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Sprinter Electrical: Solar Power

Last updated 2017-07-06 - Send Feedback
Related: Sprinter

Photographer and cyclist and Mac expert and software engineer Lloyd Chambers is available for consulting on general Sprinter considerations at his usual consulting rates via phone, or in person in the Palo Alto, CA area. Save yourself hours and mistakes by discussing issues up-front. More about Lloyd....

Get your batteries and alternator and regulator (the whole kit!) from NationsStarterAlternator.com.

AMSolar has an excellent range of solar solutions.

What is the reality about solar power for Sprinter vans and RV camping?

  • Solar is good for topping off and trickle charging and modest daily power needs.
  • Solar imposes a scarcity mentality upon its users. It is not a fast-recharge power source. so one frets over how much power is being used and how long it will take to recharge the batteries (days for a nice-size battery). Can that 2nd bag of popcorn can be microwaved? Can I use my computer another hour? No joy.
  • Solar is NOT good as primary power source, well, it is not a primary power source, period. It is a supplementary power source. Thus it is a large expense with much higher complexity that only supplements a primary source, and only when conditions allow for it.
  • There is not enough roof area on a Sprinter van for a good daily charge unless one uses little power. Solar displaces useful and fun stuff on the roof, too.
  • Solar only charges when the sun shines... and my idea of a good camping spot involves shade, which is the best air and only air conditioner I need in many places. That said, solar panels do shade the van in a modest way.
  • If you’re out having fun all day, solar can provide a good charge for modest usage—all good—but what if I want my 300 watt computer system to work on for 3-4 hours in the evening along with some microwaved popcorn? Solar falls farther and farther behind, so recharging requires a more robust charging source anyway.
  • The argument for solar when driving is absurd; a 2nd alternator can charge 20X faster. Driving 30 minutes charging via a 2nd alternator is equivalent to solar for an entire day! Since my photography involves driving at least that much just about every day, there is negative value to solar (cost, complexity, junked-up rooftop, keeping the panels clean, etc).
  • The money spent on solar is better spent on a higher capacity battery in a smaller and lighter form factor (lithium battery), recharged rapidly with a 2nd alternator.
  • Solar panels are usually mounted in a way to significantly increase drag (on a Sprinter or van), thus reducing fuel economy day and night. They also create a wind noise nuisance. Quite possibly the loss in fuel economy exceeds the gain in power from solar, and those losses in fuel economy apply for every mile driven, increasing at freeway speeds, day and night. Fully charged batteries? Reduced fuel economy, and no power stored.
  • Solar power decreases substantially at my peak travel time (September through November). And in the hot summer, I want to park in the shade so when I come back to my van it’s not 100°F inside. Late in the season, the sun peeks into canyons only a few hours and often there are clouds that greatly reduce solar output. So one has to rely on other power sources anyway.
  • Solar can damage batteries, see the note below.

Bottom line: relying on solar, you spend all your time avoiding electricity use instead of doing what you want to do. And it might actually be a net loss when fuel economy is reduced from wind drag.

In many if not most cases, solar is a feel-good irrational non-solution for anyone looking for a reliable power supply; too slow to charge, useless at night and of diminishing value in the non-summer months. That said, solar is good for those who leave their van parked for long periods. But it is very hard to justify on any other basis when a 2nd alternator is available.

Solar can damage battery lifecycle longevity

The Lifeline/Concord technical document states:

For repetitive deep cycling applications (deeper then 50% depth of discharge), chargers should have an output current of at least 0.2C (20 amps for a 100 Ah battery). If an output current is below this value, the cycle life of the battery may be negatively affected.

Translation: solar is a problematic for large batteries. The Lifeline/Concorde GPL-16T is a 400 amp battery, and I was considering a pair of them in series (for 12V). Assuming "C" of 400 amps, the amperage required is 0.2 X 400 = 80 amps. That’s about 1000 watts—virtually impossible with solar on a sprinter van under the very best conditions on the equator. Hence, guaranteed battery damage over time if one charges with solar after discharging the the batteries beyond 50% , which I would want to do routinely.

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