Electrical System

Preparations for my vacant-land-living adventure are coming along nicely. While there are open questions still remaining, I have a pretty good idea of what I’m bringing with me, and have purchased a small mountain of equipment and supplies, which is currently accumulating in a friend’s garage in Sunnyvale.

The one thing that took me the longest to make a decision on, was the electrical system. It was a particularly complex problem to optimize because I had to consider a number of factors simultaneously. I knew I would draw most of my power from a deep-cycle 12 Volt battery, but how would I charge the battery? What kind of appliances do I want to run? What are my logistical and financial constraints?

My initial plan was to bring all my power tools, including a miter saw and circular saw. Since the miter saw is rated at 15 Amps (1800 Watts @ 120V), I would need an electrical system capable of peaks of at least double that (3.6kW). The cheapest way to get 3.6kW is with a gas generator, which can be relatively cheap (around $500). The problem is, these generators are rather large; they weigh 150lb or more, and take up several cubic feet of space. So, in order to bring my miter saw, and a generator to support it, I would need a new car and probably a trailer (the Ryomobile has a 850lb cargo limit, and can’t tow anything). Of course, this seemed rather excessive, so I asked myself whether it was really worth getting a new car and a trailer, just to be able to use a miter saw. The answer, of course, was “no”.

Next, I swung in the opposite extreme. I started looking at minimizing my electrical needs so that I could run everything off of solar panels. The only appliance I plan on having plugged in full time is a portable freezer, which is rated at 2.5Amps at 12V (30 Watts). Over 24 hours, it would draw 60 Amp Hours of power. Instead of my power-hungry miter saw, I can compromise and shell out $200 for a battery powered saw, but those batteries would also need to be charged. Factor in an average of 20 Amp Hours a day for charging various batteries, and that comes out to 80 Amp Hours total. The cheapest solar panels I could find that were of manageable size generated 6.5 Amps. Estimating actual output from solar panels is hard, but if they averaged 60% efficiency during 10 hours of sunlight, that would be about 40 Amp Hours. Then factor in a 30% loss in the charging process, and we’re looking at 28 Amp Hours of actually usable power pumped into the deep-cycle battery per day. To get 80 Amp Hours per day, I’d need 3 of those panels at a total cost of about $1000.

While going solar appeals to my inner hippie, it’s not the most reliable option. For starters, if the actual output from my panels is lower than estimated or my usage is greater, I’m screwed. Although not a concern this time of year in California, solar panels also generate significantly less power when it’s cloudy. Most people who rely on solar also have a gas generator for backup, so even if I get most of my power from the sun, I’d still need a generator after all. Also, while solar panels are lighter and more compact than big honking generators, they are fragile and rather unwieldy.

My final solution was to get a small, low-wattage (and therefore quiet and fuel efficient) generator. After doing research on small generators, I settled on the Honeywell 1000i generator, which has a peak rating of only 1kW, but also weighs less than 40 pounds and costs $400 shipped. Since I still plan on using battery powered tools, I only need the generator to charge my deep-cycle 12V AGM battery. The charge controller I got sends 40 Amps of power, which should replenish a day’s usage in 2-3 hours, while drawing about 600 Watts from the generator. The downside is that I have to run a generator for 2-3 hours a day, but maybe that’ll encourage me to lower my electricity usage.

Just as an academic exercise, I tried comparing the long term costs of gas vs solar. My gas setup turned out to be cheaper by $500, which is equivalent to 167 gallons of gas (at $3/gallon), which in turn will run my generator for 1000 hours, sending 40,000 Amp Hours of power to my battery; enough for 500 days of expected usage. Solar would eventually be cheaper if I were thinking of long-term settlement, but for a month or two, gas is definitely cheaper. Besides, as I mentioned earlier, it’s good to have a generator for backup anyway, so it’s a worthy investment. I can still gradually add solar panels and lower my reliance on gas, but I won’t have to worry about running out of power.

Having written all that, I’m quite surprised by how much thought and research I had to put into getting enough electricity to run what would be the equivalent of roughly half a 60 Watt incandescent light bulb. It was also interesting to actually have to run the numbers and compare gas vs solar, and I have to say, what I learned was a bit surprising. Solar may seem like the ideal sustainable energy solution, and it may be, but it’s still prohibitively expensive for many, and not compact, efficient, or reliable enough to be depended upon as one’s sole energy source. One alternative that I didn’t consider is wind, mostly because I’m not sure how much wind I get on my property. In any case, I have a feeling I will be thinking about electricity yet for some time to come, and that my electrical system will continue to evolve.

One thought on “Electrical System

  1. Pingback: Update from the SV Dept. of Energy « Laptop and a Rifle

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