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Hybrid vehicles with solar photovoltaic (PV) panels should be part of the solution to America’s environmental problems and dependence on oil. Oil is the principal energy challenge because of supplies from unstable and unfriendly countries. PV panels added to hybrid cars are much more cost effective than PV panels added to buildings, and solar hybrid vehicles directly address the oil problem. The incremental cost of solar PV panels on hybrid cars and displacing gasoline has a payback period that is much shorter than the payback for solar PV panels on buildings and displacing electricity. The progression, as envisioned here, is from the current hybrid vehicles to plug-in hybrid vehicles and, finally, to solar hybrid vehicles. Solar hybrids utilize the larger batter of a plug-in hybrid and add PV panels to charge the battery when parked in the sun. A solar hybrid vehicle would allow someone to drive their plug-in hybrid vehicle 10 miles to work on grid power. The solar system on the car would charge the battery while sitting in the parking lot all day. Then it could be driven home in the evening on solar power. The drive home would not use any gasoline, natural gas, coal or any other fossil fuel and have zero tailpipe and smoke stack emissions. Solar hybrids would reduce America’s dependence on oil and help solve environmental problems like urban pollution and global climate change.

Solar Hybrid Vehicle Cost and Economics

The question of whether solar vehicles are viable is not about dependency on oil or being green, it’s about cost and the premium people are willing to pay above a straight economic payback. The cost of adding solar to cars is based on data from adding PVs to buildings since vehicle PV information is not available. Table 1 compares the costs and payback from both building and solar hybrid vehicles. The calculation needs the capital cost of the PV system and the displaced fuel cost. A PV panel currently costs about $5.41 per Watt . Installation on the vehicle is assumed to cost $1 per Watt, but there is no information available on this. Included in the building installation cost of $3 per Watt is a DC to AC converter. This puts the total PV system cost on a building in the range of $8 to $10 per Watt, which is a pretty standard range. The cost of adding a solar PV panel to a Toyota Prius would be about $962. Federal or state incentives could reduce the cost of the solar PV system and a 50% reduction is incorporated in the table. This incentive is included to demonstrate the benefits if solar hybrid incentives were enacted since there have often been incentives for building solar systems or the wind production tax credit.

Using a Toyota Prius for this example, a Prius can travel roughly 7 miles per kiloWatt-hour (kWh) of electricity (a kiloWatt is 1,000 Watts). A PV panel on a building can achieve a capacity factor of about 25% based on a California Energy Commission presentation . (Capacity factor is the ratio of actual generation divided by potential generation if the system ran at full output for every hour.) A Prius would be able to travel about 2,300 miles per year on solar power with a 150 Watt PV panel, a 25% capacity factor and 7 miles per kWh. Miles on solar will vary with location and will probably be in the range of 1,500 miles to 2,500 miles. Solar hybrids are more viable in southern, sunny areas than northern areas or cloudy areas. Solar hybrids are not for everyone.

In Table 1, both building and car systems are the same size for ease of comparison. In reality, a residential building PV system would be about 10 times larger. If the building application were full sized, all of the costs and savings would be scaled up, but the payback period would be exactly the same.

Three scenarios are shown in Table 1 for gasoline prices because of the uncertainty and volatility in gas prices: $2, $3 and $4 per gallon. The mileage estimate of 44 miles per gallon (mpg) on gasoline is Consumer Report’s estimate for a Prius based on what a typical person would achieve in a mix of city and highway conditions. The U.S. EPA’s official mileage numbers of 60 mpg city and 51 mpg highway are generally optimistic. Assuming 12,000 miles per year spread evenly every day (32.9 miles per day), 10-miles of plug-in power every day, and the 2,300 miles on solar per year, Consumer Report’s mileage estimate would go from 44 mpg for a standard Prius to 87 mpg for a solar hybrid Prius. The EPA mileage numbers would go from 60 mpg city/51 mpg highway for the standard Prius to 119 mpg city/101 mpg highway for the solar hybrid Prius. These calculations do not account for any change in gasoline mpg due to the weight of the batteries or wind resistance from the solar PV system.

The economics of these solar PV alternatives can be compared in terms of fuel savings and payback. Table 1 shows that a PV panel on a building would save $32.19 per year in electricity. By contrast, the same sized PV panel on a solar hybrid would save $104.52, $156,78, or $209.05 per year at $2, $3, or $4 per gallon gasoline, respectively. Payback is the number of years of savings required to return the original purchase cost. As shown in Table 1, the solar hybrid vehicle systems requires from 4.6 years to 2.3 years for the savings in gasoline to offset the cost of the PV system, depending on the cost of gasoline. It requires 19.6 years for the electricity savings to repay the cost of a PV system installed on a building even when the initial cost is reduced by 50% via an incentive. Adding solar PV system to a hybrid vehicle is considerably more cost effective than adding a solar PV system to a building.

