Background information on solar thermal and photovoltaics. Print Window Close Window From the dawn of mankind, the sun has served as both a religious and psychological symbol of strength, energy, vitality and almost everything labeled good by the multi-cultural populations that have lived their lives under its rays. Let the sun shine and the world's energy problems are theoretically solved. According to the American Solar Energy Society, a minute's worth of sunshine provides enough energy to power the earth's needs for a year. So then, what's the problem? Translating the laws of physics into practical applications often turns out to be as challenging a task as is the task of discovering those same laws. The pace of research and development in the area of solar energy, slow compared to the current energy needs of the global population, need not necessarily cast an umbrella's shadow, let alone rain on the renewable energy parade. Advances in solar energy thinking and technology have moved at the proverbial hare's pace during the past fifty years covering topics that range from cooking to space exploration. With a little patience, any child can learn to convert a pizza box into a solar oven. NASA scientists, with a bit more patience and research and development funds, have developed solar panels as a primary energy source for their space vehicles. It's also probably a safe bet to suggest they ate a good deal of pizza during the process. The language of solar energy may sound Greek to any layman's ears, however, all the terms used to describe the various technologies in use today deal with two very simple sun observations. Walk outside on a sunny day and you will notice that the sun provides heat and light. These basic observations provide the starting point for differentiating between the two different types of solar energy technologies employed today, solar thermal and photovoltaics (PV). Solar Thermal Technologies Solar thermal technologies work on some very simple principles, with albedo one of the easiest to understand. Albedo is a scientific term describing the amount of light, and consequently heat, a material reflects or absorbs. Generally speaking, lighter colored materials have a higher albedo, meaning they reflect a higher percentage of light and heat away from them. Wearing white or light colored clothes in the summer is not only fashionable, it's also practical. Darker colored materials, on the other hand, absorb more light and consequently heat. Solar thermal technologies pick up on the idea of albedo and use black colored plates as their core heat collecting device. Solar thermal technologies also fall into either a passive or active category and are usually distinguished by their having an additional level of activity connected to the heating process. The simplest example of passive solar heating is opening the draperies during the winter to let the sun in and heat the room. Passive solar thermal technologies move up the complexity ladder in instances that require a concentrated collection of sun heat, such as for heating water. Commonly a solar water heating system, for pools, residential and industrial use, consists of the collector, which gathers the sun's heat and transfers it to water passing thought the plumbing system on its way to a storage container. Solar water heating systems save money by reducing the electricity costs associated with traditional water heating. They are also environmentally friendly. Saving electricity in most cases means avoiding the types of emissions associated with electricity production. Active solar thermal technologies run the gamut of simple to complex machinery. Solar water heating systems unable to operate on basic water pressure and gravity principles, require the use of electric or other pumps to move the cold water through the collector. Larger scale solar thermal projects for electricity generation promise to be the next wave of sun heated water practices and operate on principle similar to their small scale counterparts. Even the non-scientist understands that water heated to very high temperatures turns to steam. The latest generation of solar heating technology consists of collectors (mirrors or parabolic dishes) that can either move and track or gather an adequate amount of sun to transform water to steam. The steam serves as a force to move electricity generating turbines. The environmental benefits are obvious. Emissions from steam generated electricity share little in common with their cousins, emissions from fossil fueled generated electricity plants, the primary causes of air pollution such as smog, acid rain and climate change. Photovoltaics (PV) The term photovoltaics (PV) derives from two roots, photo or photons, particles of light, and voltage, a measure of electricity. In brief, photovoltaics means electricity generated from light. The discovery of photovoltaic properties of some substances rivals the discovery of fire by an ancestor of man when he rubbed two sticks or stones together one day and created a spark. Back in 1839, Edmund Necquerel, a French physicist from a family of scientists, (his son won a Noble Prize in physics), saw electricity sparks fly, so to speak, in his laboratory while conducting an experiment. Modern day photovoltaic science traces back to 1950s with the discovery of the process for producing relatively pure silicon crystals, the material most commonly used to produce solar cells. In 1954, the Bell Telephone Laboratories produced the first silicon based photovoltaic cell, and since that time, the technology has advanced in leaps and bounds. Three different technological approaches drive current research and development practices today characterized primarily by the type of crystal used as solar cell's core electricity generating medium: single crystal, multicrystal, and thin film technology also known as amorphous crystals. Efficiency (the amount of sunlight received that can be converted to electricity) is the sine qua non of solar cell research and development and over the course of the past decade, efficiency improvements have been close to stunning. Whereas in 1997 solar cell efficiency levels of 17% or so were record setting, today's solar cell efficiency levels are reaching 32% in the laboratory, with whispers of the possibility of surpassing the 40% mark in the near future. Because solar cell efficiency levels have traditionally been relatively low, meaning the cost of producing solar energy has been comparatively high, widespread adoption of solar cells has been limited to their use as power devices for watches, calculators and other small electronic devices. Solar panels (collections of solar cells tied together) are gaining increasing acceptance as residential electricity generation tools, especially in areas remote from established electric power grids. The most recent projections from the Energy Information Agency (EIA) suggest continued growth in small scale solar projects through the year 2020, but little growth in large scale adoption of the technology. Forecasting, of course, is always a risky business. EIA forecasts for stable oil and natural gas prices through 2000-2001, for example, needed to be adjusted in light of actual events. Continued improvements in solar cell research offers the hope that large scale solar energy projects will move to the mainstream sooner rather than later. |