Doing the Math on Solar

I’ve had solar on the brains for months. I’ve been RVing long enough now to know what I need in terms of a solar setup. Soon as I can free up the cash, I’ll be ready to spend!

My battery bank is comprised of two 6 volt golf cart batteries with a capacity of about 200 amp hours. I only really get 60% of that capacity, so I have 120 amp hours available to me. By being frugal and only using power for the fridge, propane detector, and furnace, I can spend two to three nights off shore power. I can do three to four nights if I don’t have to heat. The 15 watt panel on the roof gives me about 4 amps a day, enough to recharge my laptop once a day when it’s sunny, so I don’t factor that into the equation.

So, with strict energy consumption in mind, I average 40 amps per day at 12 volts. Having 60 amps available to me would mean not having to be so careful and give me a good buffer.

Also, I have very little use for 120 volt power, except for computer charging. I don’t miss the microwave or toaster when I’m not plugged in, so I was hit with the realisation that I don’t need a whole house inverter! My little 400 watt inverter is more than enough for my needs. If I absolutely needed to print while boondocking, it’d be cheaper to just go have it done at a copy store. So, all I need is a solar panel and a regulator.

I’d like to be able to boondock in the Yukon this summer for two weeks at a stretch, the length of time you can stay in a territorial park in a 28 day period. So, that meant I’d need a solar panel capable of providing me with 840 amps of power.

This is the point in my calculations where someone came up to see what I was scribbling about. Turns out he knows solar (too funny, what a coincidence). He looked at my numbers and said “That’s an easy one. 125 watt panel and a regulator. Add two to six more 6 volts if you have the space and weight for them and you’ll never have to worry about power again.” I got a second opinion on that, and got the same answer. So, now I know what I need and I’m starting to accumulate quotes.

I think I’ve given up on the generator. It’s surely a lost cause by now. I’d probably be better off having it removed and then using the extra carrying capacity for doubling, or even tripling, my battery bank. Three people also suggested that I might be able to get enough for the scrap generator to finance a good part of my solar investment. So, that’s another thing I’m going to be looking into.

Investing in solar has been a long time coming, but I’m glad I waited because now I really know what I need and I can spend my money well.

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14 Comments

  • This has been talked about on my yahoo group boondocking with solar. Perhaps it could meet your needs.

    http://cgi.ebay.com/120W-Folding-Portable-solar-panel-w-s12V10A-controller-/270701294920?pt=LH_DefaultDomain_0&hash=item3f070df548

  • My head just spins when I try to figure out what I would need – I guess my brain just isn’t wired that way. I’m in admiration of how you manage to conserve and do so well at it.

  • Caroline: thanks for that link! At this point, I want to check in with a local provider, but this gives me a comparison point for shopping.

    Martha: nice pun. 😉 I NEVER would have thought this stuff would ever make sense to me! As I was talking to the solar guy, his jaw started to drop. Told me I’ll be able to ‘shop smart’ because I know what I’m doing!

  • Anyone looking into setting up a solar system would be well advised to go to the forums at http://www.mrsharkey.com the forum owner knows more about solar systems, batteries and their maintenance than pretty much anyone else you could come across. Some of the guys there, have had batteries lasting in good condition for well over ten years.

  • Rae,

    A solar rule of thumb “a Watt of panel for every Amp of battery storage”. For you existing battery bank that would call for 200 Watts of panels. AM Solar in Oregon is a good source with lots of experience setting up RVs.

  • Nomad, I’ll check out that site, thanks!

    Ed, doesn’t that rule apply to the *available* amps, not the battery capacity? You only get about 60% use out of your batteries, which in my case is 120A, so a 125W panel would make sense.

    AM Solar got back to me with an amazing quote on a 150W panel, so I’m going to finish scraping together my pennies and hopefully make it there for the end of March!

  • Tilting your solar panels gets more important the further north you go. While you get more hours of sunlight durring the summer, it’s at a lower angle so isn’t as bright as further south. Solar panels are rated at (the equivelent of) noon on a cold bright sunny day with the pannel aimd directly at the sun– extremly optomistic conditions.

    PS: I’ve recomended you blog to some Canadians — one a woman who purchased a Class C and traveled 2000 miles to the Rubber Tramps Rendezvous within a month of the purchase. She got some help installing a solar system there after I left.

  • Blars, I’ve already had this discussion with the installers and it will probably result in my splurging on gimbaled panels. I would assume that getting 24 hours of sunlight in the summer would make up for the weaker rays, though?

    I need to look up the Rubber Tramps. 🙂

  • It’s at cheaprvliving.com — there is talk of maybe doing another get-togther in southeastern oregon in the spring, an eastern US one, and quartzsite agaain next year. I sugested a projects gathering where working on RVs would be more the point than socializing, which also has a chance of occuring. The forums there seem broken again — hopefully it won’t take long to fix them. People in homebrew van conversions seem to be the most common there, but everyone interested in fulltiming on the cheap is welcome. My 1996 28′ Class A was definatly in the minority, and newer than most of the Class C’s there.

  • Hi Rae:
    Met you a few years back at the Abbotsford RV Show. We also have a Glendale Royal Classic 30′. Looking into being full time sometime this year.
    We are looking into getting solar panels and are doing our research just as you have done.
    Just wondering why you didn’t go with portable panels. We have been thinking it would give us better options rather than on the roof. We have a 1000 watt inverter and are wondering if we need to change it out to get a inverter/charger. Can’t quite figure out the difference of the two. Our needs are basically to be able to use the laptop, tv etc -( don’t use the microwave all that much) without using the loud, smelly, old generator
    Any thoughts you might have on this would be appreciated
    Take care

  • Hi Melissa,

    Could you please explain what you mean by portable panels?

    Your inverter sounds perfect for your needs. This is what takes the 12V power in your batteries and makes it usable by your 120V appliances, like the TV and laptop. I’d say that everything can be run on an average-sized battery bank except for a microwave an AC; you need the genny for those.

    What specifically are you thinking about when you say ‘inverter/charger’?

    How long do you want to be able to boondock? How long do you run the TV, computer, etc.? Where are you planning on boondocking? In what kind of weather? All of that will help determine how much solar power you need.

  • Hi Rae:
    Having been talking to a fellow at PapSolar here in Vancouver. Instead of mounting on the roof, they are on a pole which you can move around in order to catch the sun. That way if we are camped in a shady area, we could put the panels in an area that may have the sun.
    Like I said, I’m not sure what an inverter/charger is??
    We are hoping to be selling our home shortly and start the full time adventure. Would like to boondock as much as possible. Probably south in the winter months and then around Canada in the summer. If Rv’ing up here chances are we will be in some shady areas thus the thought of the portable panels. This fellow at PapSolar uses this type of set up for his trailer.
    We also have a slide on our motorhome and we thought if the panels are mounted on the roof it would limit us to how we park the rig in order to get the sun. As the windows are mostly on the slide area.
    Hope I am making sense.

  • Melissa, that sounds horrible for a full-timer who planes to move around a lot. They might be okay for someone who stays for months in one location. Solar panels are big and heavy; where would you store them?

    I think that tiltable roof mounted panels are a much better option. Sure, there are days when you might not be able to get as much power, but this would be a much easier solution.

    An inverter is not a charger. A charger is what puts power back into your batteries, using either electricity from being plugged in, from a generator, or from a solar panel.

  • […] I did the math to get my solar panel, I estimated that I use about 40A per day and that I’d ideally need 60A available to me. […]

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