Solar-Powered Toyota Prius Project
by Michael Graham Richard, Gatineau, Canada on 08.17.05
Green Car Congress writes about a very cool project by Canadian engineer Steve Lapp who modified his 2001 Prius by installing solar panels on the roof. It is admitted that the car is still a rough prototype, but so far the fuel economy improvement are of 10%, a respectable figure; for reference, Honda completely redesigned the Honda Civic engine for the 2006 model and achieved a 6% increase in fuel economy (the comparison is not quite fair, but I just want to point out that it can take lots of engineering efforts to gain even a few percents). "Lapp’s modelling predicts a 10%–20% fuel efficiency improvement for the 270 watts of PV (to be bumped up to 360 watts with the additional of a fourth panel)".
Here's a quote from Lapp's plan:
...the fact that [current Toyota hybrids] can run on electricity alone, with their gasoline engines off, offers the opportunity to provide them with more electricity and therefore drive further with the gasoline engine off.
Electricity can be provided from the electrical grid by charging an onboard battery, and depending on where that electricity comes from, it will have various emissions associated with it. [The plug-in concept.] However if it is provided from renewable energy sources, such as photovoltaic panels, then it is "green".
This begs the question of why not put the PV panels directly on a hybrid car and generate electricity onboard while the car is parked outside, or even while driving. The general reaction of people to this idea is that there could not be enough energy striking the roof of a car to provide enough electricity to drive any meaningful distance.
This is where the incredible efficiency of the hybrid car must be taken into account. To drive a hybrid car about 1 km, takes about the same electricity as to light a 150 watt bulb for one hour! The point is not to drive the car using only solar power, but to effectively use solar power to improve gasoline fuel efficiency.
How much gasoline can this photovoltaic hybrid car save? Well let’s look at the energy available from the sun on the roof of the car. For June and July in Kingston Ontario, about 6 kWh of energy from the sun strikes each square meter of horizontal surface. If we install 2 square meters of photovoltaic panels on the car and we collect 10% of the energy from the sun as electricity (well within present PV efficiency), we can theoretically go about 8 km each day on just the sun’s energy. If we drive 24 km on a sunny day, that is enough to reduce our gasoline consumption by 33%. This would take the Prius from 5.0 l/100km [47 mpg] to 3.3 l/100km [71.2 mpg].
And a quote from the Green Car Congress article:
The 300 VDC output of the solar subsystem is attached to the switched side of the original Prius battery, so the PV battery cannot recharge the NiMH while the ignition is off. The PV system can inject a maximum of up to 2 amps continuously into the battery while the ignition is on. [...]
The decision not to charge the hybrid when the car is off was a pragmatic choice, given the financial and time constraints of his project. Among other issues, there would need to be a thorough analysis to determined the optimal PV-NiMH energy flow/charge relationship.
::The Photovoltaic Hybrid Car Project , via the always excellent ::Green Car Congress
It can't recharge unless the ignition is on? On an average day, a car is driven for one hour. Assume that's done in full sunlight. At the efficiency level quoted in the article and the size of the panels, it would take an hour to provide enough electricity to move a 2nd generation Prius 1.23 km. I can only assume a 1st generation Prius (the car modded in this experiment) is at most this efficient, and probably less so.
So, say you're going urban speeds of around 35 km/h, that means the sun would power about 4% of your trip. So instead of getting 4.90L/100km, you'd get 4.73L/100km.
To pay off just the solar panels, you'd have to drive about 800,000 km at current gas prices.
Even if the system could charge batteries and get the maximum amount of energy from the panels on a daily basis, according to my calculations, if one drives 15,000 miles/yr (24,140 km/yr) and drives an equal distance each day of the year, this solar modification would be able to power 938 km in a year (given variations in insolation values from month to month). This results in a 3.9% reduction in gasoline consumption. Keep in mind this is under optimal conditions (car outside getting a day's full sunlight every day).
