Thanks for the forum; WY offgridder here
 

Five and a half years ago, I bought 32 acres of the nakedest prairie imaginable and started building. The land was cheap because no utilities came near it (sadly, that condition will change next week. Darn.) With a blank slate to start with, lots of sun, and absurd winds the decision to go off grid was obvious.

Nothing is finished exactly. And there are a few things I would do differently, looking back. But for the most part, the result is amazing: Two of us live in perfect modernity and comfort, running a 1200 sqft house and a full-time (60 hr/wk) cabinet shop off eight PV panels and a small wind turbine. And our total annual living costs are under $500, in one of the most brutal climates anywhere. This stuff works, it's easy, and it's cheap.

Most of our heat comes from passive solar, perhaps 80%. Active solar (in-floor radiant tubing driven by solar hot water) supplies a baseline via the floor slab; a small woodstove acts as a kicker but only runs a few hours per night. Domestic hot water is preheated by the same solar thermal, then boosted up to shower temperature by a demand propane heater. House is all steel and insulated with water-based expanding foam derived from soybeans. Shop is Arxx insulated concrete forms with cementboard siding.

We have a hybrid solar/wind electric supply, about 1200 installed watts of each. Wind provides two thirds of our power in winter. In summer, it's about half and half. The PV panels are on Zomeworks trackers and the turbine is an 8 ft Bergey XL1. Twin inverters only supply 60A at 120/240 modified sine wave, but that's been plenty. Daily consumption is a steady 4.5 kWh. We make more power than our batteries can store, most of the time. Excess energy is dumped into the hot water storage tank. The batteries are immense -- roughly 10,000 Amp-hours at the 100 hr rate, or enough to last 45 days with no charging inputs under normal usage.:eek: Telecom tearouts. That's key to the whole business: really big batteries!

Finally, we have a rare water well out here, but the water isn't real good. So we have 1000 gallons of rain catchment for drinking and landscaping. Wish we had a bit more, since we get only 8" of rain a year. We can go months without precip.

Looking forward to trading ideas. I can post photos is that's allowed, and I'm always happy to answer questions.

Bob...

Welcome to the site Bob!

Your setup sounds quite impressive. The battery setup sounds incredible! Would you mind taking some pictures of the place? We'd love to see it.

Hello Bob and welcome on board.

You have the house of my dreams... :cool:

4.5kWh/day is so little. Congrats :thumbup:

10,000 Ah of batteries is so much :eek: Also never heard about system designed for 45 days autonomy, usually it's 3-5 days.

• At what voltage are the batteries ?
• Are they low cost one or deep cycle one ?
• What is the live expectancy of your batteries systems ?

As Daox, I'm very interested in the battery system, as well as the PV, wind and solar systems, and how you can consume so little... In fact I'm interested in everything ;)

Congrats for such a great house,

Denis.

Groar: our batts are Exide/GNB 3700 long-duration cells, 2VDC each. Simple, cheap, proven, robust flooded lead acid, not easy to damage. They came from telecom tearouts via eBay: they are used as switchboard backup, then retired after 7 years -- nearly all of that spent twiddling their thumbs, unstressed. Like new for about $200 each. Twelve of these in series supply our 24V storage.

The most common error new off-gridders make is undersizing their battery capacity -- as you say, 3-5 days storage is all they plan for. That means they are constantly deep-discharging them, then recharging them hard and fast. That'll kill any battery in short order. With very large batts, you tend to stay in the top 20% of their capacity. No sulfation, no lead loss, no boiling off electrolyte. When sun and wind lack, you can coast for a long time; when sun shines and wind howls, you always have room to stuff a few more Amps.:D

I expect these batts to live 15-30 years. Hope so, cuz winching them out of the cellar won't be fun. Seven hundred pounds or so.

As for efficiency ... *shrug*. Not something we pay much attention to. The real mystery is how the median US household consumes 30-35 kWh per day. We have a small fridge, but a full-sized Energy Star model is nearly as efficient. We cook and boost hot water with propane, but our little propane tank lasts 18 months. We have no TV but two computers. No laundry (water is rusty), but a big woodworking shop pulling big horsepower for hours on end. Compact fluorescent lighting throughout, but we don't sit around in the dark. Microwave oven, toaster, coffee maker, the usual heap of electrical goodies. My goal was to build a house that, if you didn't know it was off grid, you'd never know it was off grid.

Thanks for the welcome; I'll put together a webpage of photos and post a link.

Excess energy
 

"Excess energy is dumped into the hot water storage tank.".. Nice way to save.
I'm assuming you are using a resistive heating element for that.

I have been thinking along those same lines, since I have to burn oil to heat my hot water.
However, I'm starting to think that a heat-pump hotwater heater would be a better way to go.
(Since my array is going to be pretty smallish).

Airgenerate.com | Adaptive Energy Solutions

video:
AirTap Water Heater Heating Element - Fine Homebuilding Video

I guess it uses about the same power as a small window AC..
Not suitable for storing very many KWHs, unless I get a really big water tank! :D

Huh. Never seen that AirPump before. Sez it draws 600+ watts, tho -- depending on its cycle time, that's a whole bunch. More efficient than electric resistance (which is awful), but that's a load of juice for RE to supply.

Even a small solar hot water panel can do wonders for heating water, and if you use a counterflow (external) heat exchanger you can add it to any tank water heater. A little Taco circulating pump draws less than one Amp. We only have a single 4x8 low tech panel, but over the course of the day it heats our well water from 45F to 105F. At that point, a second pump/heat exchanger turns on and moves some of that heat into the floor slab. It is really nice to have your domestic hot water most of the way to shower temperature; our Bosch/Aquastar demand heater barely needs to fire up.

The hot water heater element was an interesting quest. I had the storage tank custom made by Advance Metalpres in Canada; it's all stainless, because our water is so aggressive. They can add as many bulkheads as you like. But low-voltage DC elements are brutal, around $90 each. And you need huge wire to handle the amps. Thought about it awhile, then stuffed a $10 hardware store AC element into the tank. Wired it for 120VAC run thru a solid-state relay (silent, no moving parts). Even tho this dump load is technically for the sake of the wind turbine -- you can't let them run unloaded -- the relay is triggered by the v.smart solar controller. The turbine catches fire much less often, now that it has good dump load on it.:D

The AirTap cycle time is pretty short and won't occur too many times a day,
unless it's wash day. :)
Too bad they cranked up their price last summer. I think they may have had some hurricane damage.


Years ago (early 70s) when I had 3 Novan hotwater panels on the roof,
we had 84 gallons of preheated water to feed into the domestic coil on the boiler.
In the summer, the tank would get up around 180, and keep the boiler
from using any oil when we turned on the hotwater tap.
In the winter, it would get up to about 120, which was still a help.

After about 18-20 years, the heat exchanger died (due to bad water),
but I think those old collectors are still at work on a roof somewhere in New Hampshire.
(Wish I had kept them). I still have a couple of little brass Taco circulating pumps.
-----

I guess an AC element is about the cheapest way to go, if you need to dump some power.
If I ever get to that point, I'll have to keep that in mind.

I've read about guys using AC element space heaters in their DIY EV cars
and running them on 120-130 VDC.. Just have to change the fans.

So what is your alternative to laundry?