Power a 12V/2A (24W) system for 24h/24h, using an autonomous solar system in the Netherlands (read: not very sunny).

Initial thought

24W * 24h =~ 0.6kW and 2A * 24h = 48.0Ah , so given ourself a 100 Ah battery (AGM, deep-cycle), should last us to roughly 2 days of operation.

After first measurements my 20W Solar panel is preforming 50% less if I put it a bit into the shadow (balcony fences). Putting it into fully into the sun makes it generate roughly 1.2A/12V which is indeed as advertised. The input should run at 17.5V to make it take the full 20W.

The change controller Steca Solsum 6.6F seems to regulate the input to 12V, leaving me wondering if the panel will be fully utilized. Cause 20W/14W * 100% = 70% e.g. loosing 30% seems a bit to much.

Taking this numbers into account we need at bare minimum at least 48Ah * (100% / 70%) =~ 69Ah . Giving the fact that effectively we have 4 hours of sun in the Netherlands will this make 69Ah / 4 = 13Ah which correspond to a 160W panel.

Estimated cost for bare minimum will be:

Panel 150W             : 600 EUR
Accu 100Ah             : 200 EUR
Charge Controller 10A  :  50 EUR
Connectors and cables  :  50 EUR
Measurement Electronics: 100 EUR
Total                   1000 EUR

This setup is geared towards most optional numbers. Now take more realistic numbers into a account:

  • The sun in the Netherlands will do roughly 1800 hour, but 75(!) days of the year I will not see any sun at all. If this period last for more than 2 days my battery will be depleted, so I properly need to add extra battery-pack to my system (+200 EUR).
  • The panels are not always running at 100%, I expect average case to be 50% and worst case 25% (if sun is shying during the winter). Consequences will be that I need between 1 to 4 panels of 120W (which gives me +2400 EUR).
  • Looking at Wind Energy might be a more suitable


  • Using a dummy load (20W, I like to see if the panel is able to generate the full 20W).
  • The Current Controller needs to be build/bought to be able to generate statistics on long running experiments.



Vpmx  : Voltage at rated power.
Voc   : Open Circuit Voltage. 
Lpmax : Current at rated power.
Isc   : Short Circuit Current.


500mA - 50W - 17Ah = werked

Last modified 12 years ago Last modified on 07/21/11 23:01:43
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