1688 Views 25 Replies 7 Participants Last post by  mike kirschbaum
Yes, that's right, I am a radical new member, out to do really radical things. But I need to know something, so please humor me on this: how many photovoltaic cells do I need to propel a 1500 pound electric car down the freeway at 60 mph all day long without plugging in to charge up any batteries. I don't have enough sense to figure this out, but maybe some of you smarter chaps can figure this out for me. Thanks a mil.
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#### Duncan

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Yes, that's right, I am a radical new member, out to do really radical things. But I need to know something, so please humor me on this: how many photovoltaic cells do I need to propel a 1500 pound electric car down the freeway at 60 mph all day long without plugging in to charge up any batteries. I don't have enough sense to figure this out, but maybe some of you smarter chaps can figure this out for me. Thanks a mil.
OK lets look at this
It will take about 20 kw to drive at 60 mph in a 1500 lb car
So a standard solar panel is about 1.5 meters by 1 meter and is 250 watts in full square on to the panel sun

So to maintain that at high noon on a sunny day you will need 80 of those panels - they will not be square to the sun so you will need more of them
Call it 100 panels - 10 meters by 15 meters
at 20 kg per panel about 2 tons of panels
And that is for noon on a very sunny day - you will need more panels for morning and evening

Solar panels on a car are like filling a swimming pool with a teaspoon

Put the solar panels where they belong on your house or garage roof

#### john61ct

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gotta be trolling

#### brian_

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Too many to fit on the vehicle.

As far as I'm concerned, if you want help to understand why, you'll have to put in some effort to start and come up with some kind of guess and your reasoning for it, then get help filling in the holes and fixing the errors.

Edit: okay, I read the original post then watched a TV show before responding, and in the meantime Duncan did the work for you. And he's right, athough the 20 kW estimate is high for a very small car.

#### brian_

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gotta be trolling
Not necessarily. Many discussions of electric vehicles I see in Facebook include some clueless but presumably sincere person suggesting solar panels on the vehicle.

#### Duncan

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gotta be trolling
Run the numbers - the science/engineering is not "Trolling"

#### john61ct

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Run the numbers - the science/engineering is not "Trolling"
obviously I meant the OP

#### Duncan

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Too many to fit on the vehicle.

As far as I'm concerned, if you want help to understand why, you'll have to put in some effort to start and come up with some kind of guess and your reasoning for it, then get help filling in the holes and fixing the errors.

Edit: okay, I read the original post then watched a TV show before responding, and in the meantime Duncan did the work for you. And he's right, athough the 20 kW estimate is high for a very small car.
Mine takes 26 kw!! at 100 kph -
and its only a small amount heavier than 1500 lbs - 800 kg is 1760 lbs

#### brian_

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Mine takes 26 kw!! at 100 kph -
and its only a small amount heavier than 1500 lbs - 800 kg is 1760 lbs
That's horrible. Production EVs - even AWD 2000 kg luxury SUVs - don't use 26 kW at highway speeds. But the double or half the power requirement doesn't change the validity of the conclusion: you can't carry enough panel to drive a normal vehicle.

#### Duncan

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That's horrible. Production EVs - even AWD 2000 kg luxury SUVs - don't use 26 kW at highway speeds. But the double or half the power requirement doesn't change the validity of the conclusion: you can't carry enough panel to drive a normal vehicle.
Aerodynamics!! - my car is like a brick flying sideways

#### john61ct

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No DIYer can expect to get Tesla level results, think of the billions spent on talent, design, R&D evolution, tooling etc

#### MattsAwesomeStuff

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No DIYer can expect to get Tesla level results, think of the billions spent on talent, design, R&D evolution, tooling etc
Nonsense. There's little magic going on.

If it was your extreme goal, you could satisfy it. It's just a matter of the tradeoff.

Wind resistance being the major one, and, can you make a car that you like the look of, that also has a shape that will get you the aero you need? That's where the money in design goes. The less you care about the look, the easier it will be.

This guy is suggesting putting 20kw of panels on a car, I think it's fair to say he doesn't care much about appearance.

I saw a solar car a few years ago. Typical university project. Completely impractical but it held highway speeds using only the panels on the car. No way it would ever be road legal, or useful, but, it can be done on a DIY scale.

Of course no DIY project is going to compete in terms of getting a product to market against an auto company with billions, but, lots of that engineering can be copied and there's lots of constraints they have that a DIYer does not.

#### Duncan

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Nonsense. There's little magic going on.

If it was your extreme goal, you could satisfy it. It's just a matter of the tradeoff.

Wind resistance being the major one, and, can you make a car that you like the look of, that also has a shape that will get you the aero you need? That's where the money in design goes. The less you care about the look, the easier it will be.

This guy is suggesting putting 20kw of panels on a car, I think it's fair to say he doesn't care much about appearance.

I saw a solar car a few years ago. Typical university project. Completely impractical but it held highway speeds using only the panels on the car. No way it would ever be road legal, or useful, but, it can be done on a DIY scale.

