Tuesday, January 13, 2015

Solar Musing

I've been considering solar for the Scamp for the past three years. It would be nice if there was a magic bullet, a 'one size fits all' solution. Some vendors would suggest that's exactly the case and they'll sell a standard package. Works well if you have the mythical 'standard' RV with the even more mythical 'standard' power demands. A little study quickly showed there weren't any magic answers.

There are some very worthwhile resources that are specifically oriented to RV solar. But even those resources don't always agree. If you're thinking about solar, I'd suggest you start by carefully reading HandyBob's Blog, the section of Jack Mayer's website about RV Electrical & Solar, and the RV Solar Education section on AM Solar's website.  Both Technomadia and Wheeling It have done excellent posts about their massive (at least from our perspective) installations and their selection process. They both used AM Solar for their installations.

Before our first year with the Scamp was complete, I'd installed a Doc Wattson meter to track our 12 volt power utilization. This meter can be installed to show power usage or wired in reverse to show power input to the battery, but it can't do both. Eventually, I'll replace it with a more expensive and much more capable TriMetric 2030 Battery Monitor system. A way to accurately measure, monitor, and understand your power consumption is the first step towards sizing an appropriate system.

When boondocking, we don't have any essential requirement for 110 volt a.c. We do carry a 100 watt portable inverter to use with the camera battery charger but everything else is 12 volt or propane powered. We don't have a TV, microwave, or coffee maker to power so we don't have to account for the cost or power consumption of an large inverter. We converted to all LED lighting which is a major power savings and now average 25 amp/hr use each day. We never go over 30 amp/hr, even with extensive computer use and/or daytime heater use. Our power demands are listed on the Scamp 19 page at the top of the blog and are higher in the winter when we're using the furnace than in the summer.

We swapped out the standard Scamp battery for a pair of 6 volt golf cart batteries about 3 years ago, giving us 205 rated amp hours of battery or about 100 amps of usable battery capacity. Our batteries are Interstate brand, simply because that was what Costco carried at the time. We can go four to five days before needed to charge the batteries, but I don't like to haul and mess with a generator to charge the batteries.

With adequate battery and accurate power demand history, it was time to start thinking about options to create our own power. For a couple years we hauled a Honda generator and would fire it up every four or five days to power a high capacity battery charger. The generator didn't get much use, and it was more hassle to haul and store and keep fresh gas in it than I wanted. Of course, if I were based in the southeast where high temperatures and humidity make air conditioning a very high summer priority, I'd be singing a different tune!

Lots of friends use portable, suitcase style folding solar panels with success. The portability allows for positioning the panels for best results at each campsite. I seriously considered this style but we don't have a convenient safe place to haul it or store it when not in use, and I have concerns about the temptation factor. Someone could decide they need it more than I do.

For my RV style, (and style is a significant factor in our design decisions) I much prefer a solar system that is permanently installed on the trailer so there's no chance of leaving an essential component in the garage or at a campsite. Nice idea, but our trailer barely fits in the garage now, with only 3/4" of clearance at the top of the door after I taught the trailer to kneel. Self imposed height restrictions, other equipment installations, and preferred trailer orientation when camping all had implications for available roof real estate. I actually thought I had only one possible location until I talked with the folks at AM Solar while we were in the Northwest last summer. One of their staff suggested the location I'm using.

Solar panels come in a variety of capacities, sizes, and efficiencies. My rooftop real estate limited us to a panel nominally 21 inches wide which cut down our options. I seriously considered the GS135 that AM Solar sells, but selected the 100 watt panel from Renogy because of its higher max power voltage (Vmp) and significantly lower price. The 100 watt panel will be marginal in the winter, but should cover us as long as we tilt the panel.

The next step was to head to one of the few places that I actually enjoy shopping. I can spend hours in the hardware aisle at our local Ace Hardware adapting my mental mount design to the available hardware.

Next up - building a custom mount.

11 comments:

  1. I sometimes find the engineering of a project more fun than the actual project, itself. Walking the aisles of Lowes, or the local hardware store, and finding exactly what I needed, but didn't know what it was until I saw it.

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  2. I'll be interested in seeing what kind of mount you devise, John.

    We have the suitcase solar panel, but I wish I could mount a 150 watt panel on our Casita's roof -- that I could tilt when needed.

    The thing we run into most of the places we camp are 2 or 3 rainy days in a row. I guess we really need a generator, but, like you, we don't want to have to haul anything else along.

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    1. I've seen some really nice permanently mounted generator boxes, and Orbital Machine makes a great locking mount plate but I'd like to avoid the noise and maintenance if I can. It's going to be interesting to see if our single panel is going to do the trick for us.

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  3. I found 200 watts to be a very tight minimum for my living style. Now I have 350 watts and it has proven to be way more than enough. Two group 27 AGM batts have been enough batts with all that recharge power.

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  4. OOPS I forgot to mention that with 200 watts I had to tilt over 80% of the time. With 350 the panels I never have to tilt.

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    1. Thats the situation I'm looking at. IF I could double my panel wattage AND make sure it wasn't ever shaded, I wouldn't need to tilt the panel. Unfortunately, there are lots of trade-offs, including rooftop real estate.

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  5. Renogy had a very good deal on a starter set...don't know if this price is still available, they have some great accessories too..
    http://www.renogy-store.com/200W-Mono-Starter-Kit-p/kit-starter200d.htm

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    1. Renogy also has a 100 watt starter set but their starter sets include 12 gauge MC4 cables and a positive ground controller which could be problematic in some situations.

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  6. Renogy can't be beat for it's combination of good quality and low prices. After obsessing about my View being a few hundred pounds overweight, I decided to put 300 watts of the thin flexible Renogy panels on my roof. ( http://winnieviews.blogspot.mx/p/skinnie-solar.html ). So far, so good. They work great. But, I did notice when I was up in Nevada that by late November, if I parked N-S rather than E-W, my AC unit was shading 2 panels too much. No longer a problem down here in Baja though :-) . But I did buy another 100 wt Renogy thin panel that I plan to add in as a portable if/when the rooftop panels ever need more oomph in the future. That might be something to think about if you have limited roof & storage space.

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    1. I considered the flexible panels but they didn't helpe unless they could handle a compound curve. :-(

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