Description of the solar charging system and a couple examples.

Using PVWatts to estimate size required.

What Kind of PV Panel and Charge Controller to Use?

<explain difference between the single 36 volt panel and multiple 12 volt panels, and the charge controllers that go with them>


How Much Solar Charging Do I Need?




How to Estimate How Much Energy a PV Panel Will Provide

The amount of energy a PV panel will provide depends on:

  1. The panels nominal wattage rating.
  2. How sunny it is (or how cloudy)
  3. What season of the year it is (the sun is lower in the winter).
  4. The tilt of the PV panel and the direction it is facing.
  5. The efficiency of the charging system

Before going into the details of how to do a fairly exact job of estimating PV panel output considering all the above, here are some quick rules of thumb that will get you in the ball park and may be good enough:

<note — could use PVWatts to do a table that has summer and winter output for a few locations and for best tilt and horizontal.  With PV watts, this would be for average weather>




3 Responses

  1. Hi Gary,
    You’re welcome to use my insights. I hope they prove helpful to others who are considering adding a solar charging system to their DIY campers. We’ve really enjoyed the freedom our system has given us. On our recent trip to Yellowstone, we stayed in primitive campsites every night – mostly Forest Service or National Parks. We were able to do all the things we needed to do without ever having to connect to shore power. There’s something special about getting free energy. It almost feels like stealing, but it’s legal – even encouraged.

    I just bought the Sprinter that will become our new camper today – a 2006 2500 140WB hightop. I was able to find a solid, relatively clean van with just over 80K miles about two hours from here that was in my price range. I’ll take delivery of it in about two weeks.

    Since our return from Yellowstone two months ago, I’ve been scouring Craig’s List and a slew of used car websites looking for a van that would suit our needs at a price I could afford. I’ve also been learning as much as I could about Sprinters and Sprinter-based conversions on websites like yours and the Sprinter forum. I’ve developed 2D drawings in Adobe Illustrator to play around with different floorplans and storage arrangements.

    I’d be happy to share my experiences as I convert our new van to meet our needs. I’m sure the design process and final conversion will be much different than yours. As you can probably tell from the base vehicle, we’re on a very tight budget. My goal is to have a comfortable, serviceable camper for under $20K (purchase plus conversion cost).

    I bought the Dodge we’ve used for the last three years for $4250 with 79K miles and spent another $2-3000 doing the conversion. We’ve logged about 30K miles with it. We’ve learned a lot, beginning with the fact that we like the style of travel that it makes possible.

    I’m a wildlife painter and my wife and I are both wildlife photographers. We plan to use this camper (as we did the Dodge) as a mobile base for our photo excursions. Our main objective is space to carry the camera, art and computer gear we need, along with plenty of personal luggage to be comfortable in a wide range of climactic conditions. Our secondary objective is to be able to reconfigure the interior space fairly easily for trips to the lumber yard and the occasional outdoor art festival.

    During the hunt for our Sprinter, I’ve prepared by buying some parts that would fit in whatever van we ended up with. I had a pretty specific van that I was looking for, but I also had some variations that might be tolerable if the deal was right. Here is what I’ve bought so far:
    • Two 150W Mono crystalline solar panels ($325 delivered – Ebay)
    • Xantrex ProWatt 1000W pure sinewave inverter ($225 delivered – Ebay)
    • Morningstar TS45 PWM charge controller ($110 delivered – used on Ebay)
    • VMaxTanks 15A 7-stage smart charger ($100 delivered – Ebay)
    • Fan-tastic 1250 roof vent ($135 delivered – Ebay)
    • Camco Aero-Flo vent shroud ($12.50 delivered – Ebay)
    • Marinco 15A shore power inlet ($21 delivered – Ebay)
    • UltraGauge EM Plus with Velcro mount ($80 delivered – UltraGauge)

    Regarding your question about our cooking choices – we cook outside due to space constraints as well as safety and odor concerns. The Dodge van we’ve been using has been adequate to our needs, but barely so. Any kind of inside galley was out of the question. The Sprinter that we will be using for our soon-to-come conversion will give us more space, but we plan to use it mostly to make our hanging-around area more comfortable. I expect the planned electric teapot and possible microwave will be our only concessions.

