Solar power is the conversion of sunlight into electricity, either directly using photovoltaics (PV), or indirectly using concentrated solar power (CSP). Concentrated solar power systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. Photovoltaics convert light into electric current using the photoelectric effect.
Commercial concentrated solar power plants were first developed in the 1980s. The 354 MW SEGS CSP installation is the largest solar power plant in the world, located in the Mojave Desert of California. Other large CSP plants include the Solnova Solar Power Station (150 MW) and the Andasol solar power station (100 MW), both in Spain. The 97 MW Sarnia Photovoltaic Power Plant in Canada, is the world’s largest photovoltaic plant
Solar power is the conversion of sunlight into electricity. Sunlight can be converted directly into electricity using photovoltaics (PV), or indirectly with concentrated solar power (CSP), which normally focuses the sun's energy to boil water which is then used to provide power. Other technologies also exist, such as Stirling engine dishes which use a Stirling cycle engine to power a generator. Photovoltaics were initially used to power small and medium-sized applications, from the calculator powered by a single solar cell to off-grid homes powered by a photovoltaic array.
A significant problem with solar power is installation cost. Developing countries in particular may not have the funds to build solar power plants, although small solar applications are now replacing other sources in the developing world.
Concentrating solar power
Further information: Solar thermal energy and Concentrated solar power
Concentrating Solar Power (CSP) systems use lenses or mirrors and
tracking systems to focus a large area of sunlight into a small beam.
The concentrated heat is then used as a heat source for a conventional
power plant. A wide range of concentrating technologies exists; the most
developed are the parabolic trough ,
the concentrating linear fresnel reflector, the Stirling dish and the
solar power tower. Various techniques are used to track the Sun and
focus light. In all of these systems a working fluid is heated by the concentrated sunlight, and is then used for power generation or energy storage.A parabolic trough consists of a linear parabolic reflector that concentrates light onto a receiver positioned along the reflector's focal line. The receiver is a tube positioned right above the middle of the parabolic mirror and is filled with a working fluid. The reflector is made to follow the Sun during the daylight hours by tracking along a single axis. Parabolic trough systems provide the best land-use factor of any solar technology. The SEGS plants in California and Acciona's Nevada Solar One near Boulder City, Nevada are representatives of this technology.Compact Linear Fresnel Reflectors are CSP-plants which use many thin mirror strips instead of parabolic mirrors to concentrate sunlight onto two tubes with working fluid. This has the advantage that flat mirrors can be used which are much cheaper than parabolic mirrors, and that more reflectors can be placed in the same amount of space, allowing more of the available sunlight to be used. Concentrating linear fresnel reflectors can be used in either large or more compact plants.
The Stirling solar dish combines a parabolic concentrating dish with a Stirling engine which normally drives an electric generator. The advantages of Stirling solar over photovoltaic cells are higher efficiency of converting sunlight into electricity and longer lifetime. Parabolic dish systems give the highest efficiency among CSP technologies.The 50 kW Big Dish in Canberra, Australia is an example of this technology.
A solar power tower uses an array of tracking reflectors (heliostats) to concentrate light on a central receiver atop a tower. Power towers are more cost effective, offer higher efficiency and better energy storage capability among CSP technologies.The Solar Two in Barstow, California and the Planta Solar 10 in Sanlucar la Mayor, Spain are representatives of this technology.
Photovoltaics
Photovoltaics
Photovoltaic power systems
Photovoltaic system
Many residential systems are connected to the grid wherever available, especially in the developed countries with large markets. In these grid-connected PV systems, use of energy storages are optional. In certain applications such as satellites, lighthouses, or in developing countries, batteries or additional power generators are often added as back-ups, which forms stand-alone power systems.
