Sanity Check My Vision

[Pinstriper]

We're rural, but on-grid. Just reading the tea-leaves, we expect sometime in the next 5 years our grid power will be rationed as there won't be enough for the increased consumption from electric vehicles. In fact, they're already shutting down distribution to prevent wildfires.

We currently have two service accounts: house and barn (350' away from the house). I have just under 4 acres, and we're down to 2 goats and 2 llamas. So we have pasture space for a ground solar array, so avoid worries about the roof lifespan. Strong full sun in the pasture near the barn after 9am or so thanks to no trees. Up at the house there are unfortunately mature trees to the south and west - the afternoon shade on the house is helpful in the summer, but really makes the house roof a bad location for solar.

OK, so what I'd like to do is put in a ground based solar array, with a stout battery bank, sufficient to take the barn entirely off grid. But I also want to be able to treat the barn as my battery shed for the house, and that means, I think, running 240v off the inverter the 350' back to the house, with the attendant embiggening of the battery banks and solar array when I go to put the house on the system.

The barn use runs anywhere from 60-200 kwh/month. So it needs to be sized for the max demand, which happily occurs in the summer when solar generation would be the most, and that "excess" solar would probably keep up with reduced demand in the winter. I also intend a pair of small vertical wind turbines just as winter insurance; if its stormy and getting less sun, we're probably getting more wind.

The house runs 600-1000 kwh/month.

The house is on heating oil, forced air furnace. I'm looking at conversion to either a heat pump (which means even more electricity demand to collect and store) or an in-ground geothermal, which would be somewhat less electricity.

But of course I'd need to plan on the increased demand of charging 2 electric vehicles.

So, just starting with the barn, for an off-grid just taking the max demand because I'll not have the grid to back me up... I think I'm looking at 6kwh/day. Since that's the summer figure where we have the longest days and next to no rain, I'm figuring storing 10kwh and 2kw of solar array to charge it.

I think I'll be overkilling the heck out of it, which seems sensible to me without the grid.

Once I have the system in place and see my actual generation figures, and the actual house consumption (on the grid still) with the new heating system, I would run a line from the barn to the house, adding solar panels and batteries based on the new demand profile for the whole ball of wax.

I fully realize the payback time may never arrive, but I don't think we can expect power prices to stay where they are today, and I'm prioritizing getting out from under the control of the grid. When they decide to shut off power, it just won't be available at any price.

 

[Rednecktek]

OK, here's a few thoughts right off the top of my head:

You're rural and trying to run electric vehicles? You're brave!

Setting up a big array and system for the barn is totally do-able and shouldn't be too bad to build.

I'm guessing you're NOT doing grid-tie? Or are you going to have to because of $NewStupidLaws? If you have to do grid-tie, you're going to get really expensive real fast.

Rather than converting your PV power to AC power and then send that 240v for the 350ft, you'd most likely get much better performance if you worked on getting the PV voltage as high as possible and send that 350ft to the house where you'd convert to AC there. The reason I say this is that at my camp I had to run 4AWG wire from my pump house to my camp (that was the biggest wire that would fit in the breaker) and because of the distance it dropped my 200a service to 70a de-rated (315ft of #4AWG Al wire) for line loss. 400v DC going 350ft will get much less loss than 240AC for the same distance.

6Kwh/day is pretty easy, that's only about 1 bog standard 100Ah rackmount per day you want backed up. The house load however, if you build for the worst case of 1000Kwh/mo which is about 33Kwh/day is going to be 5 of the rackmounts every day. Conservation is going to be a "Big Deal" to get that down.

Skip the turbines, they're never worth the money. Search around for threads on those and see just how big you have to go to make them viable. More solar and battery is MUCH more cost effective.

Just my initial thoughts of things to consider. Otherwise it sounds like a good plan!

 

[Pinstriper]

Yes, the end game is to cut off the grid. Because eff them. Not getting any "smart thermostat" or giving them any more control.

I don't see how they can require me to be on the grid, while also threatening to cut me off if I don't pay. I understand their argument about charging a transmission fee to backfeed the grid and sell power back. But I don't care about that. I only care about generating and storing for my own use, and if I have extra capacity, that's just safety margin. As far as supporting the cost of maintaining the grid, if I'm not using it, its nothing to me if it exists or not.

As far as conservation goes, my figures are from actuals off my current bills, so it assumes our current uses and habits. Electric vehicles are going to forced on us sooner than later.

