A single coronavirus particle mutated and survived the transition from animal carrier to human victim, and so far with verified U.S. cases exceeding one million, there is no known therapy or protective vaccine. An unexpected consequence of mediation efforts is that for the first time in generations, Los Angeles and other urban areas have blue skies by day and visible stars at night. (Palomar is just 126 miles from LAX.)
Besides benefiting astronomers, clearing skies suggest the thick blanket of LA smog has been mitigated by the abrupt reduction of automobile and truck traffic due to Coronavirus lockdowns. No one predicted it would happen so quickly.
Earth’s inhabitants face two enormous threats – a viral plague that could return in successive deadly winters unless we find a vaccine that works, and the less immediate by ultimately far more deadly prospect of global heating.
For those who believe we can build super-insulated housing or otherwise shield ourselves from gradual temperature rise, it is instructive to consider Venus, now at climate-change endpoint. The planet named for the Roman goddess of love, several billion years ago had a mild climate, slightly warmer than earth, with abundant surface water and atmospheric oxygen. Russian and American flybys and unmanned landings on the surface in the 1960s discovered a variegated rocky surface. At a certain point, perhaps in the span of a couple centuries, disaster struck. A high concentration of (presumably) naturally-occurring CO2 initiated a runaway greenhouse effect. A dense carbon dioxide and water vapor blanket formed in the upper atmosphere. Solar radiation passed through, heating the planetary surface, but the radiation that bounced upward could not escape and was reflected back, further heating the surface. The process continued, causing the thermal barrier to thicken and become still denser, further heating the surface.
Currently, Venus is totally uninhabitable and, unlike Mars, will probably never be colonized by humans. The surface temperature today is a uniform 864°F. (462°C.), hotter than the melting point of lead and far hotter than Mercury, which, closer to the sun, nevertheless has polar ice.
Our earth is in the early stages of a similar climate change, not caused by excess water vapor as in Venus, but by a quicker acting combination of CO2, methane and other chemicals, all products of fossil-fuel combustion. This climate change is a greater threat than the deadly virus, because if unchecked it will destroy all earthly animal and plant life.
Many healthcare experts say “opening up” the economy prematurely is a horribly misguided policy. Predictions are that it may lead to new COVID-19 waves that will double or triple the number of deaths in the coming months. Probably a vaccine will be available in the coming months. Meanwhile, this horrid virus has shown us that climate change can be mitigated if we drastically reduce and ultimately eliminate our addiction to fossil fuels. This is absolutely doable.
Automobiles, heavy trucks, railroads and even aircraft can be powered by electricity, which also can heat and cool our buildings. True, electrical generators are powered by oil, gas and coal, which contribute to climate change. But clean energy, primarily wind, solar and hydro, is steadily gaining market share. These approaches are all valid – every wind turbine that is built and placed online contributes to the life and death struggle against global warming. Solar generation seems at present the most reasonable choice for a world-wide solution.
Except when the flexibility of thin-film solar cells is desired, as in photovoltaic building materials, crystalline silicon is the dominant technology. This is in part because the 1.34 eV bandgap of an ideal solar cell is close to that of crystalline silicon, so its efficiency can approach the 30% Shockley-Queisser limit.
There are at present eight principal photovoltaic technologies falling into two general categories, wafer and thin film. Wafer solar cells are crystalline silicon (c-Si) and gallium arsenide (GaAs). Thin-film solar photovoltaic cells are amorphous silicon (a-Si), cadmium telluride (CdTe), copper indium gallium diselenide (CuIGS), perovskite (CH3NH3Pbl3), organic and quantum dot (PbS) (QD).
Over nine of every ten photovoltaic installations currently in place and contemplated are made up of crystalline silicon solar cells. This technology has been around for years and will undoubtedly continue to grow and meet the challenge that lies ahead. Cost per cell has probably hit bottom, but since efficiency is improving rapidly, fewer cells are required for a given application, so that accounts for continuous cost reductions.
Besides the cost of the solar array, which consists of the solar cells, wiring, glass, encapsulation materials and frame, there is what is known as Balance of System, which includes inverters, wiring, installation, grid interconnection and financing. The solar module comprises only one-fifth of the total cost of a typical residential installation.
Gallium arsenide is a compound of the elements gallium and arsenic. In addition to its solar cell uses, it is used in microwave integrated circuits, infrared LEDs and laser diodes. Gallium arsenide solar cells are used in high-efficiency applications such as planetary exploration rovers and orbiting satellites where high temperatures are encountered and cost is not a decisive factor.
Amorphous silicon is a non-crystalline form of silicon that is used in thin-film solar cells. It is deposited in thin layers onto flexible substrates. It is less efficient than crystalline silicon, but works well in low-power applications such as hand calculators. An advantage is that unlike other thin-film technologies, amorphous silicon solar cells do not use toxic heavy metals such cadmium or lead.
Cadmium telluride solar cells are a high-efficiency thin-film technology with a bandgap approximately 1.5 eV, almost identical to the distribution of photons in the solar spectrum. High material cost and toxicity prevent this technology from being fully competitive with crystalline silicon solar cells.
Copper-indium gallium-diselenide in solar cells has a high absorption coefficient and consequently, a thin film is required, making for less use of materials and high flexibility.
Perovskite solar cells, most commonly using a hybrid organic-inorganic lead or tin-halide based material, are cheap to produce and capable of achieving efficiencies of 33%, far greater than other thin-film technologies. Therefore, perovskite solar cell technology may well be the wave of the future. However, it is still a work in progress, due to both long-term and short-term stability problems. This instability relates primarily to moisture and oxygen exposure, thermal stress and mechanical fragility. These vulnerabilities are the subject of intense research and advances in the near future a predicted.
Organic solar cells are based on the photoelectric properties of conductive organic polymers and small organic molecules. They are inexpensive to produce, have high optical coefficients and are environmentally friendly. Disadvantages are low efficiency and substantial photochemical degradation, making them another work in progress.
Another recent technology is the quantum dot solar cell. These circular absorbing disks have bandgaps that are determined by their sizes. Thus, manufacturing a range of sizes, it is possible to convert multiple portions of the solar spectrum into a usable electrical output.