I flew out to a remote ranch on the Idaho/Nevada border last week, the new (bought it 3 years ago) ranch owner was having issues with his power system. Off grid, WAY off grid, with a hydro system that was being worked on by others. I was able to find a place to land about 2 miles from the ranch, and after getting the eMontague out was making good time until I ran into mud so bad it was impossible to continue. Freeze and thaw cycles are tricky on a dirt road with no gravel, with part in the shade and part in the sun, it went from easily rideable to totally not at all rideable in about 40'!
The ranch cowboy picked me up in one of those big ATV's for the last half mile to the power building. A nice purpose built cinder block building, with a separate side dedicated to the large diesel gen set, which was roaring away. A quad OUTBACK inverter power panel, all real nicely installed, and then the bad part: two giant (3300 lbs. each) forklift type batteries, all sulfated up. With the hydro down, the ranch two homes (set up when the hydro was fully operational, with no care or attention given to power conservation) was running off of a 1650 watt PV system, and the diesel genset. The OUTBACK MATE display showed the power currently (ha ha) be used was bouncing around between 6500 and 8500 watts, a fair bit of power. The 48 VDC system was at 56 volts, but as soon as the gen set was shut down, dropped to 42! They appeared to have one of more bad cells in the battery, dragging down and screwing up the entire system. Also lots of corrosion on the interconnects.
Quizzing the cowboy about the hydro, he seemed to recall it had a 8" pipe as a penstock, at least as it entered the power shack, which was 2 or 3 miles from the power shack we were in near the ranch homes. I never did make it up there to eyeball it, no place to land and time was short. 200 PSI was mentioned, whether static or dynamic he couldn't tell me. Conventional overhead wires and utility poles connected the two power shacks, it was really a nicely setup system that had unfortunately fallen on hard times due to neglect. A very rough estimate (assuming the 200 PSI mentioned was dynamic pressure) showed that when the hydro was running as it should, they would have somewhere around 15 to 26 KW on tap, 24/7, a hell of a lot of power! Unless they had some very large intermittent loads, I questioned why they needed that monster battery pack, which was going to need to be replaced, from the looks of it, and why I was called in to consult. The place is so remote they have a hard time getting anyone to make the drive, but for me it was just another excuse to do some back country flying, a lot of my off grid work I've done is because I fly a plane that can land about anywhere, and love doing so, as a result any off grid remote area customers of mine get prompt service with a smile, assuming the weather is decent anyway!
As of now, I've gotten a quote to replace the battery bank with new packs, direct from a large wholesaler that deals in forklift batteries. They are easy to move, assuming one has a forklift or tractor, the ranch has both, being in heavy steel cases, and are more cost effective then many smaller batteries all wired together. Plus, I've found that the least amount of individual cells to reach whatever needed capacity, the better. A few monster cells, is much better then lots of small ones, less chance for the cell chemistry to get out of whack over time due to interconnect corrosion, poor maintenance etc. The last 24 VDC off grid system I set up, used just three batteries, but they were 8 volt each and weighed 340 lbs each, and it all penciled out better cost wise then compared to a boatload of L-16 types. if nothing else, many less cells to water, and NOT doing so is the primary cause of early death in off grid systems. Central watering systems help a lot, just keep the central reservoir filled, but even that sometimes get neglected. Sealed batteries side step all this, but are easily twice the dollar per stored AH, nonetheless,the ranch owner also wants a price on using them instead of flooded. The sealed types also "run cleaner" over time. They don't put out the gases the flooded ones do, which seems to lead to the corrosion on the interconnects etc., not to mention they don't need to be vented.
I took one large sealed/AGM battery system apart (24 VDC, about 1200 lbs) 10 years after I first installed it. Repeated cycling had made it do what most batteries of any type do, wear out/lose capacity. This is one reason I really like being grid tied nowadays instead of off grid like I was for 28 years! The cells were in a steel rack I welded up, and then boxed in with plywood, all on heavy casters. I did all this in my home shop, and then delivered it and the systems power panel (also prefabbed in my home shop) with the boom truck I had then, (the battery box had built in rigging points) so once on site (remote area, again) in less then an hour we had AC power. The complete power panel (with PV charge controller, 4 KW inverter, breakers, etc.) was carried by two people and screwed into the basement wall framing, and the battery rolled along side it, all I had to do on site to get instant power was hook the battery leads and the PV cables into the power panel and throw a couple breakers. But I digress, when I opened up that sealed 1200 lb AGM battery 10 years later, it having received zero attention during that time, it was as clean as the day I installed it! Zero corrosion anywhere, it just simply wore out internally, it really made me a believer in them for off grid use, despite their still much higher cost then flooded. I'll post a few pictures when I get around to it.