The attractiveness of solar power, or hybrid cars for that matter, is not strictly about cost savings. The question is whether consumers are willing to pay a premium to obtain additional benefits, such as solar power. Some consumers are willing to pay the premium for solar power on a building even though it requires many years to recover the initial cost. Consumer Repots found that only two of the hybrids currently on the market returned the additional purchase cost within five years (the Consumer Reports study considered all aspects of hybrid ownership and not just the limited scope evaluated here). Even though the gasoline savings may not justify the premium on the purchase price of a current hybrid vehicle, 205,000 buyers were willing to pay the premium for a hybrid car in 2005 because that is the number that was sold. With similar economics and very attractive environmental and societal benefits, solar hybrid vehicles would appear to be saleable. The cost premium for adding solar PV to a hybrid is reasonable, and the environmental and societal benefits are significant. The evidence from sales of solar systems on buildings and current hybrid cars indicates that many customers would be willing to pay the additional $1,000 of so for the solar PV system on a vehicle (and even less after incentives). Solar hybrids are likely to be even more marketable than conventional hybrids because the solar system makes a statement and would offer greater marketing cachet than the techy hybrid system.

Producing solar hybrids would also help bring down the cost of solar PV systems. Government incentives for solar systems on buildings is justified, in part, as a means of bringing down the cost of solar systems in the near future. Developing both building and vehicular solar systems would bring the cost down faster. It is likely that as the cost of solar PV systems come down with increasing research, development and production, solar hybrid vehicles will become fully economic before solar systems for buildings do because of the relative economics of electricity and gasoline.

Solar hybrid vehicles could have a major impact on America’s dependence on oil if they were widely adopted. The U.S. currently uses about 10 million barrels of oil per day for transportation. Solar hybrid vehicles are not for everyone, but if half the vehicles in the country converted to solar hybrids, solar would displace one million barrels per day of oil (assuming about 20% of driving was on solar). Overall, this half of vehicle fleet would reduce oil consumption by about 3.4 million barrels per day (if half the country’s cars went the current Corporate Average Fuel Economy guideline of 27.5 mpg to the overall mileage of 87 mpg for a solar hybrid shown above).

Challenges to Solar Hybrid Development

The first challenge to solar hybrids is that there does not appear to be any research and development currently being undertaken on solar hybrid vehicles, despite the promising economics and environmental and societal benefits. Additional research on solar hybrids is needed. The values shown in Table 1 are rough and need to be confirmed with real world experience. The annual capacity factor of solar systems on cars needs to be determined: cars might be able to attain higher capacity factors than fixed building solar systems by ‘repositioning the solar array’ after lunch (parking facing east in the morning and west in the afternoon). Means of installing solar PV cells to vehicles needs to be developed as well as control systems for solar PV panels on vehicles. There is much to be researched, but serious research does not appear to be going on. An Internet search on solar cars reveals virtually nothing but a few solar nuts attaching standard PV panels to the Prius. The National Renewable Energy Laboratory (NREL) is tasked with researching renewable energy, yet emails to the NREL showed that solar hybrid vehicles are not under investigation there. A quick review of the administration’s proposed budget failed to find a single dollar of funding for solar hybrid vehicles in almost 2.8 trillion dollars of federal government expenditures proposed for fiscal year 2007.

Solar hybrid vehicles need to utilize the larger battery of a plug-in hybrid vehicle, which has both benefits and challenges. The benefits of adding solar can be combined with the benefits of a plug-in hybrid vehicle. If a plug-in hybrid had a battery that provided 10 miles of driving on a charge, then adding solar panels capable of providing 10 miles a day of travel would enable the vehicle to travel a total of 20 miles on electric and solar. If the plug-in hybrid had sufficient battery storage for 20 mile of driving, then this range could be extended to 30 miles with the type of solar panel described above. However, the costs of these forms of hybrid also need to be combined. The calculations in Table 1 are for only the incremental cost of the solar PV system added to a plug-in hybrid vehicle so as to focus on only the solar costs and benefits. A challenge of a solar hybrid system is that it combines the cost of hybrid technology with the cost of plug-in hybrid technology with the cost of the solar system. All of these costs are coming down, but the combined cost could be a difficult hurdle to overcome.

