# Array sizing tool?

Solar Expert Posts: 199 ✭✭✭
I am looking for a tool -- an excel sheet or online calculator -- something that I can plug numbers into that can help me determine what size array I need. I'd like something that allows me to input the battery voltage and AH, desired DOD, genset input (optional, I guess) so that I can "play" with my options based on my measured loads and also to determine what size the array needs to be as I change those loads (lower, natually)

I did a search here but did not find what I was looking for, so I went to google and the signal/noise was too high.

• Banned Posts: 17,615 ✭✭
Re: Array sizing tool?

Check and re-check.
Almost every charge controller manufacturer has an on-line array sizing calculator to make sure you get the optimum array for that controller according to selected panels.
PV Watts can give you various outputs for alternate array sizes/angles/locations.
Your battery bank size is a function of your loads & DOD; determine the loads first, then work out how much battery is needed, then come up with the necessary array & controller to recharge.

You will almost always have to do these calcs several times in order to come up with final figures. That's why we have the rules-of-thumb initial calculations.

AC Watt hours daily / inverter conversion efficiency = DC Watt hours daily. Add DC load Watt hours (inverter consumption) for total. Divide by system Voltage = Amp hours needed. DOD factor: minimum 2X for 50% DOD, 4X for 25% DOD is better. You now have a battery bank size that will have to be adjusted up (preferably) or down (be prepared to shed loads) to meet available battery sizes.

Recharge preferably at the maximum rate recommended by the battery maker. Default value 10% of Amp hour capacity for peak charge current. Calculate array size based on: 1). for PWM, Imp rating of panels or; 2). for MPPT array Watts @ 77% efficiency typical. Adjust array size up (preferably) or down (be prepared to run the gen more) to meet available panel sizes.

Lather (work yourself into one), rinse (calm down; it's only money), repeat (until you get a workable system that fits all your needs including budget).
• Super Moderators, Administrators Posts: 31,765 admin
Re: Array sizing tool?

Over the years, we have had a couple posters make some very nice spread sheets where you plug in some basic numbers and it would give a bunch of different results...

I found them to be confusing because the person did not think the same way I did--So it was a bit difficult to ask/answer the questions the way I wanted to.

You have seen the calculations I have done--Those are all written up by hand every time I post (nothing automated, no cut and paste from a master post)--Yea, I should probably start doing that. But it only take a few minutes to run the stuff through a calculator for the results.

Because we usually type out the equations (vs telling you to get a 100 watt solar panels because we told you to get a 100 watt solar panel)--You can start to build out your own spread sheet to let you play with the numbers.

I would suggest not to become too wrapped up in the calculations, but pay attention to your loads and what your initial numbers are telling you (i.e., if you need a 3kW array and can only fit/afford a 1.5 kW array--then go back to your loads/expectations).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset