Consider a case of developing a grid-tied battery system delivering 10MW at 33kV to the point of connection for frequency regulation. The battery unit along with the inverter as packed in one single housing with the following particulars:

  1. Battery Bank rating is up to 500kW/1000kWh (AC) with scalable battery modules of 10kW/20kWh.
  2. Inverter size at 480V AC is up to 588.2kVA with scalable modules of 8.5kVA

Making some simplifying assumptions, how would one go about calculating the size of the system, i.e. number of battery banks and the nameplate ratings of each bank?

A basic explanation of the process is sufficient.


1 Answer 1


I'm not sure what the effects there are for it being specifically for frequency regulation. However if you want the batteries to be giving out 10MW at 33KV you will need to have an inverter that can supply 33KV (which is alot!) But if you managed to get it you would need to have 3300 amp hours or 10MW hours! (for one hours of supply).

With just the 480V inverter to work out how many extra modules you would need (assuming you are trying to supply 10MW with it and are ok with it being at 480v not 33kv, because adding extra modules wont increase the amount of volts its giving out, it will only increase the amount of power/current available for its load)

Then you take the amount of power you need to be supplying, e.g. 10MW and you take off the 588.2 Kw (KVA = KW) to get 9.4MW, then dividing that by 8.5w you end up needing to get about 1200 extra modules. Its gonna be a similar order of magnitude for the batteries and essentially the same way to calculate it - however there is the added element of Watt hours, which is how much charge the batteries can give out over an hour. presuming that 10kw is the maximum the batteries can give out at any time (but they can do so for 2 hours, divide the Kw per hour- 20kw by the amount of power being given out, e.g. 10kw to get 2 hours). then its the same proccess of that 10MW taking off 500kw to get 9.5MW and then dividing that by the size of the extra modules (10) to get about a thousand extra modules.

Hope this helps, lemme know if Ive misunderstood the question - I cant add comments as I dont have enough rep

  • \$\begingroup\$ Hi Bren, thank you for taking a crack at it. So I think I'll ad a bit more clarity : 1. Each battery module ( the so called increments of 10kW) are paired with their own single inverters of size 8.5kVA. 2. Modules make up a battery pack whose max rating is 500kW. Similar condition applies to the inverters. 3. The numbers are just an example and don't reflect any real system. I just want to understand how one would size the system step-by step achieving the required power output at 33kV. Feel free to assume any 90 percent round trip efficiency and p.f =1 \$\endgroup\$
    – fikacoder
    Commented Jul 7, 2023 at 22:10
  • \$\begingroup\$ I think practically, inverters don't normally pair together very nicely, as each inverter has an output that an AC wave, and getting the starting points of all the waves to be at the same time so they perfectly overlap is gonna be very difficult unless you have some kit specifically designed to do that. However if you did manage to get them to all line up (be in phase), there would likely be a value for the volts being output on each inverter. If you lined up the inverters in series then the overall voltage would increase. \$\endgroup\$
    – Bren
    Commented Jul 8, 2023 at 0:55
  • \$\begingroup\$ if we have 480v inverters, taking 33kv and dividing by 480 to get about 80. We would need around 80 of the modules in series to get 33kv, this would only supply as much current as one of the inverters by itself. But seem as thats still a hefty 10kw (have stripped it down to just the modules to make the maths abit easier) it would supply up to 330MW. And as each module has a battery that can supply as much as the inverter they will be able to provide the inverter all the juice it needs. so with an output of 10MW, the batteries could last for about 7 hours \$\endgroup\$
    – Bren
    Commented Jul 8, 2023 at 1:03

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