The factors limiting plug-in hybrid development are also limiting solar hybrid development, and commercialization of plug-in hybrids appears to be stymied by battery technology. Most existing hybrids use nickel-metal halide batteries. Nickel-metal halide batteries are heavy, however. Plug-in developers appear to be waiting for a breakthrough in lithium-ion batteries. Lithium-ion batteries are expensive; Prius conversions to plug-in hybrid using lithium-ion batteries cost $12,000.

Solar PV technology may be an alternative to bigger batteries. If solar PV panels cost less than batteries, then instead of making a plug-in hybrid with a bigger battery, use solar. Instead of a plug-in hybrid with a 20 mile battery range, it would be less expensive to make a solar hybrid with 10 miles of battery range and 10 miles of solar range. The battery size can be determined based on the amount of power the solar system provides in a day.

Solar PV panels have also improved in recent years but additional improvement may be needed for some vehicles. A few years ago, most solar panels were too weak in order for one powerful enough to recharge the car’s batteries to fit on the roof of the vehicle. Now, or in the near future, car-roof-sized PV panels will be able to provide significant range in many cases. Some vehicles may still be limited by their ability to fit a sufficiently powerful PV system on the roof. As PV panels continue to be improved over time, solar PV panels will be able to provide additional range on a day’s recharging. Improvements in PV technology will mean that more vehicles will be able to utilize solar power, range will be extended, and costs will come down.

Rapid Technological Change and Unlimited Potential

Solar hybrid technology is undergoing rapid change. Five years ago, solar vehicles were pie-in-the-sky, Buck Rodgers type of technology. Then the hybrid drive system was developed, and the revolution started. With hybrid drive systems, it became practical to combine gasoline and electric propulsion systems in vehicles. Electric vehicles are no longer limited to the distance that can be provided by batteries; the gasoline motor (or, preferably, a flex-fuel engine) can be used as a back-up. In addition to this paradigm shift in automotive technology, solar PV panels became more efficient and are now powerful enough to recharge car batteries in a reasonable amount of time. The recent increases in the cost of gasoline have also improved the economics of solar hybrid vehicles. Solar hybrids are now viable and economic. As shown using the rough values in this article, solar PV panels added to hybrid cars and displacing gasoline are more economic than solar PV panels on buildings that displace electricity. Solar hybrid technology warrants further research to more accurately determine its economics and to overcome its challenges. Incentives for solar hybrid vehicles are also warranted as a way to overcome the challenges facing this technology and as a means of bringing down the cost of solar panels. Solar hybrids vehicles offer unlimited potential.

References
1. Retail PV costs from May, 2006 survey from www.solarbuzz.com

2. The California Car Initiative, www.cal-cars.org, email dated 4/28/2006 from calcars-news@yahoogroups.com. Reported 146 Watts-hours per mile. Inverting and changing decimal places gives 6.85 miles per kiloWatt-hour. This was rounded to 7 miles per kilowatt-hour assuming that a factory production product would perform better than a home conversion.

3. Miller, Sandy, Emerging Renewables Program and Performance Incentives Update, Solar Forum, Sept, 12, 2005

4. Consumer Reports, The dollars & sense of hybrids, http://www.consumerreports.org/cro/cars/new-cars/high-cost-of-hybrid-vehicles-406/overview.htm

5. http://www.whitehouse.gov/omb/budget/fy2007/budget.html

6. http://www.edrivesystems.com/faq.html

Readers Comments

Date

Comment

Len Gould
5.22.06

I just seems more logical to install the PV cells in a fixed location on optimal trackers, then "plug in" the parked vehicles in the parking lot to the solar array. What additional benefit is there in carrying the PV cells around on the vehicle, with the

a) reduced directional tracking

b) added weight on vehicle

c) extreme added cost due to required vibration protection, reliability, maintainability, etc.

d) huge compromise in wind resistance due to suboptimal surface characteristics of solar cells v.s. vehicle paint.

Jim Beyer
5.22.06

I've analyzed this option several times and come to the conclusions that:

1) As Chris Neil says, it is one of the best uses of solar electric power, given one has a plug-in hybrid to charge.

2) It is never very much power, so while it does do good, it doesn't do MUCH good.

3) Like Len Gould says, it probably isn't worth the bother. I'd cite added cost, risk of theft, damage.

50 gallons/ yr sounds impressive, but that's really due to the PHEV, not the solar cells. 329 kw-hr is only about 1 kw-hr per day. Even at renewable energy costs, that's about 8-10 cents per day. Better off leaving some panels on your garage roof and using additional, stationary batteries.

I was interested in this as a way of extending range, but at 1 kw-hr, that only gives you 44/7 or 6-7 miles. Probably not worth it. (Compare this with a remote charger, allowing one to plug in at the workplace, a much more attractive option. So definitely do this (remote chasrger) first.)