And once again, the payback for the panels alone should take about 800,000 km - or about 33 years, if the car and the panels were to actually last that long. Then you'd still have to pay for the inverter, batteries, etc, and given average battery lifespans, it would never pay for itself.
Interesting experiment, but not really practical. There's a lot easier ways to get 4% efficiency gains - like, say, driving 4% less.
Well its still a fun prototype to provoke thought. My concern is more with structural damage cutting design life. Look at the roofs of cars over 5 years old and there are often scratches and small dents. Just a car branch of edge of a garage and bang its dead.
However, it does make more sense to put SPV panels on a garage roof and use to recharge the car when its there and sell into the grid when its not there. That way, when the batteries are fully charged (by chance) the payback is still hapenning.
I once similarly calculated that the wattage needed to run a 12V thermoelectric cooler in my van, while parked, required a panel area larger than the surface area of my van's roof at todays' conversion efficiencies. Gave that one up.
I think Joseph's comment above is a little unfair - kind of a strawman objection using the figure of one hour a day charging for the whole analysis.
It says at the foot of the article that charging only while the car was running was a pragmatic decision for this experiment. Admittedly it might have been nicer if they had taken the reverse approach - charge while off - but that is a different experiment.
BTW one thing that i'm surprised nobody is doing yet is running solar powered aircon on parked cars...even just a small fan ought to improve the return to car experience in a sunny climes.
Maybe someday we'll even be able to cover the entire car in a thin PV film or PV paint, which would be much lighter and cover more surface area!
When the ignition is off, the solar panels charge an auxilary battery. This second battery then charges the main NiMH when the ignition is on. So the power from the solar array is collected at all times. This is clearly less efficient than charging the main batteries directly but avoids having to modify the stock battery management system.
From the article:
"The stock NIMH battery is carefully controlled by the cars battery ECU, and we do not want to mess with that, so an additional battery will be added and charged from the solar array, this battery will then feed into the main original battery through a custom designed power converter that is controlled by the battery SOC."
Joseph, the PV array has its own battery, so it collects power while the ignition is off. It only transfers that power to the car's battery while the car is on. The PV system's battery does add extra weight, but it allows the car to use the extra power that you are concerned about.
Also note that this is a prototype made on a limited budget. Not gonna be perfect in those conditions, but its great to see someone doing this. Hopefully it will spur more people and firms to look into the possibilities.
As others have said, we have to remember that this is a prototype. If it was a final version of a product released by Toyota, some criticism would be warranted, but for what it is, I think it's supremely cool and my hat is off to Mr. Lapp.
My eco-projects aren't near as cool as this, unfortunately.
Treehuggers, you're in luck. I'm about to share with you my million dollar eco-business plan on the condition that if you swipe it and it proves successful, I expect you to buy me the following with your new found millions - 1 diesel dirt bike, 1 new 12" powerbook and a jukebox.
The most effective use of PV on the roads would obviously be within the trucking industry. They've got huge, flat roofs and spent most of the day on the road under the sun.
Couple the PV potential of big rigs with a growing interest in biodiesel among
truckers and finally, throw in the holy grail of diesel-hybrid engines and you've got yourself a paradigm shift in the shipping/transport industry.
Now someone out there go forth and make it happen!
The 6% improvement in economy in the Civic hybrid was not the goal of the redesign.
It makes 25% more power for the same weight and cost, in less space.
Brian
You are right, Brian. It's for that reason that I wrote that "the comparison is not quite fair". But still, examples of optimizations that lead to only a few percent improvement are many.
I, for one, would have really liked Honda to keep power close to equal and raise fuel economy more than 6%.
I agree that it sounds like a good idea/step in the right direction. I also agree with the fellow that thinks that the hybrid/biodiesel/solar revolution should start with truckers: even a 5% reduction in fuel use can mean millions of dollars and the difference between bankruptcy and solvency in an industry running on such tight profit margins.
