Resources for Green Living in the Chesapeake Bay Area

Few power-generation technologies have as little impact on the environment as photovoltaics. As it quietly generates electricity from light, PV produces no air pollution or hazardous waste. It doesn't require liquid or gaseous fuels to be transported or combusted. And because its energy source - sunlight - is free and abundant, PV systems can guarantee access to electric power. http://www1.eere.energy.gov/solar/pv_important.html

What do we mean by photovoltaics? First used in about 1890, the word has two parts: photo, derived from the Greek word for light, and volt, relating to electricity pioneer Alessandro Volta. So, photovoltaics could literally be translated as light-electricity. And that's what photovoltaic (PV) materials and devices do — they convert light energy into electrical energy (Photoelectric Effect), as French physicist Edmond Becquerel discovered as early as 1839. http://www1.eere.energy.gov/solar/pdfs/solar_timeline.pdf

Commonly known as solar cells, individual PV cells are electricity-producing devices made of semiconductor materials. PV cells come in many sizes and shapes — from smaller than a postage stamp to several inches across. They are often connected together to form PV modules that may be up to several feet long and a few feet wide. Modules, in turn, can be combined and connected to form PV arrays of different sizes and power output.
The size of an array depends on several factors, such as the amount of sunlight available in a particular location and the needs of the consumer. The modules of the array make up the major part of a PV system, which can also include electrical connections, mounting hardware, power-conditioning equipment, and batteries that store solar energy for use when the sun isn't shining. http://www1.eere.energy.gov/solar/pv_physics.html

The energy used to heat up domestic hot water makes up about 20% of the average home’s energy costs. One way to lower the energy needed for these systems is to install a solar hot water heating system in lieu of an electric or gas water heater. I like these systems because they use the energy of the sun, the most abundant source available on Earth, and gives off no CO2 emissions at the home or at the electrical power plant. The system is almost energy independent, except for a small circulating pump to push a water/glycol mixture through the solar heating panels. Below is a picture of some evacuated tube solar heating panels installed on a sloped residential roof:

These systems cost around four to six thousand dollars installed. They work in series with your existing hot water heater, be it electric or gas. The existing hot water heater will act as a back-up system to the solar system in case of multiple days of shade or bad weather. The components of a solar heating system consist of a glycol loop of piping with a pump that circulates the solution through the solar panels and into a heat exchanger. The domestic hot water circulates across the other side of the heat exchanger to keep the two liquids independent. The solar heating system will have its own water tank, basically the same size as your existing hot water heater. The discharge of the solar heating tank will be plumbed to the inlet of the existing water heater, and the rest of your system remains the same. Some manufacturers of solar heating systems in the United States that are available to the public are Thermomax and Heliodyne. Below is a diagram of the solar heating portion of the system.

Most solar heating system manufacturers provide the pump, the controller, and the panels as a packaged system which can be installed by most plumbing contractors. The cost for these systems are between four to six thousand dollars, with a payback for a family of four around ten years. The solar heaters themselves are extremely durable, and most manufacturers will warranty them for 15 to 20 years. These systems can also be installed as pool heaters.

Solar heating harnesses the power of the sun to provide solar thermal energy for solar hot water, solar space heating, and solar pool heaters. A solar heating system saves energy, reduces utility costs, and produces clean energy.

The efficiency and reliability of solar heating systems have increased dramatically, making them attractive options in the home or business. But there is still room for improvement. The U.S. Department of Energy (DOE) and its partners are working to design even more cost-effective solar heating systems and to improve the durability of materials used in those systems. This research is helping make these systems more accessible to the average consumer and helping individuals reduce their utility bills and the nation reduce its consumption of fossil fuels.
To help more Americans benefit from these systems, the U.S. Energy Policy Act implemented a 30% tax credit for consumers who install solar water heating systems. To be eligible for this tax credit, the systems must be certified by the Department of Energy's non-profit partner, the Solar Rating & Certification Corporation (SRCC). Alternatively, residents of Florida and Hawaii can use their state certification programs. http://www1.eere.energy.gov/solar/solar_heating.html

Photovoltaic power systems (PV) have steadily grown in popularity over the years as the price of the photovoltaic panels significantly decreased since their inception. Unfortunately the economic benefit of installed PV systems is typically non-existent in most states without government or utility grants to help with first time costs. Some grants do exist in Maryland for photovoltaic installation, and that information can be found here: http://www.dsireusa.org/. Even considering a substantial grant for the first time cost, such as $1 per watt installed, the economic payback on a system will be in the neighborhood of fifty years. The other engineering examples given in this essay have paybacks of 5-10 years.

That being said, PV still represents one of the most sustainable engineering technologies available; taking the suns energy and putting it directly to use as electricity. The system is off the grid and has a zero carbon footprint. The reasons for installing the system are clearly not economic, but they are real just the same: to lower CO2 emissions, as a demonstration project, to encourage further development, therefore, further economic justification, or as a way to get “off the grid” in far flung places. We see more and more photovoltaic installations in the United States despite the high costs (usually $7-$8 per watt installed), even in the dense urban setting of Philadelphia where I do business. The demand remains very real, which is encouraging.

Below is a diagram of how the typical residential photovoltaic system looks:

The solar modules convert the suns energy into DC power. This DC power is run through an inverter to covert it to AC power, the kind used in your home. The inverter feeds a spare breaker in the electrical panel where other connected loads can draw the energy provided from the sun. The panel remains connected to the utility grid through a utility meter the same way as a typical home, which feeds electricity to the panel when the solar modules are not producing enough energy. On days where the solar modules produce more energy than the home is consuming, this electricity is transferred “backwards” through the meter and feeds into the grid. If you were standing in front of a meter as this was happening, you would see the numbers on the meter counting down instead of up, lowering your electric bill by decreasing your KWh used.

As you can see the effects of this installation are very real and easily observed. As the cost of the installation decreases, as is clearly the trend, and the economic benefit becomes more real, we will see a proliferation of these installations not only in higher education and forward thinking private businesses, but on residential rooftops throughout the country.