The Promise of Solar Energy
All life on earth is supported by the sun. This amazing resource radiates energy and provides us both heat and light by fusing hydrogen into helium at its core. We call this solar radiation. Only about half of this solar radiation makes it to the Earth’s surface. The rest is either absorbed or reflected by clouds and the atmosphere. Still, we receive enough power from the sun to meet the power demands of all mankind — millions of times over. Solar energy—power from the sun—is a vast, inexhaustible, and clean resource.
Sunlight, or solar energy, can be used directly for heating and lighting homes and businesses, for generating electricity, and for hot water heating, solar cooling, and a variety of other commercial and industrial uses. Most critical, given the growing concern over climate change, is the fact that solar electricity generation represents a clean alternative to electricity from fossil fuels, with no air and water pollution, no global warming pollution, no risks of electricity price spikes, and no threats to our public health.
The solar resource is enormous. According to the US Department of Energy, the amount of sunlight that strikes the earth’s surface in an hour and a half is enough to handle the entire world’s energy consumption for a full year. Just 18 days of sunshine on Earth contains the same amount of energy as is stored in all of the planet’s reserves of coal, oil, and natural gas.
And, once a system is in place to harness the solar resource and convert it into useful energy, the fuel is free.
The Growth of Solar Energy
Since 2008, U.S. installations have grown seventeen-fold from 1.2 gigawatts (GW) to an estimated 30 GW today, enough to power the equivalent of 5.7 million average American homes. Since 2010, the average cost of solar PV panels has dropped more than 60% and the cost of a solar electric system has dropped by about 50%. Solar electricity is now considered to be economically competitive with conventional energy sources in several states, including California, Hawaii, Texas, and Minnesota.
The Basics of Solar Energy
So, what are the basics of solar energy systems? First of all, solar energy systems vary depending on application and size. Residential systems are found on rooftops across the United States, and businesses are beginning to install solar panels to offset their energy costs. Utilities, too, are building large solar power plants to provide cleaner energy to all customers connected to the grid.
Regardless of the specifics of a given installation, there are two main types of solar energy technologies—photovoltaic (PV) and concentrating solar power (CSP). Most people are familiar with PV technology because of the solar panels they see more and more on the tops of buildings or ones placed on the International Space Station. When the sun shines onto one of those solar panels, photons from the sunlight are absorbed by the cells in the panel, which creates an electric field across the layers and causes electricity to flow. PV installations may be ground-mounted, rooftop mounted or wall mounted. They may be mounted in a permanent orientation to maximize production and value or they may be mounted on trackers that follow the sun across the sky. Rooftop PV panels make solar power viable in virtually every part of the United States. In a sunny location such as Los Angeles or Phoenix, a five-kilowatt residential system produces an average of 7,000 to 8,000 kilowatt-hours per year, roughly equivalent to the electricity usage of a typical U.S. household.
The second technology is concentrating solar power (also called concentrated solar thermal and CSP). It is used primarily in very large power plants and is not appropriate for residential use. This technology uses mirrors to reflect and concentrate sunlight onto receivers that collect solar energy and convert it to heat. The heat is used to drive a heat engine, usually a steam turbine, that is connected to an electrical power generator which is then used to produce electricity.
Our future clearly depends on our ability to utilize solar and other renewable sources of energy. Expanding technologies, tax incentives, and utility companies adapting to solar customers are all encouraging developments in the field of solar energy. Most important, however, is to remember that averaged over the entire surface of the planet, a square meter collects 4.2 kilowatt-hours of energy every day from the sun, or the approximate energy equivalent of nearly a barrel of oil per year.