However, back to this Prius: my first reaction to the design is "what about the aerodynamics?" I've seen reports that something as simple as adding a properly designed spoiler (yes, I know spoilers are obnoxious) can improve fuel efficiency by as much as 10%. If this solar array is making the drag coefficient worse, adding extra solar panels is probably an issue of getting diminishing returns.
As an example, I point to my own car, a '98 Mercedes CLK 320. with a 215 hp 3.2 liter V-6, its a torquey beast (scares the hell out of my passengers when at full throttle), but owing to its low coefficient of drag (.32), on the highway I still get a respectable 32.3 mpg even though I usually drive well in excess of posted speed limits.
I guess what I'm saying is that with a little clever engineering from someone who knows aerodynamics, this solar cell array could both gather energy from the sun and improve the aerodynamics to garner truly astounding gains in fuel efficiency. At the very least some attention should be payed in further redesigns to making sure the solar arrays aren't defeating their own purpose so-to-speak.
"I think Joseph's comment above is a little unfair - kind of a strawman objection using the figure of one hour a day charging for the whole analysis."
I agree, but in that comment I was just working with the constraint set out by Mr. Lapp.
So, I also did an analysis using actual variations in insolation values for Kingston, and surprisingly enough, it still only saved about 4% in terms of gasoline consumption -- and that's under ideal conditions (full sunlight exposure during any given day).
My first comment in the following thread over at Green Car Congress elaborates:
http://www.greencarcongress.com/2005/08/solarpoweraugme.html
I can upload a spreadsheet to my server if anyone wants to see the details of the calculations.
Bottom line is that the solar mod should save about 1 gallon of gas on average per month. That's what happens when you're trying to improve on something that's already highly efficient -- the law of diminishing returns at work.
RE: "BTW one thing that i'm surprised nobody is doing yet is running solar powered aircon on parked cars..."
This is an option on some current model Audi and Mercedes cars, and even on the discontinued 1993 Mazda 929.
I think an idea like this is not economical for A) Toyota or B) Prius owners. Like someone said before, solar panels (and related equipment) are far too expensive right now for even a 25% boost in car efficiency to be economical.
A better start would be for Toyota to manufacture Priuses that can accept standard PV panel input (built-in charge controller). That way they wouldn't have to commit to purchasing a large number of expensive solar panels and the consumers could still go the extra mile (literally) and add PV panels to their Prius as after-market add-ons.
The current electrical system of the Prius is not cost effective for this, however.
-Riskable
http://www.riskable.com
The solar panels on top of the prius remind me of Japan taxis in the past where they clamped fiberglass cover on top of the taxi. There is about a quarter inch air space between the fiberglass and the roof which serves as insulator against the sun. In this way, they are able to save on airconditioning and keeps the car cooler. I guess Joseph could factor this-in in his cost justification for the solar panels.
With regards to keeping the interior of cars cooler while parked under the sun, I used to have a small solar powered exhaust fan which is installed by placing it inside the car and clamped between the edge of the side window glass and the rubber seal of the car. It worked perfectly but it requires direct hit from the sun so I ordered 2 sets which I installed on both side windows at the back passenger seat area. Unfortunately this is not available for sale now for unknown reason.
I hope that people should continue exploring the potential of the sun and that more people would buy solar panels and eventually lowering its initial cost.
to CLK320 owner:
--first, your car does not get 32.3 mpg on the highway on average. Perhaps on a long trip with the cruise set at 80mph and the A/C off you once got 32.3, but even the manufacture admits maximum 29 mpg on the highway. If you believe you are then you are not figuring out your mpg properly.
--Second, you only have 230 ft-lbs torque in a 3200 lbs car. That is not a "torquey beast", regardless of whoever you believe it scares.
you can look up your own numbers at carpoint.com, but having owned a E320 (same engine) I can attest that the car is nothing spectacular in terms of fuel efficiency or torque.
Anyway, back to the article. If anything this experiment shows solar panels are not sufficient for normal car use yet.
