V.1. Solar Electricity
(originally published May 28, 2007)
In the first 4 posts in this series, I’ve started an outline of the bright future for an energy delivery system that will meet our increasing demands for power/energy and also tread more lightly on the planet than the current fossil fuel dependent system. This clean energy delivery system turns out to be a familiar one, electricity, but with substantial modifications and upgrades to handle the increased demand and new applications associated with electric transport and heating. In the last post, I reviewed the fossil-fuel-driven technologies that we currently use to generate electricity and highlighted how the efficiency of electricity and electric motors as replacements for combustion engines can diminish the impact of the dirtier technologies and helps magnify the benefit of the less carbon-intensive fossil fuel electricity generation strategies. Though by no means ideal, burning petroleum in a modern efficient power plant to generate electricity that is then used by efficient electric motors, would yield in most situations much more useful work than burning the petroleum in internal combustion engines.
Despite the ability of an electricity-based energy distribution system to generate in Amory Lovins’ terminology, “negawatts” or “negabarrels” through energy efficiency gains, the future success of the electron economy is predicated on the widening use of today’s natural energy flux to generate electricity renewably and cleanly. With the exception of biofuels, natural energy fluxes (water and gravity, wind, sun, waves, tidal, geothermal) are already being used or could fairly easily be harnessed in the near future to generate electricity. Key in the early development of human industry and mercantilism (water- and windmills, sailing vessels), the power of natural energy fluxes was ignored or eclipsed during the last century and a half of industrial development fueled by the stored energy of coal and petroleum. Now renewable sources of energy are again the focus of interest for all parties interested in combating climate change and building a sustainable economy.
The growing number of technological, financial and political developments that favor the use of renewable energy is exciting and promises a bright future for cleaner generation of electricity. Today’s post is the start of a mini-series within this series on the electron economy that will highlight specific renewable technologies. Emphasis will be placed upon where clean renewable energy can practically contribute to the energy needs of industrial and developing countries today and in the next 5-10 years.
While it would be best to review all renewable power generation alternatives together to compare and contrast, it would make a still longer post than my usual mini-dissertations… I am starting with solar, in part arbitrarily and in part because solar is growing fast and uses a generally reliable and widely available primary energy source, the sun. Because of the constancy and timing of its primary energy source, solar will have a crucial role in generating power at times of peak power demand, replacing fossil-fuel plants that generate peak power.
Peak power and Baseline Power
Power engineers and system operators distinguish between baseline and peak power. Typically power demand spikes during the day and afternoon, representing sometimes double or more the baseline power demand during the middle of the night. Baseline power generation sources are “always on” power plants designed to meet the minimum requirements for power throughout the day, month and year. Seasonal variation affects baseline and peak power demand; in countries with widespread air conditioning the summer months represent the yearly peak of power demand for both day and night.
Peak power and baseline or base load power are typically generated by different power generation facilities and technologies. Peak power is often driven by natural gas facilities that can efficiently be turned on and off depending upon demand. Coal and nuclear are typical baseline power generators as they are not so easy to start and stop. Hydroelectricity in combination with pumped storage can generate both peak and baseline power. Usually a mixed portfolio of peak and baseline generation facilities using different primary energy sources powers the grid.
With the exception of hydroelectricity, most renewable energy sources have been faulted in the past by skeptics as being unreliable as either peak or baseline power because system operators have not yet placed a high priority on carbon emissions and sustainability. Increasingly, solar, due to the match between its usual peak power output and the grid’s peak power demand, is being seen as an ideal means to reduce use of carbon-intensive primary power sources during peak periods. This is called “peak-shaving” and forward-looking electric utilities such as Northern California’s Pacific Gas and Electric see solar as way to reduce future capital costs to build peak power generation facilities.
Solar along with wind power is one of the two fastest growing means of generating electricity renewably and has a huge future potential for growth. Solar can be used directly as a heat and light source but here I am addressing its potential to generate electricity. Solar electricity generation can be divided into two categories: photovoltaic and solar thermal electric. Most development and innovation in solar energy is concentrated on photovoltaic applications. With some allowance for the sun’s variability, solar fits well into power operator’s grid management philosophies as it can meet much of the demand for electricity during the mid-day period. Though summer early evening peak use falls outside solar’s maximum output, a good portion of peak demand can be “shaved” during the hottest hours of the day by any one of a number of solar electric options.
Potential of Solar
The Sun’s power is enormous, with small portions of the world’s deserts receiving more than world energy demand. Using 10% efficient solar panels, 100 mile square (10000 square miles) of Nevada could cover all US electric demand. To tap into the sun’s energy effectively in a way that addresses electricity demands of both developed and developing countries would allow us to sustainably power civilization for millennia to come with no carbon emissions. The sun shines only during the day and occasionally hardly at all so, in most scenarios, solar would need to be supplemented by other power sources. Alternatively, in a theoretical purely solar future, the energy of the sun would need to somehow be stored over a period of at least 16 hours if not over a period of weeks to ensure power demand could be met in night-time or overcast conditions.
