40 Watt Solar Panel

[Dave Lyon]

I'll be dry camping for 3 nights this summer am wondering if a 40 watt solar panel will be able to keep my group 31 battery topped up, assuming I arrive with it fully charged and there is sunlight.

The only electrical demand would be:

• the water pump for taps/toilet. Likely wouldn't use the shower.
• fridge
• Co2 detector

We've always camped with electrical sites, so, I have no idea what to expect.

Thoughts on whether a 40 W panel will be sufficient.

[Flybob]

A 40 w solar panel will provide about 2A per hour after taking into account efficiencies and losses ( controller and cabling). Under optimum conditions, for an 8 hour day, you can replace 16Ahr to your battery. That means that during a 24 hr period, you will only be about to use approx 600 mA/hr from you battery to to break even. Therefore it is unlikely that a 40W panel will suffice. There several threads here with links with Solar system requirement calculators. The learning center at https://www.solar-electric.com/ is a good one. I suggest starting with a minimum of 100W panel with a controller that will handle 300W to allow for growth. Also remember you don't have 8hrs full sun every day so you need reserves.