80kWp off-grid

rabbit_39
rabbit_39 Solar Expert Posts: 43 ✭
in Solar Beginners Corner #1
Yea, I know. But that's what I heard someone discussing here. I wondered how the design was going to go. Especially since 80kwp off-grid is the only thing the customer knows he wanted. No load calculations, etc.

So anyway, in trying to exercise what I'm learning from all y'alls, here goes.

From 80kWp of panels, I will harvest:
80kWp * 4.25PSH * 0.52 derating = 176.8kWh/day

Battery storage if I assume I'll be using 125kwh/day:
125kwh * 1/0.85 inverter efficiency * 2 days * 1/0.4 max discharge = 750kwh

And for brevity's sake, I've done the calc to get around 8% charging rate
750kwh * 0.08 charge rate * 1/0.77 derating = 77,922 watts of panels

If I use 48VDC banks, it would require a single bank of about 15,000Ah! Or 4 banks of 4000Ah each.

To charge each of the 4 banks, I will need separate chargers for each bank? or separate charges going into the bus bar that connects the battery banks to make the parallel connection? If i remember right, each charge controller has to have their own solar input rather than sharing the array.

So let's say 20kWp per charge controller, charging at 54V. *gulp* 370 amps each? Boy that's a lot of amps! Even with a Midnite Solar 250Voc limit, that's still a lot of amps. I think at 48VDC the limit is still around 60 amps.

The big question is, what's the common way to design larger systems like this?

Thank you.
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Comments

  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #2
    Re: 80kWp off-grid

    Those are a lot of assumptions for a plant that size. If this is just for curiosities sake, here's an example of a pretty big system that powers a whole island:

    http://www.windandsun.co.uk/Projects/eigg.htm
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #3
    Re: 80kWp off-grid

    When designing a system of that size you can't just take the simple rules of thumb used to build a small system and the multiply them to build a large one. It would really require studying the specific case very VERYcarefully.
    - Exactly when are the peak loads?
    - What other power sources are available? Wind, hydro, diesel, veg oil?
    - Exactly what is the consumption at different points in the year?
    - What type of loads are they - can they be time shifted, e.g. can you choose to pump water at specific times of day/times of the year.
    etc.
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  • rabbit_39
    rabbit_39 Solar Expert Posts: 43 ✭
    #4
    Re: 80kWp off-grid
    stephendv wrote: »
    Those are a lot of assumptions for a plant that size. If this is just for curiosities sake, here's an example of a pretty big system that powers a whole island:

    http://www.windandsun.co.uk/Projects/eigg.htm

    Right now it's just a curiosity, but if the sales person convinces the customer, someone will end up having to take the bill of materials and shop for the components.

    I'm still in the learning stage, but hopefully will be able to graduate and design some of the smaller systems. And I really want to be able to see the bill of materials and see that there might be something amiss.

    Thank you.
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