Thousands of homeowners are using solar power to heat their homes and their water, as well as provide natural lighting.
Solar Electric System Basics
A stand-alone solar electric system consists of 4 basic parts. Photovoltaic (solar electric) panels, charge controller, batteries and inverter. The photovoltaic panels make DC electricity, which is fed to the charge controller. The controller feeds the current to the batteries at a regulated rate. The batteries store electricity for when it is needed and then sends it to an inverter, which converts DC to AC current. This output can be wired into your standard circuit breaker box. In addition to the basic components, there are various switches and fuses to make the system safe and to protect the electronic components from the high currents possible from batteries. The National Electric Code puts requirements on wiring these systems.
Photo is Greek for Light and Voltaic is after Allesandro Volta pioneer in the study of electricity. Thus photovoltaic means *light to electricity*. The photovoltaics (PV) convert sunlight directly to direct current (DC) electricity by use of a semiconductor. The most common type is made from the chemical element silicon. Silicon is one of the most common substances on Earth. For example, sand and glass are made of silicon dioxide. Our entire electronic age is built upon silicon. Almost all integrated circuits (chips) are made of silicon. What is a semiconductor? The essential miracle of a semiconductor p-n junction is that an electric field is maintained purely by virtue of the material. In other words, no external voltage need be applied. For a solar cell, this means that when light hits the cell, electrons are bumped from atoms and drawn to one side of the junction by the internal electric field. Current flows. You get electricity.
Silicon PV comes in several varieties. Shell PV panels are made with single-crystal silicon. The cells are cut from a single crystal of silicon. Single crystals give the highest efficiency of conversion of light to electricity, 15 to 17%. Solarex panels are made of polycrystalline silicon. These are close in efficiency but polycrystalline cells are easier to make because small crystals take less time to grow than big ones. Astropower PV panels are made of microcrystalline silicon, which again is easier to make. A very different type of cell is made of amorphous silicon, that is completely non-crystalline. Efficiencies of these cells is about 6%, much lower than crystalline. However, amorphous silicon is a thin film material which can be made in ultra thin ( micrometers) on thin backing. It can be made into flexible products such as the Unisolar PV shingles and PV Laminates.
There is one other type of PV which is common in the aerospace industry, gallium arsenide. These cells can be 30% efficient (some even higher) and are resistant to radiation damage (in the environment of low orbit). They are still very expensive and used only on spacecraft.
Because the solar cell is a solid state device, it can last for decades. The only part of a panel which can degrade is the material which encapsulates the relatively fragile cells. Some of these encapsulants will brown if subjected to multiplied sunlight (such as by a focusing mirror), or after many decades of regular exposure. The panels are not fragile. They are subjected to hail tests (1 inch hail at 50 miles per hour) at the factory. All indications are that solar panels installed today, will still be working perfectly in 30 years. Most panels have a 25 year warranty from the manufacturer.
The charge controller is a solid state electronic device which measures the charge state of the batteries and turns the current from the PV on if the batteries need charging or off if they don’t. This protects the batteries from over-charging which can shorten their life.
Stand-alone solar electric systems use lead acid batteries to store power for cloudy weather or for nighttime. Lead acid batteries can be made to withstand deep-cycling, that is discharging them to near-empty. They do not have any *memory* like NiCds do. They can even be re-invigorated if they are abused, for example, sulfation can be reversed, more water can be added, etc. If charged properly, good lead acid batteries will last for years. The larger deep cycle batteries last 10 to 15 years.
An inverter is another electronic device which takes the direct current from the batteries and changes it to alternating current (AC). Most households run on AC because AC wiring is cheaper and somewhat safer than DC wiring. Inverters are made to convert from 12,24, 48, 225, or 400 volts DC to 120 or 240 AC. The AC output of inverters is either a modified sine wave or true sine wave. Get a true-sine-wave inverter for whole-house systems and net metering systems.
Since solar electric systems are basically DC, they have wiring requirements different form AC systems.
