solar

naturist wrote:
Not enough information to hazard a guess, IMHO.

Yep, people stating as fact you need X watts solar and Y amps battery have no clue what you really have, so they could be completely off.

Some items to look up:
- How many days do you want to operate without alternative sources of power (shore power, generator, connected to the truck, etc)?
- What is the running wattage of the fridge? Running is different from starting. 12v DC vs 120v AC doesn't matter as much as the wattage. If it's 12v DC, there is a small advantage that you can skip the inverter.
- What is the duty cycle expected? The compressor doesn't run 24/7 but it cycles on and off. When it's off, it's not drawing power. So if it's a 50% duty cycle, there is roughly have the watt-hours used per day compared to 100% duty cycle. So if it's 50w while running and 50% duty cycle, 50w * 24hr * 50% = 600 w-hr used per day (this matches the rating on our 12v fridge but a true residential is likely significantly higher).
- Solar panels don't generate their rated wattage 24/7. A good estimate is to take the wattage rating and multiply by 4 to get watt-hours generated per day. So a 100w panel would generate around 400 w-hr per day.
- Batteries (assuming lead-acid) are rated in amp-hr but if they are 12v multiply the amp-hr by 12 to get watt-hour. There is a catch, you can only use about 50% without causing damage. So a 200amp-hr battery holds about 2400w-hr but you only have about 1200w-hr that is usable (lithium are a whole different ballgame).

Now if you want to run for multiple days, 1200w-hr of usable battery bank will keep 600w going for a couple days. If you want to stay out longer, you either need a bigger battery bank or break out a generator (or other source) to recharge the batteries.

A few additional thoughts:
- 20-30% oversizing is a good idea. You may have missed something in the calculations. Also battery banks tend to lose capacity over time.
- Are there any other 12v draws? If you can't turn them off or you want to run them, you need to increase the size to account for them.
- Inverters aren't 100% efficient, so you need to add a little more storage to account for that plus most will use a little power just in standby not powering anything...again that adds a little power demand.