You are my sunshine...

Okay, so ethanol is not going to free us from fossil fuels, but we can turn to solar and wind power. Right?

Of course we can, if we're willing to pay a whole lot more for electricity than we do now, and don't mind the lights going off from time to time. When we talk about solar power or wind power we're talking about electricity (although I do like the idea of a wind mill on the roof of my Honda powering the engine - the faster I drove the more electricity I'd produce :). Today, both solar and wind power produce kilowatts that are much more expensive than kilowatts from coal or nuclear power, and a whole lot less reliable. Given these economics, neither wind nor solar is going to supplant coal or nuclear power any time soon.

Our US electrical grid is made up of a mix of coal-burning plants (we burn about 1 billion tons of coal a year to produce electricity), nuclear power plants (there are about 100 nuclear plants operating today in the US), and a smattering of natural gas, diesel and hydro plants. This is an on-demand system, there's no storage. We generate electricity as we need it, and use every last (electron) drop as it passes through the wires. Because demand fluctuates, peaking during hot summer afternoons in warmer climes, and on blustery winter evenings in the colder climes, production has to be able to ramp up flexibly. To meet peak demands we shovel more coal into the boilers (and turn on standby plants that only run when demand is highest because they are most costly to run).

The economic beauty of an on-demand system like this is that we only have to pay for enough production capacity to meet our daily needs, plus a little extra. Most of the time we can run our most efficient (and least expensive) plants, and turn on the handful of more expensive systems only when demand peaks (and prices) are highest. This design, unfortunately, does not match up well with solar and wind power systems.

There are three factors in electricity costs - power plant installation, base operation and peak demand generation. The cost per installed kilowatt of a coal plant is about $1,300. The cost of an installed solar kilowatt is about $7,000. For wind power the cost of an installed kilowatt is about $1,000. The cost of an installed kilowatt for a nuclear plant is about $3,000. It would seem that wind is a great deal now (and it can be, under certain conditions), and that solar is not too far behind nuclear power.

As far as operating costs go, wind and solar systems are almost free. After all, we don't have to shovel coal into our wind turbines. But given the intermittency of wind (ideal winds for power generation are steady at 15-25 MPH, but actual wind speed fluctuates considerably, and even the windiest sites can have calm spells that last for days) and sun (half our 24 hour day is dark, and cloud cover significantly reduces PV panel output) it turns out that an installed solar or wind plant runs at 20-25% of potential capacity. Comparing this to coal and nuclear plants, which run steadily at 60-80% of their installed capacity, we can see that the installed kilowatt cost by itself is misleading.

And the economics of solar and wind power only get worse when one has to design a system to meet peak demand. In the Northeast our demand peaks vary by time of day and time of year. We see one peak in the late afternoon to early evening in the fall and winter, when families are returning home, turning on lights, cooking dinner, etc. We see another peak increasingly in the summer in the middle of the afternoon on hot sticky days, when homes and businesses are cranking the air conditioning. It's during these peaks that operators turn the dial up to 11 on coal and nuclear plants, and fire up idle diesel and natural gas plants that are too expensive to run during times of low demand. Wind and solar power can't "ramp up", they produce when the weather accommodates. Solar and wind can't replace coal or nuclear plants unless and until they can reliably meet peak demand needs. Such a peak demand alternative power system would not only have enough capacity to meet our needs on sunny and windy days, but also enough storage and spare capacity to meet our needs during a 3-day spell of calm, or during the nights and cloudy spells.

Think of it this way. I can install a solar or wind plant for my home which is also connected to the grid, and live with the vagaries of a system that only produces during sunny or windy days (during which times I'd happily watch it run my electrical meter backward) because I know that the grid (backed by the nuclear plant in Seabrook and the coal plant in Bow) is there when I need electricity at night, or during cloudy or calm spells. But if I want to live "off the grid" I'd need to install a solar or wind system that not only meets my needs during sunny or windy days, but that has enough excess production capacity to charge a large (expensive) battery bank that could get me through a 3-4 day "dry" spell. Scaling this up, a wind or solar system that could replace a 1 megawatt coal or nuclear plant now becomes a 3-4 megawatt installed plant with a 3-4 megawatt bank of batteries.

Wind power (if we are willing to pay quite a bit more for electricity), and even solar power (if we are willing to pay a WHOLE LOT more for electricity), has a role to play in our power grid today, but that role is limited. Denmark has invested much more heavily in wind power than the US or other European countries. Today wind generators meet about 15% of Denmark's overall electricity needs. Danes are willing to pay more for green power, but even so they'll soon stop installing wind generators. They've learned that no matter how many wind plants they install, wind can at best meet about 20% of their electricity needs. Installing additional wind generators above that 20% threshold provides no additional usable output. In Denmark nuclear and fossil fuel plants will continue to provide the other 80%.

I'm not saying that we should stop pushing for wind and solar power. Some of the apparent economic advantage of coal power stems from our refusal to pay for the externalities - such as the environmental destruction and health costs due to coal mining and smokestack releases of heavy metals and greenhouse gases. But we have to be realistic about the limitations of wind and solar power, and ask ourselves "how much are we willing to pay for green electricity?".