Some slightly alternative notions might be adding panels to truck tops (they might defray electrical needs) and adding panels to RVs. (They sit many months of the year, so they could dual function as stationary power for the home.)

Dursun Sakarya
5.22.06

Chris, you've been standing under the Sun too long. Lets do something simple like raise the CAFE level. The CAFE level started at 18 mpg in 1978, it when up to 27.5 mpg in 1985. Today, 21 YEARS later...... it's 27.5 mpg.

Tam Hunt
5.22.06

I'm inclined to agree with Len and Jim B. on this one, but reserve the right to wholeheartedly endorse VIPV (vehicle integrated PV) if solar PV panels either come down in price significantly or increase in conversion efficiency significantly. I'm also open to the PR value of PV on cars - it gets noticed and gets people thinking about alternative energies. Last, in my case, I only commute about 8 miles per day anyway (when I don't ride the bus or my bike), so 6-7 miles per day from solar panels on top of my car has a certain elegance. I think the markets will safely decide this one.

Chris Neil
5.23.06

I need to correct Jim Beyer's statement above that most of the benefits are from the plug-in hybrid electric vehicle (PHEV). All of the benefits in the table are from the solar system only. The PHEV benefits are in addition to the solar benefits. The total impact is the combined benefit of the hybrid system, the PHEV system and the solar system. This is the 87 mpg to 119/101 mpg cited in the article.

With regard to the comment on the CAFE standard, that is an issue that I plan to address in a future article. My suggestion is to incorporate a certain percentage of plug-in and solar hybrids into the calcualtion of the CAFE standard to both signficantly impact oil consumption and to encourge the production of plug-in and solar hybrid vehicles.

With regard to Tam Hunt's comment that the markets will decide the fate of solar hybrids, there need to be products (solar hybrids) on the market before it can render its decision. Some R&D and incentives are needed in order to jump start the market and get some solar hyrbrids out there.

Chris Neil

Jim Beyer
5.23.06

Chris,

You misunderstand me. Or perhaps I didn't make myself clear. The hidden benefit of the PHEV is the 7kw-hr/gallon (equivalent). If you didn't have a PHEV, you couldn't make that assumption. There would be no place to store the solar power. Without that high conversion rate, the system become that much more problematic.

If you are advocating the use of solar panels on vehicles, you need to compare that with an ordinary PHEV being charge with solar stationary panels, not an ordinary car using fuel. The PHEV people (in general) seem to be confused by that. (Ask them to explain how PHEVs reduce GHG (basically, compared to an ordinary hybrid, they don't) and they get all squirmy. But they still make sense because they can use solar power efficiently (as this article shows) and do reduce oil dependency.)

I think a huge problem with analyzing energy systems is being unclear with the baseline, which leads to unclear results. Solar PHEV is favorable, compared to what? Ordinary cars? PHEVS?

That being said, this notion is still attractive. If you think about the marginal costs of GETTING useful energy to the wheels of a vehicle, they are very large (25-30 cents per kw-hr). Much higher than the cost of solar PV today, for example. The problem is that not all that much is available and recoverable from solar energy beating down on the car itself. But the margin is so high, it's hard to not think about it.

Incidently, a more immediate use of this technology is using solar electric to pre-heat/keep heated the catalytic converter on existing vehicles. Apparently, this would have a large impact on emissions and fuel efficiency for short trips.

Mark Kapner
5.23.06

Your value of 7 miles per kWh is much too high. Medium size EVs get about 3 to 4 miles per kWh.

Chris Neil
5.23.06

Mark,

Yes, medium sized vehicles are more in the 3-5 miles per kWh range. This example used a Prius, which is why it was higher.

Chris

James Hopf
5.23.06

The bottom line is that whereas PHEV's make a great deal of sense, the case for using PV cells as the electricity source is still subject to the same (poor) economics that still prevent PV from being used as a power source in general. In fact, it's likely that this situation is even worse.

Whereas the power from a fixed PV array will always be used, it's not clear what will happen when the car is parked and the batteries don't need any more charge. For a capital-intensive source like a PV array, any downtime (i.e., non-utilization) is absolutely deadly to the overall economics. And I haven't even mentioned the likely additional costs associated with incorporating this PV array into a moving vehicle (Len touched on this). The only way to make full use of the array would be to make sure that the vehicle is plugged in when parked, so it can sell any excess power to the utility. And of course there are all the costs associated with administering this myriad of tiny back and forth transactions (enough to make it all not worthwhile).

