Today, 85% of the United States’ energy mix comes from carbon-rich fossil fuels: oil, natural gas, and coal (1). With demand increasing worldwide, existing oil reserves could peak within 20 years (2), followed by natural gas and coal. Growing fuel use is increasing CO2 and CH4 emissions and the risk of global warming. The United States has responded by sponsoring research into alternative energy (3). However, because research success is not predictable, an effective plan must be based on proven technologies. We propose to switch our economy slowly (over 30 to 50 or more years) to nonfossil energy sources by using proven technologies and available, expandable distribution systems.
Because all available energy technologies have limitations (see table [in original]), a comprehensive plan should include several options:
1. Concentrated solar thermal (CST) energy with storage, a proven technology for electricity generation (4), can provide variable energy, to compensate for fluctuations in demand, for a large fraction of U.S. energy needs.
2. Nuclear energy. New and safer designs, not yet built on a commercial scale, merit construction. The implementation of a large nuclear capacity [1000 gigawatts (GW)] requires study regarding the long-range availability of nuclear fuel and the disposal of accumulated waste. Present nuclear plants are used for base power, only 40% of our electricity needs.
3. Geothermal and hydroelectric plants. However, their total output is limited.
4. Wind. The amount of uncontrollable electricity the grid can accept from this highly variable source is limited.
5. Solar cells. Sunlight is available for only part of the day. Like wind power generators, solar cells lack storage capacity. However, unlike CST, solar cells can be widely distributed.
6. Biomass. The only renewable source of industrial petrochemical feedstocks and fuels for trucks and aviation that cannot be provided by electricity is biomass, but only a limited amount can be grown. Proven technologies for generating syngas by combining carbon oxides (from partial oxidation of biomass) with H2 (from electrolysis) can currently generate three to four times the product yield obtainable by fermentation (5).
A discussion of decarbonization should also include CO2 sequestration, a technology available only for new coal power plants (6). This technology depletes valuable fossil fuel resources and is more expensive than CST and nuclear (4). It is doubtful that it will play a major role in the near to midterm future.
…Conclusions
Except for H2, all the technologies we consider could become competitive with crude oil at $70 per barrel. Our main objective, however, should be to implement the best technology for eliminating dependency on fossil fuels rather than to compete with coal or cheap oil. Investment in demonstration plants and in large-scale implementations will be required.
Approximate cost estimates (4, 7) to replace 70% of our fossil fuel use (including most coal) are about $170 to $200 billion per year over 30 years. At current levels of CO2 emission, a tax of $45 to $50 per ton of CO2 would pay for the whole investment and provide incentives for implementing renewable technologies (5).
We must start now, as our country does not have the resources to complete this switch within a few years. The United States must create long-range incentives (such as a CO2 tax or tax credits) large enough to induce companies and utilities to implement proven technologies and to provide the required infrastructure. A successful U.S. program can set an example for the rest of the world, as many of the key technologies are well suited to developing countries. Once the technologies are established on a large scale and are mass-produced, these costs should go down by a factor of 2, making them competitive and reducing the need for subsidies. The required increase in the electric distribution system poses problems, such as obtaining rights of way for new distribution lines, that only the federal government can handle. There are political hurdles, but we believe they can be overcome.
