The Solar Solution

The key to the quest for "good" heat is right outside; solar energy may be the most viable substitute for fossil fuels.

Humans are slowly waking up to the fact that massive population growth combined with industrialization over the last two centuries is having a major impact on the planet on which we live, including extensive deforestation, conversion of vast tracts of land to monoculture, critical depletion of fisheries, unsustainable drawdown of aquifers, and a significant (36 per cent) increase in the CO2 content of the atmosphere resulting principally from the burning of fossil fuels.

There is concern, particularly, that the latter effect is causing warming of the Earth’s climate, which could result in major environmental changes. There is still some debate about the cause and likely extent of the latter effect, and I do not propose to comment on this further here, except to note that from a geological perspective the Earth’s climate is always changing, and only as recently as the 1960s it was feared we would soon be entering a new Ice Age. That said, as with any pollutant, excessive CO2 emissions cannot be good for the environment, and every effort should be made to reduce or eliminate them where possible.

A less widely held, but nonetheless very serious concern (because of its inevitability) is that the natural resources of this planet are finite, and current and increasing consumption rates will eventually deplete them. This is perhaps critically true and critically important for fossil fuel resources, especially oil and gas, upon which modern society is dependent for most of its energy needs.

There is thus a pressing need, both on resource conservation and environmental grounds, to find a viable, large-scale substitute for fossil fuels. Many alternative fuels or energy sources exist, with nuclear energy being a current favourite in some quarters because of its low output of greenhouse gases. But uranium supplies are quite limited, and would be rapidly depleted (within 10 to 20 years) if large-scale conversion to nuclear energy were to occur. Nuclear fusion would solve many apparent problems because the fuel (hydrogen) is abundant, but achieving sustained fusion reactions remains tantalizingly out of reach, despite several decades of research. Geothermal energy is another attractive possibility, but application on an industrial scale is currently restricted to areas of the Earth with high heat flow, such as the volcanic regions of New Zealand, Japan, and Iceland. This leaves renewable energy sources, which, with the exception of tidal power, can be linked by their derivation of energy from the sun. These sources include direct energy from sunlight (converted to electricity through photovoltaic cells, or simply used to heat water), and indirect sources such as wind and wave energy, and biofuels, which represent conversion of solar energy into kinetic energy of the atmosphere and oceans (used to drive turbines to generate electricity), or into energy-rich molecules via photosynthesis.

The rules of thermodynamics dictate that the conversion of energy to work is not 100 per cent efficient, so a single step conversion of solar energy into electricity is likely to be the most efficient overall process in comparison to, for example, biofuels, which involve intensive agriculture followed by conversion of plant materials to fuel, which is then converted again into useful work though combustion. When the additional diversion of arable land use from food production and water use for irrigation are factored in, biofuels drop further in terms of efficient resource utilization.

Utilizing solar energy also has one major advantage over other energy sources, in that it introduces no new thermal energy into the Earth’s surface environment. In fact, it captures and redirects energy that would otherwise be dissipated as heat (which is the root cause of Earth’s surface warming). In contrast, burning fossil fuels, fissioning uranium, or fusing hydrogen all release large amounts of energy that was stored in the fuel material, a significant proportion of which (as required by the laws of thermodynamics) is lost as waste heat. This heat contributes directly to atmospheric warming, while burning fossil fuels also contributes indirectly via greenhouse gas generation.

The sun delivers about 6,000 times as much energy to Earth’s surface than our current needs, and most of this energy simply heats the environment. The sun is, therefore, both the problem and the potential solution. By efficiently harvesting solar power (either directly, or secondarily from wind and waves), humans could: (a) satisfy their need for energy; (b) eliminate net greenhouse gas emissions from energy-generation; and (c) marginally reduce the sun’s atmospheric heating effect.