Simply put, the power from these cells will be measurably more than the current ~25 cent/kW-hr cost of PV, due to the additional engineering challenges and the frequent periods of non-utilization of a fixed-cost resource. The competing method for charging PHEV batteries will be to charge them at night with off-peak utility power. Such power runs at ~3 cents/kW-hr (4 cents at most).

As for benefits, baseload plants don't run on gas or oil either. Nor do they have to pollute (renewables, clean coal, or nuclear).

In terms of the PV cells vs. bigger batteries idea, unless the author is suggesting that the PV cells can produce power at a level that is a significant fraction of energy consumption at highway speed, he must be referring to charging the car up while at work, thus cutting the range requirement in (exactly) half. To this I would say that a better solution is to arrange for the car to be charged from an outlet during the day. Even peak power is far cheaper than PV, even including any costs of a charging infrastructure.

As with all other applications, the cost of PV need to come down by a factor of 3 or 4 before it's ready for prime time. Then, who knows.......

Todd McKissick
5.24.06

Since the consensus seems to be one of a fixed array with the capability to supply on demand (when the cars are actually parked there - day or night), this suggests that the lot itself would work most optimally with storage. This would best be applied as a smaller scale solar thermal system with the heat stored onsite and the generator outputting DC directly from a demand which has a slower response time, such as Stirlings do. Capitol cost and valdalism risk would both be roughly 1/4 of that of a PV array and output would be 3-4 times PV for a given collector area.

Having a dedicated small one at home and another 'leased' area at work could provide all the juice needed for both trips up to quite a bit farther commutes, plus both systems would be collecting energy for the same car all day long. Getting the economics in line with the consumer's current costs is key to market acceptance, early adoption and sustained growth. Win-win-win.

Chris Neil
5.25.06

Mark Kapner indicated above that 7 miles per kWh was too high and that medium-sized electric vehicles achieved only 3 to 4 miles per kWh. I might have responded without thinking this through. One aspect, as I mentioned, is that the Prius is smaller and more efficient than “medium-sided” electric vehicles referenced by Mark.

It also appears that hybrid gas-electric vehicles can achieve greater electric mileage than pure electric vehicles because the electric motor and gas engine are sharing the effort. This conclusion is based on a very small sample of reported data – the single plug-in Prius developed by CalCars. At speeds below 34 miles per hour, this Prius runs exclusively on the electric motor and gets 5 miles per kWh. Above this speed the electric motor and the gas motor share the load. As CalCars explains, at 55 mph, the electric motor may be providing three-quarters of the effort and the gas engine one-quarter. At 75 mph, the electric motor may only be able to provide one-quarter of the load and the gas motor provides three-quarters. Because of this sharing of the load, this vehicle achieves almost 7 miles per kWh in normal driving conditions using both the electric and gas motors. This is better than what most pure electric vehicles have achieved and illustrates that the viability of hybrid vehicles should not be judged based on results from the old, pure electric vehicles.

The electric mileage is an important variable in determining the economics of both plug-in and solar hybrid vehicles. There would be more confidence in these values if there was a larger sample from which to draw the results. This is one of the factors that need to be studied in a R&D effort, and one where it is difficult to understand why the government is not studying this.

On an entirely different subject, several of the comments have been about solar on garages or parking structures instead of on the car. This is an interesting alternative. If batteries are used to store the solar energy so that the vehicle can recharge at night, then this doubles the batteries needed as the vehicle already has a set. Batteries are expensive, and the additional cost of batteries would adversely affect the economics. If a vehicle was charged directly (without batteries), then it would avoid the extra set of batteries and would have similar economics to what I showed in the article.

Another option along this line would be if a building owner was installing a solar system for the building use. Some of this power could be directed to hybrid vehicles when the vehicles were there and to the building or grid needs when the vehicles were not there.

I still believe that solar panels on the vehicle are the alternative that will have the most widespread success, however. Once plug-in hybrids become available, solar panels on them are too obvious an addition to be ignored. Solar hybrids are marketable by the auto industry, and I expect that consumers will be receptive if the price is in line.

Chris Neil

Glenn Andersen
5.27.06

I thank Mr. Neil for his well thought out article. Incorporating solar panels into the construction of the vehicle, whether passenger car of package delivery car, seems to make a lot of sense. Just as in home construction there are new PV roof shingles that replace normal roof shingles, it should be possible to construct PV material that would integrate seamlessly with the upper portion of the vehicle. PV panels integrated into the body of PHEVs will not solve all of our electrical problems, but they may be both necessary and practical at some point.

Having solar panels as part of parking structures and on roofs also makes a lot of sense, I think. It is not a question of which is better overall, but of which is better in a particular application. It might even be practical to plug a solar PHEV into an external solar grid while the vehicle is parked in the sun, and thus charge batteries faster and more completely.

