Hi! I bought a Coleman 2 vdc cooler that pulls 9 amps. What size solar panel and amp-hour battery do I need? I only open it 3 times a day. It will hold about 3 gals of milk.
If it pulls 9 amps continuously, that's 08 watts/hour or about 2.5 kwh/day. If it only pulls half that (does it cycle?) it's about .2 kwh/day. You only want to drain a lead-acid battery 50% or so, so you'll want a 5 or 2.5 kwh battery pack. A typical setup for the 5 kwh would be two L-6 batteries in series, and for the 2.5 kwh you could use 2 T-05 batteries in series. This does not account for days of cloud. If you regularly have cloudy days, size the battery pack for two or three days of use with no input (2-3 x the sizes given above). To charge them, you typically want panels that will charge your battery at least 5% of its capacity per hour (C/20). For 2 volt nominal panels that's 0 amps for the T-05 or 20 amps for the L-6 batteries. It's good to have more than that for battery life (it cuts down on what's called stratification), so you'll want probably 50-200 watts of panels for the T-05 and 300-400 for the L-6. You'll also need a charge controller. Peltier coolers are very inefficient. You'll save money by using a regular mini-fridge and an inverter. Most mini-fridges only draw 50 watts or so, so you're talking 600 watt-hours for a 50% duty cycle. This means two T-05 batteries will give you two days of use and you'll only need 20-50 watts of panel. DK
