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solar parking recharges electric vehicles

Florida electric vehicle station uses solar energy. The author contends that even with the high cost of solar cells, it costs less to run vehicles on solar energy than on gasoline.

Solar PV Is Cheaper Than Gasoline

Charging an electric vehicle with sunlight costs less than running a vehicle on gasoline

By Stephen Killough

Are solar cells a waste of money? Not if you compare them to gasoline.

Most people consider solar cells to be impractical. They always make comments like solar cells are too expensive, useless at night, ugly, undependable because of clouds, and would require cutting down trees. For the typical home application, these are unfortunately valid complaints, mainly because solar cells have to compete against cheap coal. However, compared with gasoline, solar cells can be quite competitive.

This example deals with one of the largest users of gasoline, people driving to work. Of course I am talking about battery-electric cars recharged by solar cells, but for a different twist I am proposing that the cells be located not at the owners home, but instead in the parking lot where the owner works. Why at work? Because when the sun shines, that’s where the car is. In addition, expansive employee parking lots are not shaded by trees, and shade from cells mounted above the car keep the car from becoming hot on summer days, and can reduce rust and paint fading caused by rain and sunshine. And nobody will accuse you of harming the appearance of their beautiful asphalt lot. The nine-hour stay in the parking lot is compatible with the recharge time for most batteries, and the lower voltage of the cells is safer than regular electrical outlets, especially in wet outdoor locations. The employer would not have to provide anything except anchor points to keep the panels from blowing over.

Even more interesting are the economics. A typical parking space is 9 by 18 feet, or 2.74 by 5.48 meters, for a total of 15 square meters. A typical latitude in the U.S. is 35 degrees, so tilting the panel to face the sun allows more panel space to be mounted above the same parking space, or 18.3 square meters. Typical solar radiation is 1000 watts per square meter, and using high efficiency solar cells like the 20% efficient A300 units from Sunpower, 200 watts can be obtained per square meter. Without a tracking mechanism to continually point the cells toward the sun, the average power over 9 hours is 60% of the peak power, or 120 watts per square meter. All this adds up to around 20,000 watt-hours for a typical 9 hour work day. This is a significant amount of energy that can be collected from one parking space, although this also points out how much land we waste parking our cars, but that’s a story for another day.

The present day cost for solar cells is about $5 per peak watt, so the 3660 peak watt system described here would cost $18,300. Using a mortgage calculator we can calculate a loan for this system using a 20 year loan and 6% interest rate. This comes out to a cost of $131 per month.

An efficient battery electric car, such as an EV1, consumes 170 watt-hours per mile. The 20,000 watt-hours collected by the solar panel would thus power this car for 118 miles per day. A typical month has 22 working days, during which the solar panel could power the car for about 2600 miles. Compare this to a very efficient gasoline powered car that got 40 miles per gallon, traveling 2600 miles and paying $2 per gallon for gas. The monthly gasoline payments would be $130, essentially the same as the solar powered case.

Some of you may think that it would be better for the environment to connect the solar cells to the electric power grid to displace the use of coal. Per basic heating power, gasoline does generate less carbon dioxide than coal because much of the heat comes from the hydrogen in the gasoline molecules. However, coal generating plants are more efficient than internal combustion engines, so the carbon dioxide emissions are similar whether using gasoline in a car or coal in an electric power plant. Therefore solar cells can displace a similar amount of emissions in either case. But my objective is to promote more solar cells, and the way to do this is to sell them in a market where they are already competitive, which is the gasoline market. Furthermore, in many cases solar power does not displace coal, but displaces more expensive fuels like natural gas, even though natural gas is cleaner. Economic wise, it will always be difficult to displace coal because it is so cheap. After all, the commodity can be simply scraped off the ground from huge coal fields in Wyoming, delivered in railroad cars without even requiring a lid to shield it from the weather, sent to the furnace after very little refining, and usually burned without any treatment of the combustion products.

Another reason why solar cells, and even wind power, can me more useful charging electric cars is that battery charging is forgiving of one of the main problems with renewable energy, which is the reduced available power during cloudy and low wind conditions. The electrical grid requires a specific amount of power to match demand at any given instant, whereas battery charging can use fluctuating power levels as long as the total energy produced for the day is adequate. Even if it is not adequate because of an anticipated weak solar day, the batteries can be partially topped off at the employee’s home from the electrical grid at non-peek hours.

Of course this is all academic if no one sells battery-electric cars. However, plug-in hybrid electric cars may soon become available, and their expected battery-only range of 50 to 100 miles will be a good match to the output of the parking space sized panels. And there is always hope that someone will start making battery electric cars again. If your commute takes you only through neighborhoods with 35 mph speed limits, you can drive a battery electric GEM car today. Hopefully GEM or another battery electric car manufacturer will take the next step and upgrade to a highway capable car soon.

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