I was already pricing out spools of 1/0 wire.

 

[Bvillebob]

I'm a few miles south of you. Realize that in December, January and February your panels will average at best 10 percent output. Then, figure out how many panels you'll need to do what you're talking about. I have about 20 kW of panels and 60 kWh of batteries, it runs my fridge, lights, freezers and shop, most of the time. Six months of the year I have more power than I know what to do with, 3 months I get by, 3 month are very, very lean

 

[JoeHam]

I was already pricing out spools of 1/0 wire.

That’s the motivation to run 400Vdc or more back to your SCC’s.

Keeping the oil heat is probably the most doable.

Not sure how big the house is but could a few mini split’s work for you? That would likely consume less than a heat pump, which will be a beast to satisfy in the winter with reduced solar generation.

Otherwise, a good sized backup generator may be in your future.

 

[John Frum]

From your description the house uses far more power than the barn.
Even at 240VAC there will be significant voltage drop over the ~700 foot round trip.
For acceptable voltage drop you will need very thick and expensive wires between barn and house.

Interactive Wire Size Calculator

Battery Chargers, Inverters, Solar Components, and Wiring Supplies for Boats, RVs, and Off-Grid Applications.

baymarinesupply.com

 

[Pinstriper]

I'm a few miles south of you. Realize that in December, January and February your panels will average at best 10 percent output. Then, figure out how many panels you'll need to do what you're talking about. I have about 20 kW of panels and 60 kWh of batteries, it runs my fridge, lights, freezers and shop, most of the time. Six months of the year I have more power than I know what to do with, 3 months I get by, 3 month are very, very lean

This is why I am doing the barn first, and then I'll have real data to refine the sizing when it comes to the house. It is also why I was thinking to throw a few windmills in - because we have more wind in the winter. I was expecting more on the order of 25%, though.

 

[Pinstriper]

That’s the motivation to run 400Vdc or more back to your SCC’s.

Keeping the oil heat is probably the most doable.

Not sure how big the house is but could a few mini split’s work for you? That would likely consume less than a heat pump, which will be a beast to satisfy in the winter with reduced solar generation.

Otherwise, a good sized backup generator may be in your future.

Oil heat was great when I could fill the 675g tank for a grand. Those days are gone, and at 3 grand and going up, it just isn't realistic.

I don't know where I'll land - the geo is one route that I need to investigate. Whatever I do, it will happen while I am still grid connected so I can see my actuals and then plan the solar and battery expansion. The house is the same 1600' split-level "day ranch" house built by the millions in the early 70's.

I have an 8kw generator already. Keeping it fed would be worse than the heating oil supply and pricing. For that matter, I have a diesel tractor and could buy a pto generator and feed it from my heating oil tank. I have zero confidence that the supply, pricing, and legality of heating oil or diesel fuel and ICEs for generation will be....unmolested, I guess is the word.

Again, this is not an economic decision, but a move to be energy independent. I get that makes me sound like a kook.

 

[Pinstriper]

From your description the house uses far more power than the barn.
Even at 240VAC there will be significant voltage drop over the ~700 foot round trip.
For acceptable voltage drop you will need very thick and expensive wires between barn and house.

Interactive Wire Size Calculator

Battery Chargers, Inverters, Solar Components, and Wiring Supplies for Boats, RVs, and Off-Grid Applications.

baymarinesupply.com

Thanks for the calculator.

So....the power from the street is from a pole that is about the same distance to the house as the barn is. And that's coming off the pole at 240vac, right ? So I was thinking I'd end up matching the same wire they ran from the pole to the meter.

 

[Rednecktek]

So I was thinking I'd end up matching the same wire they ran from the pole to the meter.

And this is where physics gets in the way. AC breakers usually can only take up to a 4AWG wire in their terminals, and that wire from the power pole is a LOT thicker than that.

Again, this is not an economic decision, but a move to be energy independent. I get that makes me sound like a kook.

Not to me, but I've been trying to get my cabin in the mountains to self-sustainable power for about 4 years now. ?

 

[JoeHam]

Again, this is not an economic decision, but a move to be energy independent. I get that makes me sound like a kook.

That is the only reason I’m involved in solar, and I’ve been called much worse than a kook. ?

I have my refrigerators, sump pump, garage door opener and a few more circuits running off solar on a critical loads subpanel powered by solar, backed up by the grid.

I continue to slowly grow the system and move more things over from the main panel but my heat pump and water heater will be the last to move. If I ever get them moved.