Photovoltaic (PV) cells are specially designed tiles or sheets that are composed of a combination of semiconductors and conducting material. When photons from light of specific wavelengths hit these tiles, electrons are displaced from specially prepared semiconducting material into the adjacent conductor and an outgoing electric current is induced by the cell. Solar cells can be put together into modules of a wide variety of power outputs, shapes and sizes.
The maximum power output of a cell or panel under ideal test conditions yields a wattage rating that is used to calculate the overall power capacity of an installation of these cells. Actual power and energy produced by the cell depends on the amount of the cell’s maximum power capacity that can be utilized during sunlit hours. Solar panels can be positioned on moveable racks that track the passage of the sun and maximize power output. Tracking systems can pay off for system owners who do not wish or need a flat installation and don’t mind maintaining moving parts. The siting of all PV systems is crucial as yearly insolation (sunshine per unit area) should be maximized and shading of the PV array by trees and surrounding buildings avoided.
Traditionally, PV cells use high purity crystalline silicon (the very common element that makes up sand and quartz) a rock-like ”metal” that is cut into wafers during the cell manufacturing process. For the last few years, there has been a shortage of crystalline silicon, as silicon manufacturers had not anticipated the acceleration in solar PV demand in the early part of this decade. Furthermore, the cyclical nature of the other silicon-based industry, the computing and micro-electronics sectors, had burned the makers of raw silicon who had not wanted to build out facilities without consistent demand.
Newer manufacturing processes are creating microscopically thin (thin-film) photovoltaic materials that promise to be less expensive per watt than traditional solar cells by using less expensive materials, though so far they have tended to produce less electricity per unit area. There are also cells made that use non-silicon semiconductors like CIGS (Copper Indium Gallium Selenide) that are intended to produce a lower cost solar cell with efficiencies in the area of 12%, a quite respectable number. The so-called thin film products have the advantage of generating more electricity under diffuse light conditions that are common through many parts of the world with frequent clouds and haze. The more highly structured crystalline silicon cells are most productive when they are hit by direct sunlight.
Photovoltaic cells, more than most other forms of electricity generation, do not typically lose power or efficiency when they are applied in small arrays. These cells now are ubiquitous and essential in off-grid applications like self-powered calculators, watches, communications satellites, and lights/telephones in remote locations.
Because of its efficiency at smaller scales, photovoltaic more than other technologies, supports the Ecotopian ideal of distributed power generation, even off-grid living when paired with electric storage. Beyond Ecotopia, photovoltaics open up the market for a home or office power industry, as an investment of as little as several thousand dollars or for middle-sized businesses a few million can buy a clean power plant and insulation from fluctuations in energy costs. With net metering and the ability to “spin electric meters backwards”, grid-tied photovoltaic allows for property owners and businesses to generate power without significant operations and maintenance costs and without needing to worry about having enough power, which can be drawn from the grid as needed. As they do not have moving parts, are largely silent, can be sized according to space available, and in some contexts and forms aesthetically neutral or pleasing, PV arrays have been used to power buildings or monetize the rooftop space of buildings both large and small.
The efficiency of solar cells in converting the energy of light ranges from 5% to 40% depending on the type of cell. Most traditional crystalline silicon cells now have an efficiency of somewhere in the range 14-21% while thin film cells are usually rated between 8-12%. While these numbers may seem low when compared with the other efficiency numbers we are dealing with, they are capturing energy that has no cost and has been previously untapped. Recently some very complex and expensive multi-layer “multi-junction” cells, which capture more wavelengths of light and therefore more of the energy of sunlight, have achieved efficiencies in the range 35% to 40%. Solar cells heat up when light strikes them, which represents both lost energy and a potential for performance degradation if cell temperature goes over a certain threshold.
For most grid-tied applications, photovoltaic electricity is still too expensive without a carbon tax, incentives or favorable government subsidy to compete with hydro, nuclear, and fossil fuel energy generation. With feed-in tariffs used in not-so-sunny Germany and sunny Spain, which guarantee profitable returns for the installation of renewable power facilities, expansion of the solar industry in these areas of the world has been explosive. Furthermore, we are currently at what is deemed to be the tail end of a silicon shortage that has further delayed even more rapid growth of this industry. Much of the innovation in the commercial solar industry is focused on reducing the per watt and per watt-hour cost of solar electricity by reducing the need for expensive silicon either by concentrating the sun on smaller pieces of silicon, making thinner sheets of silicon via thin film technology or using non-silicon semiconductors.
One of the more promising technologies in this area is CIGS thin film technology that is claimed to be able to be printed onto thin rolls of specialized material, thereby saving material and energy costs of solar cell production. CIGS contains some exotic, expensive elements (indium and gallium) but would use a lot less material than crystalline silicon to create a comparable photovoltaic effect. Nanosolar, a company backed by venture capital and by Silicon Valley luminaries, has announced that it is building a facility that will make 430 MW of solar cells per year, which will in effect triple the US production of solar panels. Nanosolar claims that its panels will cost many times less than traditional solar panels and can be easily mass-produced. Nanosolar claims that its panels will have an energy payback of less than one month, meaning that in a 20 year lifetime, the Nanosolar panels will yield over 200 times more energy than it required to make them. Crystalline silicon pays back the energy it requires to make them within 3 years, a substantial difference. Competing thin film companies, Miasole and Heliovolt also have announced similar printing technology breakthroughs though have received less attention than Nanosolar.
