Hydro-electric power. Originally thought of as a clean, non-polluting, environmentally friendly source of energy, experience is proving otherwise. Valuable lowlands, which are usually the best farmland, are flooded. Wildlife is displaced. Where anadromous fish runs are involved as in the Columbia River system with its 30 dams, the effect on fish has been disastrous. Only to a small extent is hydro-electric power truly renewable. This is when the "run of the river" without dams is used, as, for example with a Pelton wheel. If reservoirs are involved, in order to provide a dependable base load as is the case of most hydro-electric facilities, hydro-electric power in the longer term is not a truly renewable energy source. All reservoirs eventually fill with sediment. Some reservoirs have already filled, and many others are filling faster than expected. A dam site can be used only once.
We are enjoying the best part of the life of huge dams. In a few hundred years Glen Canyon Dam and Hoover Dam will be concrete waterfalls. And, again, the end product is electricity, not a replacement for the important use of oil derivatives (gasoline, etc.) in transportation equipment.
Wind energy. This energy source is similar to solar in that it is not dependable. It is noisy, and the visual effects are not usually regarded as pleasing. The best inland wind farm sites tend to be where air funnels through passes in the hills which are also commonly flyways for birds. The bird kills have caused the Audubon Society to file suit in some areas to prevent wind energy installations. Locally and even regionally via a grid (e.g. Denmark) wind can be a significant electric power source. But wind is likely to be only a modest help in the total world energy supply, and the end product is electricity, no significant replacement for oil. As with solar energy, the storage problem of large amounts of wind generated electricity is largely unsolved. Wind cannot provide a base load as winds are unreliable.
The french electricity production has been 506 TW.h in 1997 (1 TW.h = 1.000.000.000.000 W.h).
In order to produce this amount (that is 506.000 GW.h) with windmills delivering 20 GW.h per km2, we should "plant" a surface of 506.000 ÷ 20 = 25.000 km2, that is roughly 5% of the country, or the equivalent of the whole surface occupied by cities, roads and parking lots, even if the required land is only partially mobilized and remains available for other uses (agriculture among others).
With machines of 1 MW of nominal power (that are about 80 m high), yielding roughly 2 GWh per year in a favourable zone, it would be necessary to install more than 250.000 to produce the above mentionned 506 TWh http://www.manicore.com/anglais/documentation_a/windmill.html
Wave energy. All sorts of installations have been tried to obtain energy from this source, but with very modest results. Piston arrangements moved up and down by waves which in turn move turbines connected to electric generators have been tried in The Netherlands, but the project was abandoned. Waves are not dependable, and the end product is electricity, and producing it in significant quantities from waves seems a remote prospect.
Tidal power. It takes a high tide and special configuration of the coastline, a narrow estuary which can be dammed, to be a tidal power site of value. Only about nine viable sites have been identified in the world. Two are now in use (Russia and France) and generate some electricity. Damming estuaries would have considerable environmental impact. The Bay of Fundy in eastern Canada has long been considered for a tidal power site, but developing it would have a negative effect on the fisheries and other sea-related economic enterprises. It would also disturb the habits of millions of birds which use the Bay of Fundy area as part of their migration routes. Tidal power is not a significant power source. The end product is electricity.
Ocean thermal energy conversion (OTEC). Within about 25 degrees each side of the equator the surface of the ocean is warm, and the depths are cold to the extent that there is a modest temperature differential. This can be a source of energy, using a low boiling point fluid such as ammonia which at normal atmospheric temperature of 700F (210C) is a gas, colder water can be pumped from the deep ocean to condense the ammonia, and then let it warm up and expand to gas. The resulting gas pressure can power a turbine to turn a generator. But the plant would have to be huge and anchored in the deep open ocean or on a ship, all subject to storms and corrosion, and the amount of water which has to be moved is enormous as the efficiency is very low. How to store and transport the resulting electricity would also be a large problem. OTEC does not appear to have much potential as a significant energy source, and the end product is electricity.
What about free energy? Didn't Nikola Tesla invent some machine that produced free energy? Couldn't we just switch to something like that?
While free energy technologies such as Cold Fusion, Vacuum Energy and Zero Point Energy are extremely fascinating, the unfortunate reality is that they are unlikely to help us cope with the oil depletion for several reasons:
1. We currently get absolutely zero percent of our energy from these sources.
3. We've already had our experiment with "free energy." With an EPR of 100 to 1, oil was so efficient and cheap an energy source that it practically was free.
4. The development of a "free energy" device would just put off the inevitable. The Earth has a carrying capacity. If we are able to substitute a significant portion of our fossil fuel usage with "free energy", the crash would just come at a later time, when we have depleted a different resource. At that point, our population will be even higher. The higher a population is, the further it has to fall when it depletes a key resource. The further it has to fall, the more momentum it picks up on the way down through war and disease. By encouraging continued population growth, so-called "free energy" could actually make our situation worse.
5. Even if a functional free energy prototype came into existence today, it would take at least 25-50 years to retrofit our multi-trillion-dollar infrastructure for such technology.