Virtually unlimited power is available from our nearest star, the Sun. In just one hour, our planet receives more energy from the sun than the entire world uses during an entire year. Electricity-producing solar panels have only been around for the last 60 years, yet they have completely transformed how we harness solar energy.
In 1839, a nineteen year-old French physicist named Alexandre-Edmond Becquerel discovered the operating principle of the solar cell, known as the photovoltaic effect. It wasn’t until 1876 that this effect materialized into a viable method of producing electricity, through the work of William Grylls Adams. He discovered that by illuminating a junction between selenium and platinum, a photovoltaic effect occurs; electricity could now be produced without moving parts.
Revolutionary as they may have been, the selenium solar cells were not efficient enough to power electrical equipment. That ability occurred in 1953 when a Bell Laboratories employee, Gerald Pearson, had the bright idea of making a solar cell with silicon instead of selenium. The New York Times heralded the discovery as “The beginning of a new era, leading eventually to the realization of harnessing the almost limitless energy of the sun for the uses of civilization.”
Just in time for the space race, the first solar panels made their debut in the satellite industry. Vanguard I, the first solar-powered satellite, celebrated its 53rd birthday this year, setting mileage records and holding the title of being the oldest artificial satellite still in orbit.
Whereas the first solar modules were only efficient enough for space applications, the Sun’s radiation is much stronger. Eventually, satellite research paved the way for Earth-based technology. The 1990s were pivotal years for photovoltaic technology. Innovations in solar cells allowed for greater efficiency while lowering the cost of production. Germany and Japan led the way with long-term solar power incentive programs, helping lower the cost to the public, and spurring the growth of a robust photovoltaic industry in both countries.
California Leads the Nation
In 2006, California, made a major commitment to solar power by passing the California Solar Initiative, a ten-year incentive program with the goal of installing 3000 megawatts of solar panels on the equivalent of one million rooftops. California leads the nation in solar panel installations. This incredible boom has taken place mostly due to California’s Renewable Portfolio Standard, which required that 20 percent of the state’s electricity come from renewable resources by 2010. In 2008 the state decided that it was not moving fast enough to meet these goals and enacted a feed-in tariff, requiring utility companies to buy back excess power produced by homeowners and private photovoltaic installations. That same year the state also increased the Renewable Portfolio Standard to 33 percent by 2020, greatly helping spur growth in the renewable energy industry.
How Solar Panels work
Photovoltaic solar modules are composed of multiple, interconnected solar cells, which effectively trap photon energy between layers of silicon wafers. Negatively charged electrons are then knocked loose from their atoms, allowing them to flow freely through the semiconductors. Separate diodes and P-N junctions prevent reverse currents and reduce loss of power on partially shaded panels.
Since the flow of electrical current is going in one direction, like a battery, the electricity generated is called Direct Current (DC). Sunlight conversion rates are typically in the 5 to 18 percent range, with some laboratory experiments reaching efficiencies as high as 30 percent. Future possibilities include the development of multi-junction solar cells that are capable of harnessing a wider bandwidth of useable light. We are still considered to be in the “early” stages of solar cell technology.
Solar Panel Components
Photovoltaic solar panels are the main building block in a solar power system. Since each solar module produces a limited amount of power, installations usually consist of multiple panels, called an array. The array produces DC, which can be stored in batteries or instantly converted into AC (Alternating Current) required by conventional appliances.
The equipment that converts power from DC to AC is known as a solar inverter. Solar inverters come in a few varieties; they can be modified sine wave or pure sine wave And are further classified based on the type of system they will be used in, whether it is off-grid or grid interconnected. Recently the innovation of micro inverters has greatly simplified installations, making it easy to add panels to an installation. Each solar module is paired with its own micro inverter, which then coverts the power directly at the panel. In off-grid installations the use of a charge controller is necessary to properly manage the power harvest, charge the batteries, and prevent overcharging.
