Author Topic: Solar cell roofs for EV cars.  (Read 4461 times)

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Offline BrianHG

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Solar cell roofs for EV cars.
« on: February 14, 2018, 07:26:35 am »
Seriously, will this even make a realistic dent in drive distance of a full size EV?

Maybe an extra few Km a day if you park outside in an unshaded area (ie away from buildings which create a moving shadow during the day.) on a 0 cloud day in the summer.
 

Offline station240

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Re: Solar cell roofs for EV cars.
« Reply #1 on: February 14, 2018, 10:04:42 am »
Really only of use for keeping the 12V battery charged. Vampire Drain is a big issue with EVs, as there is no way to switch everything off, electronics to maintain the battery and other systems does add up.
The usual setup is to have the HV battery supply power and charge via a DC-DC converter, which then slowly drains the big battery.

1-2kW of solar cells won't do anything useful to charge the main battery, especially in hot climates where parking in the sun means wasting power to cool the now hot car/battery. 
 
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Offline rrinker

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Re: Solar cell roofs for EV cars.
« Reply #2 on: February 15, 2018, 02:55:20 pm »
 But then, where is the best place to park an EV? In the shade created by the roof over the whole parking area to hold the solar panels that run the chargers.....
 

Online sokoloff

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Re: Solar cell roofs for EV cars.
« Reply #3 on: February 15, 2018, 03:01:18 pm »
Being generous, let's assume that the solar panels could be about 1 square meter which could generously generate 250W for 8 hours. That's 2 kWh per day or about a 1/2 mile / 1 kilometer of driving, assuming no further losses in the charging circuits.

It's much more gimmick, "statement", or decoration than practical improvement to the car. You would still be better off economically parking your car in the garage for the day.
 
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Offline tszaboo

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Re: Solar cell roofs for EV cars.
« Reply #4 on: February 15, 2018, 03:34:30 pm »
Really only of use for keeping the 12V battery charged. Vampire Drain is a big issue with EVs, as there is no way to switch everything off, electronics to maintain the battery and other systems does add up.
The usual setup is to have the HV battery supply power and charge via a DC-DC converter, which then slowly drains the big battery.

1-2kW of solar cells won't do anything useful to charge the main battery, especially in hot climates where parking in the sun means wasting power to cool the now hot car/battery.
In my 3rd gen Prius, the DC-DC only works when the car is running. If you leave the light on, the 12V might discharge completely, while the traction battery is still fully charged. That is personal experience  :-[.

It also has a solar panel (sol premium package). I wouldnt have payed more for this, but I bought used, and it comes with the sunroof, which is nice.
So the solar panel in that one does not charge the battery, because they had EMI problems with the radio.  It runs the AC unit's fan, and that is very very useful. On a hot, very sunny Belgian day (haha, good joke) it just lowers the temperature inside the car.
I guess people dont realize, that plug-in and electric cars could have their AC or heater operational, when the battery is charged, so even in a cold winter, you can sit into a warm car in the morning.
 

Offline Red Squirrel

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Re: Solar cell roofs for EV cars.
« Reply #5 on: February 15, 2018, 06:59:46 pm »
This could be useful as you drive to work then car is parked all day it could help add a bit of charge to the battery.  But in winter it will just get full of snow/ice anyway.  The extra cost is probably not worth it for the small amount it will add to the battery, whether it's an option or simply built into cost of car.
 
 

Offline Someone

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Re: Solar cell roofs for EV cars.
« Reply #6 on: February 15, 2018, 09:48:27 pm »
Being generous, let's assume that the solar panels could be about 1 square meter which could generously generate 250W for 8 hours. That's 2 kWh per day or about a 1/2 mile / 1 kilometer of driving, assuming no further losses in the charging circuits.

It's much more gimmick, "statement", or decoration than practical improvement to the car. You would still be better off economically parking your car in the garage for the day.
Rather than being generous you've fallen off into completely unbelievable. The PHEV Prius claims more than an order of magnitude better economy with 12.5kwh/100km, or realistic examples around 20kwh/100km. Take a feasibly poor capacity factor of 5% and you could see 80kWh a year for roughly 400km of extra travel.