To highlight some of these:
All disconnects and fuses have to be rated for DC
- Large wires between the panels and controller are required to avoid voltage loss if the panels are far from the controller. For example, a 24 volt system of panels 150 feet from the controller will require wire 0.6 inches in diameter, costing $1.1/foot.
- A large switch with fuses is required between the inverter and batteries to protect the inverter. Batteries are capable of putting out thousands of amps.
How to Choose a Solar Power System
Check with your utility company before installing. There is a range of federal and local incentives. Your utility company will know the ins and outs. Most solar panels are guaranteed for 25 years with inverters warranted for 10. They are extremely reliable with no moving parts, so for 15 years, you can expect to have no electric bill. Your power company is required to buy back any excess electricity that you generate at full retail rate. To do that your system has to convert the generated DC to alternating current, AC, the sort of power we use in our homes. The box that does this is called an inverter, which is essential to hook you up to the power grid. On a bright sunny day when your family is away, your meter will actually run backwards as you get paid for the power that your system is generating.
Hire a reputable contractor. Your utility can provide a list. Bring in your electric bills over the past year and discuss any changes in your consumption that you foresee. Get an estimate and begin rebate and incentive paperwork. When choosing your equipment, make sure that it qualifies for incentives. On the federal level, you can get tax credits for solar hot water – unless it is used to heat a swimming pool. You want a system that is big enough to cover your projected electric needs for the life of the system. Some homes simply won’t get enough light or have enough roof area to do that. In those cases, you should consider much more efficient panels to use.
Get an estimate and arrange financing. Most systems can be installed in a single day. If you finance your system with a home equity loan, the interest is tax deductible.
Sizing A PV Array:
1. Determine what your KWh electric consumption is. Then match PV production to your electric consumption.
For example, if you consume 600 kilowatt-hours per month (KWh/month) and want to produce 100% of your
electricity with a PV system with no battery backup. Do this equation to calculate; 600 KWh/month x 12
months equals 7,200 KWh/year or approximately 20 KWh/day.
Most of the U.S. has 3.5 to 5 Sun Hours of solar input. This means that a 1 kilowatt AC PV system in a 4.5 Sun Hour region will produce 4.5 kilowatt-hours per day. 20 kWh/day divided by 4.5 sun hours equals 4.4 KW AC.
Go to "PVWATTS" at: http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/
and enter your location, 4.4 KW, your roof tilt and orientation. See your monthly and annual estimated PV production for a 4.4 KW system or any other size system.
2. Match your PV array size to your roof space. You need full sun on your solar array all day (from at least 9am to 4pm). Trees, chimneys, vents and other buildings can block the sun or make array installation difficult. Square footage examples; 225 sq. ft. array (Qty of 32 - 70 Watt modules) / 140 sq. ft. array (Qty of 20 - 75 Watt modules).
3. Match your PV system cost to your budget. PV modules are about half of the total system cost. The other equipment you may need depending on your system configuration are mounting hardware, combiner boxes, disconnect switches, power center, charge controller, inverter, battery bank and wiring.
*Find out what State / Provincial or Federal Government incentives are available in your area.
Different mounts available
Mounts for your solar photovoltaic system can come in all shapes and sizes; some are stand-alone, others are designed for special situations, such as pole mounts designed to track the sun in the sky for optimal output. We will cover the most common types of solar panel mounts, and you will discover what mount or solar panel rack is best for your photovoltaic system. Considerations that will be addressed include size, affordablility, utility, and convienience.
Types of Solar Panel Mounts
Solar Panel Mounts are available in three primary categories: flush mounts, roof/ground (or universal) mounts, and pole mounts. Each type of solar panel mount has its own merits and disadvantages, and if you are installing a solar panel mount you should weight in these factors when making your final descision.
Flush mounts are the cheapest and most simple solar panel mounting solution available, and are achieved by placing a metal end bracket on each side of the solar panel, elevating it several inches from the surface. Flush Mounts are typically used with small solar arrays on rooftops and RVs, because the structural design of a flush mount cannot support large solar panels. When installing a flush mount with your solar panel, be sure that you have ample clearance between the surface of the roof and the underside of your solar panel. This distance should be at a minimum of 2-4 inches, so that air can flow under the unit and keep it cool. This is vitally important for your flush mount system: if you do not allow clearance, your solar unit will rapidly overheat and the functional lifespan will be significantly reduced.
