Solar panel results
 

I had to remove the solar panels from my van earlier this year. 2x180W panels. 180A Smart alt, stop-start, 1.6 diesel.

So I've compared the last six fill ups from this year without panels vs same period last year with panels.

Results:

Without solar panels: 7.55l/100km (31.15MPG)

With panels: 7.24l/100km (32.5MPG)

So approximately a 5% improvement. It's probably greater than that as I was still running one panel, but due to a wiring issue it was only putting out 10-20Wh/day at best. It was completely disconnected about half way through. I was also occasionally grid charging the battery.

Since a 180A alt can be a pretty big draw on a 1.6l engine, having a solar charged battery makes the van noticeably more lively at low revs.

I believe I'm the only one on here that's shown an improvement from solar panels in an otherwise stock vehicle (no alt. delete).

5% is a pretty long payback but there's also less battery deg, belt wear, alt wear, and you'll never come out to a flat battery in the morning.

I always wonder about the energy needed to overcome air resistance represented by solar panels installed on a vehicle vs the power they provide to the system. Variables include air resistance and efficiency of the panels, speed of the vehicle, and 12vdc power demand and drag from the 12vdc alternator.

In your case, you seem to be getting more from the solar panels than they're taking. Good for you! Of course, that grid charging is a thumb on the scale :-)

So it seems to justify. BTW what about the accessory drive? With the solar panels, an electrically-driven air conditioner seems to be a reasonable option too.

This thread makes me want to plaster the tops of both my cars with small solar cells.

If you have a consistent light source, this is a good modification particularly for cars that aren't daily driven. The alternator works pretty hard to charge a dead battery, since lead acid batteries are so inefficient, and alternators are also inefficient.

With a very high current capable lithium ion battery, the charging efficiency goes up, but the alternator is still burning fuel.

On my (deceased) MR2, I put a few solar panels on the dash to keep the small lithium ion battery topped up, as I only drove it maybe once or twice a month. No more slow struggling cranking, no more battery damage, probably some amount of fuel savings.

I was thinking more like using the solar cells to charge the high voltage hybrid battery in my case.

If you do a good job integrating the panels, they won't add much aero drag.

On my last small van, I needed the roof rack at least once a week so decided to leave it on permanently. I mounted a flexible panel on aluminum strips between the (teardrop) racks, so that they didn't present any frontal area. The added benefit of this is you have a Landrover style safari roof, so your car is always in shade which should save A/C use.

If I decide to keep my Suzuki SX4 (my current short trip, gets kept outside car), the 'safari roof' factor would be just about enough for me to add flexible panels to the factory roof rails.

On the current van, I actually have a recess in the centre of the roof. The (again flexible) panels sit inside that recess and again, don't add much if any frontal area, and they actually cover the ribs that transversely run across the roof.

Grid charging is a thumb lifting the scale since I was doing that without panels fitted, so the difference between panels/ no panels would get greater without grid charging.

I get about 600Wh a day max, I still park in the shade where possible, because A/C is a far bigger draw than 12v. 600Wh would only run the A/C for 10-20 minutes a day. I'd love electric A/C, but I'll wait for the Cybertruck to offer that from the factory.

Yup, with a 1.6 in a two tonne van, I can tell my state of charge by the low end throttle response. It sometimes feels like someone's switched my 'Eco' mode off. It's just about worth doing this mod just for the extra low end torque.

Whenever I see some all-electric refrigerator units for transport of perishable products, even though the load compartment is usually well insulated with lots of fiberglass and styrofoam, it seems quite tempting to look at a 12-volt compressor out of those as a possible replacement for the engine-driven compressor of an air conditioner. Even though insulation is not nearly as efficient, since the cabin of most compact cars is smaller compared to the load compartment of a refrigerated van, it seems quite reasonable.