Figures online suggest the option is priced under $2000, so for an everyday user of the car thats no going to pay off if you could charge from the power grid or buy more fuel.
 
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Offline tszaboo

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Re: Solar cell roofs for EV cars.
« Reply #7 on: February 15, 2018, 11:02:32 pm »
Being generous, let's assume that the solar panels could be about 1 square meter which could generously generate 250W for 8 hours. That's 2 kWh per day or about a 1/2 mile / 1 kilometer of driving, assuming no further losses in the charging circuits.

It's much more gimmick, "statement", or decoration than practical improvement to the car. You would still be better off economically parking your car in the garage for the day.
Rather than being generous you've fallen off into completely unbelievable. The PHEV Prius claims more than an order of magnitude better economy with 12.5kwh/100km, or realistic examples around 20kwh/100km. Take a feasibly poor capacity factor of 5% and you could see 80kWh a year for roughly 400km of extra travel.

Figures online suggest the option is priced under $2000, so for an everyday user of the car thats no going to pay off if you could charge from the power grid or buy more fuel.
Wow, they charge that much for the solar roof (no sunroof this time)? You need to be soft in the head to buy that.
Although, buying the Prius Prime alone is ridiculous. It is 27KUSD in the USA, and 42KEUR here (52KUSD). I mean, seriously? I dont think they sold a single one here.
Which is a bit of a shame, because it is the better looking Prius. I wonder if the next prius will be designed by space ninjas, and it will be priced against a small house.
 

Online sokoloff

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Re: Solar cell roofs for EV cars.
« Reply #8 on: February 16, 2018, 12:13:09 am »
Being generous, let's assume that the solar panels could be about 1 square meter which could generously generate 250W for 8 hours. That's 2 kWh per day or about a 1/2 mile / 1 kilometer of driving, assuming no further losses in the charging circuits.

It's much more gimmick, "statement", or decoration than practical improvement to the car. You would still be better off economically parking your car in the garage for the day.
Rather than being generous you've fallen off into completely unbelievable. The PHEV Prius claims more than an order of magnitude better economy with 12.5kwh/100km, or realistic examples around 20kwh/100km. Take a feasibly poor capacity factor of 5% and you could see 80kWh a year for roughly 400km of extra travel.

Figures online suggest the option is priced under $2000, so for an everyday user of the car thats no going to pay off if you could charge from the power grid or buy more fuel.
Yup. I got my math backwards on the last step (applying the miles/kWh). Under those (amazingly generous) assumptions for power created, it would be ~7-8 miles of range added.

Still, at $0.40/day of power generation (assuming as above) and assuming 365 days of such sunshine per year, you'd generate at most $146 of power per year, under the best of circumstances.
« Last Edit: February 16, 2018, 12:14:59 am by sokoloff »
 

Offline Someone

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Re: Solar cell roofs for EV cars.
« Reply #9 on: February 16, 2018, 01:23:42 am »
Being generous, let's assume that the solar panels could be about 1 square meter which could generously generate 250W for 8 hours. That's 2 kWh per day or about a 1/2 mile / 1 kilometer of driving, assuming no further losses in the charging circuits.

It's much more gimmick, "statement", or decoration than practical improvement to the car. You would still be better off economically parking your car in the garage for the day.
Rather than being generous you've fallen off into completely unbelievable. The PHEV Prius claims more than an order of magnitude better economy with 12.5kwh/100km, or realistic examples around 20kwh/100km. Take a feasibly poor capacity factor of 5% and you could see 80kWh a year for roughly 400km of extra travel.