Of course no DIY project is going to compete in terms of getting a product to market against an auto company with billions, but, lots of that engineering can be copied and there's lots of constraints they have that a DIYer does not.
Good points Matt
I helped the local High School win the "world championship" (of American high schools) with our Solar Stealth
It would almost meet the 60 mph in full sunlight

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#### brian_

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No DIYer can expect to get Tesla level results, think of the billions spent on talent, design, R&D evolution, tooling etc
I agree, but even a DIY project shouldn't be far off the energy consumption of a production car of twice the size (weight).

It really doesn't matter to the original question anyway, since the vehicle's power consumption at highway speed will be an order of magnitude too high to run directly on solar power.

#### brian_

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I helped the local High School win the "world championship" (of American high schools) with our Solar Stealth
It would almost meet the 60 mph in full sunlight
And it's not a usable car, and my guess is that it's not even close to 1500 pounds. But it does illustrate the impracticality of direct solar power for a car.

#### brian_

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This guy is suggesting putting 20kw of panels on a car, I think it's fair to say he doesn't care much about appearance.
I think he's suggesting gluing a few cells on a conventional small car, and has no idea how many kilowatts of output are needed.

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OK lets look at this
It will take about 20 kw to drive at 60 mph in a 1500 lb car
So a standard solar panel is about 1.5 meters by 1 meter and is 250 watts in full square on to the panel sun

So to maintain that at high noon on a sunny day you will need 80 of those panels - they will not be square to the sun so you will need more of them
Call it 100 panels - 10 meters by 15 meters
at 20 kg per panel about 2 tons of panels
And that is for noon on a very sunny day - you will need more panels for morning and evening

Solar panels on a car are like filling a swimming pool with a teaspoon

Put the solar panels where they belong on your house or garage roof
Gentlemen, thank you for your input, but I need to add to what I have said: about thirty years ago a Swiss school teacher passed by here driving a small three-wheel electric car, he was driving around the world in the car. The car would do sixty mph on the freeway all day long and never needed to be plugged in to charge up his three or four regular car batteries. The car had no photovoltaic cells on his car. So how did he do it? Here is how: the car was pulling a semi-flat bed trailer with the cells on the trailer! At night he could unhook the trailer and drive to a grocery or convenience store with the batteries he had on the car, and in the morning he would hook his trailer back up, and away he would go! This guy really had it figured out! This car had two disadvantages: you can't go long distances at night, and the car with the trailer is hard to park in congested areas. However, I visualize a fold-up flatbed trailer.

#### brian_

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Gentlemen, thank you for your input, but I need to add to what I have said: about thirty years ago a Swiss school teacher passed by here driving a small three-wheel electric car, he was driving around the world in the car. The car would do sixty mph on the freeway all day long and never needed to be plugged in to charge up his three or four regular car batteries. The car had no photovoltaic cells on his car. So how did he do it? Here is how: the car was pulling a semi-flat bed trailer with the cells on the trailer! At night he could unhook the trailer and drive to a grocery or convenience store with the batteries he had on the car...
So although you asked about driving "without plugging in to charge up any batteries" you really meant using a trailer-mounted array to charge a battery. And that guy didn't drive "all day long" with that car; I have no idea who you are talking about, but I'll bet you a million dollars that it couldn't do that.

You really should work out how much energy is needed to move the vehicle "all day" at 60 MPH, and how big a solar array you would need to produce that much energy per day. Until you start dealing with facts, you won't have an answer to your question.

#### john61ct

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And the huge weight of a true semi-trailer would not be suitable, kill efficiency even further.

A custom featherweight 40' by 8' platform would be hood, say for a demonstration project on the Bonneville salt flats

but not practical for normal roads, and certainly not using a regular production tow vehicle.

Sent from my Nexus 6 using Tapatalk

#### OR-Carl

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The guys name was Louis Palmer, who drove a vehicle called the Solartaxi around the world (32,000 miles) in about a year and a half.

The car and trailer together only came in at 1650lbs, boasted a top speed of 55mph and claimed to get 133wh/mile. The solar panels on the trailer came in at about 6 square meters. It used a liquid salt Zebra battery, and claimed 250 mile range, but it also mentions 14kwh when discussing battery costs, so I might be missing something. The whole thing feels a little light on facts, which I am guessing is because it does not quite deliver all it promises. Or because the whole thing was built by a bunch of engineering students, and the guy who drove it did not really fully understand how it all worked.

So, yeah, that array, if it was really efficient would be nearing 1.5kw. My array happens to be that size, and on a sunny summer day at 45degrees north lat. I can pull in 6kwh in a day. If that was feeding a car that used 133wh/m, it would equate to a 45 mile range. Some form of battery would be a must, as you would burn through that 45 miles in a couple hours, while needing a good 7 or 8 hours of sun to accumulate that much energy.

Anyway, it sounds like the OP wants someone else to do all the work for him, so maybe try contacting some local universities? I will say I am fairly impressed with the stats that this thing manages to put out. Granted, a relatively fit person could easily outdistance it on a bicycle, and since it is a fair weather proposition anyway, it would be a lovely bike trip.

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