Although flush mounts are simple and cheap to install, they offer no flexibility in the orientation of your solar panel, and they can only support small photovoltaic units.
To the left is a typical flush mount.
Roof-Ground (Universal) Mounts
Roof-Ground solar panel mounts are typically used with larger solar panel systems, or in areas away from the city electric grid. Roof-Ground mounts are called by that name because they can be installed both on the ground and on rooftops. Roof-Ground mounts are typically constructed by a grid-like system of supports, and are typically bulky and unsightly, and many cities and neighborhoods have shamefully passed ordinances against them for asthetic reasons. You would be wise to consult with your residential director before installing a roof-ground solar panel mount.
There are many ways to install custom roof-ground mounts or increase the heights of your system by adding poles or concrete blocks to elevate your system above plants and vermin on the ground.
Many Roof-ground mounts are adjustable, and if you change the tilt of your solar panel at the prescribed 1/4 year interval, your system will produce a little more power than a standard unit.
Roof-ground systems are more expensive than flush mounts, and they may be difficult to install on rooftops due to heavy wind resistance or city ordinances, but they may be your only solution if you have a paticularly large solar panel system.
Pole mounts are divided into 3 subcategories: top of pole mounts, side of pole mounts, and poll tracking mounts. These poll mounts are differentiated by how they are positioned on the pole.
Pictured is a typical top-of-pole mount.
Top of Pole Mounts are comprised of a metal rack and rail unit that is bolted to a large sleeve that rests on top of the pole. In order to install a top of pole mount, you will need to use an existing pole at least 3-8 inches wide with a concrete base, or construct one yourself. The mount simply slips over the top of the pole, and you can bolt (or weld) your solar panel unit into place.
Large Top of pole mounts can encounter a substantial measure of wind resistance and can be very heavy, so you may need a small crane or several able-bodied men at hand in order to install a large top-of-pole system.
Side of Pole Mounts are typically fastened and bolted to the side of telephone or utility poles. Side of pole solar panel mounts typically involve small solar panels, for larger units, it is reccomended that you use a top of pole solar panel mount.
Tracking pole mounts are top of pole mounts with a special function - tracking pole mounts track the motion of the sun in the sky throughout the course of the day. This maximizes the operating efficiency of the solar panel unit.
"Daylighting" is one of the easiest and most cost-effective ways to use solar energy at home. This technique involves building a house to take advantage of the sun's rays.
The architect and builder work together to "site" the house on the lot to bring in natural sunlight throughout the day. Windows are strategically positioned to provide adequate light without overheating the area, and the interior design is planned to diffuse the light throughout the room.
Solar Water Heating
Another "passive" method of using solar energy at home is a thermal solar water heater. These systems use the familiar flat glass or plastic panels seen on roofs and in backyards.
Sunlight passes through the panels and is collected by a dark absorber plate. The plate warms liquid passing through pipes - either the household water supply or an antifreeze solution that is used in a heat exchanger in the water storage tank.
Solar water heaters are popular in areas that do not have natural gas service - replacing an electric water heater with a solar model can reduce water heating costs by 50 to 80 percent every year. And over the 20-year lifespan of the equipment, more than 50 tons of carbon dioxide emissions will be displaced.
If you're interested in a solar water heating system, be sure to check your local building codes - many communities require a conventional water heater as a back up.
Solar Glossary Of Basic Terms:
AC (Alternating Current): An electrical current whose direction alternates. AC is the form in which electricity is used in our households and businesses. It can be thought of as “standard” electrical power.
DC (Direct Current): An electrical current whose direction stays constant. The photovoltaic cells on solar panels capture energy from sunlight in the form of DC. Batteries also hold and put out DC. In order to power your home, this current must be converted to AC by an inverter.
Electrical Current: The flow of charged electrons through a circuit. Depending upon its behavior, an electrical current can be alternating or direct (AC or DC).
