Solar charging DIY

nice

 

i often have thoughts of getting a flexible solar panel for an RV (or 2 depending on if it will fit on the roof,) or equivalent and then getting the solar roof components from a JDM or EDM Prime.

 

Only in perfect full sunshine, only when the panels are squarely pointed at the sun. Clouds, haze, and angled sun will all reduce that. As will high summer temperatures.

Any car-mounted solar panels will suffer sub-optimum solar exposure conditions, i.e. more shade and poorer exposure angles than typical home solar systems. Car-mounted systems will also suffer additional air and weight drag.

It generally seems that the most powerful, productive, and cost effective way to 'put solar' on a plug-in car is to put grid-tied solar modules on a home rooftop, bank the energy with utility net metering, then use the credits for ordinary plug-in charging. This way all the hardware is always working at the full production capacity available in the local climate zone, without causing extra vehicle drag. And when the system is producing energy that the car cannot use or store, all the available production capacity still gets put to use for something useful, instead of tossed overboard and wasted.

 

If you're using flexible mats, do it all with adhesives. If they're rigid panels, the hardware for decklid spoilers and roof racks is more appropriate.

I think your insolation and conversion estimates are optimistic. I think I would first experiment with one such mat, duct-taped to an old car hood and balanced on sawhorses in the driveway. You could use that as a 1/3 scale model to figure out the delta between optimum collection angle and what the car contour mount would give.

The car hood is suggested mostly for ease of holding the project material but it would also give you experience working with paint less valuable than what's on your car. Additionally it shows you the honest effect of a convex curved mounting surface for fit, finish and power production.

 

Id put paint protection film on the surface and use neodymium magnets to secure the panel.

If you want to drive with them on, you can use a basic aerodynamic equation to estimate the suction placed on them.

1/2 the air density * the surface area * speed^2

(pv^2S/2)

Make sure all the units match up. For air density use kg/m^3, speed use m/s, and area use m^2.

That will leave you with kg*m/s^2. Force, in this case, lift.

That's just a back of the envelope calculation, but it'll give you an idea about how much pull they're gonna get.

Keep in mind lift goes up exponentially with speed so going from 65 to 70 is a bigger deal than going from 55 to 60.

 

Rob43

 

Panels mounted on the car won't have the same 30 degree tilt to the south used for the home solar production estimates. And if the car is used the same as many other cars, the panels won't won't be in shade-free locations all day every day, further cutting the total solar harvest.

I lean towards home roof-top systems because of the greater collection duty cycle of the PV modules, and the less investment needed in support hardware (per kWh harvested), at least for systems large enough to make a difference.

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Separately, I should point out that the above site's advice on optimum tilt angle (for maximum annual harvest) is too simplistic:

"Optimal Tilt Angle (No Adjustments)
If you never want to bother with adjusting your panels, set them at a tilt angle that is equal to your latitude."

Unfortunately, that supposed 'optimum' fails to account for seasonal differences in cloudcover and length of daylight. Online calculators at NREL will provide more detailed results. Here is a chart I made from an older NREL calculator for my location, clearly showing that a more shallow tilt produces better results here, weighting more towards long clear summer days over short cloudy winter days. And that simply putting my panels in the same plane as my roof (4:12 pitch), to minimize mounting difficulty and wind loading, causes only a few percent loss.

 

Two more things to consider:

- The Prius charger can be turned down to just 8 amps, or 960 watts. If this mode is persistent (not needing to be hand selected each time), then it may ease your design a bit.

- Does the charger start filling the battery immediately, or is there some significant delay before it starts giving some charge to the battery? I have vague memories of a problem here (or is it just old age creating false memories), but you'll need to ask real Prime owners about it. A delay could eat up a bunch of the available energy each cycle.

 

There is some delay while the current ramps up, but it's not too long, probably less than a minute. I think it wastes some power during that time, but it's maybe wasting around a hundred watts at most not the full charging current.

I think it does switch off the battery relays while not charging.

The current limit is set by the EVSE (but the car takes the current it needs up to the limit). It might be possible to modify one to have a lower current limit.

 

Here are things to keep in mind.
The charging system in the prius plug in/prime uses significant amount of power about 100-200 watts just to charge, plus add the inverter you need to use and any losses in the middle you need at least 250 watts just to run the charging system, you need an inverter of at least 1800 watts and a battery big enough to power the inverter, if the inverter doesnt get enough power it will simple shut down, if you really want a solar panel the best way is to connect it to the 12v battery

 

I find all of this a moot point...

If this were doable, Toyota would offer it for Extra $$ in some top level trim package. But they don't because Toyota can't offer a worthwhile* charging benefit from some sort of highly efficient rood panel system.


Rob43

* My definition of worthwhile is at least a 70% charge from 0% during the course of one day when parked outside in full sun.

 

Mr. Chris Jones posted something like op is proposing. The pictures of his system was #16 on the thread "Estimated Miles / Best Actual Miles on Ev Charge". He also gave us his part list for his system at #23.

Posted via the PriusChat mobile app.

 

uhh...toyota DOES offer a solar charge system. Its the pussy lawmakers here in the USA that couldn't bear a "non rollover safe" solar roof and made Toyota eliminate the solar roof. why else does JDM and EDM primes have solar roofs?

And your definition of worthwhile is physically impossible in the footprint of a car today. Solar technology in 50+ years might but by then, we'll be driving nuclear powered EV's anyway.

 

...And that's why its no good ...


Rob43