Figures online suggest the option is priced under $2000, so for an everyday user of the car thats no going to pay off if you could charge from the power grid or buy more fuel.
Wow, they charge that much for the solar roof (no sunroof this time)? You need to be soft in the head to buy that.
Although, buying the Prius Prime alone is ridiculous. It is 27KUSD in the USA, and 42KEUR here (52KUSD). I mean, seriously? I dont think they sold a single one here.
Which is a bit of a shame, because it is the better looking Prius. I wonder if the next prius will be designed by space ninjas, and it will be priced against a small house.
Pricing and availability vary wildly, the option is not even available in Australia (nor is plug in)...

But the incremental option for the hybrid drive over the conventional engine is more compelling, again due to limitations in range and options we can compare a limited set of versions in Australia.
Basic Corolla 24,000 AUD
Mid Corolla 30,000 AUD
Hybrid Corolla 31,500 AUD (same fitment as Mid)
Prius 41,000 AUD

Given the relative fuel savings promised from the hybrid drive, it would be a good investment if you were otherwise going to pay for the mid range fitment. While the differential from the base model to the hybrid requires 300,000 km life to pay off (feasible but beyond most peoples use of a vehicle).

Yup. I got my math backwards on the last step (applying the miles/kWh). Under those (amazingly generous) assumptions for power created, it would be ~7-8 miles of range added.

Still, at $0.40/day of power generation (assuming as above) and assuming 365 days of such sunshine per year, you'd generate at most $146 of power per year, under the best of circumstances.
Thats it, simply not competitive with the other energy sources available. There are some neat ideas which work better when the energy generation/consumption ratio of a vehicle change drastically so that you can drive around town 30-40km/day without external energy sources but for the Prius its just marketing.
 

Offline John Heath

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Re: Solar cell roofs for EV cars.
« Reply #10 on: February 16, 2018, 04:39:32 am »
A solar powered car no but a solar powered car pulling a trailer is a different story.
 
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Online radar_macgyver

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Re: Solar cell roofs for EV cars.
« Reply #11 on: February 16, 2018, 04:55:31 am »
That's 2 kWh per day or about a 1/2 mile / 1 kilometer of driving, assuming no further losses in the charging circuits.

Not sure where you got those numbers, my Bolt EV gives me ~2.5 miles (~4 km) when I'm flogging it. When I drive carefully, I get about 5.5-6 mi/kWh. But yes, 2 kWh doesn't do much for range. Could keep the battery conditioning happy though.
 

Offline raptor1956

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Re: Solar cell roofs for EV cars.
« Reply #12 on: February 22, 2018, 09:10:55 pm »
I don't think the particular application is all that effective but solar cells could provide upwards of half a daily commute for a passenger car.  Extend that to an RV with trailer where you might have the roof and both sides covered with solar cells and be able to produce 10kw or more and over a day produce 50kwhr or more.  That much could provide 30-50 miles of added range and perhaps more importantly permit you to dry camp without using a generator for many days.

There are clearly con artists looking to take advantage and new tech is rife with such opportunities.  But to suggest solar is some kind of quack tech is foolish -- other than nuclear power ALL energy comes from the Sun and solar is far more efficient at converting solar energy into useful energy that anything out there and by orders of magnitude.    Of course, even nuclear power is the result of stellar processes so its fair to say 100% of energy comes from stars.

If all the buildings and homes had solar panels on the roof that alone would provide about 50% of all the energy needs we have and doing so with current efficiencies and without requiring ANY additional land beyond that which is needed for the FAB's that produce them.  No matter how you slice it solar is the way to go -- sooner or later.


Brian
 

Offline IanMacdonald

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Re: Solar cell roofs for EV cars.
« Reply #13 on: March 21, 2018, 01:11:06 pm »
"No matter how you slice it solar is the way to go -- sooner or later."

Maybe in Oz, but here, solar PV is only a tenth of summer output in winter.
 

Offline raptor1956

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Re: Solar cell roofs for EV cars.
« Reply #14 on: April 01, 2018, 04:43:06 am »
"No matter how you slice it solar is the way to go -- sooner or later."

Maybe in Oz, but here, solar PV is only a tenth of summer output in winter.


