Solar package specs

PolychrestPolychrest Registered Users Posts: 17 ✭✭
There's a big, long-established solar power company here in Ontario with eight or nine franchise locations that sells and installs predefined solar power kits. From what I've learned here and elsewhere about system sizing, it appears to me that their kits come with either too little array or too much battery. Here are the relevant specs from their latest blurb about what you get:

with Cottage Kit #4:
-240 watt solar array ( 13.89 amps of charging current @ 12 volts)
-eight, 6 volt batteries (864 amp/hrs. @ 12V)

with Cottage Kit #5:
-470 watt solar array (13.3 amps of charging current @ 24 volts)
-twelve, 6 volt batteries (648 Amp/hrs. @ 24V)

with Cottage Kit #6:
-705 watt solar array (19.94 amps of charging current @ 24 volts)
-sixteen, 6 volt batteries (864 amp-hrs @ 24V)

Seems to me that with these systems, sooner rather than later you're going to have dead batteries to deal with. What do you folks think? I've had dealings with this company in the past, as have some neighbours, and we've found them to be quite happy to exploit our collective ignorance about such things to pad their bottom line.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar package specs

    I'll try to refrain from laughing. :roll:

    Here's the formula everyone can try themselves at home!

    Peak charge current in Amps * 100 / Amp hour rating of battery bank. The result should be between 5 and 13 percent.

    Like this:
    13.89 Amps * 100 = 1389 / 864 = 1.6 percent. FAIL!

    I could question their choice of battery bank size for the 12 Volt system too, as that many Amp hours on a 12 Volt system is ridiculous. Not even a FM80 would supply the 10% target current, and it would have to be backed up by about 1600 Watts of array. Not 240 Watts.

    But that's just my opinion. No one has to pay any attention to it. It isn't my money you're spending. :p
  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    Re: Solar package specs

    Besides the first admonition: People way underestimate their loads and way over estimate the output of a solar PV system...

    The second is that people tend to throw batteries at a a problem, when, usually, the answer is to throw more solar panels at the problem.

    So, back to the normal 5 steps:
    • Conservation--Choose your appliances/loads to be the most efficient you can find (laptop instead of desktop computer, CFL/LED lighting instead of filament, no heating/cooking power usage for small systems, convert to propane for heating/cooking/possibly refrigeration for cabin use).
    • Site--If you have trees and mountains blocking your solar array, you will not be able to use a solar array.
    • Plan your battery size based on 2-6x your daily loads (1-3 days of no-sun load support)
    • Plan your solar array based on both your battery size and daily load / available sun (big battery banks may need more solar panels to properly recharge--typically 5% to 13% of bank 20 Hour AH rating). Don't let the batteries set for days/weeks/etc. below 75% state of charge or batteries will sulphate.
    • Pick your hardware. Inverter size, battery bank size (based on average and peak loads, etc.)--Revisit your sizing equations to make sure you did not fall outside the recommended rules of thumbs.
    • Spend your money.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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