Everyone loves microwave ovens, even those of us who have plenty of time on our hands. But the convenience of quickly heating a burrito requires a lot of electricity. How much? Let’s see.
Before getting too deeply into technical details, here’s the quick answer for powering a small 600 Watt microwave:
200-400 Watts of solar panels
200-400 Amp hours of deep cycle batteries
2,000 Watt DC-to-AC pure sine wave inverter
We’ve explained solar panels and deep cycle batteries several times before, so let’s focus on inverters for a while.
Inverters convert (invert) the DC current of solar panels and batteries to the AC current standard plug-in devices use. There are two types of inverters: modified sine wave and pure sine wave. Without getting into the technical reasons why, suffice it to say you need a pure sine wave inverter for electronics, like microwaves and TVs. And you need one large enough to handle the draw of a microwave—as well as its higher start-up draw. My inverter is a Xantrex SW 2000.
However, you’ll probably want two inverters. Inverters suck a lot of power, even when they’re turned on with nothing plugged into them. (To conserve battery power, turn your inverter off when not in use.) And most things you want to power don’t require 2,000 Watts. Using a big inverter would be a waste, like driving a 40-foot RV to the store instead of the tow’d. Something more like a 400 Watt modified sine wave inverter will do.
My 600 Watt microwave actually draws nearly 900 Watts while cooking. Within seconds it can run my mid-day, full-sun battery power down from 14.3 Volts to 12.2 Volts. When I use the microwave at night, the voltage can drop into the 11s. Inverters are set to shut down when incoming power gets too low. So you need a lot of reserve power to run a microwave. And you need enough solar panel wattage to recharge the batteries quickly the next day—while still powering whatever else you’re using.
I won’t get into stuff like amps-per-minute or the Peukert Effect. I think you already understand the main point: you need some serious power to run a microwave. Now you need to decide whether you have the money and space to make it happen.
I have been lurking on this site for awhile now and wanted to add my experience(s) about using and powering a microwave. I had acquired a Bioenno Power 24V, 100A LiFePO4 battery that weighed 60# and I put it into a cubby above my frig. That battery was rated for 60A continuous so the search began for an inverter. First, I had to determine the watts needed for the 900W micro with turntable that came with my trailer. I borrowed a Kill-O-Watt meter from the local library, put 2 frozen TV dinners on the turntable, plugged the microwave into the meter and hit start. 1350 watts for 8 sec and then 1150 watts for the duration. I knew I needed at least 10% “headroom” for the inverter and so I eventually settled on a GoPower 1500W, 24 volt PSW. I had 3 ft cable runs for power from the battery, so I could use 6AWG cabling. Both the inverter and the battery are grounded to a bus bar and the bus bar is grounded to the trailer frame so it is a closed loop system entirely separate from the 12V house system in the trailer. As my 60# battery was was starting to pull all of the pocket screws out of the wood frame of the cubby, I purchased a 24V, 60A LiFePO4 battery from Amazon that weighed 29#, A view of the spec sheet on the new battery said that it was good for 60A continuous draw. Well, 1350 watts divided by 25.6 watts for a 24V battery = 52.37A and for the 1150 watts running = 44.92A Now, I had the “overhead” for the inverter that I needed to cover the 8% loss of efficiency for the inverter. I was below the 60A continuous for the battery, I was using Anderson SB120 connectors and not the SB50 connectors, so I was optimistic! Let’s back up: 44.92A, you say? Yep! Let’s examine the logic here. Microwave frozen dinners need 4-6 minutes. To be conservative, let’s say 10 minutes. That is 1/6th of an hour. So, 44.92A divided by 6 = 7.49A (round to 7.5A). That is for 10 minutes so it almost certainly would be less. If you run the micro twice for 10 min you would use 15A out of a theoretical 60A Can you replenish 15A during the day? You bet! If it is cloudy, you would be good for 3 days. Oh, I forgot: My 4 cup coffee pot uses 675W or 4.4A and I make two pots – one to get me going and one for the thermos. So, run your first pot of coffee to get you going, micro your baking potatoes and then let them cool off while you make another pot for your thermos and then put the cooled potatoes in your fridge. Let the sun top up the battery. At night, you will be more than ready, power-wise, for the TV dinners, popcorn, or whatever. All of these 3 items for me – the battery, the inverter, the microwave are the only items on a closed 24 volt circuit so no worry about other items using power. “Other” items are run off the 12V battery (lights, charging items, tv, 12 fan, etc) My 24 volt “system” runs quite well from a 60 watt, 24V panel. After a year of boon docking with no shore power, I am going to add 2 more 24 volt 60w panels in series to a mppt controller and see if I can bring my butane usage that I use for my stove down to almost zero. I say almost, as I do use the butane stove for hot water for general hair and body anti-scruffy maintenance If I was using any lead acid derivation, I would probably need 2 batteries and much more solar. Lead acid absorption can take 2-3 days with a solar system and your 2 batts may not be at 100% even if your meter says so. Not so with LiFePO4. It might also be useful to remember, that modified sine wave inverters run at 80% efficiency and not 92% as a PSW does. This is my experience with my micro wave and 4 cup coffee pot. I suppose the old adage of YMMV applies. Enjoy the coming camping season as much as I will. Thanks for reading. Your comments appreciated.