Inverter/ batteries without solar panels

BB. wrote: »

Xantrex and Magnum (others?) now offer native 120/240 VAC 60 Hz inverters--So you don't have to play with the "stacked" 120 VAC inverters or auto-transformers for 240 VAC from 120 VAC inverters.

The real question is what are the "off peak" loads. We talk about running batteries from afternoon through the night, and running a genset in the morning (if needed) to help an undersized solar array.

Some places I have read about (Africa for one) are doing the "hybrid power" systems. Run the genset from evening until bedtime (people cooking, needing lights, home work, washing clothes, etc.) and then run the inverters/batteries for the rest of the time. The idea being that you run the generator when you have steady and "heavy loads" (50% or more of rated genset capacity, including battery bank charging--would be my first suggestion).

I tend to suggest a "small genset" running a couple more hours than a large genset that quickly settles well below 50% rated output (kWH per gallon of fuel drops with most gensets).

With diesel gensets, there is the ~40-60% minimum load recommended for many (avoid "wet stack", carbon build up, glazing cylinder walls--so much, that sometimes load banks are needed to keep the diesel engine well loaded). Using a "hybrid" system of generator + battery bank + inverters can help minimize fuel waste with load banks.

-Bill

Cariboocoot wrote: »

3 kW hours per day is not unreasonable, but it is probably low. I use almost that much daily at the off-grid cabin and we've had a lot of practice at keeping consumption down. This includes running a refrigerator, satellite modem, computers (laptops), lights, water pumps, basically everything.

On a 48 Volt system 3kW hours AC will be at least 80 Amp hours. If you go for a 25% maximum depth of discharge that's an easily obtainable 320 Amp hour battery bank. If it needs to go to 50% DOD (6kW hours) it would still work. The Magnum would have no trouble charging it either. Likewise if the daily need was 6kW hours and you did need a 640 Amp hour 48 Volt bank.

The only other issue is maximum loads. You need to have a number for the most power that will be demanded at any given time. With big things like washing machines and water pumps being powered this can get quite significant. You may want to change the wiring a bit so that heavy loads are on "strictly generator" lines and can't be mistakenly used from the inverter, or you may find that 4kW is enough for everything (people usually don't turn it all on at once). If necessary, the Magnums can be stacked up to four in parallel providing 16kW @ 240 VAC.

Cariboocoot wrote: »

Without refrigerator and water pump? 3kW hours is probably too much. This is the trouble with not having a definite power use reference figure; you either buy more capacity than is needed or the everything shuts down at an inconvenient moment.

You can add more batteries later, but for a given value of "later". The longer the time and/or the more use the faster batteries age. So a set of 320 Amp hour L16's bought one year an be sufficiently lowered in capacity by next year that it is not a good idea to add more batteries. This is especially true if the reason for doing so is that the batteries are being cycled too deeply.

If this is a full-time residence an electric refrigerator will be more economical than propane (especially if the 'frige needs replacing). Plan for that even if it isn't the case now. Depending on what the well pump is, it may be a good idea to run that off the inverter too. It can be done: I do it.

You might also want to revisit the solar possibilities. Just because an installer has said it can't be done doesn't make it so. It could just mean it doesn't have the typical Southern exposure most of them think is necessary to make panels work. Panels only have to face the sun; they don't really care in which direction or at what time. Considering how low the price is on panels now, even an inefficient array can be worth the money over fueling a generator for that last couple hours of charging.