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I have a 100w solar panel on top of my car...to tend a 12v battery. It's got a Dewalt battery charger, mikrotik ltap, and raspberry pi hooked up to it. Little h

by pchew 1y ago

I have a 100w solar panel on top of my car...to tend a 12v battery. It's got a Dewalt battery charger, mikrotik ltap, and raspberry pi hooked up to it. Little hotspot with multiple sims and resource server(mainly just for fun). Anyone that can do basic math should immediately realize there's just not enough area to make an appreciable difference in regards to mileage.

jollyllama 1y ago
Very nice. How long does that tend to stay alive for? And what kind of cold weather conditions do you have to contend with?
barnas2 1y ago
The Prius Prime solar panel roof I think can net 3-6 miles a day under ideal conditions (which we're probably close to here in Arizona). I think that's a little more than people would expect, but still only applicable in niche conditions (tiny daily commute, or a longer non-daily commute). I think the math works out to ~4-6 years to break even for the cost of adding the solar roof assuming $0.15 per kwh, which isn't terrible. If solar tech gets more efficient or cheaper, I think it starts becoming a much more attractive option in some areas. If you get into the 10+ miles per day range, that would cover a lot of peoples commutes in certain areas.
- jeffbee 1y ago
  The Prius Prime solar roof is a $610 option available only on the top XSE trim level, so a hypothetical buyer is paying ~$7500 to access this effectively negligible amount of energy. ETA: and the fact that this option is tied to the significantly less efficient 19" wheel package, instead of the standard 17" wheels, means that this will never, ever be a net benefit.
  - mattmaroon 1y ago
    Not if they were getting that trim level anyway.
- beAbU 1y ago
  Does the extra 3-6 miles factor in the need to now run the AC much more aggressively because the car will be hot from sitting in the sun all day? If this quoted number comes from the manufacturer itself, then I think the answer is "no".
  - kgermino 1y ago
    I don’t think you’d have to run the AC any more aggressively with the solar panels than with a traditional steel roof? If you’re suggesting it wouldn’t work in a garage, that’s obviously true (and another factor in whether car solar makes sense) but many (most?) people park their cars outside during the day anyway. I for one can’t remember the last time I parked under cover
  - danans 1y ago
    > Does the extra 3-6 miles factor in the need to now run the AC much more aggressively because the car will be hot from sitting in the sun all day? Most cars are already sitting in the sun all day.
    - aziaziazi 1y ago
      Not here in European cities where they’re either within a multi story park or in the side of a half day shaded tiny street.
      - parsimo2010 1y ago
        You are not getting the 3-6 mile per day boost if your car is parked in the shade.
        tstenner 1y ago
        That's his point. You won't get any reasonable charge because you (mostly avoid parking your car in direct sunlight
      - sdenton4 1y ago
- singpolyma3 1y ago
  That's still 3-6 fewer miles worth of charging to do from more expensive sources. Even if it can't come close to covering your full use it's still covering something
  - IAmBroom 1y ago
    Not if it won't recover it's own costs.
    - cma 1y ago
      It may still lose on this, but you would also want to include the externality costs that the consumer doesn't themselves bear for whether it is worth it overall.
    - dzhiurgis 1y ago
      Cost is convenience. Manufacturing cost is like $40 cells, $20 electronics and $200 in glass fusion, mounting, etc. My car eats 200W just being online so it would be useless to charge from solar.
- thegrim33 1y ago