I can guarantee you that over the past five years, calculations at the pump (odo/gas added) have consistently rung up higher than 32 mpg when I am travelling on the highway. In-town gas mileage is lower, but most of my miles are done cruising between 80 and 90 with the airconditioning set to 75.
As far as performance: If I turn off the traction control, I can break out the rear end by flooring the gas. There are many more powerful cars out there, but the aggressive transmission, shorter gear ratios and flat torque curve make it plenty fast to me.
The point I am making is that aerodynamics can make all the difference, and I think this stands. The CLK has a much better drag coefficient than the E class sedans from that era.
Rishi Mukhopadhyay,
Do you have any kind of independent evidence that your Mercedes with a 3.2 liters engine, which is rated at a combined 24 mpg (21/29), can do consistently over 32 mpg (especially if going at high speeds of 80-90mph where wind resistance is high, and with air conditioning) on the highway?
It is incredible hard to believe and I suspect errors in your fuel economy calculations.
If you are aksing me if my car has been tested by anyone other than myself and my father, then no. But I do keep the tires to the proper inflation, the odo generally jives with my gps readings (when the gps is turned on), and I can't think of anything else that might be inaccurate. I stress, once again, that in-city the gas mileage is lower and highly variable, but on the highway at those speeds with the AC on, this is what I'm getting. The fuel economy of the car did improve a couple years after we bought it when Mercedes changed its official recomendations on what sort of engine lubrication to use. This may explain the discrepancy between published figures and what I'm getting. Indeed, they even issued a rebate on a future oil change and extended the warranty owing to oil sludge problems caused by their original recomendation.
Anyways, I'm not actually that surprised given the a CD of .32 is extremely low for a car in that (ie: non economy, non high-end sports) class. Also, a subjective test for exactly how much wind resistance you are getting at 80-90 is to simply let off the gas pedal and see how much you decelerate (I suppose I should pop it into neutral to get the best idea). In general, not nearly as rapidly in the CLK as in other cars I've driven regularly (namely a Volvo station wagon and a Honda Element).
Also, I'd like to point out that I'm a graduate student on a fairly tight budget (the car itself was a graduation gift/hand-me-down from my father), so I tend to watch these numbers pretty closely, and I was blown away by the fact that despite requiring premium fuel, this car was cheaper to run than my old Honda Element was.
I dunno, maybe with all the statistical error inherent in any manufacturing process, we "got lucky" with this one. It doesn't hurt that we've taken good care of it over the years, either, though.
Rishi,
Well, good for you if you are getting these fuel economy figure. The other possibility is that you have very sane driving habits, and if it is the case, keep it up!
Sure, it might not be worth it financially yet to add the panels, but if the demand for solar goes up, the individual panel prices should come down...kudos to the first penguins of the world! I'd love to increase the efficiency of my Prius someday!
I like Garth's idea of the solar panels on the trucks, but my first thought is the majority of truckers just pick up those containers from the ports, which are stacked several high on ships...so the panels would have to be unbelievably durable to withstand that kind of punishment, or more likely they would have to be fully retractable (maybe rolled up thin film types), so they stay with the cab of the truck and can be quickly deployed and removed before and after delivery... (I'd like an ipod for my contribution to the project :D...)
In regards to the disagreement of the ability of Rishi's CLK320 and James. Are you both living in America? If Rishi is in a commonwealth country, you could both be right. British gallons are 4.55 litres and American gallons 3.82 litres.
Ian
In regards to the disagreement of the ability of Rishi's CLK320 and James. Are you both living in America? If Rishi is in a commonwealth country, you could both be right. British gallons are 4.55 litres and American gallons 3.82 litres.
Ian
Ian,
It is indeed a possibility. I don't know if Rishi will read your post, but if so, I am curious to know his answer.
