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Heat, hot water, refrigerator and stove are LP and the modified sine-wave inverter isn't up to the task (true sine-wave inverters are much less expensive now) and burned out the electronics in her Staber washer - but only after seven years. Despite this shortcoming, she's had seven plus years of comfort, all the satellite TV/DVD watching and plenty of CFL lighting for those cold winter nights.
The windmills didn't work out. They're nearly a half mile from the house on a ridge and the cost of the #0-1 copper wire alone was incredible - and would be prohibitive now. Then the building inspector insisted the windmill towers not be higher than 30' and that the run down to the house be installed to utility standards. Way too much money invested for any reasonable payoff and the power production is spotty, at best. Add to that those comical rednecks who think shooting at someone else's property is downright hysterical.... Yeah, we lost one.
The sixteen 80 watt solar panels (~$12K installed with an Outback PWM charger), on the other hand, generally have the batteries fully charged by 11 a.m. on a sunny day, and she can't use power fast enough while the sun is shining to avoid "wasting" electricity - laundry, fans, vacuum cleaner and stereo.
The battery bank is set up with three strings of Trojan T-105's at 48v/615 amp hours - a total of 24 batteries costing ~$1,350. There is monthly watering and yearly cleaning to keep the batteries in good condition and, using about 30 amp hours/day (actually, pretty wasteful), she's got a 16 day reserve for sucky winter weather.
Batteries can't remain in a discharged state for long or they'll develop sulfate crystals and lose capacity - eventually to the point of total failure. However, I am not aware that she's gone more than three days at a time without charging, even in the dead of winter. AFIK, as long as they're being charged, they don't have to get to 100% every day to be protected from sulfation.
It's hard to find reliable information on sulfation on the nets 'cause there are so many people and companies selling additives and gadgets to prevent it, with the opposite stance being "overcharge, overcharge, overcharge". The middle ground is "maintain, charge regularly and equalize (overcharge to balance the cells) once a month.
Given that the solar panels and Outback charger never supply more than 16 amps in direct sunlight (~2.6% of the battery capacity) there is little to no possibility of heating the batteries to destruction when equalizing. However, you've got to be careful pumping too much amperage into any battery bank - 10% capacity is pushing it, so both capacity and projected use need to be considered when sizing the battery bank. Bigger, within reason, is always better and will last longer.
Additionally, larger batteries, like those used on forklifts, have a much longer lifespan than smaller batteries with multiple cells, but you pay for that extra capacity and lifespan up front.
Finally, the plates inside the battery have got to be covered with distilled water/sulfuric acid solution or they will be ruined. They should always be filled before equalization, but we've found a monthly check to be sufficient.
If I were to do it all again:
1) Total DC system with DC appliances - including a marine refrigeration system, car stereo and RV appliances. The $2.5-$4.5K saved on the sinewave inverter would buy a lot of extra batteries, panels and 24v electronics.
2) Industrial batteries.
3) One small windmill near the house to capture energy on stormy nights and during bad weather. The chemical process batteries utilize to store energy is finite. Keeping the batteries charged to capacity as much as possible at all times will increase the lifespan immensely.
4) Small, really well insulated passive solar house.
5) Wood stove (and enough land for a woodlot).
6) Solar hot water and an on-demand LP water heater instead of the tank heater.
I'm not preaching Gospel here, just what I've observed in practice in eight years and tried to learn over the past thirty. Please do check any facts and figures 'cause, as I said, there's a lot of misinformation out there and I may have got a bum steer or two along the way.
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