solar

[Henry]

I just want to operate a residential fridge thru my inverter. How many 12v batteries and will a 100w panel work?

[time2roll]

jshupe wrote:

pianotuna wrote:
Start with an energy audit. Decide how much reserve capacity you want. From that design the battery bank. Build a solar panel system that will recharge the battery bank.

This is the proper way to go about it.

I prefer to max out the solar and deal with the consequences.
Solar is so inexpensive today there is no reason to aim for the minimum.

[n0arp]

pianotuna wrote:
Start with an energy audit. Decide how much reserve capacity you want. From that design the battery bank. Build a solar panel system that will recharge the battery bank.

This is the proper way to go about it. If you refuse to do an audit or don't have the ability to do so for some reason, most 18-22cf residential refrigerators use around 2kWh/day, which will need to be added to your assumed base load.

[wintersun]

An electric only fridge is a poor choice for dry camping. It will take 300AH of battery capacity and 300W of solar panel production at a minimum. With lead acid batteries the 300AH will provide only 150AH for the fridge and everything else in the RV as going below 50% SOC will greatly decrease their useful life and increase the time it takes to recharge them.

For an electric only fridge the best solution is to invest in lithium phosphate batteries that can take a 80% discharge without damage and that can be recharged at 4 times the rate of lead acid batteries so the generator run time will be greatly reduced and solar charging will be more effective during the limited hours of daylight.

[ajriding]

At some point you have to do math and see how much all the batteries and solar panels will cost,
and how much a propane fridge that needs little to no electricity to run cost.
Cost in propane to run a propane fridge: negligible .
Cost of batteries if you run resi fridge all the time and wear out batteries quickly?
Replacement cost of batteries that you wore out?
How often to replace the batteries that are quickly wearing out?

Don't forget about the Danfoss 24/12 volt or 120 household voltage (which converts to 24 for fridge) compressor refrigerators (typically in chest configurations).

[valhalla360]

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.

[pianotuna]

Start with an energy audit. Decide how much reserve capacity you want. From that design the battery bank. Build a solar panel system that will recharge the battery bank.

[naturist]

Not enough information to hazard a guess, IMHO.

[Gdetrailer]

time2roll wrote:

Henry wrote:
I just want to operate a residential fridge thru my inverter. How many 12v batteries and will a 100w panel work?

Plenty of reports that have 4 batteries and 500 watts solar still needs a generator at times. You will get more power from your solar with lithium. Solar is good for maybe 5-6 hours a day, fridge runs 24/7.

Actually the fridge will generally on run the compressor 20minutes to 30 minutes per hr so in reality fridge runs 12 hrs or a bit less per 24hr..

Inverter can be an issue but if you have an inverter which has a power save feature you can reduce the amount of energy used by the inverter when it only powers up when there is a AC load demand large enough to turn it on.

For the record, I am only using one pair of 6v GC2 batteries to power my home fridge conversion for 24 hrs between charging..

[time2roll]

Henry wrote:
I just want to operate a residential fridge thru my inverter. How many 12v batteries and will a 100w panel work?

Plenty of reports that have 4 batteries and 500 watts solar still needs a generator at times. You will get more power from your solar with lithium. Solar is good for maybe 5-6 hours a day, fridge runs 24/7.

[Lwiddis]

Running a residential fridge in an RV while dry camping takes planning.

[ORbiker]

Henry
We have a residential frig in our Solitude. It will draw a little bit more then 100AH in a day. I put 4 100AH lithium batteries and 4 160W panels on the roof. I should have done at least 6, but I have 200W of portable, so We are ok.
Having the big battery bank I think works well. I have a Honda 2000i for a backup and the lithium batteries charge way faster then wet cell batteries. KEN

[Lwiddis]

Henry, a 100 watt solar panel under ideal conditions will produce 5.6 amps per hour...nominal 12 volts. Solar is great but you can’t do much with one 100 watt panel. You need adequate panels, batteries, a controller and large size wire...all based on an energy survey.

[wanderingaimles]

A resi fridge will draw upwards of 1000 watts on start up, a smaller unit (10 cuft) may draw a little less, you'll likely need a pair of GC batteries and two 100 watt panels as a minimum, and will not be able do much of anything else from them. and a couple of rainy/cloudy days will likely overtax that. Better to look at 4 batteries, and at least three 100 watt panels and 4 would be better.
A very rough rule of thumb is to try to match watts of solar to amps of battery, ie for a single battery with almost 100 amp hrs capacity to a 100 watt panel.
An audit of your actual usage, and then sizing a system to be 50 to 100% above your indicated usage is preferred to allow for partial shade or overcast conditions.

[Lwiddis]

Is your fridge 12 volt or 120 volt? How many amps does the fridge use when running? How efficient is your inverter? How many amp hours will your batteries hold? Are you sure the fridge is all you want the batteries to power? Better approach is to do an energy survey to determine your needs...then times 1.5.