Solar thermal electric
Solar thermal generation of electricity avoids the cost of silicon or semiconductor materials but is only applicable in large installations sited in areas with daily intense direct sunlight (i.e. deserts). Solar thermal facilities, concentrate sunlight upon a thermal fluid that is heated and either drives a turbine or a heat engine to create rotational energy and drive a dynamo. Solar thermal electric has the advantage over photovoltaic of using, until now, lower cost materials and also the ability to store the collected heat and generate power during the night or evening hours.
There are a number of projects in desert areas of the American Southwest and southern Europe that use various solar thermal technologies to generate megawatts of solar electricity for use by the grid. The typical size of these projects is over 10 MW and they usually take up many acres of land. The future Nevada Solar One is projected to reach 64MW maximum power. The European Commission supported Solar Tres project in Spain, modeled on now de-commissioned Solar One and Solar Two in the Mojave desert, will have a maximum generating capacity of 17 MW and use of field of mirrors covering 142 hectares (350 acres) to concentrate the sun on a thermal fluid. The Solar Tres project claims that they will be able to generate power over 70% of the time in the summer, a very high usage factor for a solar or other renewable energy project.
Criticisms of Solar
The critics of solar energy have tended to focus on its high cost and/or the use of favorable government incentives in Germany or California that have stimulated its growth. If we take note that fossil fuels and nuclear energy have benefited from massive subsidies and have not yet been taxed in the US for their negative effects this criticism is less incisive. If the US government had not built the elaborate US highway system, for instance, fossil fuel would be a lot less valuable as a commodity here.
More important is the fact that current solar technologies generate most of their electricity when the sun shines; so solar alone may be inappropriate for baseline power generation, i.e. replacing always-on fossil fuel power plants. Solar thermal does have the potential to generate during the night as well, so some of this criticism is focused mainly on photovoltaic. Some more speculative designs would store heat during the course of the day and generate power during the night but this remains an unproven alternative. Furthermore, sunshine in most areas is variable, so power generation and power demand would not necessarily match in a pure solar or majority solar grid system without massive energy storage. If one were to use solar exclusively to generate all electric power, there would need to be either thermal, electrochemical, or physical storage of the sun’s power to smoothly meet electricity demand.
Speculative Solar Energy Projects
The current alternatives in solar are not necessarily the limit in solar electric power generation. In Australia, a company called Enviromission is proposing building a solar updraft tower that is over 1500 ft tall. Solar updraft generates electricity by using the thermal difference between heated air at the ground level and the cooler air higher in the atmosphere. The air rushes up the tower turning air turbines that generate electricity. Thermal storage is also possible allowing for power generation during the nighttime. It has not be established whether this design is feasible or desirable. The massive tower and large solar collection area would be a major disruption to the landscape.
An even more speculative idea is the creation of solar power farms in space that “beam” power to the earth. The sun outside the earth’s atmosphere is more intense and these satellites could generate power all the time by remaining away from earth’s shadow. Power beaming via lasers has not only been the subject of sci-fi speculation but also been batted around by NASA.
The Future of Solar in an Electron Economy
Solar, despite its current cost and the above criticisms, has a bright future as it uses an abundant free fuel in a carbon neutral manner to generate electricity during peak electricity usage times (daylight hours). Innovations in the manufacture of solar cells in the next few years appear to be poised to substantially reduce costs which should potentiate explosive growth in the use of solar as a separate power generating unit or integrated into building materials.
With current and soon-to-be introduced solar technologies, there is no reason that industrial societies cannot handle most daytime peak demand using a variety of solar technologies. Solar as a “peak shaving” technology has already demonstrated an effect in Germany and Japan despite a low but still world-leading market penetration and far-from-world-leading strength of solar radiation (insolation). It will soon be part of standard building design that peak electricity production facilities will be integrated into sun-exposed building materials. With increased experience, solar thermal and energy storage technologies may increase the contribution of solar to baseline power and on-demand super-peak power generation.
Solar PV is a natural fit for rural areas of the developing world in tandem with cheaper storage technologies in areas without an electric grid. Private charities, mini- and micro-lending institutions, and government development agencies could lay the framework down for a cleaner energy infrastructure in developing societies that have not yet become addicted to fossil fuels.
I have no problems with government aid that lowers the threshold of adopting solar technologies yet also encourages solar business efficiency and the eventual independence of the solar industry. Many extractive industries have received direct and indirect subsidies that are meant to ensure our “energy security” that has now turned into our energy insecurity. To suddenly now declare the beginning of the libertarian free-market ideal in the energy industry is to disadvantage carbon neutral newcomers in favor of the established carbon-intensive industries. In addition, those who want new renewable technologies to pay back their costs within a short time-frame, are often turning their backs on the past, present and future environmental costs of the heavily subsidized fossil fuel industry.
In my next post, I will discuss wind, another “hot” renewable energy source.