    Thank you for the warning about the energy consumption of microwaves. I’ve read several similar warnings. Some things can’t be said too often though. From what I’ve read, it seems a 700W microwave should be safe with our 1000W inverter as long as the wires from the battery are adequately sized.


  2. Hi Steve,
    That was quite a trip — sounds like you passed within about 50 miles of my house near Yellowstone.

    Good practical information on you solar electric system — thanks.

    This page on the website is one I’ve clearly not finished, and I’d like to incorporate some of your info for smaller demand electrical systems if that’s OK with you?

    It sounds like you avoid cooking with the campstove inside the van — is that for safety or odor or other reasons?

    One thing to be careful of on microwaves is that unlike most electrical applicances they are rated on their output, and the input power they use is greater than their nominal rating (eg a 1000 watt microwave might pull 1200 watts when running).

    If you want a place to document your build, I’d be happy to add an article on it here in the Conversions section — see the Contact page for how to get hold of me.

    Thanks Gary

  3. Great website – lots of useful information and resources. Thank you. I have some practical experience with a PV charging system. I converted a Dodge raised roof van to a simple camper and my wife and I have been using it for the past three years. This year we spent just over a month in it traveling from our home in western MA to the Yellowstone area. We camped every night on the trip.

    I have a 105ah FLA battery with about 250 watts of capacity in my (flat-mounted) solar array, fed through a Xantrex C35 PMW charge controller. Our electricity needs are small – we don’t have most of the big consumers – furnace, microwave, refrigerator. We use the system to charge camera and computer batteries, run a single LED light and a Fantastik fan. The only backup power or charging capability we have is a shore power port.

    In our experience, the solar system is enough, even when camping in the PV-marginal northeast in semi-wooded conditions. We seldom have shore power available and when it is available, seldom pay the additional fee to use it. That said, I’m always concerned that we’ll run into a string of cloudy days that will cause us to build up a usage/recharge deficit. In my next conversion (I’m planning a Sprinter build), I will have the means to charge the house battery from the alternator. Since we haven’t needed it so far, I’ll go the ad hoc route, using a small “smart charger” through a small inverter plugged into the dash power supply. To date, my so far successful strategy has been to have plenty of headroom in my system, both in the battery and in the charging capacity.

    A few things I’ve learned along the way:
    1. There are three varieties of PV panel – monocrystalline, polycrystalline and amorphous cell.
    2. Of those, the mono and poly are the most efficient – you need about twice the area of amorphous panels to equal the capacity of a given array of either mono or poly.
    3. Amorphous panels are much more tolerant of marginal charging conditions than mono or poly. A friend who covered his house roof with amorphous panels has demonstrated that they will even charge under a full moon. By contrast, many mono and poly panels will shut down completely if only a couple of square inches are shaded. Further, if you don’t design your system to prevent it, the shut down of one panel can disable your entire system.
    4. Like any DC system, it’s very important to be aware of voltage drop and keep the wiring between your PV array and your charge controller and battery as short as possible and to use an adequate wire size. I don’t think there’s any danger in using over-large wires to be on the safe side.

    In the Sprinter build I’m planning, I’ll be increasing both the battery and the PV capacities to 155ah (AGM) and 300w respectively, besides adding the alternator charging capability. With our current system and usage patterns, we’ve seldom discharged our 105ah battery below 75% and always been able to recharge to 100% during daylight, but we’d like to have the freedom and capacity to add some creature comforts.

    I had hoped to be able to use an electric teapot, but haven’t been in our current setup. At 1000w (running for 5-10 minutes typically), it was too much for our 600w inverter. I’ve bought 1000w pure sine wave inverter for the new van (a Xantrex Prowatt) and I have a 750w teakettle that I’ll use if the 1000w is too much for this inverter. The lower wattage means a longer run time, so there is no economy in using it though.

    I’d also like to have the capacity to add a small microwave oven. so far, we’ve done all our cooking outside on a propane campstove. I plan to continue with that practice, but there have been times when we arrived too late to set up our outdoor kitchen. For those times, it would be nice to have an alternate means of cooking. We’ll continue to use a cooler, rather than adding a refrigerator – either electric or propane. For the vast majority of our electric usage, we’re using DC power direct, rather than AC through the inverter. I turn on the inverter only when it’s needed to avoid the phantom power drain.

    Steve (Huntington MA)

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