Solar Power for Electric Vehicles

Harry Zervos | Oct 21, 2010

Most of the companies developing photovoltaics have been obsessed with reaching grid parity meaning competitiveness with conventional grid electricity generation which is often highly subsidized. More recently, it has been realized that the market for disposable photovoltaics on consumer goods is at least as large and even the potential on electric vehicles by land, water and air, could be an enticing billion square meters a year, comparable to that for buildings.

To realize all of this, we need to progress from heavy, rigid structures, that are expensive to ship and install, to conformal, thin, lightweight photovoltaics. Then the market will segment into some that are very efficient because area is at a premium, some which is transparent so it even fits over windows and lighting and other versions, probably including stretchable and edible ones. On vehicles, life needs to be 15 years -- approaching the 20 years of building photovoltaics. That is unless it is so low cost and easy to fit that it can be replaced during a service call. Rethinking the on-road vehicle is long overdue and biomimetics -- copying nature -- tells us that we have many options for pleated, unfolding and unfurling solar cells on vehicles as well, particularly when they are parked. Indeed, solar fabric on seats and as internal body and floor covering will also generate useful amounts of electricity even though it is behind glass. It will also be possible to make a "rag top" convertible generate electricity from its fabric.

Lightweight flexible photovoltaics are already available from several companies and it is good for evolution that they use different materials and assembly techniques including roll to roll printing. The technologies include organic ink, Dye Sensitised Solar cells DSSC, which employ organic and inorganic materials, amorphous silicon and fourthly copper indium gallium diselenide CIGS.

So far, they tend to be about one tenth of the weight of conventional crystalline silicon solar cells but that is offset by having about one tenth of the efficiency. They are not yet cheap -- a flexible panel similar to the one on a solar bag that charges your mobile phone currently costs about $30. They cannot be tightly rolled or folded and life is usually only 2-5 years. None are yet transparent so there is work to be done because most of them are potentially transparent, low cost, tightly rollable and foldable and even lighter in weight. Indeed, new photovoltaic technologies such as the so called quantum dots can also achieve all of this and harvesting of infrared and even ultraviolet has even been demonstrated with some options.

Rethinking Vehicle Design

Already some photovoltaic options are very good at converting polarized light reflected from snow or glass, low level light and light at narrow angles of incidence. It is therefore reasonable for the electric vehicle industry to plan for solar conversion from the whole vehicle and unfurled panels, this providing enough energy for more that the "hotel facilities", such as air conditioning, currently served by heavy, square "afterthought" panels seen on the roof of a car today. These first appeared at least 20 years ago and the Toyota Prius, the best selling hybrid car at last has a solar panel as an option. It can drive a fan to keep the car cool when parked.

One car manufacturer has been looking at solar curtains in the car. An opaque long life, flexible technology such a CIGS printed reel to reel can be made fairly transparent by applying it to say a sunroof glass in thin lines. Spray deposition of some chemistries is proving possible (work at NREL on spray painting organic solar cells and at the University of Texas at Austin in spray deposition of CIGS) and Fiat is working with Solarprint, an Irish PV company dedicated to the development of DSSCs, developing options for components on and in vehicles. There are also new ways of using rigid technologies. For example, tinted glass can contain photovoltaics that have 15 years life, removing the need for expensive encapsulants.

Developments are already happening in photovoltaics technologies that are making new types of components possible and the prospect of integration into a vehicle manufacturing line is not considered science fiction anymore. It is important to note though that similar advances have to be made in the deposition of all other layers of a PV cell, not just the active material. Electrodes,(back electrode and transparent ones) barrier layers for encapsulation, assuring electrical connections are issues that need to be tackled if one is to imagine a complete vehicle generating electricity from the sun from every part of its surface. This might push feasibility further into the future but does not in any way prohibit the development of intermediate applications that help achieve the incremental advances necessary for this final target to be achieved.

