Mr. Plumb's Solar Spill Solution

By Bill Moore

Posted: 25 Nov 2012

Meet George Plumb: Mitsubishi i driver and solar power user.

George sent me the photo to help illustrate an article he wrote and EV World reprinted here.I think his photo tells an interesting story about the future of transportation.

In a follow-up email I asked asked him about the power output of the solar tracker, a huge array of some 25 panels. I guessed it was somewhere around 5,000 to 7,000 watts. He replied that it produced some 6,000 kWh of electrical power annually as it slow turns to keep its photovoltaic cells pointing toward the sun all day.

I got to thinking, what's that much energy translate into if all it that sunlight were used to power just his Mitsubishi electric car? So, I sat down and worked it out as best I could starting with assuming the car uses 330 watt hours of energy per mile. Those 6,000 kWh would allow George to travel just over 18,000 miles annually.

Not too shabby, but how's that compare to a gasoline car? Assume a Mr. Plumb were driving a gasoline car, instead, that averaged 30 miles per gallon. It would burn, literally, 600 gallons of fuel or the equivalent of 30 barrels of oil (each 42 gallon barrel of crude can produce about 19-20 gallons of gasoline). The gasoline version of the 'i' in Japan is rated at 54.5 mpg, so it would consume 330 gallons of fuel.

Now here's where it gets interesting. Mr. Plumb's solar array represents about 300 square feet of surface that will produce power for at least the next 20 years, or the equivalent of 360,000 miles. It never has to get bigger or take up more space, unlike those 600 gallons of gasoline, which equals 80 cubic feet of liquid, weighing close to two tons. Converted into a more understandable volume, that's a cube just under four and half feet on a side. That's manageable, I suppose, but let's see what happens over the minimum 20 year life span of George's 300 square feet array just in terms of occupied space.

I guess that the volume of space his array physically occupies is roughly 7,500 cubic feet. This is the approximate 625 square feet footprint on the ground multiplied by 12 feet into the air above his head.

Let's see what happens to that annual 600 gallons of gasoline over the same 20 years. That 80 cubic feet cube expands to one more than 11.5 feet on each side holding some 12,000 gallons of gasoline.

But this doesn't include the CO2 that is created. A gallon of gasoline weights 6.3 pounds (2.85 kg). Vaporize and combust it in an internal combustion engine and you produce close to 20 pounds of carbon dioxide, along with a long train of very nasty chemicals and particulates. So, that 12,000 gallons of fuel now becomes 240,000 pounds (108,862 kg) of CO2.

If my math is correct - and please double check me, this wasn't my strength in school - uncompressed, at atmospheric pressure, all that carbon dioxide now occupies a volume roughly just under 150 feet on a side and 15 stories high; and that's just one automobile.

While George's array simply sits there quietly, effortlessly collecting free photons pretty much year-round, never getting any larger or costing much more, oil companies have to invest billions of dollars to find, extract, transport, refine and transport again the petroleum they convert into gasoline, sometimes fowling the land and oceans in the process, and certainly polluting the air we all must breathe. Oh yes, and occasionally killing people in the process in oil rig explosions and refinery fires, not to mention all the people who die prematurely from breathing all that poisoned air.

Looked from that perspective, Mr. Plumb's array looks like a pretty smart investment. In the words of an Internet meme, What do you call a solar spill?

A sunny day.

It's amazing what a photo can tell you, isn't it?

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