Using Solar Roofs To Power Hybrids

A lot of those numbers don't add up.

This is a great post. I've always wondered why this wasn't done already...

First of all "watts of energy per hour" doesn't make sense. Watt is a unit of power- not energy. Power is energy divided by time, so watts per hour is energy divided by square time, which doesn't make sense. That would be something like the acceleration of power output, which is totally non-applicable to the context. The article loses credibility right out of the blocks.

OK...now that that is out of the way, this system is not a good idea- the solar panels would be far more useful if they were mounted to a building instead of a car. That way, they could always be angeled towared the sun, increasing efficiency. They also wouldn't add weight to the car, would be less vulnerable to damage, and the energy could be put on the grid during the day, when demand is higher. Putting power on the grid also represents lower losses than charging a battery. Then you take your plug in hybrid home at night and charge up on the grid, when power is being wasted by idling powerplants anyway.

Powering your cars with solar energy is great. Putting the solar panels directly on the car tends to be a wasteful, inefficient "look at me" solution.

IT LOOKS AWESOME!!!!

First of all "watts of energy per hour" doesn't make sense. Watt is a unit of power- not energy. Power is energy divided by time, so watts per hour is energy divided by square time, which doesn't make sense. That would be something like the acceleration of power output, which is totally non-applicable to the context. The article loses credibility right out of the blocks.

OK...now that that is out of the way, this system is not a good idea- the solar panels would be far more useful if they were mounted to a building instead of a car. That way, they could always be angeled towared the sun, increasing efficiency. They also wouldn't add weight to the car, would be less vulnerable to damage, and the energy could be put on the grid during the day, when demand is higher. Putting power on the grid also represents lower losses than charging a battery. Then you take your plug in hybrid home at night and charge up on the grid, when power is being wasted by idling powerplants anyway.

Powering your cars with solar energy is great. Putting the solar panels directly on the car tends to be a wasteful, inefficient "look at me" solution.

I love all the ways people trick out their priii. I think something like this makes sense though. I have a car to drive it to work and while i'm working it doesn't do anything. this would be the perfect time to recharge it.

g.
http://www.cheapgreencar.com

It isn't efficient, but it is interesting to consider in future.
Some universities organise a race of solar powered cars and most of the cars are covered with cells like this one, but those cars are very light, for one person only and that solar power can give them serious speed and milage..

It IS a substantial contribution.This is a large panel. Unlike houses, these cars already have a battery system all set up! This would be a great way to get photovoltaics working now.

Why are the solar panels rated at 200-300 Whr? a W-hr is a unit of energy, not power. Solar panels are usually rated in the amount of power they generate, such as 1 kW. In other words, they produce 1000 Joules of energy per second.

When the company puts up solid numbers instead of press releases and FAQs, then post about this again. Until then, these numbers don't make any sense.

It does look nice, but as adam says it's not the best way to capture solar energy.

How about a fold out roof that pops up when you park - it could use GPS data to work out where you are, where the sun will be, and then position itself accordingly. Hopefully it could sense when you are in multi storey car park too and then......not pop up :)

Adam -

While you are correct that for most installations a permanent, grid-feeding solar array would be best, your dissection of "watt-hours" is incorrect.

Watt-hours is a measure of power consumption (or generation) over time. It's how you pay your electric bill (usually billed in "kilowatt hours").

- Bob R.

@donato Its watt*hour not watt per hour ding dong know it all. It is a way of measuring power consumption. It is how they rate everything that uses power. Please take a look at your eletric bill.

Some people commenting here (BobR) don't seem to grasp some of the electrical concepts.

So, as an actual electrical engineer, let me make it very easy for everyone:

Watt-hours (or the more-used measure, kilowatt-hours, KWh) is a measure of energy, plain and simple.

Forget phrases such as "power consumption over time."
No knowledgeable person says that. Do you say, "I drove my car today and used 200 horsepower over two hours"? Of course not.

You are billed KWh by your electric company because, within certain limits, your electric company does not care about the power you use. They care about the energy.