Development and deployment
Deployment of solar power to energy grids
The early development of solar technologies starting in the 1860s was driven by an expectation that coal would soon become scarce. However, development of solar technologies stagnated in the early 20th century in the face of the increasing availability, economy, and utility of coal and petroleum. In 1974 it was estimated that only six private homes in all of North America were entirely heated or cooled by functional solar power systems. The 1973 oil embargo and 1979 energy crisis caused a reorganization of energy policies around the world and brought renewed attention to developing solar technologies.Deployment strategies focused on incentive programs such as the Federal Photovoltaic Utilization Program in the US and the Sunshine Program in Japan. Other efforts included the formation of research facilities in the US (SERI, now NREL), Japan (NEDO), and Germany (Fraunhofer Institute for Solar Energy Systems ISE).
Between 1970 and 1983 photovoltaic installations grew rapidly, but falling oil prices in the early 1980s moderated the growth of PV from 1984 to 1996. Since 1997, PV development has accelerated due to supply issues with oil and natural gas, global warming concerns, and the improving economic position of PV relative to other energy technologies. Photovoltaic production growth has averaged 40% per year since 2000 and installed capacity reached 39.8 GW at the end of 2010, of them 17.4 GW in Germany. As of October 2011, the largest photovoltaic (PV) power plants in the world are the Sarnia Photovoltaic Power Plant (Canada, 97 MW), Montalto di Castro Photovoltaic Power Station (Italy, 84.2 MW) and Finsterwalde Solar Park (Germany, 80.7 MW).
Main article: List of photovoltaic power stations
| PV power station | Country | DC peak power (MWp) |
Notes |
|---|---|---|---|
| Sarnia Photovoltaic Power Plant | Canada | 97 | Constructed 2009–2010 |
| Montalto di Castro Photovoltaic Power Station | Italy | 84.2 | Constructed 2009–2010 |
| Finsterwalde Solar Park | Germany | 80.7 | Phase I completed 2009, phase II and III 2010 |
| Ohotnikovo Solar Park | Ukraine | 80 | Completed 2011 |
| Solarpark Senftenberg | Germany | 78 | Phase II and III completed 2011, another 70 MW phase planned |
| Lieberose Photovoltaic Park | Germany | 71.8 | |
| Rovigo Photovoltaic Power Plant | Italy | 70 | Completed November 2010 |
| Olmedilla Photovoltaic Park | Spain | 60 | Completed September 2008 |
| Strasskirchen Solar Park | Germany | 54 | |
| Puertollano Photovoltaic Park | Spain | 50 | opened 2008 |
Solar Electricity Basics
The three most common types of solar-electric systems are
grid-intertied, grid-intertied with battery backup, and off-grid
(stand-alone). Each has distinct applications and component needs.Grid Intertied Solar-Electric Systems
Also known as on-grid, grid-tied, or utilityinteractive (UI), grid-intertied solar-electric systems generate solar electricity and route it to the electric utility grid, offsetting a home’s or business’ electrical consumption and, in some instances, even turning the electric meter backwards. Living with a grid-connected solar-electric system is no different than living with grid power, except that some or all of the electricity you use comes from the sun. In many states, the utility credits a homeowner’s account for excess solar electricity produced. This amount can then be applied to other months when the system produces less or in months when electrical consumption is greater. This arrangement is called net metering or net billing. The specific terms of net metering laws and regulations vary from state to state and utility to utility. Consult your local electricity provider or state regulatory agency for their guidelines.
Grid-Intertied Solar-Electric Systems with Battery Backup
Without a battery bank or generator backup for your gridintertied system, when a blackout occurs, your household will be in the dark, too. To keep some or all of your electric needs like lights, a refrigerator, pump, or computer running even when utility power outages occur, many homeowners choose to install a grid-intertied system with battery backup. Incorporating batteries into the system requires more components, is more expensive, and lowers the system’s overall efficiency. But for many homeowners who regularly experience utility outages or have critical electrical loads, having a backup energy source is priceless.
The following illustration includes the primary components of any grid intertied solar electric system with battery backup.
