The number one question I get asked all the time is "Can I power my fridge using solar?"
Short answer is NO. Your refrigerator is designed to run on propane gas or shore power.
Typically, most RVs come with a 3-way refrigerator. That means the fridge operates either on propane gas or AC electric that is supplied from shore power or a generator. The "3-way" refers to the battery power (DC electric) that is used to power the electronic ignition that lights the pilot on the propane refrigerator. So really a 3-way refrigerator either operates on AC electric or propane gas. Some manufactures now supply a residential type of refrigerator that operates solely on AC electric supplied from the onboard generator or from shore power. Residential refrigerators are more efficient, however, they require shore power or a generator. While on the road, this type of refrigerator receives its power from an inverter that converts DC electricity from the batteries to AC electricity to power the refrigerator. Once parked, the refrigerator must be plugged in or it will quickly drain your batteries. DC refrigerators are manufactured for use in off-grid homes. This type of refrigerator is more efficient if all your power comes from solar and stored energy in your batteries. Typically, DC refrigerators are not used by RV manufacturers because they are more expensive and the RV manufacturer assumes you will be using shore power or a generator.
Unless you live fulltime in your RV and design a different refrigeration system you should plan on running your RV refrigerator on propane gas.
How much solar is required to run my refrigerator?
Here is a simplified example for a "residential" type of refrigerator supplied with a modern 5th wheel RV trailer:
- 5 hours sunlight per day for San Diego (number used in solar calculations)
- Full sun, no shading, no clouds, zero days of autonomy
- No phantom loads in RV (in reality there are many phantom loads that use up battery power)
- 18 cu. ft. residential refrigerator, 8.5 amps, 115 volts, 60 Hz
The refrigerator is rated at 8.5 amps x 115 volts = 977.5 watts. A typical assumption for a residential refrigerator is that the compressor motor will run 1/3 of the time (this is assuming it is operating in an ambient temperature of 70 degrees.)
978 watts X 24 hours/day x 1/3 operational time = 7824 watt-hrs/day.
Batteries should not be discharged below 50%, therefore, you will require 2 times the stored power capacity.
7824 watt-hrs/day x 2 = 15,648 watt-hrs/day
Based on a 12 volt battery system, the amp-hours of storage capacity will be:
15,648 watt-hrs/day / 12 volts = 1304 amp-hrs
The AGM 8A27M heavy-duty, deep-cycle, RV/Marine battery I have on my website has a reserve capacity of 175 amp-hrs. Therefore, the number of batteries required will be:
1304 amp-hrs / 175 amp-hrs/battery = 7.45 = 8 batteries
The number of 160 watt panels required would be:
7824 watt-hrs/day / (160watts/panel x 5 hours sunlight per day) = 9.78 = 10 panels
Besides the 8 batteries and 10 panels, a couple adequate sized charge controllers and a Smart Battery Charger would also be required for this example.
As you can see operating a large refrigerator on just solar can become very expensive. I see a couple different options:
- Design a bit smaller solar/battery system and plan on running the generator a couple hours each day and installing a smart battery charger so the batteries are properly topped off (This way you can get through the night without the generator. Based on the assumptions above, you will still require 6-8 batteries and 6 panels.)
- Remove the residential refrigerator and replace it with a 3-way refrigerator that uses propane gas, then design a system that can operate most everything in your RV while boondocking (except the refrigerator and AC unit. 4 batteries and 3 panels would probably do.)
- Add a small 3-way refrigerator to your RV (keep the large fridge for generator/shore power,) operate only that fridge on propane while boondocking, and design a solar/battery system based on no fridge requirement (4 batteries and 3 panels.)