Hi all,
I am the original owner of the CLK320 that is now Rishi's. He is correct on the 32 mpg+ highway mileage and we are talking US gallons (as opposed to the imperial gallon). Actually my experience is 34 mpg at 70-75 mph on very flat terrain recorded several times (280 mile trips during the summer months--with a/c on--from the Detroit area to upstate Michigan, and back). I will also say that the first two years or so of ownership the mileage was more like 28. MB changed its lubrication specs around then. They increased the engine warranty to 150,000 miles, instead of the 100,000 miles it came with to start, to reassure its customers. The car is 7.5 years old with 103,000 miles. It just had its first tuneup. Servicing has always been performed per factory recommendations by the same MB dealer.
About the torque: it does have an adaptive transmission and will automatically adjust with quick shifts to an agressive driver during in-city driving.
This may not be the only 1998 CLK320 that is delivering 32+ mpg on the highway. I wonder what's the best place to find out. Any ideas?
-Uttam
"even just a small fan ought to improve the return to car experience in a sunny climes"
I am in no way advercating this particular product or company but just a FYI this type of product has been available in Australia for more than 10 years, I don't know how well they work, most of us just leave the window down half a centimeter and run if it starts raining.
http://www.amerimark.com/cgi-bin/amerimark/cat_item.html?prod=23288&media=G00798&days=XVQ
This solar powered prius is not going to happen.
The best option is the plug in prius.
I heard these plug in Prius get like 100 mpg.
Some even get 120 mpg.
A few years ago, Volkwagon built some car that got 282 mpg.
It was a small concept car.
I dont think it went into production.
Interesting read. 180mpg Prius and up to 30 miles on battery power is claimed in the article.
http://www.freerepublic.com/focus/f-news/1378468/posts
THE BIG SQUEEZE
Two Prius owners compete to get one more mile from the last drop of gas in their hybrid cars
Published on: 09/08/05
Like a typical Toyota Prius driver, Jim Hartzfeld is engaged in a mortal competition to squeeze every last mile per gallon he can from his high-tech hybrid.
read more here:
http://www.ajc.com/news/content/living/0905/08prius.html
Why not install less expensive laminated steel solar panels on the house roof, and charge the Prius batteries overnight when you get home?
You would be able to use the least expensive technology, re-use power in the house, and not worry about dammaging the aerodynamic efficiency, weight, or circuits of the car.
As a Prius owner I would welcome an inexpensive adaptor to integrate a plug in at home and even additional electrical storage. The rural areas many americans live in require them to commute to work in the cities thus creates desires for more efficient automobiles yet strives for clean air and good citizenship. The technoligy is apparently stiffiled by oil companies and red tape from government representitives backed by none other than oil companies as well as being stock holders in oil companies themselves. Someone tell me how to overcome the mountain of profits received by those mentioned and to help the working class continue to travel to work and pay those taxes to continue to fund america.
Points I want to make.
currently prius electric engine,
max 1200 watts,
201 volts
6 amps.
Solar panels have improved dramatically.
300 watt panels x 4. You do the math!
It could power the car during daylight hours.
Something to think about as regards the "how long does it take to recoup the costs of the PV panels in saved fuel" argument. How long does it take to recoup the costs of a 71" plasma screen TV? Or a new T-shirt? Or the Prius itself!?! There are other benefits to these green mods beyond just saving nickels/dimes/quarters on your next tank fill. It's knowing that you're doing your part, feeling good about what you drive when/if you drive it, etc.
Is no one chasing after using PV on their houses to produce hydrogen fuel? Given 20 square meters of panel, how much H2 could I produce on a given day? At that point I have zero emissions and zero fuel costs. I would be curious to know if I could make my seven mile drive to work each day with this setup.
J.
I'm by no means a technical person, so a lot of the above has gone WAY over my head (add blonde into that equation, and it could be dangerous!), but I was pondering the solar-power car issue this weekend. I wonder if, along with solar panels (or has someone invented photovoltaic paint yet?), anyone's tried putting a small wind-power turbine in the front of the car (where the grill is), to generate extra power? The faster you go, the faster the wind thingy goes, the more power you create - right???