A 200 watt light bulb continuously uses 200 watts of power. The energy consumed by a 200 watt light bulb over
1 hour of time is 200 watt hours.

If the power company charges $0.10 KWH (Kilo-Watt-Hours),
then to run your 200 watt light bulb for 24 hours
it is going to cost:

200 Watts * 1 Killowatt / 1000 watts * $0.10 KWH * 24 Hrs = $0.48

Hope this example helps.

Now if only the price of batteries will drop...

-Keith

okay... i don't usually write comments... but as an electrical engineer this was just too funny.

I believe that Donato is trying to disprove the existence of the Watt-hour unit.... Watt = J/s.... hours can be reduced to seconds.... when you put Watt and hour together... you get..... Joules.

So, 1 Watt-hour = the amount of energy that would be used by a 1 Watt lightbulb over a period of 1 hour.

Before you post something like this, check it out on wikipedia or something:
http://en.wikipedia.org/wiki/KWh

also... don't quote stuff that doesn't exist in the article... where are you getting "watts of energy per hour"?

I was studying this a few weeks ago, and really to have a big impact, you have to leave your car out all day in the sun. You're only getting 200-300W out of the cells, which is about a mile of battery only range per hour that you leave the prius in the sun (the prius gets about 250Wh/mi depending on driving conditions).

Their numbers dont add up though.

If you work 8-5 and left your car in the sun all day, you'd get 9 extra miles per day under ideal conditions. Most solar cells really only output at most 80% of their rated capacity, so you're looking at less than that, maybe 6-7 miles. Thats great if thats your commute but for most folks its closer to 10-15 miles. At $2000 for the unit, and an extra 5mi/day of free power five days a week is 1300 miles per year, and at the prius's 40mpg, its only a savings of $130/yr, you'd pay it back in 15 years.

Even if you add a plugin option that you can charge the batteries through the cheap (well, cheaper) power from the wall you still havent paid back the total cost in a reasonable amount of time. A kWh might cost 10c and get you 3-4 miles, so even at 40 miles, you only paid $1 or at most $1.50. Much cheaper than gas. From there, at 15mi/day seven days a week (because you plug it in every night in your garage) saves $300/yr. Once you combine these two you're still only at $430/yr means its about five years to payoff the system.

All in all, you need way more efficient cells - you'd need to be able to generate about 500W from the top of the vehicle, plus plug in and 25mi all-electric range. An 8 hour day in the sun would generate about 12 miles of all electric mode, enough to keep most people from needing to go into gas/electric mode at all. Now you're talking about $750/yr in savings. Realizing the cost in under three years.

Hey for all those people who don't understand what a Watt hour is, a what a measure of joules per second, a watt hour is joules per hour. So 300Whr is the amount of energy a 300W load would draw in an hour.

how can they drive those cars ? it should be hot inside. solar roof can make them hot.

Jenny
http://www.Spaml.com

No, it's not the MOST efficient system. But it is self contained and it leapfrogs any personal infrastructure requirements, such as a home where panels could be mounted for optimal charging. Most importantly it is vehicle-centric which remains the primary focus for the consumer market. I'll take a 50% solution that thousands buy into over a 99% solution that only finds roots with the hard-core devotees. To criticize this as a “look at me gimmick” is silly, you could start by asking lance Armstrong to take off his little yellow bracelet and just make a donation.

LOOKS very cool. $3000 paying for itself in three years sounds like a decent investment, if accurate (I somehow doubt it).

I was ready to run out an buy one for my prius, then I got to thinking about leaving my car in the Blazing sun for three years. No thanks.

I wonder how many of those 200 watt hours are used to air condition the 120° oven that is my Prius when left for hours in the hot sun?

I wonder what the break-even time is for parking the car in the shade instead of at the closes parking space. Let's see... cost is $0 + ~2-5minutes of extra walking, which burns ~75 calories... hmmmm. Also, no power used to manufacture additonal solor panels and batteries.

I think parking in the shade is better.

