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Bob McGovern · 02-15-09, 11:12 AM

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.

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.

02-15-09, 11:12 AM	#4
Bob McGovern Lurking Renovator Join Date: Feb 2009 Posts: 24 Thanks: 0 Thanked 0 Times in 0 Posts	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. 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.