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Possibly stupid question

  • 13-09-2017 10:04pm
    #1
    Registered Users Posts: 3,288 ✭✭✭ dresden8


    New to this electric vehicle lark.

    But why don't electric cars have solar panels in the roof?


Comments

  • Registered Users Posts: 8,287 ✭✭✭ n97 mini


    Because solar panels generare very little electricity in comparison to what's required to power the car. You're probably looking at 2% of total power required and quite often the cost of the solar panels would have a huge payback time.


  • Moderators, Society & Culture Moderators Posts: 31,961 Mod ✭✭✭✭ Gumbo


    dresden8 wrote: »
    New to this electric vehicle lark.

    But why don't electric cars have solar panels in the roof?

    I have a 3kw solar PV array on my house roof. It generates 3,432kw at its peak.
    If it maintained this for an hour, it would provide 12.5% charge to my Leaf. That equates to about 15-20km travel distance.

    Ohh yeah, did I mention that the array takes up 17 Sq. M!

    So not really viable currently.
    Although, my Leaf does have the optional solar panel on the rear spoiler that trickle charges the 12v battery.


  • Registered Users Posts: 4,197 ✭✭✭ -=al=-


    kceire wrote: »
    I have a 3kw solar PV array on my house roof. It generates 3,432kw at its peak.
    If it maintained this for an hour, it would provide 12.5% charge to my Leaf. That equates to about 15-20km travel distance.

    Ohh yeah, did I mention that the array takes up 17 Sq. M!

    So not really viable currently.
    Although, my Leaf does have the optional solar panel on the rear spoiler that trickle charges the 12v battery.

    That is actually pretty cool! :pac:


  • Closed Accounts Posts: 1,480 ✭✭✭ thierry14


    A mini wind mill on the roof might be better lol


  • Registered Users Posts: 3,270 ✭✭✭ cros13


    -=al=- wrote: »
    That is actually pretty cool! :pac:

    Unfortunately it generates so little power it doesn't even compensate for it's own weight. It does have one advantage and that's preventing the 12V battery from running down if the car is left parked for months.

    There are exercises in extreme energy efficiency like Delft's Stella (~2.2kWh/100km) but that's not a practical model for a vehicle people would actually want to buy (made of ludicrously expensive materials, no creature comforts, little suspension, bicycle tires, can't carry cargo, no performance to speak of, not possible to manufacture at scale).

    In all honesty the best place to put solar panels is on your roof where 4kW of solar (a typical install size in the UK) pointed south in Dublin will produce 3462kWh per annum. That equals average household electricity consumption or is enough to drive a 15kWh/100km EV for 23,080km (the average annual mileage in Ireland is 17,000km).

    For the latest generation of panels a 4kW install is only 12 panels. The average panel is ~€200 ex. VAT.
    A car roof is about the worst possible place conceivable to put a solar panel.
    1. Surface area is limited. The Leaf's roof is ~1.5 sq m. With premium 19% efficient solar cells you'd get 300W peak in the most ideal conditions (read: near impossible) from 1.5sq m (for ref. the Leaf's motor draws ~13,000W maintaining 100km/h on a flat road with no wind)
    2. A cars roof is not angled correctly toward the sun, is often dirty, is usually shaded when parked (and even the slightest shading..say of a small corner of the panel could drastically impact power generation (up to 100% loss for shading of less than 5% of the area in some cases))
    3. Solar cells weigh a non-zero amount. When they are not generating power you still need to carry them around... and the result will likely be a net-loss
    4. Automotive specced panels would resist standardisation and cost way more. The solar roof Toyota sells in Japan on it's Prius Prime is 180W peak and costs over €2000. A 180W panel for your roof at home can cost as little as €100, and pointed in the right direction generate as much as 3-4 times the power of the car roof panel per day (assuming the car is left in the sun all day). For €2k you could buy more than 2000W peak of solar for your roof.

    Land is cheap and commercial/residential roof space is basically free. Solar panels on cars make no sense.
    And there is no technological path toward it making sense. If a hypothetical solar cell was 100% efficient (and currently silicon cells are limited even in theory by the shockley–queisser limit of 32%) it still wouldn't generate enough power to be worth the tradeoffs.


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  • Registered Users Posts: 1,270 ✭✭✭ reboot


    The economy 7 overnight is a good way forward I pay around 8p/ unit, about half the daytime rate.
    AFAIK, the leaf solar panel is 5 watts, at 12 volts that's less than half an amp, an EV draws about 100 amps, just to start moving.


