Ever get the impression that everything is more complicated than it seems?  It’s true!

There seems to be some controversy these days about  “green energy” sources such as wind, solar, and hydro, in terms of whether their net impact is in fact “green.”

The thesis seems to be: “If you dig up the dirty laundry behind green renewables, you’ll see that they are just as bad for the environment as fossil fuels.”  In fact, although it is true there is some dirty laundry with any approach to sustaining our modern energy demands, we don’t need to throw out the baby with the bathwater, and belief in a fossil fuel-free future is indeed justified.

An apt analogy might be using rags instead of paper towels to clean things.  True, re-using rags involves laundry detergent and running a washing machine, perhaps even a dryer; but you’ve avoided the tree harvesting, pulp processing, chemical treatments, resultant hazardous waste, packaging, shipping, disposal etc. involved in the many, many paper towels you might need for the same work.

Let’s take solar panels, or photovoltaics (PVs).  Some criticize PVs for requiring lots of energy to produce, for involving the mining of silicon sources, for posing a waste disposal problem.  But let’s examine these criticisms with quantitative tools.

First: Some claim that more energy is needed to produce a PV than it will generate in its lifetime.  This can be addressed with a “life cycle analysis,” or LCA, which calculates how much energy it takes to produce, operate, and dispose of the item in question. It includes such things as the energy required to extract and transport all of the necessary materials, to refine the materials and assemble the panels, to transport and install the arrays, and finally to dispose of or recycle the materials involved.

According to the most recently published LCAs on photovoltaics that we’ve found, a typical 1000W solar array requires about 4000 kWh of energy to produce, install, and decommission. So we need to compare this with the amount of energy that PVs produce here in Maine (among the toughest testing grounds!) in order to tell whether they in fact produce more energy than they consume.

Here in Maine, the 1000W array mentioned above will produce around 1450 kWh of energy in one year, so its energy payback time is a little less than 3 years. If the panel continues to produce electricity for 30 years, it will have produced more than 10 times the energy invested in it. (By the way, that same panel in the sunny southwest US would have an energy payback of about 20 months.)

So we’re clearly producing more energy than we’ve used, and in fact can demonstrate a very respectable payback time.  But another critique is hastily advanced:  “It takes fossil fuels to produce those panels, and therefore the energy they produce is actually “dirty!”

OK, yes, fossil fuels are currently involved in PV manufacture, but let’s look at it quantitatively before we draw conclusions.

To start with, a measure of the impact of an energy source on greenhouse gas production is how much CO2 is released in the production of one kilowatt hour of electrical energy. For a coal fired power plant that number is about 1000 grams of CO2 for every kWh of electricity produced.  For a natural gas plant it is about 400 grams per kWh.

For the solar panel, obviously no CO2 is generated while producing energy–nearly all the CO2 production occurs during its manufacture and installation.  We average this over its useful life and find that it involves between 30 and 90 grams of CO2 per kWh of power. Note that this is somewhere between 11 and 30 times less than coal. Some projections for the future of PVs estimate their CO2 to decrease to between 8 and 14 grams per kWh.

So what about the silicon in the PVs?  Quartz is mined to produce the silicon wafers that make up PVs. To produce a 1000W array, around 17 kg of quartz is required to produce the 4 kg of refined silicon used in the 1000W array.

In Maine this array, with its use of 17 kg of quartz, will produce about 44,000 kWh of electricity over its lifetime.  To produce that much energy from coal would require about 16,000 kg of coal; from oil about 5,000 gallons.

But quartz shouldn’t even be an issue, as the relative abundance of quartz in the earth’s crust is orders of magnitude greater than coal or oil.  Silicon is the second most abundant element (second only to oxygen) in the earth’s crust, so there’s no shortage!

We’ve all heard the adage that “there is no free lunch.”   But in truth, the benefits of photovoltaics in terms of energy production and CO2 avoidance currently outweigh their costs by a long shot. Moreover, ongoing advances in the technology are reducing the cost of solar electricity ever faster.

Let’s face it – the only free energy is the energy you don’t use. So maybe there is no free lunch – but maybe a “reduced” lunch? And hopefully, one day soon, a  CARBON-free lunch!

Paul Stancioff, PhD., is a professor of Physics at the University of Maine Farmington who studies energy economics on the side.  He can be reached at [email protected]  Cynthia Stancioff, MA, Public Administration, is an amateur naturalist and wordsmith.

Comments are not available on this story.