Mobile Solar Electricity with PV

Hey everyone! Happy Monday!

So as you may know all last week I was in Vermont attending an intensive photovoltaic design/installation class (at the Yestermorrow Design/Buidl School – check it out here). By the end of the week, I realized it would be very difficult to sum up everything I learned, so I think I’ll just get into it little by little. There are so many factors and variables when designing a PV solar electric system for your (tiny) house or mobile house. Weight and stability came up a lot, as well as mobility concerns with roof mounted systems.

For today, I thought it would be fun to introduce you to some of the stuff we covered in the course with an activity you can do yourself. It’s really enlightening and will definitely surprise you if you’ve never really thought about how much energy you use.

For this it’s helpful to know that Volts x Amps = Watts. It’s also really helpful to have a Kill-A-Watt meter around, so that you can plug in your electronics and see how much power they use.

Here’s a Kill-A-Watt meter like the one I used.

Also, note that my calculations are in Watts, because I am dealing with mostly smaller electronics and appliances, but usually if you were sizing a whole house system or something larger you would use kilowatts.

*Efficiency first! Make sure you consider your efficiency before sizing a PV system. Consider phantom loads, insulation, and other factors to see how you could use less in the first place! For example, I am choosing not to have an electrical pump (my faucet will have a hand or foot pump which creates water pressure, and my solar shower will be gravity fed). Because I am going off-grid in a small space, I really have to be careful about where I use electricity.

Basically, we are calculating how many watt-hours we use in a day in order to be able to accurately size an off-grid solar PV system. Finding out how much energy you use in day is really cool, and I feel like it immediately makes you think more about what you use and when. I made a chart with the headings Appliance, Watts, Hours/Day, and wH/Day in order to break down my energy usage. From this I could figure out how much energy I use in a typical day. My chart is pretty simple, and I only have a couple of power-using appliances. The stove and heater in The COMET run on propane (PV cannot efficiently produce heat with electricity). Like I said, no electrical pumps for water. All of my lights will be LEDs to cut down on watts (which is generally an expensive endeavor – to replace all of your lights with LEDs – but I only have about 4 wall sockets so it’ll be affordable and worth it in the energy-usage long run!). Also, I overestimated in some cases just to be safe.

Here’s my chart!

So you can see that I only have a few electricity-using appliances. The other thing to consider here, especially for me because I spend a good amount of time on the road (and even more once the I live in The COMET camper) is that I often charge my phone and other things in the car. Anything with a USB port usually gets re-charged on the road.

I hope this is useful in helping you figure out how much energy you use. For some of your appliances, you will be able to see how many watts it uses on a spec sheet or by looking it up online. For others, it’s just easier to plug it into the Kill-A-Watt. And if you have the voltage and amperage of an appliance, you can figure out the watts by multiplying V x A. The total watt-hours/day ( that 790) will be integral to figuring out how much PV you need for an off-grid system. I will go into that later!

At this point, the DC column at the end of the chart may not make sense, but I will do another post later about why that column is so important! I am figuring out a way to have a much more efficient PV system than most, and I think you will find it interesting to think about! So stay tuned for that later on.

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