PV Gap

Cindy Said:

What solar energy projects are cost effective?

We Answered:

From a mico-economic (personal) perspective conservation often holds the most pay back dollars. Photovoltaic systems in the lab are now around 40% efficient with projections up to around 60%. What you can currently buy is around 14% efficient. This does not mean the same thing as a fueled system where operating costs are the primary consideration, but it does have an impact on how much of a system you will have to buy. Photovoltaics are still dependent upon subsidies and tax credits.

Solar water heaters depend upon a different principal. Solar thermal collectors are from 60 to 80% efficient now. The vacuum tube collectors are effective in cloudy weather and in cold environments. There are several reasons for this. Getting heat from the sun goes back thousands of years and there were solar thermal panels and water heaters in California in the early part of the 20th century. So it is a much older technology. Also the inefficient part of the photovoltaic systems are partially because of reflected energy and energy that is transformed to heat. A solar hot water system to get around 80% of required domestic hot water has a pay back period of 2 to 3 years. After this the savings go in the bank. This makes solar hot water systems cost effective.

Other solar thermal applications would include more south facing windows and a solar room (greenhouse.)

Solar thermal is also being used on a large scale to produce electricity. Pilot plants have three main designs:

Power towers where heliostats reflect sunlight onto a target. This system seems to work well as a hybrid with a gas fired power plant to take over when needed.

A hyperbolic dish reflector eliminates the need for much of the moving hardware of the above needed to track the sun.

A trough collector system eliminates even more of the tracking hardware. There are several other options.1

But I haven't seen any numbers that indicate that these facilities are competitive without the subsidies that nuclear, petrochemicals or coal receives There are advocates that propose to strip all subsidies but this would collapse the nuclear industry2 and who knows where the others would fall.

Wind energy is very close to par. I have seen some numbers around 6 cents per kwh with the goal being around 5 cents per kwh. Again not counting the "true cost of coal." But the problem with any renewable source regardless of its efficiency or cost effectiveness is that it will only work with some kind of a back up system To the extent that this is "the grid" and someone can be producing when someone is not the cost of duplication will have to be compared to the cost of overbuilding and the increase in efficiency over the current systems production which is around 30%.

To the extent that we have to build more storage into our grid, be it batteries, flywheels, pumped hydro, CAES or something else, it will become more efficient but will also have a price tag associated with it. This is progress.3

But just where do you want to stop considering the financial issues? Solar would be a "domestic" product where, for the US both nuclear fuel and petrochemicals are imports. Protecting the foreign supplies is our very expensive military. India and China are huge nations that want more industrialization. This will be dependent upon energy. Will we use our military to make sure neither of these countries become industrialized? If competition makes our supplies dwindle our costly military may be of little help to us. The silent subsidy of our military may then be more of a liability than a benefit to our energy policy.

Coal fuels slightly less than 50% of our electrical grid. But there are costs in pollution from this activity that go beyond what we pay for each kwh of electricity. I lost a slate roof to acid rain. If I were to add the cost of replacing that roof to my electric bills it would appear that coal can be quite expensive. This is not to speak of health issues or their cost and associated suffering.4