Portland General Electric (PGE) is developing an inverter-battery (1 MW – 240 kWh) at NREL before installation of a full size testing and demonstration of the 5 MW – 1200 kWh rated device.

Hope this answers your question.

There’s only one number we need to know, and that is – the battery – ?MWh.

5MW doesn’t tell us anything meaningful.

I’m assuming that fast discharging causes the battery to heat up and heat = lost energy.

Up until very recently deep cycle/thick plate lead acid batteries were the most common storage for off the grid. I’m sure some people were using something else, but I’ve never encountered one of those people.

Apparently lead-acid batteries, the kinds available until lately, don’t do well if completely discharged. So people, in general, would try to avoid more than a 20% discharge and use enough batteries to carry them for 2-3 sunless days.

Trojan has recently released a new thicker plate battery designed for off-grid storage. It’s rated at 4,000 20% DoD cycles or 1,000 100% DoD cycles. 4,000 cycles is about 11 years of daily discharge. Their regular golf cart batteries are good for 5-7 years.

http://www.trojanbatteryre.com/PDF/datasheets/T105RE_TrojanRE_Data_Sheets.pdf

The idea is to size your battery bank so that it will carry you through a short period of no sunshine. Perhaps 2-3 days. Start with your daily use and work back.

If you need 3 kWh to get through a winter day then you need 9 kWh to get through 3 days.

If you’re going to use 6 volt batteries then you need 8 in parallel (8 strings) to give you 48 volts. You’re going to store 1/8th of the needed power in each string. So, in this case 9,000 Wh / 8 = 1125 Wh / 6 volts = 187.5 aH per string.

If you are willing to discharge your battery 100% then a single T-105 RE would do. They are 240 AH at 6 volts each when discharged slowly. If you want to stick with 20% maximum discharge then you’d need about four per string.

WARNING: I’m not sure I’ve got my math correct. I’m sticking it up for others to crank through and confirm or shoot down.

And I suspect that if you did use 100% discharge you might find your inverter shut down when battery voltage reached a certain point. Mine does, but that might be adjustable. Check rather than assume.

I understand your frustration the way some things come out in the news. Having said that lets try to see why its really tough to put numbers to everything.

First of all 500 customers is quite small so if its midday and Monday through Friday; all the people are up, t.v.’s are running, toasters going, washing machines and electric dryers are running, lights are on and the AC is cycling off and on if its summer. My GUESS, and I am of course guessing, the average per household consumption would be about 10-30 kWh’s per home for some given time period.

Now lets say the electric grid goes down in the evening instead of during the day. This time it’s after dinner, the kids are in bed, windows are open since its a nice summer evening, so AC is off, washer and dryer have stopped, showers have been taken and basically its dad and mom watching a little TV before they go to bed. Their home might be, and again this is a guess, drawing 2 or 3 kWh from the grid.

As you can see the ration or change between say some average of about 20 kWh daytime use to about 3 kWh in the evening is significant; and to further complicate things it depends on where the community is located. The electrical usage patterns are different for rural areas than for say multi-family dwellings. Multi family dwellings typically have fewer sq.ft. per family member and therefor typically consume less energy but this is certainly not always true.

So if you happen to live in the area, pull out your electric bills for let’s say the last 6 months and total up the kWh’s used. Divide that by 6 and then again by 30 and you will get some idea of what your home is using per day [ 24 hour time period]. That should give you some idea what a typical home in the area [if your home is typical] is using.

If those 500 homes are like yours and the people living in those homes live about the same way as you do, then you will have some approximation of how long those 500 homes could be served. But remember we haven’t factored in TIME YET. The time when the grid goes down is going to effect how long you can continue to watch T.V. Is it summer or winter or daytime or nighttime. Is it a retirement community or does it have a younger population. Are there any big energy consumers and will they be automatically taken offline when the grid goes down. All factors we haven’t taken into consideration yet.

Hope this helps a little. Have a great day.

Dave2020, good question, if they are using 5kw then it would be two hours. If they only use 1kw per hour then 10 hours. Probably some where in between.

For five minutes? For half an hour? Nobody wants to say, not even PNNL.
https://www.pnnl.gov/news/release.aspx?id=990

If anything please title it as a microgrid back-up system and not storage for intermittent power resources.