  13.6 kWh battery. 39mile EPA range. Equals 2.87 miles of range per kWh. Leaving it out for 8 hours straight, on a sunny day, in LA, netted 915 Wh. Or, 2.86 miles. [0] Not 3-6, 2.86. 2.86 miles of charge, but only if left outside, uncovered, in full sun, on a fully sunny day, for a full 8 hours, in a place that gets effectively the maximum amount of solar radiation per day out of anywhere in the entire country. Now, do the same experiment anywhere else in the country, that doesn't get max solar radiation, or that can't get full sunlight for full 8 hours, or where it's cloudy at all, or rainy at all. 2.86 miles per day is the practical MAXIMUM, given perfect conditions. For the average scenario it'd be some fraction of that. The 6 miles figure is what they said you'd get if, in addition to perfect conditions, "if the sun shifted its orbit" (?) and gave perfect sunlight for 12 hours straight. Which is a number which should obviously not be thrown around as if it's obtainable. The fact that they're quoting numbers about what range you'd get if the solar system was constructed differently also makes me doubt the impartiality of their experiment and the numbers they provided. [0] https://www.motortrend.com/features/the-2023-toyota-prius-primes-battery-could-take-three-weeks-to-recharge https://www.motortrend.com/features/the-2023-toyota-prius-pr...
  - conjecTech 1y ago
    EPA range tends to be pessimistic for EVs as it assumes you are always traveling at highway speeds. Even small reductions in speeds can make EVs much more efficient since drag is quadratic. A quick google search shows Prius prime owners reporting 4-5.5 miles/kwh, so the 3-6 mile range is entirely plausible.
    - slaw 1y ago
      EPA's city cycle speed is an average 19.6 mph, highway speed is an average of 48.3 mph. City range weighted at 55% and the highway range at 45%.
      - bangaladore 1y ago
        I don't think it's that simple. IIRC you don't have to do the city testing. https://www.epa.gov/greenvehicles/fuel-economy-and-ev-range-testing https://www.epa.gov/greenvehicles/fuel-economy-and-ev-range-...
- roamerz 1y ago
  There is going to be a parasitic drag loss to figure into it as well. I think the only way to accurately calculate that would be in a wind tunnel or maybe an amp meter with a before and after installation under identical conditions.
AdamJacobMuller 1y ago
I just started doing this with my car, mostly to add a camera/temp monitoring for when I leave my dog in the kennel in the car (she's well watched over, please don't fret over it). I'm hooking it up via starlink specifically so it works in remote areas with no cell coverage too. Monitoring and proxying everything via an RPI as well. Victron DC-DC inverter to keep the bluetti battery pack charged with bluetooth relay boards so we can turn loads (camera/starlink/others) on/off programmatically (it only turns the starlink on when there's no good/known wifi for example). Fun project, combines software dev (which I'm fairly good at) with hardware work (which I'm less) and my dogs (which I'm a big fan of).
- theoreticalmal 1y ago
  It’s interesting to see how many people in this thread have the same idea. I’m doing something similar and learning that hardware is just plain hard
ben_w 1y ago
The maths says that the *mean* number of miles driven by a vehicle is surprisingly low, and that tiling the surface of a car can get to about 80% of that *mean* in places where the car is just left out on the street and not shaded parking. But! That's a practical consideration at the level of "should a government require EV makers to design the roof, bonnet, doors etc. to be tiled in PV in order to reduce, but not eliminate, the induced extra demand on the grid" and definitely not "should I personally bolt a small, fixed, PV panel and inverter into my EV as an aftermarket DIY job?" The former gets wind-tunnel tests for efficiency, QA, designed around all the other safety concerns cars have e.g. crash safety. The latter, doesn't.
andoando 1y ago
If only we didnt start off with having 3000+ lbs of metal to move a 100-200lb person as a design limitation