Off-Grid Solar-Electric Systems
Although they are most common in remote locations without utility grid service, off-grid solar-electric systems can work anywhere. These systems operate independently from the grid to provide all of a household’s electricity. That means no electric bills and no blackouts—at least none caused by grid failures. People choose to live off-grid for a variety of reasons, including the prohibitive cost of bringing utility lines to remote homesites, the appeal of an independent lifestyle, or the general reliability a solar-electric system provides. Those who choose to live off-grid often need to make adjustments to when and how they use electricity, so they can live within the limitations of the system’s design. This doesn’t necessarily imply doing without, but rather is a shift to a more conscientious use of electricity
Understanding the basic components of an RE system and how they function is not an overwhelming task. Here are some brief descriptions of the common equipment used in grid-intertied and off-grid solar-electric systems. Systems vary—not all equipment is necessary for every system type.
*Solar Electric Panels*Array Mounting Rack*Array DC Disconnect*Charge Controller*Battery Bank
*System Meter*Main DC Disconnect*Inverter*AC Breaker Panel*Kilowatt-Hour Meter*Backup Generator
Solar-Electric Panels
AKA: solar-electric modules, photovoltaic (PV) panels
PV panels are a solar-electric system’s defining component, where sunlight is used to make direct current (DC) electricity. Behind a PV panel’s shimmering facade, wafers of semiconductor material work their magic, using light (photons) to generate electricity—what’s known as the photovoltaic effect. Other components in your system enable the electricity from your solar-electric panels to safely power your electric loads likelights, computers, and refrigerators.
PV panels are assigned a rating in watts based on the maximum power they can produce under ideal sun and temperature conditions. You can use the rated output to help determine how many panels you’ll need to meet your electrical needs. Multiple modules combined together are called an array.
Although rigid panels are the most common form of solar electricity collector, PV technology also has been integrated into roofing shingles and tiles, and even peeland-stick laminates (for metal standing-seam roofs).
PV modules are very durable and long lasting—most carry 25-year warranties. They can withstand severe weather, including extreme heat, cold, and hail stones.
MOUNT RACKS
Mounting racks provide a secure platform on which to anchor your PV panels, keeping them fixed in place and oriented correctly. Panels can be mounted using one of three approaches: 1) on a rooftop; 2) atop a steel pole set in concrete; or 3) at ground level. The specific pieces, parts, and materials of your mounting device will vary considerably depending on which mounting method you choose.
Usually, arrays in urban or suburban areas are mounted on a home’s south-facing roof, parallel to the roof’s slope. This approach is sometimes considered most aesthetically pleasing, and may be required by local regulators or homeowner’s associations. In areas with a lot of space, pole- or ground-mounted arrays are another choice.
Mounting racks may incorporate other features, such as seasonal adjustability. The sun is higher in the sky during the summer and lower in the winter. Adjustable mounting racks enable you to set the angle of your PV panels seasonally, keeping them aimed more directly at the sun. Adjusting the tilt angle increases the system’s annual energy production by a few percent. The tilt of roofmounted arrays is rarely changed. Adjusting the angle is inconvenient and sometimes dangerous, due to the array’s location.
Changing the tilt angle of pole- or ground-mounted arrays can be done quickly and safely. Pole-mounted PV arrays also can incorporate tracking devices that allow the array to automatically follow the sun across the sky from east to west each day. Tracked PV arrays can increase the system’s daily energy output by 25 to 40 percent.
The DC Disconnect
The DC disconnect is used to safely interrupt the flow of electricity from the PV array. It´s an essential component when system maintenance or troubleshooting is required. The disconnect enclosure houses an electrical switch rated for use in DC circuits. It also may integrate either circuit breakers or fuses, if needed.
Charge Controller
AKA: controller, regulator
A charge controller’s primary function is to protect your battery bank from overcharging. It does this by monitoring the battery bank. When the bank is fully charged, the controller interrupts the flow of electricity from the PV panels. Batteries are expensive and pretty particular about how they like to be treated. To maximize their life span, you’ll definitely want to avoid overcharging or undercharging them.
Most modern charge controllers incorporate maximum power point tracking (MPPT), which optimizes the PV array’s output, increasing the energy it produces. Some batterybased charge controllers also include a low-voltage disconnect that prevents over discharging, which can perma nently damage the battery bank.
