Wednesday, January 16, 2008
Solutions to Global Warming: Part 2
Residential Energy Sources
Some important savings can be made by making greater use of natural energy sources. Home heating and residential water heating could be switched almost entirely to solar and solar-heat-pump systems. Passive solar heating techniques can be built into homes. The remaining residential applications would mainly be cooking, which could almost entirely be converted to electricity. These changes would reduce CO2 emissions by 367 million metric tons, or 6.1% of the total.[source]
Wind power is already providing some electricity at a price which is only a little higher than electricity from fossil-fired power plants.[source] What limits wind power is the need for storage, since neither homes nor businesses can stop functioning when the wind power is unavailable. Currently, only one form of bulk storage is available for energy: existing hydroelectric dams, which account for 6.6% of total US electrical capacity.[source] There are limits to how much storage can be used, since dam operators have to maintain minimum water flows and also have commitments to irrigators, but it's conceivable that wind power could provide a few per cent of the country's energy.
If some sort of bulk energy storage could be developed, that could make wind energy practical. The storage method closest to practicality is pumped storage. In fact, there is a small amount of pumped storage in use now. A rough calculation shows, however, that there aren't enough places to install pumped storage for wind power to become the main electricity source.
A different strategy would be to have fossil-fired power plants standing by to back up wind power. Since wind turbines have a load factor of 25 to 35%, that would seriously hamper the effort to reduce greenhouse-gas emissions because the fossil-fired plants would have to operate a large portion of the time.[source] But the existing fossil-fired plants will be around for some decades while replacement capacity is built. In the meantime, they can be used as backup for wind turbines and other renewable sources. So, in the short term, wind power can be a major power source until replacement sources are constructed and the wind turbines wear out.
Solar photovoltaic systems are presently too expensive to compete with other energy sources, but over the years can be expected to become cheaper.[source] They already are becoming popular in remote locations where connecting to the electrical grid is impractical. If costs continue to fall, solar energy can complement wind power but the unavailability of bulk storage will apply to solar energy as well.
Geothermal energy presently supplies 0.34% of the energy used in the US.[source] There are two types of geothermal energy: wet and dry. The wet type is being exploited about as much as it can be. There is a lot more available in dry form; unfortunately, there aren't any practical ways of extracting it.
Biofuels represent a possibility. To use them unblended as motor fuels would require new engine designs, but that will be unavoidable with any change from petroleum-based fuels. Currently, the best estimate is that it takes 0.75 gallons of fuel to produce the energy-equivalent of 1 gallon of conventional fuel. That's only true if credit is given for the value of the leftover material as animal feed; once the demand for animal feed is satisfied, the payoff ratio won't be as good. It is believed that the fuel input could be reduced to as little as 0.4 gallons with advanced technology that allows agricultural waste to be used as the raw material.[source] Agricultural waste is what gardeners call mulch; it hasn't been determined what would be the adverse consequences of diverting mulch away from fields. Research is being done on different biomass plants and chemical processes that could give better results.
The International Energy Agency estimates[source] fossil-fuel use at 388 exajoules per year worldwide, which may be expected to double or triple in this century. It also estimates that to supply 300 exajoules/year, a goal attainable with moderate effort, would require 7% of Earth's landmass, requiring forest clearing and insecticides and synthetic fertilizers. In comparison, 13.3% of the landmass is arable, including 4.7% already under cultivation.[source] The IEA concludes that biofuels can be an important means of reducing greenhouse-gas emissions on a global scale. For the US and Europe, though, given their limited free agricultural land and their high dependence on liquid fuels, the main effect would be switching from oil-rich suppliers to land-rich ones. Presumably, the benefit of reducing global warming would justify the higher cost.
Many other systems have been proposed: wave engines, tidal engines, and ocean-thermal-gradient engines, to mention only a few. People have suggested micro-hydroelectric power, installing small turbines on thousands of creeks and streams, but never have addressed the legal obstacles to extinguishing hundreds of species. Fusion research continues apace, but no projections are made regarding when it could become practical. Schemes have been suggested for energy storage, such as compressing air in caves, or building mammoth flywheels. All of these ideas are exactly where they were over thirty years ago: nowhere.
But one idea has real potential: hydrogen. Presently, hydrogen use is hampered mainly by the low energy efficiency (around 30%) of converting water to hydrogen at ordinary temperatures.[source] There are more efficient processes, but they require high temperatures and are poorly suited to renewable energy sources. Alternatively, research is going on to improve the efficiency of photosynthetic production, currently around 2%.[source] If the efficiency could be improved, then there is a real future for hydrogen. Storage technology is ahead of production technology, and fuel cells are already proven. Hydrogen could be a fuel substitute and could well be the main element in future energy delivery.
However, there is a trap in something this attractive. For over thirty years, Americans have chosen to stay with fossil fuels based on the promise that something new and better was almost ready to displace the use of fossil fuels. The new and better something never materialized, with the result that fossil-fuel use now is threatening the planet's climate. Is it safe to continue this way, or should we look for other solutions that are available now?
There are two time-frames to consider. With present technology, renewable energy can displace a big part of fossil-fired electric power, but will lose that capability as the backup fossil-fired plants wear out. In the long run, the world must focus on non-fossil energy sources. Unless some form of bulk energy storage is invented, renewable sources will only be able to provide about ten per cent of the energy the US uses. Conservation, if pursued aggressively, could hold energy consumption to its current level.
The next few articles will take a look at nuclear energy.