OK, just a thought. I could be completely off mark here. Was just wondering if it would work. And if, with a combination of wind and solar, along with a light-weight car body and minimal electrics required (no electronic gadgets), one could create a competely fuel-free car?
I praise Steve Lapp's Solar Toyota Prius. I had similar ideas that powers the car even more without the gasoline.
Hrm, I am very surprised that a Prius can drive 1km on 150 watt-hours.
"To drive a hybrid car about 1 km, takes about the same electricity as to light a 150 watt bulb for one hour!"
The Think electric vehicle (which is all electric and also smaller than the Prius) requires 227 watt-hours...I find it unlikely that a smaller car like the Think would require more energy than the Prius.
--
editor note: Good observation. Could it be that 150watt/hour is what is needed to keep the Prius moving once it has reached cruising speed?
What nobody mentioned is the increase in RANGE that this could provide an all electric car (like the EV1-RIP)
Toyota Prius mileage question: I've googled all over for this answer with no luck. Maybe someone out there has done some research into this matter: How does the mileage screen for average mileage on the Prius (I have a 2006) compare with actual mileage? It appears that when the gas engine is on, there is some type of flow meter on the gas line, injectors, etc. whose readings are calculated with current speed, which would be a pretty good indicator of mileage. However, when in an all electric mode, the default mileage for this calculation seems to be 100 mpg. True mileage for all electrict driving would be infinity, wouldn't it, since no gas is being used? But infinity wouldn't work in the overall calculation, so 100 mpg is used.
If I'm correct on the above, wouldn't the actual mileage be higher than that shown on the screen? I've heard it's hard to figure mileage the old fashioned way with a Prius due to the variablity of filling the tank to "full" due to the emissions bladder in the tank. (I've tried it over numerous tankfulls, but my wife will invariably fill up and forget to take notes!)
Has anybody done a long term "old fashioned" mileage calculation on the Prius?
I commend anyone who is doing anything to fight GHgases: The Prime Minister of the United Kingdom has given 10 to 15 years for the point of no return. The UK has a petrol based ecomomy; so I believe we have more like 5 to 10 years. http://digg.com/general_sciences/Half_of_world_s_oxygen_comes_from_phytoplankton#c3522339
Michelle: Plus friction in all parts, the car would have to use more energy to fight the extra drag caused by spinning the turbine than the turbine would be able to generate itself. This is the conservation of energy, and is why perpetual motion machines are impossible without some kind of constant energy input. The net result of adding a wind turbine would be decreased mileage.
"Points I want to make.
currently prius electric engine,
max 1200 watts,
201 volts
6 amps.
Solar panels have improved dramatically.
300 watt panels x 4. You do the math!
It could power the car during daylight hours.
"
Solar Panels have improved and continue to improve. The daylight driving benefits would be real in areas like the SW, where you have very few days of inhibited sunlight. But the number of "inhibited sunlight" days may actually break the concept since you want to build a product for mass appeal. Areas on the other end of the spectrum would have almost no gain from the costs the manufacturer would have to incur to properly integrate the PV into the aerodynamics.
I live in the SW and long drives to NM, NV and UT would likely see the benefits in extended range of the car. Even if the PV only off set the AC electrical requirements. I for one am interested in the PV idea, however, I believe the Elec.Motor will need to provide more influence at 80MPH to show the benefits of the PV cells. On a flat road with no headwind, my Prius at 80 runs off the Gas motor and only uses the Elec.Motor for acceleration or additional power up hills. City driving >30MPH, traffic light to traffic light, the PV idea might perform better, since you need more torque off the line and the Elec.Battery is in use more.
Never the less you may find this article interesting.
" Solar Cell Breaks the 40% Efficiency Barrier"
http://www.renewableenergyaccess.com/rea/news/story?id=46765