5 ms·

Wouldn't that affect the aerodynamic drag of the car negatively?

Ekaros 3y ago
Yes, even designed skiboxes or rails add drag. This doesn't seem even well designed. And I wonder about long term safety too. Is it sturdy enough over time so at some point someone driving behind does not get hit by a panel flying off...
Retric 3y ago
They fold up in use, so the drag hit probably isn’t that much. If he’s getting 5-20kWh per day and the use case is a parking lot at work without EV chargers, it could easily pay for itself both in terms of energy and cost. Probably worth removing on a road trip.
- kevin_thibedeau 3y ago
  Without a cowl, the drag is still significant when folded up.
  - Retric 3y ago
    He’s getting “20 to 75 miles of extra range” midpoint is ~45 miles per day * 365 days = 16,000 miles per year. If he’s seeing 25% extra drag at highway speeds he would need to drive over 60,000 miles per year of highway driving to be in the negative.
    - masklinn 3y ago
      > He’s getting “20 to 75 miles of extra range” He's not "getting" that, he's estimating that he might possibly get that. > midpoint is ~45 miles per day The estimate above, which is already not fact, is "for sunny days". Taking the midpoint of a ridiculously imprecise number pulled out of one ass as an average makes no sense whatsoever. And the car can't be driven with the panels out, so any actual use of the car has to be discounted. Not to mention the pictures are for a 2000W (9*175, per the official website: https://www.dartsolar.com https://www.dartsolar.com) array, the 4kW array would need double the space, double the volume, and double the weight, and the footprint might be so large it would not be deployable in public spaces.
      - Retric 3y ago
        There were actual experiments not just wild ass guess for those numbers. I took the midpoint in reference to the conditions being neither the absolute best or worst. > so any actual use of the car has to be discounted. Use of the car during the day needs to be discounted. This is an impractical art project so driving a solar car at night is perfectly on theme.
- masklinn 3y ago
  > They fold up in use, so the drag hit probably isn’t that much. The folding is a huge square box on top of the car, so the drag definitely increases a lot. Just a roof rack will have a minor but noticeable impact on drag, a ski box is 10~15% efficiency loss (http://kootenayevfamily.ca/model-3-roof-rack-consumption-test/ http://kootenayevfamily.ca/model-3-roof-rack-consumption-tes...). This is the worst designed roof box in history, I'd say 20~25% efficiency loss is lowballing it, unless it's only ever crawled at urban speeds, slow enough that drag is not relevant. > If he’s getting 5-20kWh per day AFAIK the best panels are circa 25% efficient, so 20kWh/day is not even within physical plausibility, let alone actual. I don't know if they were ever tested by independent third party, but FWIW Lightyear's estimates for their 5sqm curved solar panels (so no loss of efficiency) was 70km/day best-case (at the height of summer, with the car in full illumination at all time), at 96Wh/km (advertised WLTP) that comes out to 6.7kWh. Again, best-case, and without a Cd hit.
  - Retric 3y ago
    Panel efficiency is calculated before rated power. 4kW * 5 hours that’s 20kWh. At ideal tilt with solar tracking you can get close to 30 kWh/day from a 4kW worth of panels in ideal conditions, but flat panels are significantly worse. The quote was 20-75 miles per day of range. Let’s assume 25% extra drag at highway speeds. That puts breakeven at 80-300 miles of highway driving per day which most people don’t do.
    - masklinn 3y ago
      > The quote was 20-75 miles per day of range. The quote is specifically > calculations and experiments suggest that, on a sunny day, he could gain anywhere from 20 to 75 miles And according to the official site (https://www.dartsolar.com https://www.dartsolar.com) it's 9x175W.
      - Retric 3y ago
        Interesting, I just assumed 9*220W panels but I can see why went cheaper.
masklinn 3y ago
Very much so, it also increases the weight, and given what solar panels produce, you're probably not making out the difference. Lightyear advertised a best case of 70km (44 miles) per day from panels, best case, out of 5sqm of fully integrated curved solar panels and a Cd of 0.175. And then it was cancelled (and back-named a proof of concept, I'm sure the 2 years delay and unit price going from an original 175k estimate to 250k didn't help). Supposedly they've started work on a more reasonably priced model, ETA 2025.