Couple of points:

The car is a rolling solar powered battery. This has utility beyond merely adding a few miles of free travel a day, tho that is not to be sneezed at. One could use it for camping. Or you could power your home at 120v off the battery charged by solar energy only, in emergencies. In theory, if you installed a 12 volt electrical system in your home, you could run a lot of LED lighting fixtures, not to mention a PC or two (LED LCD monitors coming real soon), just off the battery in the Prius, charged by the solar cells on the roof. Instant solar power plant, anywhere you go.

Second point, response to a meme: always I seem to see a tight focus on the costs of alternative energy systems, down to pennies and precise number of months to total payback. This is well and good, but never do I see the same rigor applied to the rest of the wasteful habits of our lives. Do we calculate the relative costs of walking 12 miles a day opposed to the hours spent working to afford to pay for the car that "saves" us time by getting us there quicker? Or the costs in building a world where we "make" money by building far-flung suburbs and office complexes while never considering the costs incurred in taxes to build and maintain the roads and pay for the salt trucks and the police presence and all that? Our cost accounting seems a way of excusing us from changing our habits, and even so is not even accurate.

The numbers presented here are wrong. A 300 watt panel is not going to give 20 miles of all electric range on a Prius. You would need a panel many times that wattage to enable

MG2 in the Prius uses 50,000 watts of power under full load. A 300 watt panel in the sun for 12 hours would give enough power at full load for 4 to 5 minutes or at half load for 10 mins.

Finally according to thier own website they use a 215 watt panel on the Prius.

If they could get a 500 watt panel on there it would start to get interesting.

The system costs $2,000-$4,000. Let's use $3K as our working figure. Let's also assume that gas prices actually reach their projection of $4/gallon (we're not nearly there yet where I live). That means that installing these panels will be the financial equivalent of saving 750 gallons of gas, but at an installment rate equivalent to the efficiency difference. My current real-world Prius mileage is about 47.5mpg. So I will need to drive ((750 gallons * 47.5mpg)/.29 increased efficiency) = 122,844 miles in order to break even, not counting interest on the $3K investment and assuming the panels actually perform in the real world at the stated rate.

They are very cool, but no way do those panels pay for themselves in 2-3 years.

Hi,
I think its a pretty appealing system.

The difference between a PV panel mounted horizontally and one mounted at the ideal tilt (tilt = latitude) is about 23% on a full year basis. Horizontal panels actually collect more energy in the summer than do panels tilted at an angle equal to latitude. 23% is not so huge a loss. You may be willing to sacrifice the 23% for the convenience of a self contained system.

Granted, a fixed system can be adjusted in tilt or even be made to track the sun, but the great majority of people don't do this.

The fact that the panel is horizontal, and does very well in the summer, but less well in the winter might work well for climates that have more cloudy weather in the winter.

I think its nice to see stuff like this coming out.

Gary

Uh guys and gals,
The 2-3 year payback is on the left side of the web page where it says:

"Provides significant tax incentives, thus reducing the net cost of both systems and creating a break-even point for the SEV system of 2 to 3 years."

WITH TAX INCENTIVES it gets it down to 2-3 years. That means for a few people in California.

Although, if you spent your tax credit for buying a Prius on the solar system, then maybe it will work out for you.

What the hell is wrong with most of you people? Nitpicking about exactly how long until you get your money back. God. Get your head out of your butt. If it's saving gas... ANY amount of gas... Then that's pollution that you and your loved ones don't have to breathe it. That's reduced global warming that you and your loved ones won't have to suffer from. That's less time you'll spend filling up at the gas station and thus more time you can spend doing fun things with your friends and family. How much money do you WASTE? Do you need every Starbucks coffee you buy? Or do you just buy it because it feels good? Do you need the fancy paint job on your car, or do you just get it because it looks good? Well, the solar panels will make you feel good everytime you look at them. They'll make other people feel good. They'll make other people think about doing good things for the environment. They'll look pretty darn cool. You'll look a lot cooler than if you tricked out your car with a new spoiler or rims. And as a bonus, you will be saving money, bit by bit. Heck, I'm sure you've gone for several meals that were over a hundred bucks. Do you sit there counting every penny you spent there? If you can afford a car, you can afford some cool solar panels for it. Especially considering that eventually they will pay for themselves. And remember, in the end, you're benefiting from cleaner air. It's not some hypothetical, philosophical benefit. YOU are breathing in LESS POLLUTION. What's that worth to you? How many lives do you have? Oh, and who's the guy saying that it would be better to get solar panels for one's house? Well, so get the panels for the car AND your house. What kind of justification for trashing the car panels is "they'd be better on the house?" Stop being angry, scared, bitter people. Start doing good things for your own health and for your long-term financial benefit.

