

[GuitarStv]

That's a really cool shed.

[Blatant]

Super-sweet work, man. I love it.

[Syonyk]

You could look into marine equipment since they are usually DC.  Since they are lower volume products, they may be more costly.

Marine DC equipment is boat-priced.  So very, very expensive.  And not really useful for me.  I don't need a fridge or anything in there.

My main problem with the DC bus is that my pack equalize voltage is too high for the bulk of the cheap converters out there - equalize is over 60v, and that exceeds the limits on most of the 48v DC-DC buck converters.

I'm planning to get a fancier converter with a suitable voltage range to come from my pack voltage (so 46v-62v, give or take) down to a 24v bus, then run that around.  Some of my gear (mostly my wireless radios) will run on 24v directly, as will some of my monitors.  Then, from a regulated 24v bus, I can use cheap buck converters to come down to 12v for things like lighting and some of my other networking gear, with a few 5v points for powering random test equipment (a lot of my electronics gear is powered via USB).

I've got a couple kWh of old ebike batteries laying around as well, and I'm going to set up a system to charge those and use them as backup power for the DC bus - float them at 40v or so, and be able to run the DC bus from that as well.  My goal is to have all the critical loads (my networking gear and lighting, mostly) on that.  That gives me a good buffer if I'm dealing with poor solar conditions in the winter.  I can shut down the inverter and have zero load on my main pack so it can charge on heavily cloudy days while I'm still running.

Or so goes the theory.