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 59,697 CMod ✭✭✭✭ unkel


    cros13 wrote: »
    (a typical install size in the UK) pointed south in Dublin will produce 3462kWh per annum. That equals average household electricity consumption

    I am in Dublin. My roof is 100% south facing. My annual consumption is 3,500kWh per annum. If there was any chance at all that a typical 4kW install would provide all my consumption, the panels would be on my roof already.

    Problem is production <> consumption

    In fact, most of your production is just lost to the grid and most of your consumption is when you don't have production. The only solution here is battery storage. Which is either eye wateringly expensive (Powerwall and the like) or technologically not yet feasible for reasonable money (EV storage)

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 6,634 ✭✭✭ zilog_jones


    cros13 wrote: »
    Automotive specced panels would resist standardisation and cost way more. The solar roof Toyota sells in Japan on it's Prius Prime is 180W peak and costs over €2000.

    It's an optional extra at over €2,400 here. Toyota UK claim you'll get about 600 km EV range per year from it in this part of the world. Compared to the cost of charging off the mains it's pure madness. (note: "Prime" is US only, it's the Prius PHV here and in Japan)

    I've also heard of problems of the solar roof in the first gen Prius Plug-in delaminating and corroding - out of warranty, of course :) And that one couldn't even charge the traction battery (12V system only, and optional extra at similar cost).


  • Registered Users Posts: 2,797 samih


    People spend 10k to a kitchen without blinking an eye and there is absolutely no payback from that.

    I could see myself investing in a battery backed solar array in the future, especially after expected further price reductions in the hardware.


  • Registered Users Posts: 1,270 ✭✭✭ reboot


    cros13 wrote: »
    Automotive specced panels would resist standardisation and cost way more. The solar roof Toyota sells in Japan on it's Prius Prime is 180W peak and costs over €2000.

    It's an optional extra at over €2,400 here. Toyota UK claim you'll get about 600 km EV range per year from it in this part of the world. Compared to the cost of charging off the mains it's pure madness. (note: "Prime" is US only, it's the Prius PHV here and in Japan)

    I've also heard of problems of the solar roof in the first gen Prius Plug-in delaminating and corroding - out of warranty, of course :) And that one couldn't even charge the traction battery (12V system only, and optional extra at similar cost).
    Agreed, over many short years I've had panel failures, always at the aluminum weld under the glass, almost impossible to fix. Am wrestling at present with " flexible" panel, it was the worst, in that it flexed the connections until three went open circuit.


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  • Registered Users Posts: 6,634 ✭✭✭ zilog_jones


    Were they covered by warranty, or was there significant cost in repairing/replacing them? Do you get much from FIT? (you're in NI, right?)


  • Registered Users Posts: 1,270 ✭✭✭ reboot


    Small sale setup, maybe a few hundred watts at 12 v DC, for workshop projects, down to 5v USB etc.
    Never had help from anyone here in NI, in fact oil and coal have vat at 5%, PV panel, 20%.
    If a glass cutter eventually gets me to a voltage it will be coming from an aluminum strip, impossible to solder, and conducting adhesives, not waterproof, so another panel in the skip today, mind you I got a decade out of it.It was possibly my favourite, as it was amorphous, good in low light, plenty of that ahead, thanks.


  • Registered Users Posts: 1,270 ✭✭✭ reboot


    Sorry about multiple, incontinent posting, tried to edit typo, big finger wee tab.


  • Registered Users Posts: 1,270 ✭✭✭ reboot


    As posted elsewhere, the new series of Fifth Gear Recharged,which only deal with EVs, test the new IO, which is covered in flexible pv cells.They claim it will charge,just sitting outside, and deliver 15 miles .



  • Registered Users Posts: 3,028 ✭✭✭ Lantus


    one car that does use it is the aptera. This is an ultra lightweight aerodynamic ev based more on plane tech and it's pv panels do offer a small but meaningful charge of up to 40 miles albeit at our latitude and weather not very useful.


    It's drag coefficient of 0.13 is the key to it's long range. Leaf is .28 and even a Tesla is .23.



  • Registered Users Posts: 1,270 ✭✭✭ reboot


    Most interesting , hopefully as PV become more efficient and flexible, it's worth considering incorporating cells into the ,car esthetics allowing. Also weight of the vehicle is a consideration,some of the early Teslas said to weigh 2 and a half ton. I assume the drag coefficients precludes my EV having a roof rack,that's why I can't have one? Thanks.



  • Registered Users Posts: 2,706 ✭✭✭ Type 17


    For the record, the "too much trouble for too small a payback" issue is also why E-bikes don't have regeneration for slowing down (which many people ask, knowing that BEVs have it).



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