Wind and solar power depend on the wind and sunlight at the generating plant. While the grid can move power long distances, if it’s shady and calm everywhere at the same time, those sources can’t run your lights, computer, dishwasher, TV or electric water heater.
What’s the probability of that?
Here’s the cloud cover picture for mid-morning on Tuesday, February 19th. (Blue indicates clouds, white means clear.)
On average, about half the US has its sky obscured by clouds to the degree that a solar plant there wouldn’t contribute to the grid.
But plants in the remaining 50% could, to the degree they have sunlight.
That’s solar. What about wind power?
Here’s the wind chart for a similar time. Basically anything that is light blue or brighter has sufficient winds to be contributing to the grid.
Again, the number is about 50% of the land area could contribute in some way, some more than others.
That’s a “contribution”, mind you, not the whole ball of wax. To carry the entire load, we’d need an enormous number of wind and solar plants.
In practice, traditional sources are still needed for the bulk of our energy requirements. They are needed because 1) their power is available 24 hours per day, regardless of wind or sun, and 2) their “power density” is enormous. For the number of square feet they occupy, they are capable of generating huge amounts of power.
The power grid, of course, balances it out, channeling power from the “have more than we need” to “we’re having a calm, cloudy day” areas.
That’s provided there is sufficient power overall, of course, because when you see a brown out, that means your area isn’t getting enough and the grid couldn’t make up the difference. Either the demand has outstripped what can be instantaneously channeled in, or the supplies they can tap can’t keep up.
Figuring out a viable balance between wind, solar, nuclear, water (dams) and fossil fueled power sources is the trick. Each has a different set of constants for initial cost, environmental impact, weather variability and speed of ramp up or ramp down.
Wind and solar have near zero ramp up and ramp down times. As soon as you need it, they can be switched in, or out, of the grid — assuming they can contribute at that moment, of course.
Dams take a little longer to react as water channels are widened or narrowed to admit more or reduce the water flow but if they’ve got water stored up, they can contribute within minutes.
Nuclear and fossil fuels, if they aren’t already spinning, are the slowest to come on-line. Their sources are used to heat water and make steam that ultimately spins turbines that generate the electricity so, to fire up a one of these generator takes time measured in hours. And while you could have them running on stand-by all the time, that would increase their maintenance costs and, ultimately, what you pay at the end of the month.
The power engineers sitting in the power stations are constantly watching the demand and, in coordination with guys (and ladies) sitting in other power stations, they are turning their power generators up and down, buying and selling power with other power stations and, in turn, channeling it across the grid and through substations before ultimately reaching the power meter next to your electrical panel.
Green energy is a nice idea, but it’s not a complete answer.
Energy from solar and wind is available only when conditions are right. And while we could blanket the country with solar cells and wind mills, if we wanted them to carry the full load, the cost would be enormous because 50% of them would be “down” at any given time. We’d need double the number of plants to account for that overall, average down time.
Traditional fuel plants, on the other hand, have very high availability. Indeed, the overall grid has an up-time of 99.97%. It is true, of course, that individual generators go off-line for maintenance but the bottom line is that nuclear, fossil and water (dam) sources have extremely high availability whereas green sources don’t.
Green is good, yes, but only half the time.
Someday when we all have our Mr. Fusion reactors like the one that powered the DeLorean in Back to the Future parts II and III, this will all be moot.
But until then, green can only be an accessory.