Yes, even designed skiboxes or rails add drag. This doesn't seem even well designed. And I wonder about long term safety too. Is it sturdy enough over time so at some point someone driving behind does not get hit by a panel flying off...

Retric 3y ago

They fold up in use, so the drag hit probably isn’t that much. If he’s getting 5-20kWh per day and the use case is a parking lot at work without EV chargers, it could easily pay for itself both in terms of energy and cost. Probably worth removing on a road trip.

kevin_thibedeau 3y ago
Without a cowl, the drag is still significant when folded up.
- Retric 3y ago
  He’s getting “20 to 75 miles of extra range” midpoint is ~45 miles per day * 365 days = 16,000 miles per year. If he’s seeing 25% extra drag at highway speeds he would need to drive over 60,000 miles per year of highway driving to be in the negative.
  - masklinn 3y ago
    > He’s getting “20 to 75 miles of extra range” He's not "getting" that, he's estimating that he might possibly get that. > midpoint is ~45 miles per day The estimate above, which is already not fact, is "for sunny days". Taking the midpoint of a ridiculously imprecise number pulled out of one ass as an average makes no sense whatsoever. And the car can't be driven with the panels out, so any actual use of the car has to be discounted. Not to mention the pictures are for a 2000W (9*175, per the official website: https://www.dartsolar.com https://www.dartsolar.com) array, the 4kW array would need double the space, double the volume, and double the weight, and the footprint might be so large it would not be deployable in public spaces.
    - Retric 3y ago
      There were actual experiments not just wild ass guess for those numbers. I took the midpoint in reference to the conditions being neither the absolute best or worst. > so any actual use of the car has to be discounted. Use of the car during the day needs to be discounted. This is an impractical art project so driving a solar car at night is perfectly on theme.
masklinn 3y ago
> They fold up in use, so the drag hit probably isn’t that much. The folding is a huge square box on top of the car, so the drag definitely increases a lot. Just a roof rack will have a minor but noticeable impact on drag, a ski box is 10~15% efficiency loss (http://kootenayevfamily.ca/model-3-roof-rack-consumption-test/ http://kootenayevfamily.ca/model-3-roof-rack-consumption-tes...). This is the worst designed roof box in history, I'd say 20~25% efficiency loss is lowballing it, unless it's only ever crawled at urban speeds, slow enough that drag is not relevant. > If he’s getting 5-20kWh per day AFAIK the best panels are circa 25% efficient, so 20kWh/day is not even within physical plausibility, let alone actual. I don't know if they were ever tested by independent third party, but FWIW Lightyear's estimates for their 5sqm curved solar panels (so no loss of efficiency) was 70km/day best-case (at the height of summer, with the car in full illumination at all time), at 96Wh/km (advertised WLTP) that comes out to 6.7kWh. Again, best-case, and without a Cd hit.
- Retric 3y ago
  Panel efficiency is calculated before rated power. 4kW * 5 hours that’s 20kWh. At ideal tilt with solar tracking you can get close to 30 kWh/day from a 4kW worth of panels in ideal conditions, but flat panels are significantly worse. The quote was 20-75 miles per day of range. Let’s assume 25% extra drag at highway speeds. That puts breakeven at 80-300 miles of highway driving per day which most people don’t do.
  - masklinn 3y ago
    > The quote was 20-75 miles per day of range. The quote is specifically > calculations and experiments suggest that, on a sunny day, he could gain anywhere from 20 to 75 miles And according to the official site (https://www.dartsolar.com https://www.dartsolar.com) it's 9x175W.
    - Retric 3y ago
      Interesting, I just assumed 9*220W panels but I can see why went cheaper.

masklinn 3y ago

Very much so, it also increases the weight, and given what solar panels produce, you're probably not making out the difference. Lightyear advertised a best case of 70km (44 miles) per day from panels, best case, out of 5sqm of fully integrated curved solar panels and a Cd of 0.175. And then it was cancelled (and back-named a proof of concept, I'm sure the 2 years delay and unit price going from an original 175k estimate to 250k didn't help). Supposedly they've started work on a more reasonably priced model, ETA 2025.