The greatest innovation in charge controllers would have to be the relatively new feature called Maximum Power Point Tracking (MPPT). This method of charging batteries constantly monitors peak power voltage from the array and input voltage on the batteries and adjusts amperage to compensate for the fluctuations. This provides the most efficient means to manage the power harvest. The function of MPPT charge controllers is analogous to the transmission of a car, keeping your charging system in the ‘right gear’. Other components of the solar system include wiring and mounting hardware, and some installations use a tracker that changes the tilt angle and direction of the panels throughout the day.
Types of Solar Panels
Solar panels are classified into three classes: mono-crystalline (single crystal), poly-crystalline (multiple crystals), or amorphous silicon. Mono-crystalline use a continuous, unbroken sample of silicon. This method uses very pure silicon grown in a complex growth process, and then sliced into wafers that compose the individual cells. This was the first method used to manufacture solar cells, and is still highly regarded because of its efficiency ratios.
Poly-crystalline panels are composed of many crystallites of varying size and orientation. These multi-crystalline panels are generally less expensive and slightly less efficient than mono-crystalline modules, yet lately the difference in efficiency is very small. Like their mono-crystalline counterpart, the cells are also cut into wafers that make up the individual cells of a solar panel.
Amorphous solar panels use the non-crystalline, allotropic form of silicon, in which a thin layer of silicon substrate is applied to the back of a plate of glass. These panels are much cheaper and less energy efficient, yet they are more versatile in how they can be used. For example, amorphous solar panels can be manufactured into long sheets of roofing material. Thin Film solar panels also fall into the amorphous category. These cells can be mounted on a flexible backing, making them more suited for mobile applications.
Each of the solar panel types is estimated to last at least twenty-five years. Electricity production declines gradually over decades. The longevity of a solar panel refers to the number of years before the unit starts producing only 80 percent of its original power rating. The industry standard for warranties is 20 to 25 years, although it is not uncommon for panels to produce adequate power for more than 30 years.
Off-Grid versus Grid-Tied
Solar panels are used extensively in rural areas, where access to the grid is non-existent or inaccessible. These installations are called off grid (or independent, stand-alone) solar power systems, and require the use of batteries to store the energy for use at night or on long stretches of overcast weather. The energy stored in the batteries leaves the batteries as DC electricity which can power DC appliances (as in RVs) or be converted to AC for use with conventional appliances. Much like running your own mini utility company, this method gives you full independence from the national grid.
You can eliminate the cost of batteries by going with a system that connects right into your home’s main junction box and use the grid as your power source at night or on long stretches of inclement weather. These installations are known as grid-tied or grid-interconnected systems. This version of solar system enables you to sell any excess power you produce back to the utility companies who have chosen to support net metering. Once you are signed up on a net metering program, your utility company will have a smart meter installed known as a Time of Use Meter, which will actually run backwards when you are producing excess power. It is wise to keep in mind that grid-tied systems without a battery backup are only functional when the grid is operational. Due to anti-islanding features on grid-tied inverters, which protect utility workers from working on a live line, grid-tied systems without a battery back up will not continue to produce power during a power outage regardless of whether you have sunshine or not.
Since solar panels produce DC they must be coupled with a solar inverter to convert the energy from DC to AC. In a grid-tied system this can be done by a large central inverter, or each solar panel can be outfitted with its own micro inverter. Once the power is converted to alternating current and its phase is synchronized with that of the grid, it is then tied in to your main junction box, which is ultimately connected to the national grid.
Q. With solar, will I still have power when the utility power goes out?
A. Only if you buy a system with battery backup. Many companies offer systems both with and without battery backup. Systems with battery backup are somewhat more expensive and less efficient, but they give you the peace of mind of never being without power.
Q. Will the utility company send me a check if I produce more power than I use?
A. No. However, if you produce more power than you use in any given month, the utility will bank that electricity and you can draw down that electricity credit for up to one year.
Q. Isn’t solar still really expensive?
A. NO! Solar is actually far more economical over the long term than buying your power from the utility. After state rebates and tax credits, if you finance the system over a 10-year period, the monthly cost of solar can run about the same as your current electric bill. The big advantage is that this cost will never increase, while the cost of electricity from the utility has increased at an average rate of 6% per year over the last 30 years. Solar is a great investment for the long term.
