Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. Today he discusses running a residential fridge on a solar panel and battery.
Running a residential fridge on solar
I just picked up my first trailer, a Wildwood FSX 179DBK. It has a two-burner propane stove, microwave, and a fridge, but no oven. Not knowing any better, I assumed the microwave was also a convection oven but, surprise, it is not. I thought the 11-cubic-foot fridge was a dual-service fridge. During the inspection, my inspector found it was not but it has a 300-watt inverter connected to a 12-volt line. He also pointed out that none of the 110v outlets will work unless I am connected to shore power or to an inverter generator.
Questions: Is that normal? Am I better off changing our fridge to a 12v or a dual propane/electric fridge? I was planning on boondocking Nov.-Feb. near Phoenix, AZ, with a 190w solar kit on top of the RV. Is that setup on one GMS battery enough? —Randall
To start with, your Wildwood is not set up to boondock very well as most of the appliances and outlets you have are 120-volt dependent. Plus, a 300-watt inverter and one battery will typically only power the TV. If you plan to boondock for four months, you will need to evaluate your amp-hour requirements and upgrade your batteries, inverter, and solar panels. If you want to use the outlets for the 120-volt operation of items like a coffee maker or to charge computers or other items, that will need to be supplied by an inverter as well.
Figure out the power draws
Step one is to identify what AC and DC draws you will have and how often you will have much more than just your refrigerator running down the batteries through the inverter. Visit Go Power!, where you will find a list of common AC and DC appliances and what they typically draw. This worksheet also has formulas to calculate the number of hours you think each appliance will run per day and get approximate total amp-hours per day.
For example, an AC refrigerator is listed as 10 amp and you will need to calculate how long it will run each day. This will be determined by the ambient temperature in your rig. However, the side note to this is they are rating a 4-cubic-foot refrigerator. Most RVers will be using a much larger unit that could draw 30-40 amps.
Other 120-volt AC appliances that might be powered by the inverter and drain the house batteries are the microwave at 100 amps, TV at 4 amps, and computer at 25 amps. 12-volt DC appliances or functions that will draw directly from the house batteries include lights, vent fans, water pump and more. Hopefully, you have LED bulbs as they draw one-tenth the power at about .05 amps. Other items include roof vent fans (4 amps), and water pump (4 amps). Even your LP appliances such as the water heater, stovetop, and furnace will draw 12-volt house battery power, especially the furnace fan at about 8 amps.
Calculate power usage for amount of time
Next, you will need to multiply the total amp hours you estimated by the number of days or weeks you plan to boondock, which in your case is four months. Then match your solar panel size, inverter, and battery needs. Go Power! also has a quick guide showing different RV configurations and days out that shows a travel trailer about your size would need 380+ watts of solar panels, 2,000-watt inverter and 400 Ah+ if using AGM and 200+ Ah if using lithium, as they can be drawn down to almost 100 percent of available amp hour capacity.
Not a perfect science!
Even armed with all this information, it will be just an estimated guess and none of us can truly calculate how long the refrigerator will run, the lights will be on, or how often the furnace kicks in. And what about cloudy days? I do recommend adding portable solar panels to your system as they can be placed out in line of sight to the sun while your trailer is parked under shade to cool it down. Arizona does get a little hot even in the winter. If you are boondocking, you won’t be able to use your roof air conditioner. Parking in the shade can cool the rig down 20+ degrees, but you get no sun to your roof-mounted solar panels.
Another good source of information on solar panels and systems is Zamp Solar, which along with Go Power! is now owned by Dometic. And as always, when it comes to calculating electrical needs I would recommend reading Mike Sokol’s articles.
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