Bit of help needed with my maths

[Lightspeed]

Hi Bonnox

Your math is correct.

Your panel is rated at 2A ( 24w at 12v 48w at 24v) This will be peak output at optimum operating temperature. Conditions to achieve peak output are cool and clear midsummer days with sun overhead. Output drops off with greyer winter conditions, and of course the number of daylight hours drops off at that time of year too.

A charge controller for your setup need not be expensive. This one will do the job. It's rated 10A and is 12v and 24v compatible, price is less than £7 delivered: http://www.ebay.co.uk/itm/10A-CMP-Solar-...5af59c51ea

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BTW although your 75 AH battery is able to deliver 1A for 75 hours, it is good practice never to completely drain the batteries as this will shorten their operating life.

Aim for 30% discharge before recharging to prolong their operating life.