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Please help check my system

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Good Day

I'm putting together a system just to run 3 x 5w led lights and a 48W TV

I will run the following with one day battery backup

3 x 5W led lights for 8 hours a day

1 x 48W TV for 5 hours


I won't put all my calculation but just the results. Any corrections welcome.


1 Total PV panels energy needed  676 Watts
2 Size the PV panel 141 Watts
3  Inverter sizing 260 Watts
4 Battery sizing 85 A/h
5 Solar charge controller sizing 11.128 Amp



Thank you

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15W for the lamps, times 8 hours, that is 120Wh.

48W TV for 5 hours is, let's just say 50*5 that is 250Wh.

Total required is 370Wh. Add in inverter efficiency (85% to 90%, if we're not too optimistic) and that gets you around 460Wh. Times two, because you only want to discharge the battery to 50% (assuming you want to use a Lead Acid battery). So you need about 900Wh of battery. Divide by the volts. If we assume 12V, then you need roughly a 75Ah battery. Might as well aim for 100Ah then, those are easier to find.

To recharge 460Wh, in SA you have roughly the equivalent of 5 hours of peak sunshine, so you need to get around 100Wh into it for each of those hours, which means you need a minimum of a 100W of PV. Again efficiencies come into it. If you're using a cheaper charge controller, add 30%. Also, if you use lead acid, you really want to be finish the bulk phase around 2PM so you have plenty of time to float-charge the last few percent, so better to err on the side of bigger.

A 100Ah lead-acid battery should ideally charge no more than 15A (20A if you push it a bit), and 15*12 = 180W. So you want PV around the 150W-180W bracket, in my opinion.

Now it gets even more interesting. Again, I assumed you want to go 12V (at such low power levels that would be the way to go). For that you ideally want 36-cell solar panels, because they make around 18V at peak power. So when you use a cheaper PWM charge controller, there is less wastage. Above 150W PV modules tend to be 60-cell or 72-cell combinations, so this again cements the 150Wp panel choice. It's about the max you can go anyway, unless you upgrade to an MPPT charger so you can use higher-voltage panels.

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38 minutes ago, Eastboy said:

I will be using a gel battery I assume they are better than lead acid

That's lead-acid, the gel part just means the electrolyte doesn't spill out like a flooded battery would. Usually they have better cycle life than an AGM. But basic chemistry is lead-acid and the rules are similar. Same depth of discharge recommendations, can usually charge and discharge slightly higher (up to 20A no a 100Ah I'd say).

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