The sun shines upon the northern Pacific Ocean, and the westerly winds blow over it. The sun evaporates some of the water, and the wind carries it up the slopes of the Cascades, the Sierras, and the Rockies. The water vapor loses the heat it has picked up, and becomes water again, but at the altitude of the mountains. With luck, most of the heat radiates into outer space. So the net effect of all that solar energy is to have purified and lifted the water a few thousand feet.
Notwithstanding the shocking inefficiency of this process, the hydroelectric dams, which the US government and others have caused to be built on various watersheds to take advantage of it, supply over 5% of US electric energy consumption. This is because the collector area is in effect a huge area of ocean. Once built, they emit no toxins, acid gases, nor carcinogenic particulates, and no carbon dioxide. They have the immense virtue of being highly dispatchable, that is, when demand changes suddenly, they can respond swiftly. Lamentably, it has been discovered that they are not entirely benign environmentally.
It is generally unnoticed by the press and the public that the most crucially useful property of hydroelectric generation is that it can respond with extraordinary promptness to changes in electric demand. If there is water behind the dam, and a turbine spinning in synchrony with the power grid frequency, a simple change in the angle of its driving vanes can increase or decrease the rate of flow, and thus the power level supplied.
The people of California were held to ransom - nine billion dollars worth - by certain power company suppliers in 2000, in large part because the snows of the previous winter were inadequate.
If a distributor of electric power cannot schedule enough 'peaking' power to meet a sudden peak demand, the generating plants that are attempting to meet the load may slow down randomly enough to be sending power at the wrong phase of the AC cycle. In other words, they may be sending voltages that cancel each other out. This is obviously worse than being totally shut down. The cost of failure to meet the load is that the distributor's entire grid collapses. It follows that the cost to the distributor of failing to supply the last few megawatts of peak demand, is far more than the customer would pay for it, if promptly offered the choice of "switch off or pay $10/kwh"
There is even a class of hydroelectric plants that do not depend upon rainfall.
It is called "pumped storage".
Off peak, the turbines become electric water pumps, and transfer water from a lower reservoir (possibly a river) to an upper reservoir.
When the demand rises above a certain level, the turbines generate electricity like any hydroelectric plant.
The process is about 75% efficient, which I believe is better than lead-acid batteries, or any other energy storage device.
It is worth while, because base load generators are cheaper to run, but more expensive to build, than those that are designed to be quickly started up and shut down.
The expected lifetime of such a plant is of course far better than any known rechargeable battery.
see Dinorwig — one of the world's most imaginative engineering and environmental projects
But note that "When it was fully commissioned in 1984, … ", Dinorwig did not belong to its present owner. The imaginative engineering came from the Central Electricity Generating Board, a UK government agency, which was 'privatised' by the Thatcher government.
My own brother was the chief environmental officer.
The most remarkable feature is the value of "spinning reserve" supplied by such a plant. One of these turbines, spinning in compressed air, under no load but ready for instant pickup, consumes 2 MW just to do nothing. This is worth while, because it can respond in a fraction of a second to a demand load of over 200 MW. I believe that as many as two (out of six) turbines may at times be kept running to meet such demands.
On the following basis, I compute that 410 square miles of woodland are needed to produce one gigawatt-year of thermal energy per year.
According to a British energy saving website, Short Rotation Coppicing of willow can produce "between 6.5 and 16 dry tonnes per year out of your 2 acres once your SRC is established"
Willow was the recommended crop for a wood burning furnace. An optimistic estimate of productivity, 8 tonnes per acre, gives = 640*8 tonnes per sq mile. = 5120 tonnes/sq mile
Oak Ridge National Laboratory says that wood gives about 15 GJ of energy per tonne.
So per square mile, biofuel productivity of wood is about 76,800 GJ per year.
One kJ = kiloJoule = 1000 Joules. One GJ = gigaJoule = one million kiloJoules.
1 Watt = 1 Joule per second
So one Joule = 1 Joule-second.
1 kW = kilowatt = 1 kiloJoule per second
1 kwh (kilowatt-hour) = 3600 kJ (kiloJoules)
1 kw-year = 3600*24*365 kJ
i.e. One kilowatt-year =31,536,000 kJ
One gigawatt = one million kW.
One gigawatt-year is 31,536,000 GJ
On this basis, 410 square miles of woodland are needed to produce one gigawatt-year of thermal energy per year. It is unlikely that any other biofuel method (Algae ??) can beat this by enough to reduce the needed area by a significant factor.
According to SCE, the agreement, which is subject to California Public Utilities Commission approval, calls for the development of a 500-megawatt solar project approximately 70 miles northeast of Los Angeles. SCE noted that the agreement includes an option to expand the project to 850 megawatts, with Stirling to initially build a one-megawatt test facility using 40 of the company's dish assemblies. Subsequently, a 20,000-dish array would be constructed over a four-year period.Each of the 20,000 dishes would feed sunlight to a Stirling engine, generating 25 kW each.
But the worst part is, that puny as they are, they are big and ugly, and they kill bats and birds.
Remember, a decent sized generator is at least hundreds of megawatts.
To replace one coal plant, you need a gigawatt.
The biggest wind turbines are 600 feet from base to highest blade-tip, and generate 6 MW if the wind speed is about 35 mph, one level less than a gale.
The wind power is proportional to the cube of the windspeed.
So when a 35 mph wind drops 6 mph, the power drops 44%
You have to shut them down completely if it's gusting to 50 mph.
So the wind turbines that Houston, Texas put up after their power supplies failed in Hurricane Katrina, aren't going to do much good in the next hurricane either.
Do you imagine that wind turbines are environmentally benign?
Remember the salmon and steelhead problem of hydroelectric dams in the Pacific Northwest?
It turns out that wind turbines don't seem to bother bats in strong winds. That's because the insects and the bats don't fly much in high winds! But nighttime bat migrations have been seriously affected by the fact that, even without hitting the bat, the turbine blades can cause a drop in pressure, immediately downwind of the blade, enough to burst a bat's alveoli. That sounds like a horrible death, and bats consume night-flying insects.
At the 584-megawatt Altamont Pass wind center there is a serious bird toll. Note that 584-megawatts is less than a 0.6 gigawatts, in the strongest wind the entire project can handle.
When the windspeed is half that for which the turbines are rated, the power available is only one-eighth of the turbine's rating.
The statement that "One megawatt of wind energy can power about 250 to 300 homes with no emissions." is humbug. It is true if the wind is blowing hard enough, and if the 300 homes are using an average of 3.3 kilowatts each. In fairness, the allowance of 4 kW per home implied by the figure 250 is considerably more generous than we usually see in "renewable and solar" puffery.
But it's still meaningless. If 300 "homes" switch on an electric stove plate, say a 750 W load each, then that's 225 kW added to the 1000 kW estimate. This kind of thing happens when a popular TV program goes into commercial.
Wind turbines probably don't bother robins, sparrows, finches, swallows, or hummming birds. But big birds, hawks, eagles, ospreys, probably albatross and pelicans, tend to fly in straight lines, and do not possess the ability to dodge suddenly when a turbine blade comes speeding at them. Smaller hawks and falcons, the ones that hover to watch for prey, are also at risk because they're not accustomed to watching out for huge objects dropping upon them from the sky.