Excuse me?  Australia has some of the highest solar irradiance on the planet.  Your winter will have fewer hours of sunlight just as happen EVERYWHERE on the planet.  Are you saying you have non-stop rain in the winter.  Please point me to the data you base your 10% statement on.

Take a look at this -- took 10 seconds on Google to find.

https://www.altestore.com/howto/solar-insolation-map-world-a43/


Brian
 

Offline BrianHG

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Re: Solar cell roofs for EV cars.
« Reply #15 on: April 01, 2018, 01:12:39 pm »
Excuse me?  Australia has some of the highest solar irradiance on the planet.  Your winter will have fewer hours of sunlight just as happen EVERYWHERE on the planet.  Are you saying you have non-stop rain in the winter.  Please point me to the data you base your 10% statement on.

Take a look at this -- took 10 seconds on Google to find.

https://www.altestore.com/howto/solar-insolation-map-world-a43/


Brian
You can't optimally tilt a solar panel on a car.  It wont be aerodynamic & what happens when you drive in another direction?  Or if there are trucks to the left or right of you, or you are driving in the city where there building lining the streets?  That map is for optimally tilted solar panels without obstructions as it says just below it.
 

Offline raptor1956

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Re: Solar cell roofs for EV cars.
« Reply #16 on: April 01, 2018, 05:52:15 pm »
Excuse me?  Australia has some of the highest solar irradiance on the planet.  Your winter will have fewer hours of sunlight just as happen EVERYWHERE on the planet.  Are you saying you have non-stop rain in the winter.  Please point me to the data you base your 10% statement on.

Take a look at this -- took 10 seconds on Google to find.

https://www.altestore.com/howto/solar-insolation-map-world-a43/


Brian
You can't optimally tilt a solar panel on a car.  It wont be aerodynamic & what happens when you drive in another direction?  Or if there are trucks to the left or right of you, or you are driving in the city where there building lining the streets?  That map is for optimally tilted solar panels without obstructions as it says just below it.


No, you can't optimally tilt the solar cells on a car -- that's why you'd cover the whole thing not counting the glass.  So, if the Sun is hitting the drivers side that side produces max power and the passengers side produces almost nothing.  Also, given the option you'd want to use the most efficient cells you can.  A small car won't provide very much surface area for solar cells so it's at the least practical end whereas larger vehicles tend to have much more surface area to work with.

If you imagine a small car with 4m^2 on the top with 3m^2 on each side or a total area of 10m^2 and 20% cells you could if all sides were fully illuminated produce 2KW.  In practice the top and one side will be illuminated and neither at a normal angle so figure 70% for both top and one side -- about 1.4KW x .7 or about 1KW.  Over a day in the parking lot at work the car might receive 6KWHr or more and for many folks that could equal half or all the energy needed for the commute home.  Also, with some additional smarts the car could be programmed to run a fan to keep the interior cooler and then fire up the AC a couple minutes before you get in for the drive home.

One area that needs work is making solar cells less obvious so that they are not noticed.  One of Musks businesses is solar roof tiles for your home that do not look like solar panels at all -- you would not know by looking at them.  They are not terrible efficient, however.


Brian
 

Offline raptor1956

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Re: Solar cell roofs for EV cars.
« Reply #17 on: April 05, 2018, 09:15:17 pm »
I should add that there has been some work into making glass that produces some amount to solar electric output primarily for use on large office buildings.  I can imagine the efficiency of such glass would be much less than 5% but anything gained would be a plus.  There is a fair amount of glass on cars and SUV's so even the relatively small output would be in addition to the main cells over the rest of the car.  This could increase the total energy produced by 20% or maybe more.  So, in combination with the main cells the total daily output could exceed 7KWHrs.  The Telsa cars seem to average about 360WHrs/mile so 7KWHr could power the car for over 19 miles (31km) -- I'd wager that the majority of people live closer to work than that.


