I am a solar energy enthusiast. The energetic parts of the universe are clustered around stars. We sit here on this dusty ball of rock and water, heated continually by the Sun. The difference between when we face toward our local star and when we face away from it is — in the most literal sense — day and night. Our lives on Earth are already solar-powered; the plants (and plant-eating animals) we eat get their energy from photosynthesis. The trees and other biomass we have used for energy for much of our history, as well as the fossil fuel reserves we use today are forms of stored solar energy from earlier organisms that died and were trapped under the Earth. Wind energy and tidal energy are perturbations of dynamical systems heated by solar energy. Even the nuclear energy we use extracted from fissionable uranium and plutonium is stored from supernovae in early stars that exploded and pushed the complex elements — including the carbon, nitrogen and oxygen in our bodies — out across the universe.
It is not so much a question of whether we use solar energy, but whether we use direct solar energy, or some derivative form. As our civilisation has advanced and grown, we have had to tap into larger sources to meet the demand for cheap and easily-accessible energy. Our technological sophistication and understanding of basic physics and chemistry has had to grow with our energy hunger to take advantage of different forms of energy; windmills, steam engines, oil refineries, cold water reactors and photovoltaic panels, and so on. In the long run, it is a mathematical certainty that to sustain our civilisation at present levels, or to grow and increase energy consumption we must transition to renewable energy both because quantities of fossil fuels and star fuels like uranium and plutonium on Earth are finite.
All that is necessary in the long run for renewable energy sustainability is that the level of output exceeds the level of input enough to provide a reliable energy source. Even at current solar efficiencies — and thus assuming that the technology won’t improve — photovoltaic solar generates seven times more energy than it takes to generate:
While this is not currently as good as oil or natural gas or coal, it already beats shale oil and biofuels. The beautiful thing about solar energy is that there is so much of it that the technology does not have to be greatly efficient. And prices are falling and efficiencies are improving. While some renewables like wind and hydroelectric are more efficient, they are not abundant enough to even cover the bulk of our energy needs today. In the short run, combined with hydroelectric and wind and nuclear there is a real basis for long-term renewable energy sustainability. To smooth the transition, renewable technology needs investment and development.
In the long run, while obviously renewables still cost a lot more than non-renewables in the marketplace, but we have already established that that cannot last forever. Even the supply of uranium is limited. While we may discover superior technologies like cold fusion, we should be completely prepared for the eventuality that we don’t discover a better technology. While photovoltaic solar remains the largest and most long-term source of available energy — and thus the best hope for the continuation and expansion of sustainable human civilisation — it should receive a bulk of funding and development, and we should assume that in the very long run it should meet the bulk of our energy needs. There are still challenges like solar energy storage, but these challenges are being surmounted with improved battery technologies, and improved distribution technologies such as microgrids.
Of course, if the photovoltaic solar price trend known as the Swanson Effect that has seen solar fall over 99% in cost since the 1970s continues, then solar will reach and exceed parity with other energy sources and be crowned the winner by the market based simply on low cost. After all, solar energy is superabundant compared to the alternatives, so it would not be at all surprising for it to become the cheapest. But even if the Swanson Effect does not play out and solar does not become super-cheap, direct photovoltaic solar is extremely likely to play a major role in continued human civilisation on this planet and elsewhere.