Q. Do I need to buy a system that will eliminate my electric bill?
A. No. Many people buy systems that only eliminate part of their electric bill. The utilities have adopted a rate structure that increases the cost of electricity as you use more of it. Many people choose a system that will only eliminate the most expensive electricity. This increases the return on your investment.
Q. What size system do I need?
A. A properly designed solar electric system can easily produce all the electricity you need for your home. Systems are available in many different sizes to meet individual needs, and are sized primarily based on your old electric bills, which show how many kilowatt-hours per month you typically use.
Q. Will solar work on any house?
A. No, but it works in many locations. You need an unobstructed south, east or west facing roof top, with limited shade on the area where the solar panels will be installed. Alternatively, you can mount the system on the ground.
Q. How much space does it take on my roof?
A. Solar electric power systems take approximately 100 sq ft of surface area (collector area) per 1 kilowatt of generating capacity. Therefore the average 4-kilowatt system would require about 400 sq ft of area of good southern exposure.
Q. Does it have to go on my roof?
A. No. While roofs are usually good locations because they are high enough to be above any shading from trees, and many times they are facing south, there are many different mounting options for these systems. Detached structures, garages, covered patios, trellises, and ground mounts are a few other installation options.
Q. Will I ever have to pay another electric rate increase if I buy this system?
A. If you opt to purchase a solar electric system that covers your entire electricity usage, you won’t ever have to pay for power again. Investing in a solar electric power system is like buying insurance against future rate hikes; you’ll never get another electric rate increase for the next 30 years and you become your own power company. You’ve bought the PV system, now the fuel (sunshine) is free
Q. How do I get credit from the utility company for solar electricity I produce?
A. With a grid-tied solar electric system you still have your line-coming-in from the utility, just like before, only now you also have a line-out to send your extra electricity back to the utility grid. The Net-Metering law (in place in several States), requires the local utility company to credit you for the amount of solar electricity your system produces and feeds into the grid.
The utility meter measures the difference between the electricity you buy from the utility and the electricity you generate with your solar electric system. When you are making more electricity than you are using, your extra electricity automatically gets metered back out (sold) to the utility grid. You receive credit for this power at the same rate they sell it to you. Net Metering allows you to use the electric utility grid like a bank account. You can put electricity into it that you don’t use immediately and you can withdraw the same amount later on at no net cost to you.
The Net-Metering billing system is a 12-month billing cycle. Because you make more in the summer, and less in the winter, they allow you to credit your summer months into your winter months. Generally the utility will NOT write you a check, net-metering requires the utilities to credit you for up to the amount that you use. The idea is to get a system that just meets your needs and avoid paying any electric bill at all.
A number of factors will determine your eventual costs and savings, from the future price of electricity to how long your system operates. Connecticut residents pay an average of 20 cents per kilowatt-hour for electricity from utilities. Combining the Connecticut rebate and net metering with federal tax incentives and tax-deductible low-interest financing could mean cost savings over the life of your PV system, especially if electricity prices keep climbing. Consult a tax advisor regarding potential tax savings.
Why Go Solar?
Solar Photovoltaic Systems:
- are reliable, pollution-free, and use a renewable source of energy.
- help preserve the Earth’s finite fossil fuel resources and reduce air pollution.
- allow owners to add an energy-producing improvement to their property and over time to recover the cost of the system through reduced electric bills.
- make owners less vulnerable to future increases in the price of electricity.
Solar Photovoltaic System Costs
The average cost of a residential solar photovoltaic system in Connecticut is $6 to $8 per installed watt. The average system size installed under Connecticut Clean Energy Fund (CCEF) rebate program is 7.2 kW and costs between $43,200 and $57,600 with an estimated payback of 8 to 12 years. The CCEF rebate amount will depend on the design efficiency of your system. The rebate generally pays for about 20 percent of the installation cost.
Estimated price per kW is based on the actual average price per kW installed under the CCEF Solar PV Rebate Program in calendar year 2010. Actual price per installation can vary due to installation conditions and other factors.
In addition to the CCEF rebate, a homeowner may claim a 30% federal tax credit for qualified expenditures for the installation of their solar PV system. For more information about state and federal incentives visit www.dsireusa.org.