Brian
 

Offline BrianHG

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Re: Solar cell roofs for EV cars.
« Reply #18 on: April 05, 2018, 10:41:53 pm »
What if my employer has given me a dedicated parking space indoors?
Parking outdoors in winter means snow and cold, where as snow also will cover the solar cells...
What if my given parking spot is in the shadow of the building, or under a shadow cover to keep the car from getting too hot in the sun?
What equates to less power being lost, being in the sun and using more electricity than the solar cells produce to keep the interior from burning up, or, parking in the shade and forgetting about running the AC while parked?

 

Offline raptor1956

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Re: Solar cell roofs for EV cars.
« Reply #19 on: April 06, 2018, 08:47:40 pm »
What if my employer has given me a dedicated parking space indoors?
Parking outdoors in winter means snow and cold, where as snow also will cover the solar cells...
What if my given parking spot is in the shadow of the building, or under a shadow cover to keep the car from getting too hot in the sun?
What equates to less power being lost, being in the sun and using more electricity than the solar cells produce to keep the interior from burning up, or, parking in the shade and forgetting about running the AC while parked?

If you park indoors you won't get any energy from the Sun -- this isn't rocket science! 

In a prior I mentioned you could run a fan to reduce heat build-up and then perhaps, a minute or two before the owner arrives to drive home power up the AC to cool things down -- I did not say to run the AC ALL FRICKIN DAY!.  In places where heating would be an issue, like Phoenix in the summer, you also have a very high solar flux meaning you're generating a lot of power/energy.  In places where heating is less of an issue you generate less power/energy but also need less.  And yes, when the car is covered with snow you will generate less power/energy -- again, this isn't rocket science.

But, being able to generate enough energy to drive home all on the Sun's dime is not a bad deal now is it.

In one of my last posts I mentioned solar glass and while that's still a bit off and not likely to be as efficient as regular cells the calculations made by the developers are higher than I would have imagined.  They indicated that if all the glass in office building etc were of the solar glass type that could generate over 40% of our entire energy needs -- that's higher than I would have imagined and would suggest my calculation of an additional 20% for a car may be an underestimate by a factor of 2.  If so then a typical small car might receive 8-9KWHrs over the day and as the efficiency of solar cells increase that number would also increase.

The very northern climes are not the ideal location of solar but even in Canada it will, in time, produce a substantial fraction of all the energy needs.  Given enough time it will generate just about all of it.


Brian
 

Offline james_s

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Re: Solar cell roofs for EV cars.
« Reply #20 on: April 06, 2018, 09:40:41 pm »
I suppose it could be useful for running the AC throughout the day so the car isn't 5,000 degrees inside when you leave work. That's something I dislike about parking outside in the summer, not only is it hard on the interior of the car but it's extremely unpleasant to climb into a hot sauna.
 

Offline raptor1956

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Re: Solar cell roofs for EV cars.
« Reply #21 on: April 06, 2018, 10:17:34 pm »
I suppose it could be useful for running the AC throughout the day so the car isn't 5,000 degrees inside when you leave work. That's something I dislike about parking outside in the summer, not only is it hard on the interior of the car but it's extremely unpleasant to climb into a hot sauna.


People from other parts of the world, particularly Europe, have no idea what a summer in Phoenix is like where the average daytime highs can be over 45C for weeks at a time and reach over 50C on occasion.  With a solar powered car you might have the fan on low most of the day, then put the fan on high for 10 minutes, then kick the AC on for a few minutes before the owner arrives to drive home.  A similar or different scheduling could be done elsewhere where it's not so hot.  Doing this need not consume a great amount of energy but it won't be without some cost in energy.

The southern half of the USA and particularly the southwest can be murderously hot in the summer and summer can be half the year.  In the southeast the temps are not so high but the humidity can be brutal.  The heat in Phoenix is dry and it might be assumed that a dry heat is tolerable -- tell me that after you've spent a few days in August.

The upside to Phoenix is the solar flux is real high making for great solar energy production.  The winters are wonderful and Flagstafs is only about 145 miles north and at about 6900 feet (>2100m) elevation the temps in Flagstaff can be 30C cooler.


Brian
 


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