At the "this is an inefficient use of PV-panels" reactions:

If you want the biggest environmental bang for the buck right now you should not install PV-panels at all, but put you energy in energy efficiency and energy saving.

Nevertheless it makes sense to invest in PV because these investments are essential for the development of the PV industry and technology that will make PV competitive with dirty energy.

It is the same with this car. It is a good proof of concept. And some day in the future it will make sense to stick solar cells, on you house on your car and even on you clothes (to power your i-pod).

Nitpicking about exactly how long until you get your money back. God. Get your head out of your butt. If it's saving gas... ANY amount of gas... Then that's pollution that you and your loved ones don't have to breathe it.

Do you understand the concept of cost/benefit analysis? If not, it's like it sounds -- you weight the benefits of somethng with its costs, and ideally, compare it to alternatives. Since people's financial resources are limited, it is prudent to be wise about how best to use them. In the case of this scheme, since the payback period far exceeds the useful life of the vehicle, there are many other things one can do for a lot less money which will have far more positive impact on the enviornment.

Well, the solar panels will make you feel good everytime you look at them. They'll make other people feel good. They'll make other people think about doing good things for the environment. They'll look pretty darn cool.

That's your subjective opinion. Other people might think that it's a doubling of the "smug factor" of the vehicle, and if people were to understand how cost-ineffective they are and how little good they do, they would then think that the owner is a fool and would rather not have anything to do with such a vehicle or the person driving it.

And as a bonus, you will be saving money, bit by bit.

No. No, you won't. It will never pay for itself, despite the seller's advocacy of such a claim.

The panels make sense if your PRIMARY goal is to minimize CO2 emissions....and some of the cost savings helps offset the extra cost.

If your PRIMARY goal is saving $$, then waiting a few years till the cost comes down (and gas goes up) probably makes sense.

Many of us are capable of both the electrical and financial calculations but they won't influence anyone else's core beliefs. Only help support your own.

Personally my PRIMARY goal is the safety of my kids, so my indecision comes from wondering about getting rear ended by an SUV while they're sitting in the back seat.

There are a lot of smoke and mirrors here about how much farther you can go with the solar panels. But, as in anything, follow the money, and the truth will come out. If you check the solar irradiance charts, 212 watt panels in California, provided they are NOT kept in a covered garage somewhere, will produce an average of 1.378 kilowatt hours of energy per day. This is based on 6.5 hours equivalent 100% irradiance. This is a bit conservative, so let's be incredibly generous and say that there is 13 hours of 100%, might happen on one really rare day, and you get 2.756 kilowatt hours, with a value of $0.2756 per day.

Assuming a $3,000 investment, and pretending that we live in a fantasy world with no cost to our capital, the payoff is just under 30 YEARS!!!! That's right, do the math, divide that $3,000 by those 27 cents per day. And, people, it won't be 27 cents per day, it will be more like an average of 13 or 14, IF you keep your car outside all day, and oriented properly towards the sun, and don't put it in the shade. And yeah, when you do this, you turn your car into an oven, so you will be spending an extra dollar a day to power your air conditioning.

Solar powered cars - a good idea IF we make ultralight vehicles that can be powered by small energy sources. The solar races would only need a set of pedals in them, and a small storage battery to help with acceleration and hills in order to be viable for commuters everywhere. We just have to stop driving 3,000lb vehicles where 100lb vehicles would be more than adequate.

