Designs for a New Energy Economy

The greatest challenge for the widespread adoption of renewable energy sources is fitting them into an energy system that was designed around fossil fuels—fuels that have the advantage of being concentrated and easily stored.

To seriously de-carbonize the energy economy, ways must be found to power everything from transportation to the latest electronics on seemingly ephemeral energy sources such as solar energy and wind power.

Electricity is the single most important element of today's energy system, essential for lighting, cooling, electronics, and many industrial processes; its role will only grow as new technologies allow grid electricity to be used for plug-in hybrid cars and to heat and cool homes efficiently through ground-source heat pumps. Electricity also happens to be the output of the largest and most easily replaced contributor to carbon emissions: coal-fired power plants. It is therefore fortuitous that solar, wind, geothermal, ocean, and bioenergy are all able to produce electricity.

From the generator's viewpoint, the main disadvantage of most of these electricity sources is their intermittency—wind and solar, for example, tend to be available only 25-40 percent of the time, depending on the tech

Building a Low-Carbon Economy

Table 6-3. Estimates of Potential Contribution of Renewable Energy Resources

Energy Source

Potential Contribution

Solar water heaters Solar cells Solar power plants Wind power

Biomass

Geothermal heat Wave and ocean thermal energy

Could provide half the world's hot water

Could supply 10 percent of grid electricity in the United States by 2030 Seven states in U.S. Southwest could provide more than 7,000 gigawatts of solar generating capacity—nearly seven times U.S. electric capacity from all sources Could provide 20 percent of world's electricity; offshore wind farms could meet all of European Union's electricity needs

One billion tons could be available for energy conversion in the United States in 2025, replacing one third of current oil use

Could provide 100 gigawatts of generating capacity in the United States alone Long-run contribution could be on same order of magnitude as current world energy use

Source: See endnote 22.

nology and site. Intermittency turns out, however, to be not as big a problem for renewable electricity as utility engineers once anticipated. Power companies are already accustomed to dealing with fluctuating demand, and even conventional power plants are sometimes shut down unexpectedly. So intermittency is not a new concept, though dealing with it does take planning and a willingness to make adjustments in grid operation as penetration levels rise.

Power companies in some regions have already gained experience in operating grids that include a sizable number of wind turbines. Several U.S. utilities have found that when wind turbines meet 10 percent of peak power demand, only minimal adjustments to grid operations are needed. And in areas of northern Europe, where wind contributes over 20 percent of peak power, only minor strengthening of grids and adjustments to the operations of other generators are required. Utilities with substantial hydropower capacity have the ability to quickly ramp up power generation when needed, but most use gas turbines to provide

"peak power" when demand is particularly high (or when other generators are not working.) Strengthening weather forecasting capabilities and interconnecting multiple, dispersed wind farms also enables utilities to avoid most problems related to high levels of dependence on wind power.23

As reliance on coal is reduced in the decades ahead, it is likely that many regions will move well beyond the 20 percent threshold for wind, solar, and other intermittent power sources. To do this, they can pursue some combination of three strategies: add local generating capacity using microturbines and fuel cells, move to digital "smart" grids that are more flexible in their ability to balance demand and supply, and develop the capacity to store energy economically so that it is available when needed.

The digital grid would allow the electricity system to operate much the way the Internet does—an electronically controlled grid that responds in real time to decisions made by users, providing the same kind of efficiency, interconnectivity, and precision as the digital devices that it powers. One advantage

Building a Low-Carbon Economy of such a system is that the electricity meter can be transformed into a consumer gateway that transmits price signals instantaneously and allows unneeded devices to be turned off when prices are high or renewable resources are not as available. Kurt Yeager, who directs the Galvin Electricity Initiative, believes that the introduction of digital grids will increase the ability to achieve higher levels of reliance on intermittent renewable generators.24

The ability to store energy is also developing rapidly. Wind farm operators' desire to qualify for the "capacity credits" earned when power can be generated during peak periods has pushed some to explore storage options, notably in the form of compressed air that can be kept in underground steel pipes or in geological formations. One company plans to mount a compressor under the structure that houses the generating components and send the compressed air down the tower, where it will be stored underground; when electricity is needed, the compressor is reversed, generating electricity. TXU, a large electric power company in Texas, recently canceled eight coal-fired power plants and is planning instead to build a 3,000-megawatt wind farm—larger than any now in operation—that may include compressed air storage.25

The development of less expensive, longer-lived batteries will further ease the way to greater reliance on renewable energy. Portable electronic devices and hybrid electric cars are rapidly increasing demand for advanced batteries made of nickel metal hydride and lithium; as they become less expensive and more widely used, these will allow power companies and consumers to complement distributed micro-solar generation with distributed storage. And the planned introduction of plug-in hybrid cars by General Motors and Toyota in the next few years will allow automobiles to run on sunlight and wind power as well as renew able biofuels, while the cars themselves can be plugged into the grid and used as "peaking plants" when demand is high.26

Flexible, secure electricity grids will be further aided by a new generation of micropower generators that is being developed. Small-scale gas turbines, sterling engines, and fuel cells can easily generate up to a third of the total electricity supply, with the waste heat available for use in the buildings in which they are located. And unlike the large power plants that dominate today's power system, micro-generators will be able to respond quickly to shifts in demand. In the longer run, the natural gas that currently courses through the world's gas pipelines may be replaced by hydrogen or ammonia that is produced from a broad range of renewable resources.

The ability to integrate new energy sources into the existing energy infrastructure will speed the transition and reduce its cost. Already, wind power is being blended into many electric grids, while ethanol is being added to gasoline. In Brazil, most new cars are designed to run on any mixture of ethanol and gasoline. In Germany, local producers have begun to add biogas (methane) to natural gas pipelines. And in Japan, many homeowners are generating electricity with solar cells—sending power to their local grids as well as drawing from them.27

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