One issue that may be difficult to surmount is the one already mentioned, that of vibration. Will solar panels be able to withstand the vibrations unavoidable in all vehicles? How long of a life span will the panels have when they are subjected to pot holes and speed bumps?

May I say that I think we should be able to solve all of our power generation needs if we can apply our engineering inventiveness and couple that with the political will to do something. If we insist on using small personal vehicles for transportation, then coupling solar panels with PHEVs should eventually be extremely practical.

Ron Larson
5.28.06

Comments on Chris Neill’s solar hybrid article:

1. I think this note was very well done and thank Chris for writing about the concept and for starting a very important dialog. 2. Two articles that directly relate to Chris’ article just appeared in the magazine “Solar Today”. I’ll call them 1. Penney and 2. Letendre. Both can be down loaded (for free) at http://www.solartoday.org/current_issue.htm . But I hope some reading this will avail themselves of a 19% savings right now for Solar Today (normally $29), available through following links when you google “solar panels” (or many other things) and look at the Google ads. (This is a shameless plug – as I am active with Solar Today – but I think these are directly relevant to this dialog) 3. Solar Today’s parent organization, the American Solar Energy Society (ASES www.ases.org), now 51 years old, is holding its annual conference in Denver July 8-13. The subject of solar and hybrids is featured in one plenary. At least two Forums (see full program at www.solar2006.org) will feature PHEVs and solarized versions of same. I think all of the Solar Today authors will be present there, plus more hybrid experts – such as Penney (from NREL) and the concept inventor – Andy Frank. 4. Jim Woolsey (former CIA director) will be a Plenary speaker at Solar2006 on the national security aspects of this, although the main focus of this year’s conference is global warming. I mention this as I haven’t seen enough of warming (or Peak Oil or balance of payments or jobs, etc) as a rationale in this dialog (which has been good. The solar-hybrid connection is a topic that will not be decided on the basis of today’s PV, gas and electricity economics. Something akin to a carbon tax is a necessity if we are going to be able to hold our heads high in the world and talk about thinking ahead. 5. I also think it unfair to have this discussion with today’s PV economics. Neill’s emphasis on needing more R&D is right on. Even without that R&D – mostly thanks to Germany and Japan, the cost have been (until the last few years) coming down wonderfully. 6. A few years ago, PV panels in bulk could be purchased at half the price Neill quotes. That day will return as soon as supply again meets demand. In addition, the industry still is doubling in volume about every two years – with a production cost that probably (no-one talking) is continuing its historic decline of about 20% per doubling. In 10 years (5 doublings), .8 to the 5th power means we could well be in the $1/watt range (assuming true production costs are about $3 today). And no reason to think that is the end of the cost decline 7. In addition, both the laboratory and commercially-available PV conversion efficiency has been going up continually. DARPA has a big contract out to achieve 50% within a few years (www.darpa.mil/ato/solicit/VHESC/index.htm) .Satellite PV systems are now near 40%. (Neill’s economics will look even better in battlefield situations where fuel costs alreadyare way over $4/gallon.). So I think it is great that Neill finds great economics at 150 Watts on a vehicle – but I think we should find 500 Watts can be reasonably expected to be possible in 10 years (some of the increase by using more car panel area ). 8. Penney has computations that a PHEV with 30-40 mile range will be a lot better received by the American people than one with only 10 mile electric range. Battery improvements seem to happening with regularity, but not yet there – again a reason to support Neill’s call for more R&D. 9. Tthere are many electric vehicle and solar enthusiasts who believe that an all-electric vehicle is preferable to a hybrid (both initial and operating cost). They have to think in terms of a range longer than 10 miles – and so the solar roof dialog should not be limited to hybrids. Of course any hybrid should be flex fuel. 10. I liked the term VIPV (akin to BIPV, which also needs R&D), which was new to me, and maybe can cover the topics here better than PHEV. Penney points out that a smart grid with VIPV offers the chance for handling all utility grid emergency backup and ancillary service at much lower cost than at present. 11. The most important message I get from this thread is that much increased Federal R&D, now zero on this topic (like many other promising renewable energy areas), is long overdue. Thanks to Neill for showing how good the economics are – even before we have done almost anything commercially in this area. Fortunately, we have the Germans and Japanese probably already working on this topic – because they know how to plan and think ahead, instead of waiting for global warming and Peak Oil to actually start influencing us big time. Ron

william gilmore
5.30.06

Excellent article, Chris. But I, and most of the other people in my building, park in a parking garage.

