So­lar un­der con­trol

Canal Boat - - Back Cabin: - TACOERNIE, TONY REPLIES… CB

QI’m plan­ning a 400W so­lar power sys­tem, with two pairs of 100W pan­els each con­nected in se­ries, then the two pairs con­nected in par­al­lel, send­ing 24v to my con­troller which is to be con­nected to a 12v bat­tery bank. I am look­ing at a 20amp MPPT con­troller – I un­der­stand that this will han­dle 400W at 24v, and covert this to 12v to charge the bat­tery bank. Is this cor­rect, or will I need ei­ther 2 x 20A con­trollers or one that takes more amps?

via the web­site

I think you may be mis­un­der­stand­ing things. The con­troller will au­to­mat­i­cally set it­self for ei­ther a 12v bank or a 24v one. Just en­sure the max­i­mum cur­rent and volt­age the pan­els sup­ply is within the limits for the con­troller you choose.

Most MPPT con­trollers could han­dle an in­put of 100 volts or more. If yours can, con­nect all the pan­els in se­ries (to keep the cur­rent and thus the ca­ble volt­drop to the min­i­mum, al­low­ing thin­ner ca­bles) un­less they are mod­ern 30v+ ‘do­mes­tic’ type pan­els. Typ­i­cal 21-volt pan­els will give 84 volts in se­ries, well within the ca­pa­bil­ity of a 100-volt con­troller.

How­ever, 400 Watts at a charg­ing volt­age of 13 volts gives a the­o­ret­i­cal cur­rent of just over 30 amps. That would only hap­pen if the pan­els are ever able to sup­ply their full out­put (un­likely in the UK, es­pe­cially with pan­els hor­i­zon­tal on the roof) but per­son­ally, I would be look­ing for a higher cur­rent con­troller.

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