Electric Panel: An electrical distribution board that houses electrical circuit breakers. It is the main point at which electricity is distributed throughout a building. It is otherwise known as a breaker box. The circuit breakers can be turned on or off, thus permitting or restricting the flow of electrical current to electrical outlets.
ETL Listed: The assembly is built in an ETL-approved panel shop, where it is built and tested to North American standards, and the "ETL Listed" sticker on the panel means it is legal to be connected, without the sticker it is not legal. ETL shops are government inspected, certified and reviewed every year.
Fossil Fuel: Fuels that are derived from natural resources, usually in the form of coal, oil, or natural gas. There is a limited supply of these resources, and they are only located in certain parts of the world, causing them to be subject to political and international maneuvering, and making energy prices unstable.
Greenhouse Gases: Gases that allegedly contribute to warming the planet. The most common of these gases is carbon dioxide, which is released in large quantities such as when Alberta burns coal for most of its electrial generation. Since sunlight is directly converted into electricity or heat it has no emissions and is considered “Green .”
Grid Tied System: Solar or wind electric system connected to feed back and forth with the electric utility grid.
Ground Mounted Systems: Solar system that is supported by pilings or a structure that is built specifically to support it. They are ideal for buildings with shady or undersized roofs.
Inverter: A device that converts DC power captured by the photovoltaic cells on solar panels or in your batteries into AC power that any home appliance or light can use.
KW (kilowatt): A measurement of power based on the Watt, the standard unit used to measure power. A kilowatt is one thousand watts. A typical household requires a solar power system that produces between 4-5 KW.
KWh (kilowatt hours): A measurement of energy consumption. One kilowatt hour equals one “unit” of electricity. One kilowatt hour is defined as the amount of energy consumed by a 1000-Watt appliance running continuously for 1 hour. This is the measurement your utility company uses to calculate your electric bill.
Net Metering: An agreement between a solar system owner and the local electric utility that allows the system owner to buy and sell energy. When the solar system produces excess energy, it is sold back to the electric utility at the same rate your contract says. When the system is not producing energy, the system owner can use the inputs to the grid to buy back electricity.
Off-grid System: see Stand-Alone System.
Photovoltaic Cells: More comonly called Solar cells, the small elements of semiconducting material that capture sunlight and convert it into power. A group of photovoltaic cells make up a solar panel or a photovoltaic module.
Pool Price: The price of wholesale power paid and sold by the utilities, then distibuted to us, the pool price varies widely and quickly. The price climbs as demand goes up, as during the "electricity rush hour".
Roof Mounted Systems: A solar system in which solar panels are mounted directly on the roof of a building or adjacent structure.
Solar Array: A group of solar panels collectively makes up a solar array. A solar array is the entire system of solar panels that capture sunlight and convert it into power
Solar Energy: Energy emitted from the sun.
Solar Panels: A grouping of solar cells arranged into a panel that can be installed onto a flat surface. The panel captures sunlight and converts it into usable power.
Smart Meter: A meter that varies the price you pay for electricity based on the "Pool price" of power at that moment.
Stand-Alone System: A solar energy system that is not connected to the utility grid. Also called an Off-Grid system. In order to provide continuous power, these systems must be connected to storage units (batteries) that can store excess power produced during daylight hours for use when it's dark.
TES: The acronym for Thermal Energy Storage, it serves as a place to put heat energy until it is able to be best utilized. Although it can take some exotic forms consisting of anything from caustic salts to stone beds, as a medium, most often and as we use it, it is simply a large quantity of water in a highly Insulated tank. Water has some excellent traits, it holds a lot of heat, is totally safe and it is easily transported to where the heat is required.
Tilt Angle: The angle at which a solar array is tilted towards the sun. Depending on the geographic location of a building, a solar array might be installed flat or tilted.
Utility Grid: The infrastructure that delivers electric power to homes and businesses.
Utility Meter: A device that measures the flow of electricity or gas between a site that uses electricity/gas and the utility company.
Vampire: The actual electrical name given to the transformer cubes used on many computer devices, cordless phone bases and many other devices. They have 2 fangs and suck electricity 24-7, hence the name.