Bill Gilmore

P M Dekker
5.30.06

Great article Chris!

Please visit the GENI site at this link: http://www.geni.org/globalenergy/library/technical-articles/generation/solar/iol.co.za/sa-solar-research-eclipses-rest-of-the-world/index.shtml

You will find an article about a South-African flexible thin-film PV coating which I am sure could be licensed and added to the exterior of a vehicle to do the testing needed on vibration, and efficiency, before plug-in to an additional array, either in a job-related parking lot or at a home.

Greg Johanson
5.31.06

Please see solarelectricalvechicles.com for a 215 watt custom molded PV rooftop for a 2004-2007 Pruis. We have done a white paper and hundreds of thousands of dollars of research inclunding patents on the development and design of a PV source of automotive power. The trick here is to remove and replace the 1kW battery with a 6-9kW battery pack to store the energy. Currently a small 6kW AGM lead acid pack is the most cost effective the Li-ion cost effective unit will be ready within a two year lifecycleof the AGM. Issues with warranty and batteries in interior spaces need to be resolved but those are minor issues. With the Li-ion batteries coming in 2008 as standard equiptment Pulg-in and intergated PV in car rooftops works with a two year breakeven without credits.Even faster for the lower mile per gallon Hybrid SUV's . ( See White paper on Web site) How the vaule is determined is in the marketplace and it has to decide hopfully it will go the way of the hybrid and be a wonderful thing with people deciding to make a statment to use renewables rather that a $2 trillion dollars war for 30% of the worlds oil supply which will hold us off for another 10 years while we build our nuclear plants. People will make the differance and they vote with their hard earned dollars.

Jim Friedl
6.1.06

Greg, could not seem to access www.solarelectricalvechicles.com. Do I have that URL correct?

Andrew Simpson
6.1.06

Chris, Thanks for the article. I raced solar cars for 5 years so as a long-time supporter of VIPV I'm always glad to see people getting the word out. However, your vehicle numbers need revision. My expertise is hybrid vehicle simulation and design, and I can assure you that the Prius does not achieve 7mi/kWh. I'm sure your reference is based on either a) unrealistically slow driving or b) some help from the engine. To do your economic comparison correctly you need to assume the Prius operates all-electric in realistic driving, and a more appropriate value is 4mi/kWh, based on 260Wh/mi as quoted by Calcars or the EnergyCS plug-in Prius conversions that can drive 28mi all-electric using 6.4kWh. Even with these changes your comparison will still look favourable relative to BIPV. Also, I'm no expert on solar capacity factors, but 25% sounds best-case to me. Can anyone else comment?

Tom McCarty
6.1.06

Chris, your 3.4 million BPD savings estimate is optimistic, and I'm guessing you live in a sunny location. A car solar array on vehicles in non-sunny climates like Portland or Seattle, or northern climates in the NE with snow coverage part of the year, will significantly reduce output. A 150 watt panel will average out to more like 500 watts per day over a year's time if half the US were running on solar hybrids. Lots of people live and work under trees (shade year-round),

Even at the reduced overall impact, this solar rooftop panels is a good idea for all EVs. No one solution is going to fix our oil dependence, and every little bit counts.

Greg Johanson above had a typo: it's solarelectricalvehicles.com, and it looks be exactly what you're talking about, a 215W array that generates "up to 1200 watt hours per day" on the prius. It is the "first compound convex solar module to be commercially produced", and looks slick. No prices listed on the website that I could find.

Andrew Simpson
6.1.06

Some further thoughts on your suggestion that VIPV could be a substitute for bigger batteries...

In your example, the 150W VIPV system provides 329kWh/yr or 0.90kWh/day at a capital cost of $962. This is $1067 per (kWh/day). Large-format NiMH battery systems and small-format Li-Ion systems are currently available for about $500 per kWh, which gives $500 per (kWh/day) assuming the battery is recharged once a day (overnight). High-volume projected battery costs are around $250/kWh. In the long term, your VIPV prices will need to reduce by 4X to compete with bigger batteries on a purely economic basis.

Luckily there are plenty other good reasons for adding VIPV...

Chris Neil
6.6.06

We have to be clear: solar hybrid vehicles are not for everyone.

First, there has to be sun. Places like Seattle are not the best candidates for solar hybrid vehicles. Locations further north are not going to have the economic returns that southern locations will.

Second, the vehicles have to be parked in the sun all day. Vehicles that are parked in garages need the solar panels to be installed on the garages and not the cars. The above discussions identifed some of the alternatives that can be developed, from solar panels on the vehicles to solar panels on parking lots and garages. Where solar panels are installed on houses, such as in California's million solar rooftops program, a portion could be directed to plug-in hybrid cars parked in the garage during the day.