The problem with this would be safety, you can't mix 100lb 40mph traffic with 3,000lb 100mph traffic. But if we eliminated passenger vehicles from the streets, allowed only trucks and public transit on specific routes, and everyone else putted along on solar power and pedals, we'd reduce traffic mortatlity dramatically, cut ghg emisions by 60%, reduce health care costs (people would be getting more exercise). And we'd only be using 1/30th the raw materials to build each vehicle.

The problem is NOT that the cost of gas is too high, we are still paying more per gallon for a bottle of water!!!! We are just using wayyyy too much gas!

Whatever your opinion on the payoff matter, this will give you a slightly more clean car. Imagine if you didn't buy a car at all, you would've saved some considerable money by now, but you did. You're the consumer, installing solar panels to add this little decimal to your MPG while thinking about the payoff isn't green. Money and green is a huge paradox.

I know there is something very good you all should consider: it's an electric scooter that already has hit the shelves!

Go and get one here:

www.vectrix.com

You will be impressed....

Excellent information.Were starting to finally progress to oil independence.Hybrid Cars

Pieter - - Said Since people's financial resources are limited, it is prudent to be wise about how best to use them. In the case of this scheme, since the payback period far exceeds the useful life of the vehicle, there are many other things one can do for a lot less money which will have far more positive impact on the enviornment. - - - Instead of Bitching that it wont pay for itself and their are better ways to spend your money on the environment why not list them instead of shooting down what some people might think is better then doing Nothing instead of Bitch about somebody elses bad idea. and YES Im one of those people that do think its cool looking and at least its SOMETHING environmental friendly then nothing.

How much CO2 is spent to produce one of those panels? :)

I think this is not supposed to be efficient or cost effective. Its a prof of concept of a technology that still has much to grow and I'm glad people are investing time and money on such things.

Regards.

For so long a time we have done nothing to slow down global warming. We can already see what happens as our planet gets hotter. Forget the dolars and cents for a moment at least and think about the health problems that we face due to pollution. Our planet is good to us, it supports us
in ways we cannot emagine. Please, what ever it is
where ever it is. Do something to help our planet.

The ultimate hybrid vehicle... To save money, resources or whatever you think you are saving.

Isn't that why we bought the Prius to begin with? To save something. This addition to the hybrid may not pan out right away, but at least it is a start to the alternatives that will ultimately save us something.

Who knows, we could all be driving a vehicle powered by plasma rays or mini nuclear reactors (or both). Why does a hybrid vehicle have to be limited to just two technologies? The power could be shared by multiple systems and as technologies improve, the "savings" could also improve.

Time will only tell how the savings will add up. At least I made the biggest first step by purchasing that 04 Prius instead of the Hummer.

why dont they make more cars like this?

very nice article.

Adam listen to this humans apparently neeeeed cars but they spend a fortune on gas, oil, batteries, etc. so it is good that they finally are getting smart and building something useful it's way more useful then a solar powered phone pulse!!!!! it doesn't pollute the air NO GLOBAL WARMING!

Just one thought. The person who mentioned that it would be much more efficient to hook the hybrid car to a stationary solar panel has a good point.

But for apartment dwellers (like me) that's not an option.

My car sits in a common parking light... exposed to the sunshine... but out of range of any conventional electric outlets... and without the possibility of me hooking any stationary solar collector up to it.

So -- for apartment-dwellers like me -- and there are a LOT of us.. Mounting a 200 watt solar panel on the car is the only practical solution...

Less than perfect -- as the other writer pointed out -- but a heck of a lot better than NOT getting that 20-to-40 mile range boost provided by the solar panels on the car's roof.

I own a 2008 prius and absolutly love it. I was thinking about adding solar to it, but am curious if anyone has posted the total weight of the solar panels, dc converter, and the spare lead acid battery? I want to know how bad the increased weight effects the base mpg of the car, and how much actual mpg gain is calculating in the extra weight.

I also noticed the SEV webpage lists this for the 2004 to 2006 models only... no mention of 2007+. Anyone know the reason 2007 and 2008 aren't listed? I email the company to ask, but so far no response.