by pchew 1y ago

jollyllama 1y ago

Very nice. How long does that tend to stay alive for? And what kind of cold weather conditions do you have to contend with?

barnas2 1y ago

The Prius Prime solar panel roof I think can net 3-6 miles a day under ideal conditions (which we're probably close to here in Arizona). I think that's a little more than people would expect, but still only applicable in niche conditions (tiny daily commute, or a longer non-daily commute). I think the math works out to ~4-6 years to break even for the cost of adding the solar roof assuming $0.15 per kwh, which isn't terrible. If solar tech gets more efficient or cheaper, I think it starts becoming a much more attractive option in some areas. If you get into the 10+ miles per day range, that would cover a lot of peoples commutes in certain areas.

jeffbee 1y ago
The Prius Prime solar roof is a $610 option available only on the top XSE trim level, so a hypothetical buyer is paying ~$7500 to access this effectively negligible amount of energy. ETA: and the fact that this option is tied to the significantly less efficient 19" wheel package, instead of the standard 17" wheels, means that this will never, ever be a net benefit.
- mattmaroon 1y ago
  Not if they were getting that trim level anyway.
beAbU 1y ago
Does the extra 3-6 miles factor in the need to now run the AC much more aggressively because the car will be hot from sitting in the sun all day? If this quoted number comes from the manufacturer itself, then I think the answer is "no".
- kgermino 1y ago
  I don’t think you’d have to run the AC any more aggressively with the solar panels than with a traditional steel roof? If you’re suggesting it wouldn’t work in a garage, that’s obviously true (and another factor in whether car solar makes sense) but many (most?) people park their cars outside during the day anyway. I for one can’t remember the last time I parked under cover
- danans 1y ago
  > Does the extra 3-6 miles factor in the need to now run the AC much more aggressively because the car will be hot from sitting in the sun all day? Most cars are already sitting in the sun all day.
  - aziaziazi 1y ago
    Not here in European cities where they’re either within a multi story park or in the side of a half day shaded tiny street.
    - parsimo2010 1y ago
      You are not getting the 3-6 mile per day boost if your car is parked in the shade.
      - tstenner 1y ago
        That's his point. You won't get any reasonable charge because you (mostly avoid parking your car in direct sunlight
    - sdenton4 1y ago
singpolyma3 1y ago
That's still 3-6 fewer miles worth of charging to do from more expensive sources. Even if it can't come close to covering your full use it's still covering something
- IAmBroom 1y ago
  Not if it won't recover it's own costs.
  - cma 1y ago
    It may still lose on this, but you would also want to include the externality costs that the consumer doesn't themselves bear for whether it is worth it overall.
  - dzhiurgis 1y ago
    Cost is convenience. Manufacturing cost is like $40 cells, $20 electronics and $200 in glass fusion, mounting, etc. My car eats 200W just being online so it would be useless to charge from solar.
thegrim33 1y ago
13.6 kWh battery. 39mile EPA range. Equals 2.87 miles of range per kWh. Leaving it out for 8 hours straight, on a sunny day, in LA, netted 915 Wh. Or, 2.86 miles. [0] Not 3-6, 2.86. 2.86 miles of charge, but only if left outside, uncovered, in full sun, on a fully sunny day, for a full 8 hours, in a place that gets effectively the maximum amount of solar radiation per day out of anywhere in the entire country. Now, do the same experiment anywhere else in the country, that doesn't get max solar radiation, or that can't get full sunlight for full 8 hours, or where it's cloudy at all, or rainy at all. 2.86 miles per day is the practical MAXIMUM, given perfect conditions. For the average scenario it'd be some fraction of that. The 6 miles figure is what they said you'd get if, in addition to perfect conditions, "if the sun shifted its orbit" (?) and gave perfect sunlight for 12 hours straight. Which is a number which should obviously not be thrown around as if it's obtainable. The fact that they're quoting numbers about what range you'd get if the solar system was constructed differently also makes me doubt the impartiality of their experiment and the numbers they provided. [0] https://www.motortrend.com/features/the-2023-toyota-prius-primes-battery-could-take-three-weeks-to-recharge https://www.motortrend.com/features/the-2023-toyota-prius-pr...
- conjecTech 1y ago
  EPA range tends to be pessimistic for EVs as it assumes you are always traveling at highway speeds. Even small reductions in speeds can make EVs much more efficient since drag is quadratic. A quick google search shows Prius prime owners reporting 4-5.5 miles/kwh, so the 3-6 mile range is entirely plausible.
  - slaw 1y ago
    EPA's city cycle speed is an average 19.6 mph, highway speed is an average of 48.3 mph. City range weighted at 55% and the highway range at 45%.
    - bangaladore 1y ago
      I don't think it's that simple. IIRC you don't have to do the city testing. https://www.epa.gov/greenvehicles/fuel-economy-and-ev-range-testing https://www.epa.gov/greenvehicles/fuel-economy-and-ev-range-...
roamerz 1y ago
There is going to be a parasitic drag loss to figure into it as well. I think the only way to accurately calculate that would be in a wind tunnel or maybe an amp meter with a before and after installation under identical conditions.

AdamJacobMuller 1y ago

I just started doing this with my car, mostly to add a camera/temp monitoring for when I leave my dog in the kennel in the car (she's well watched over, please don't fret over it). I'm hooking it up via starlink specifically so it works in remote areas with no cell coverage too. Monitoring and proxying everything via an RPI as well. Victron DC-DC inverter to keep the bluetti battery pack charged with bluetooth relay boards so we can turn loads (camera/starlink/others) on/off programmatically (it only turns the starlink on when there's no good/known wifi for example). Fun project, combines software dev (which I'm fairly good at) with hardware work (which I'm less) and my dogs (which I'm a big fan of).

theoreticalmal 1y ago
It’s interesting to see how many people in this thread have the same idea. I’m doing something similar and learning that hardware is just plain hard

ben_w 1y ago

The maths says that the *mean* number of miles driven by a vehicle is surprisingly low, and that tiling the surface of a car can get to about 80% of that *mean* in places where the car is just left out on the street and not shaded parking. But! That's a practical consideration at the level of "should a government require EV makers to design the roof, bonnet, doors etc. to be tiled in PV in order to reduce, but not eliminate, the induced extra demand on the grid" and definitely not "should I personally bolt a small, fixed, PV panel and inverter into my EV as an aftermarket DIY job?" The former gets wind-tunnel tests for efficiency, QA, designed around all the other safety concerns cars have e.g. crash safety. The latter, doesn't.

andoando 1y ago

If only we didnt start off with having 3000+ lbs of metal to move a 100-200lb person as a design limitation