STORAGE BATTERY
Your PV panels will produce electricity whenever the sun shines on them. If your system is off-grid, you’ll need a battery bank—a group of batteries wired together—to store energy so you can have electricity at night or on cloudy days. For off-grid systems, battery banks are typically sized to keep household electricity running for one to three cloudy days. Gridintertied systems also can include battery banks to provide emergency backup power during blackouts—perfect for keeping critical electric loads operating until grid power is restored.
Although similar to ordinary car batteries, the batteries used in solar-electric systems are specialized for the type of charging and discharging they’ll need to endure. Lead-acid batteries are the most common battery used in solar-electric systems. Flooded leadacid batteries are usually the least expensive, but require adding distilled water occasionally to replenish water lost during the normal charging process. Sealed absorbent glass mat (AGM) batteries are maintenance free and designed for grid-tied systems where the batteries are typically kept at a full state of charge. Gel-cell batteries can be a good choice to use in unheated spaces due to their freeze-resistant qualities.
System Meter
System meters measure and display several different aspects of your solar-electric system’s performance and status, tracking how full your battery bank is; how much electricity your solar panels are producing or have produced; and how much electricity is in use. Operating your solar-electric system without metering is like running your car without any gauges, although possible to do, it’s always better to know how much fuel is in the tank.
In battery-based systems, a disconnect between the batteries and inverter is required. This disconnect is typically a large, DC-rated breaker mounted in a sheetmetal enclosure. This breaker allows the inverter to be quickly disconnected from the batteries for service, and protects the inverter-to-battery wiring against electrical fires.
Inverter
Inverters transform the DC electricity produced by your PV
modules into the alternating current (AC) electricity commonly used in
most homes for powering lights, appliances, and other gadgets. Grid-tied
inverters synchronize the electricity they produce with the grid’s
utility grade AC electricity, allowing the system to feed solar-made
electricity to the utility grid. Most grid-tie inverters are designed to operate without batteries, but battery-based models also are available. Battery-based inverters for off-grid o
r
grid-tie use often include a battery charger, which is capable of
charging a battery bank from either the grid or a backup generator
during cloudy weather. Most grid-Intertied inverters can be installed outdoors (ideally, in the shade). Most off-grid inverters are not weatherproof and should be mounted indoors, close to the battery bank.
AC Breaker Panel & Inverter AC Disconnect
The AC breaker panel is the point at which all of a home’s electrical wiring meets with the provider of the electricity, whether that’s the grid or a solar-electric system. This wall-mounted panel or box is usually installed in a utility room, basement, garage, or on the exterior of the building. It contains a number of labeled circuit breakers that route electricity to the various rooms throughout a house. These breakers allow electricity to be disconnected for servicing, and also protect the building’s wiring against electrical fires.
Just like the electrical circuits in your home or office, an inverter’s electrical output needs to be routed through an AC circuit breaker. This breaker is usually mounted inside the building’s mains panel, which enables the inverter to be disconnected from either the grid or from electrical loads if servicing is necessary, and also safeguards the circuit’s electrical wiring.
Additionally, utilities usually require an AC disconnect between the inverter and the grid that is for their use. These are usually located near the utility KWH meter.
Kilowatt-Hour Meter
Most homes with a grid-tied solar-electric system will have AC electricity both coming from and going to the electric utility grid. A bidirectional KWH meter can simultaneously keep track of how much electricity flows in each of the two directions—just the information you need to monitor how much electricity you’re using and how much your solar-electric system is producing. The utility company often provides Intertied-capable meters at no cost.
Backup Generator
Off-grid solar-electric systems can be sized to provide electricity during cloudy periods when the sun doesn’t shine. But sizing a system to cover a worst-case scenario, like several cloudy weeks during the winter, can result in a very large, expensive system that will rarely get used to its capacity. To spare your pocketbook, size the system moderately, but include a backup generator to get through those occasional sunless stretches.
Engine generators can be fueled with biodiesel, petroleum diesel, gasoline, or propane, depending on the design. These generators produce AC electricity that a battery charger (either standalone or incorporated into an inverter) converts to DC energy, which is stored in batteries. Like most internal combustion engines, generators tend to be loud and stinky, but a welldesigned solar-electric system will require running them only 50 to 200 hours a year.
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