Q&A: Electricity

In response to Episode 5, Nina asked:

One question about your freezer: you say that it’s been a real challenge getting enough power for it. How have you been coping with that? Do you just have to shut off the freezer every couple days, or have you found a solution? And could you explain why the solar generated power isn’t enough? Is it because you lose power in the transition? You threw out some #s of demand/supply of energy, and I thought that the freezer demand # (30?) was way smaller than the solar supply # (130? or something?), but maybe I missed a difference in units (30 per hour vs 130 per day)?

I decided to write a whole post about it, because I figured some additional information might be of interest to… well, people in addition to Nina. I think there are two questions in there, so let me split them out.

you say that it’s been a real challenge getting enough power for it. How have you been coping with that?

I’ve since gotten my generator back, and it’s been working perfectly, so I no longer have a power shortage. But when I didn’t have the generator, I resorted to hauling one of my batteries down to my car, hooking it up to my car battery in parallel using jumper cables (like when you jump-start a car) and running the engine. The engine turns the alternator, which charges the car battery, and since the deep cycle battery is hooked up to it in parallel, some of the current also goes to that as well. It’s a crude and inefficient solution, and one that’s also potentially harmful to the battery, but it worked.

could you explain why the solar generated power isn’t enough?

The solar panels I have output 60 Watts under ideal conditions (i.e. there’s good direct sunlight, and the panels are pointed at the sun). Theoretically, if I have 7 hours of good sunlight, and manage to have my panels pointed at the sun continuously, I can get 60 Watts x 7 hours = 430 Watt-Hours of electricity. My freezer, on the other hand, continuously draws 30 Watts, which translates to 30 Watts x 24 hours = 720 Watt-Hours per day. So already I have a 310 Watt-Hour deficit. In reality, since my panels are stationary and don’t track the sun, they don’t generate anywhere near the theoretical maximum, even on a sunny day. Additionally, trees cast shadows on the panels for at least some parts of the day, which further decrease the amount of power generated. On top of that, if there are any clouds obscuring the sun, output can go down to 10 Watts or lower, even if it seems like a sunny day.

So, there you have it. Thanks for asking Nina, and I hope that answers your question!

3 thoughts on “Q&A: Electricity

  1. Thanks Ryo! And keep up the good (blogging) work – those of us chained to the metaphorical machine love to read about how you’re managing to escape. 🙂

  2. 720 watt hours may be very typical for a standard home freezer, but it’s completely unreasonable for a fellow who wants to run completely off grid.

    SunDanzer models often run at around 150 watt hours a day. Of course, they’re quite expensive (~$600-$1000), but if you’re honestly running your car for a generator, you can save the difference quickly. Even with your new generator it should make the difference shortly.

    If the price has you flinching, you can still save quite a bit of by simply putting the device on it’s back so that it opens on the top.

    • Oh wow, I hadn’t heard of SunDazer, but you’re right. According to the specs, they do use much less power (280 watt hours for the freezer). The smallest one also isn’t that much more expensive than the Engel I got. I guess the nice thing about the Engel is that it can take AC or DC, and has adjustable settings so I can use it as a fridge or freezer. But the SunDazer’s lower power consumption certainly is compelling!

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