independence-house-2011This week is Independence Day Week in the United States. In honor of independence, we are republishing several stories and blog entries that emphasize the spirit and feeling of independence embodied by, and delivered by, solar-charged driving. In fact, current solar-charged drivers overwhelmingly say the most satisfying part of plugging an electric car into a home solar system is the fueling independence it delivers. No more suckling at the you-know-what of Big Oil, no more sending your hard-earned money off to some unfriendly, undemocratic government halfway around the world, just the freedom of filling up your car with electrons produced locally via your very own home solar gas station!

gas-controversypeder-norby-guestI power my BMW Electric Mini-E with solar energy. I drive on sunshine.

My overall home solar system size is 7.5kw and that system powers both our home and car. It is a balanced energy use and energy generation solution: We generate 11,700 kWh a year and we use 11,700 kWh per year.

In the U.S., each kW of a solar PV system costs approximately $3,700 when part of an average sized residential system. The space required for that one kW is about 60 square feet, or about half the size of a small bedroom.

In California and other sunshine states, that one kW will generate approximately 1,550 kWh of electricity annually. A typical solar PV warranty is 25 years. And you can generate 38,750 kWh over those 25 years.

There is a slight degradation of annual generation over that time and one solar inverter replacement will most likely be needed as well. However the system will last a far longer than the 25 years of warranty (think of a pane of glass and how long that last), so we are going to call those data points a push.

Cost of driving solar-charged EV 7,750 miles per year
Electric cars are evolving quickly, electric cars such as the Mini-E are returning between 3.5 and 4.25 miles per kWh. The upcoming BMW i3  will be pushing the five miles per kWh threshold. For this analysis, as it looks at the next 25 years of driving, we will assume a 5 miles/kWh efficiency.

Five miles per kWh multiplied by 38,750 kWh equals 193,750 miles driven for the energy cost of $3,700. This works out to 7,750 miles per year, and a cost of $148 per year, per kW of generation. Home solar also provides absolute certainty of energy cost, as the sun never increases its price.

Cost of driving gas car 7,750 miles per year
Using the U.S. fleet average of 22 mpg, driving 7,750 miles a year, a gasoline car will consume 352 gallons of gas, or $1,442 for the first year at $4 per gallon.

An electric car driving on solar will require 60 square feet of home rooftop PV space and require a one-time investment of $3,700 to drive 7,750 miles per year for the next 25 years. In other words, solar-charging an EV will cost you one-tenth as much as it will cost you to fuel a gasoline car!

And, no you’re not reading this wrong, the cost of a 1 kW solar PV system is the same or less than buying gasoline for three years ($3,700 total cost for solar vs. $1,422 annual cost for gasoline.).

The next 22 years of driving the EV are on the “house of the rising sun” 🙂

Let’s be generous and assume that the U.S. gasoline car fleet averages 40 mpg during the next 25 years beginning at 22 mpg of today and ending at 60 mpg in 25 years. That would be an average of 194 gallons annually and 4,850 gallons of fuel for the next 25 years.

With a modest multiplier of three percent annually for the increase in gas prices, you’re looking at $35,000 in fuel cost for the next 25 years.

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The uncertainty of oil prices
If gas prices and cars maintain their current 22 mpg fleet average, that number would approach $80,000. If crazy stuff happens in the oil supplying regions and  global consumption increases dramatically, your guess is as good as mine. This is the uncertainty of energy costs.

To summarize: At a fleet average of 40 mpg, a gasoline car will use 4,850 gallons of gasoline and will cost $35,000 to drive, assuming a 7,750 miles per year average for the next 25 years

An electric car driving on solar will require 60 square feet of home rooftop PV space and require a one-time investment of $3,700 to drive 7,750 miles per year for the next 25 years. In other words, solar-charging an EV will cost you one-tenth as much as it will cost you to fuel a gasoline car!

Peder Norby is a long-time solar-charged driver from Carlsbad, Calif. SolarChargedDriving.Com would like to thank him for allowing us to re-publish this column, which originally ran on Peder’s Electric Mini Blog.

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