Solar Panel Guide (2)

New approaches for small RV’s.


After I introduced Semi Flexible Solar Panels in my previous post, questions remain about the performance of these new semi flexible modules.

Rigid Residential Flexible
Amorphous Thin Film Semi Flexible
average cost per watt 1 $ 0.80-2.00 $ 1.50 $ 2.00-7.00
low light performance average good good 2
high heat performance average good good 2
efficiency 15 watt/sf 5.5 watt/sf 15 watt/sf
weight 40 oz/sf 11 oz/sf 7.5 oz/sf
roof penetration yes no no
warranty 20-25 yrs 20 yrs 10 yrs 3
1 2014
2 Several unconfirmed user tests indicate low light and high heat performance are less than rigid panels.
3 Misuse of the limited flexibility is often given as a reason for the shorter warranty period. Product life maybe similar to rigid panels.

As a general indication, prices for these panels are double that of regular rigid modules. For that, you’ll get a substantial weight reduction and a more aesthetically pleasing finish and maybe even some improved fuel mileage.

High heat performance is probably the biggest drawback, where some users indicate a considerable performance drop during the hottest part of the day. Under low light circumstances, they seem to under perform too, however no significant amount of energy is produced those times of the day anyway.

A simple solution for these problems is to oversize your system by adding an extra panel, if needed. Test your basic system after installation and, if necessary, add a panel that you can hang on the side of your van or other location, when you are parked in the shade. Store it under your mattress while driving.

Rigid Residential Flexible
Amorphous Thin Film Semi Flexible
Kyocera Unisolar AMSolar
maximum Power (Pmax) 245W 128W 100W
voltage at Pmax (Vmp) 29.8V 33V 18V
current at Pmax (lmp) 8.23A 3.88A 5.56A
short-circuit Current (Isc) 8.91A 4.8A 6A
open-circuit Voltage (Voc) 36.9V 47.6V 21.3V
size 65.5”x39” 216”x15.5” 41.2”x21.2”
weight 44lbs 17lbs 5.5lbs



How much of a premium you are willing to pay for semi flexible panels may depend on the type of your RV that you have. When I focus on a converted cargo van or small Class B, the advantages of these new high efficiency panels probably outweigh the extra investment. Comfortable boondocking or stealth living may finally be achievable with few restrictions. One major uncertainty remains as little is known about the long term performance of these modules.

And other issues remain, such as scratch resistance and production quality. That will not stop you, if you want to push the boundaries and be among the first with this new technology.

conventional alternative
Step 1 Calculate usage needs 2 x 6V
1 x 12V
battery system 1
4 x 6V
2 x 12V
battery system 1
Step 2 Calculate panel wattage Calculate maximum number of panels and adjust for available space.23
Step 3 Calculate batteries Adjust your usage
1 A small RV or converted van can only reasonably store 2 or 4 – 6V batteries.
2 Provide enough wattage to adequately recharge your batteries.
3 Flexible lightweight panels allow you to use them as portable additions to fixed panels and store them under your bed.

semi flex book


How To Make Small RVs Comfortable By Installing Inconspicuous & Low-Profile Solar Panels.

[ Click Here To Download ]


  1. I really enjoy your site with all of your informative articles. Plan to utilize this wealth of info. as soon as I buy a vehicle to convert. Thanks

  2. Great site, thanks!
    I think that there may be a typo in the weight for the AM Solar 100W panel. The closest match that I could find on the AM Solar site is 15.5 lbs, not 5.5 lbs. If there is a 5.5 lb 100W panel, please share the link…would love to be able to use that.

    1. Hi Greg:

      The list you refer to, was a comparison between the different types of solar panels: rigid (conventional house panels), Amorphous and Semi Flexible.

      One of the major differences is in weight and despite that AMSolar currently doesn’t carry these types of panels, the 5.5 lbs weight is still appropriate for such a panel.

      An actual example is this 120W flexible panel on Amazon at 4.86 Lbs.

      Rigid and flexible panels, each have different applications. If used on a larger travel trailer or camper with flat roof, the conventional rigid solar panel has a distinct price advantage where weight is often not an issue. On smaller stealth campers, like the Ford Transit I’m working on, flexible panels are practically invisible, light-weight, can be glued on, but are more expensive and longevity is still not determined.

      Van Williams

  3. I’m converting a Transit and really love your info; it’s the best I’ve found for my build. I’m planning on AGM 12v batteries to run my MaxxFan and Whynter 65qt fridge. My lights will be solar. Is 200ah enough? I’ll mainly be camping in National/State Parks but not wanting to rely on hook ups.
    Thank you again, everything you’ve written has been so helpful!

    1. Hi Laura:
      Again, I’m not an expert at this.
      Electrical needs can be tricky. Generally, I would approach this as follows:
      First calculate your needs by writing down and adding up the number of Amps of each electrical appliance. Your fridge will likely be the largest draw at around 40-45 Amps/day, if it has a Danfoss compressor.
      When you know your daily load, you can calculate how long your batteries can support you.
      Lead-acid batteries can only be drawn down to a maximum of 50%, so the total Ah available is 200*50%= 100Ah. If you use 50Ah/day you can camp for two days.
      That’s the theory; in reality a little bit more is involved. I assume, you have solar panels to recharge (but you can also use a generator or alternator to recharge).
      In general you’ll need solar power in watts equal to the Ah’s of your batteries. You also have to keep in mind that in the southern parts of the US, in summer you may get a MAXIMUM of 5 hours of solar input, but for calculations I prefer to use the winter solar input, which can be substantially lower. It all depends on your personal situation and any calculations are just that. In reality the numbers are probably less optimistic.
      If you use 50Ah/day (very frugal), have 200AH in batteries (100Ah usable) and 200W solar panels, it could work out as follows:
      Summer/Sunny – 5(hrs)*10A (2*5A per panel) = 50A per day. This means that the batteries remain topped off.
      Summer/Cloudy – 5(hrs)*6A (2*3A per panel) = 30A per day. This means that the batteries will be drawn 20A. This means that if the weather stays the same, you could stay out for about 5 days (100Ah/20 = 5).
      Winter – solar panels are much less efficient and night temperatures could also affect your batteries.
      In Canada or northern parts of the US solar panels are always much less efficient.

      Another practical rule:
      One 100W solar panel is sufficient for the most basic needs.
      Two 100W solar panels (200W) is sufficient for a fridge and some basic needs.
      Three 100W solar panels (300W) or more will allow you to do most things on the road.

      The only accurate way to establish whether your setup is sufficient, is after it has been installed. There are too many unknowns and estimates and your personal use will affect as well. Are you a warm weather camper or do you like to go skiing? Do you use a microwave or inverter?

      All these calculations may give you a handle on whether you’re on track with the numbers, but always reckon that you may need to add an extra solar panel or battery.

      Van Williams

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