A few very lightweight vehicles use solar power entirely already, including some rickshaws, golf cars and record-breaking road vehicles in very sunny countries. Add to that the huge unmanned surveillance aircraft in the upper atmosphere and the recent record breaking 24 hour flight of the all electric Solar Impulse plane. Some autonomous underwater vehicles AUVs of the type called gliders, cruise the oceans for years, coming to the surface to charge their batteries from solar and wave energy. At ETH Zurich in Switzerland they are designing hand launched all solar aircraft for civil use and larger, unfolding unmanned solar aircraft to traverse Mars. A solar powered airship has been proposed. Pure electric manned aircraft burst onto the scene in the last year as suitably light and powerful traction batteries became available. Some offer solar panels on the wings as an extra plus solar panels by or on the hanger where they are stored. A sport plane in the open for a week before it is used for a few hours at the weekend can garner an appreciable amount of traction power from the sun.

Sanyo Electric Co. Ltd and Ryobi Group put solar panels on a bus for the latter's 100th anniversary. The "Sorabi" SOLARVE is described in the Japanese language press release as a `futuristic hybrid bus' with two different types of high-efficiency but relatively heavy Sanyo solar-electric panels mounted on its roof -- 420W HIT cells, and 378W Amorton cells generating 798W. This can drive accessories but not make a significant contribution to range.

Related Topics


"This can drive accessories but not make a significant contribution to range."

Say Nissan Leaf. 240 watt-hours per km. 2 sq meters solar cells at 20% efficiency, 1 kw per sq meter insolation, 200 watts electricity per sq meter. Each hour that the cells were properly oriented to bright sunlight, the solar cells would provide enough electricity to take the vehicle 2 x 200 / 240 = 1.6 km.

Does that make any sense? The solar collection needs to be installed at a fixed location and grid-connected.

This has been looked at before. I agree with Len.

The bottom line is: Yes, solar panels do make sense to put on vehicles economically, but no they cannot contribute significantly to vehicle range -- so they may very well not be worth the bother.

An interesting take on this topic (in a general sense) are EVs in Hawaii. How do you charge them? Since 75% of the grid power in Hawaii comes from petroleum, why not just burn the fuel (in the vehicles) directly? The solution is apparently to use RE sources (wind and solar) to charge EVs. They are competitive with the expensive electricity there and could avoid some gasoline use on the islands.

Solar carport charging stations in the State of Tennessee is an innovative utilisation of solar energy to charge electric vehicles.
“With electric vehicles (EVs) starting to hit major consumer markets this year, solar carports can help keep your car charged up and running. With a roof covered in solar panels, energy from the sun (as opposed to electricity from the grid) can power the batteries in electric cars so your ride is even greener. In other words, no gasoline and no fossil-fuel-based electricity!
The state of Tennessee hopes to take the lead in renewable EV charging with the installation of a new solar carport charging station. The solar energy generated by the charging station in Pulaski can be used to re-charge up to 12 electric cars at a time. Extra solar electricity will be fed into the regional grid, operated by Tennessee Valley Authority.
Its the first of several solar carports in Tennessee. Two more charging stations will be installed in Pulaski and Knoxville. All three facilities will be installed by Outpost Solar through a partnership between the state, USDA, Pulaski Electric System and the Tennessee Valley Authority.
Outside of Tennessee, you can find solar carports at the Google Headquarters in California (see video above). Smaller, residential-size solar carports are also available for purchase. Expect the market for solar carports to jump as EVs start hitting the roads in greater numbers.
Time to start thinking about solar carports for your residence or business!”(Source: Solar Carports Charge Electric Vehicles, Solar Panels – Green Power,August 2010).
Dr.A.Jagadeesh Nellore(AP),India

"Doing the numbers", such as Len did in his comment, will divide the dreams from the practically implementable solutions.

Automobiles parked in the sunlight for an 8-10 hour workday, in a sunny climate, MIGHT benefit from having a couple of square meters of solar panel integration, to top off batteries inside the car. But wouldn't it be far cheaper if the roof of a parking lot or garage included significant area of solar panels, with charging plug-ins routed down to the parking spaces. Now you're not talking 2m^2 per car, but 10-20 m^2. This can be a revenue source for the lot owner, and/or a perk provided for employees & shoppers.