Advantages of solar on vehicles include factory development, engineering, integration, purchasing, production and marketing.

Chris Neil

Len Gould
6.6.06

What if we looked at the economics, from the POV of eg. a fleet operator of eg. rental autos. A typical auto powerplant can be purchased for approx. $25 / peak kw and will last as long as the useful life of the rest of the machine, say 10 yrs. O&M might amount to 10% of capital / yr. Gasilone can be purchased for approximately $0.082 / kwhr potential, and at eg. 20% engine efficiency provides useful power at approximately $0.411 / kwhr. A typical auto fuel tank can store 584 kwhr (12 gal) and costs essentailly $0.

A comparable electric engine and controls can be purchased for say $20 / peak kw. O&M wil be essentially zero. Batteries might cost $500 / kwhr. Solar cells might cost $3000 / kw and at 1.25 kwhr/kw/day cost $2400 / kwhr / day.

A typical gasoline drivetrain can provide 100 kw peak and perhaps 15 ? kw continuous.

A typical auto might be used 10800 mi/yr at average 45 mph = 240 hrs eg 360 days / yr, 0.66 hr/day or 30 mi / day and burn 2 gal / day gasoline, requiring 48.66 x 2 x 20% effic. = 19.46 kwhr useful energy output to the wheels.

A 150W solar cell array mounted on the rooftop capable of providing 0.90 kwhr/day can provide 4.62% of this usage. Lets double that for the added benefits of hybrid drive, then reduce it to 90% of that for electric storage and drivetrain energy losses, say 8%, and save the owner 8% x 2 gal x $4/gal = $0.64 / day.

The solar cells will cost eg $1000, and the batteries $500. The electric drivetrain perhaps 10 kw x $20 = $200 (way low for hybriding but anyway..) So adding $1700 worth of capital cost to the vehicle saves $0.64 / day. 360 days / yr x 10 yrs x $0.64 = $2,304. Surprisingly close to a reasonable payback IF those $500 batteries will last 10 yrs.

Chris Neil
6.7.06

RE Andrew Simpsom's comment that batteries cost $500/kWh: could you provide more information on this. I know very little about batteries and need to understand more to better understand plug-in hybrids. $500/kWh seems very low compared to the cost of several thousand dollars for adding batteries to hybrids to result in plug-in hybrids, especially for Lithium ion batteries. Also, the units seem wrong - it would seem to me that batteries would be priced in terms of $/kW and not $/kWh.

Thanks,

Chris Neil

Malcolm Rawlingson
6.22.06

While I doubt the current economics of Solar Hybrids the future economics will be better.

While we are stuck in the notion of PV panels it is much more likely that PV coatings incorporated into the vehicle paint will be the likely mode. ie the PV cells will be sprayed on. This technology is already under development and shows promise to 1) Reduce the cost per kw and 2) Increase the efficiency of PV collection. All of the vehicle surface becomes a solar collector. Wind resistance is the same as if a car were simply painted.

We also seem to be stuck in the notion of very heavy batteries that need time to charge up. That notion is also rapidly changing. Lightweight "supercapacitors" now under development would completely change this picture. Power to weight ratios will show significant improvement with these technologies. Charging a supercapacitor will take minutes not hours.

I do not think that the time is all that far off when these newer technologies displace the "hybrid" component of the solar vehicle.

It is just a matter of time. I can recall the day when my four function, three quarter inch thick calculator was top of the line technology. Now you can put a thousand times more computing power on a pinhead.

Rather than try to make solar fit the current technology it needs a leap of thinking to converge all of the various technologies together to make solar electric vehicles a reality.

A few years down the road yet but I suspect but it is coming faster than you think.

Malcolm

Richard Easton
7.12.08

Solar electric on vehicles is today best used on very light vehicles at low speeds. A NEV weighing less than 700 lb. including 200 lb. of AGM lead-acid batteries, and driving at less than 35 mph could use a 4M^2, 480 W array. Five hours a day of insolation typical in Los Angeles, if parked in the sun, would give 2.4 kWh, sufficient to drive a 1.5kW car for 1-1/2 hours at 25 mph. This is enough range. The advantage of VIPV is that you can operate without regular access to a charging socket. If the socket is available, you have a solar assisted PHEV. Not for everyone, but attractive to a small number of eco enthusiasts, especially if the cost of petroleum keeps going up, which is a possibility. Cost of the array might be $2,400 installed. Car might be an additional $5,000. $7,500 is attractive to some.

Solar Hybrid Vehicles

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