Solar carports at home may have to have either an intermediate storage system, or implement swappable battery packages for cars. They might also provide the electricity required for a hydrogen generating station, which could enable a hydrogen powered vehicle to be refueled when it returns to home each evening.
(Same goes for the large parking lot application as outlined above.)

The areas available to, and costs for, "portable" solar cells simply do not permit use in energy intensive applications, such as manned vehicle uses. Charging your cell phone or laptop is one thing, but generating many kwh of stored energy is just "not in the numbers".


What good would solar car ports be Monday through Friday when the cars and their batteries will be away at the work location? Unless there is an energy storage system, like batteries connected to the solar panels, it is hard to see the value in this scheme.

Herschel Specter


The short answer is that you tie the solar car ports to the grid and make use of them in that way.

You can play around with these scenarios all you want, but at the end of the day, you are faced with three realities, one cold and two, um, warm ones? The cold one is that solar electricity is expensive, and intermittent. Probably 2-3X compared with conventional sources. And did I say intermittent?

One warm reality is that gasoline is expensive. Assuming $3 gasoline, minus taxes that's $2.50 per gallon. A gallon holds about 35 kW-hrs of energy. Assume 20% conversion efficiency in the engine, so about 7 kw-hrs gets to the wheels for every gallon of gasoline used. That equals about 35 cents per kW-hr. Way more expensive than electricity costs and way more expensive than even solar electricity costs.

True, you have to account for the costs of the battery packs, but that's probably not more than about 10 cents per kW-hr, so you are still left with about 25 cents per kW-hr in net fuel price differential between an EV/PHEV and a gasoline vehicle.

Warm reality number two is that EVs/PHEVs need not be charged at any particular time, at least not precisely. As a result, they can function as sheddable load which makes them attractive conditional sinks for power on the grid. This SHOULD make them less expensive to charge, overall. (I'm not a huge proponent of vehicle-to-grid, though I understand an economic case can be made for them.)

So charging PHEVs is probably a good way to displace oil use. Where the electricity comes from is secondary. It comes from the GRID, which may or may not have solar panels tied into it.

People don't know it, but they have an oil well on their roof.
I agree with Jim Beyer that grid-connected solar car ports make a lot of sense when compared to gasoline. Here in central Washington State it only takes 400 square feet of solar modules on your garage to produce as much energy as a Nissan Leaf would use driving 15,000 miles per year.
I would further argue that solar will eventually be installed on gasoline/electric hybrids or all-electric vehicles because, even though vehicle-integrated solar may provide only a fraction of the vehicle's total mileage, solar will be incrementally less expensive than gasoline. Solar cells on the car’s roof and hood may only add two to five miles per day to the driving range of a hybrid, all-electric or PHEV, but that is still a 5% to 10% reduction in gasoline usage, which works out to an annual savings of $50 to $100 per year.

Last time I checked, it rains a lot in Washington State. In fact, I use to live in Olympia. There are a lot of big fir trees there as well. Installing photovoltaics on your roof or carport for charging your vehicle (or providing power to your house) is economically nonsensical, particularly when considering the low cost of power (compliments Bonneville Power Authority) in the Pacific Northwest.

Ditto for Tennessee, with a low incidence of solar energy and reasonably priced power from TVA. The idea of using taxpayer money for such a scheme pretty much epitomizes the just plain irresponsible approach of the "green" movement and their enablers, the Democratic Party.

If you are looking to reduce transportation costs while reducing emissions, get a hybrid or turbo-diesel.

I dunno Michael.

I appreciate that the greens/dems are not good with the numbers in terms of the economics of these things to date. On the other hand, dependence on the declining resource that is foreign oil is also an eventual death sentence to our economy. Unfortunately, I don't think we can any longer pawn that problem off on the next generation. Oil is peaking right about now.

You cite Washington State and the TVA region, but those are literally the only two places in the country with low cost, emissions-free electricity. I'm not sure those are appropriate straw men, overall.