EUROSOLAR, in collaboration with KfW-Bankengruppe, will award the annual European Solar Prize again this year. Established in 1994 it has since rewarded towns and municipalities, community businesses, societies or organizations, architects, journalists and individuals for their outstanding contribution to the use and development of renewable energy.
—– sausa Fabricadecercetare —–
Surface Calculator on installoation of photovoltaic solar panels
A photovoltaic solar panel:
Cost kW installed: 2000 euro
Capacity factor: 15%
Annual production: 1,3 MWh
Green certificates/MWh: 5
Price without subsidy: 65 euro/year, so return of 3,3%, and 31 years amortization.
Minimum cash: 215 euro/year, so return of 11%, and 9 years amortization.
Maximum cash: 365 euro/an, so return of 18,2%, and 5,5 years amortization.
—– source U.S. Demartment of electricity —–
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Solar technologies produce electricity from the sun's energy.
Small solar systems can provide electricity for homes, businesses and other consumers in the distance.
Large solar energy systems provide power more for the contribution to the national electricity system.
Photovoltaic materials and devices for converting sunlight into electricity are commonly known as solar cells. Photovoltaic cells can be literally translated as light or electricity.
First used in about 1890, the word "photovoltaic" has two parts: photo, derived from the Greek word for light, and volt on electricity pioneer Alessandro Volta. Photovoltaic materials and devices convert light energy into electricity, as Edmond Becquerel discovered the French physicist since 1839.
Becquerel discovered the process of using sunlight to produce an electric current in a solid material. But it took more than a century to really understand the process. Scientists eventually learned that the photoelectric or photovoltaic effect caused certain materials to convert light energy into electricity at the atomic level.
PV systems are already an important part of our daily life. Simple PV systems provide power for small consumer products such as calculators and wristwatches. More complicated systems provide power for communications satellites, water pumps, lighting, devices and machines, in some homes and jobs. More traffic and road signs are now powered by PV. In many cases photovoltaic systems are the cheapest ways to produce electricity for these tasks.
Photovoltaic cells, or solar cells, use the photoelectric effect to produce electricity. Photovoltaic cells are the building blocks of all photovoltaic systems because they are devices that convert sunlight into electricity.
Known as solar cells, individual PV cells are electricity-producing devices made of semiconductor materials.
Photovoltaic cells come in many sizes and shapes, from smaller than a postage stamp to several inches in diameter. These are often connected together to form photovoltaic modules, which can scale up to several feet long and several feet wide.
In turn, modules can be combined and connected to form PV arrays of different sizes and output power. Matrix modules make up the largest part of a photovoltaic system, which may include electrical connections, mounting hardware, air conditioning equipment and batteries that store solar energy for use when the sun does not shine.
When light shines on a PV cell, it can be reflected, absorbed, or pass through it. But only the absorbed light generates electricity. The absorbed light energy is transferred to electrons in the atoms of the PV cell semiconductor material. With this new energy, these electrons escape from their normal positions in the atoms and become part of the electrical flow in a circuit. A special electrical property of the PV cells-called "buildings – in the electric field" supplies the power, or voltage, needed to drive the current through an external load, such as a light bulb.
Crystalline silicon cells
Crystal silicon solar cells are the most common solar cells currently used. They are the oldest successful photovoltaic devices. Therefore, crystalline silicon solar cells provides a good example of functionality, typical for the photovoltaic cells. Learn more about crystalline silicon cells and how these solar cells work as semiconductors and build an electric field.
A photovoltaic (PV) or solar electric system is made up of several photovoltaic solar cells. A solar cell is usually small, producing about 1 or 2 watts of power. To increase the output power of photovoltaic cells, these are connected together to form larger units, called modules. Modules, in turn, can be connected to form larger units called panels, which can be interconnected to produce more power and so on. In this way, PV systems can be built to meet almost any electric power need, small or large.
By themselves, modules or networks do not represent an entire PV system. The systems include structures which directs to the solar point and components taking electricity produced by modules and usually conditions it by converting it to alternating current. Photovoltaic systems may include batteries. These items are listed as components to balance the system.
Combining modules with balancing components creates an entire PV system. This system contains everything needed to satisfy a special energy demand, such as powering a water pump, devices and lights in a house, or, if the PV system is large enough, all electrical requirements of a community.
Flat photovoltaic systems
This tipe of panel shows a design that uses a metal substrate, glass, plastic, or to provide structural support behind, an encapsulated material to protect cells and a transparent cover of plastic or glass.
The most common designs for photovoltaic panels are using photovoltaic modules or flat photovoltaic panels. These panels can be fixed in place or are allowed to follow the sun movement. They respond to direct light or diffuse sunlight.
Even on clear sky the diffuse component of sunlight is between 10% and 20% of total solar radiation on a horizontal surface. In the partly sunny days, up to 50% of the radiation is diffuse and in the cloudy days 100% of the radiation is diffuse.
The simplest photovoltaic panel consists of flat photovoltaic panels mounted in a fixed position. The advantage of a fixed panel is that it lacks moving parts, as there is virtually no need for additional equipment, which are relatively light. These characteristics make them suitable for many locations, including most residential roofs.
Because the panels are fixed in place, their orientation to the sun is usually at an angle less than optimal. Therefore, the immobilized panel collects less energy per unit area than the panel presenting the tracking function. However, this disadvantage is balanced against higher cost tracking system.
Concentrator Photovoltaic Systems
Photovoltaic concentrator uses less materials for the solar cells than other PV. Photovoltaic cells are the most expensive components of a PV system, calculated per-area. A concentrator uses relatively inexpensive materials such as plastic lenses and metal housings to capture solar energy shining on a fairly large area, focusing energy on a small area of solar cells. A measure of the effectiveness of this approach is the concentration ratio, in other words, how much concentration receives the cell.
Concentrator photovoltaic systems have several advantages over horizontal systems. First, concentrator systems reduce the size or number of cells needed and allow certain models to use more expensive semiconductor materials. Second, the efficiency of solar cells increase under concentrated light.
The design of photovoltaic cells greatly influences the increase of solar cells efficiency and the materials used. Third, a concentrator may be made of a small number of cells. This is an advantage because it is more difficult to form large areas of high-efficiency solar cells than produce small areas of cells.
However, there are some challenges for concentrators. First, the required optical concentration is more expensive than simple coverage thet flat panel systems require, and most concentrators must track the sun throughout the day and the year to be effective. Thus, achieving higher concentration relationship is through the use of more expensive mechanisms with precise tracking systems. Both reflectors and lenses have been used to focus light for photovoltaic systems.
The most promising targets used in photovoltaic applications are Fresnel targets that use a miniature sawtooth design to focus the input light. If the teeth run in straight lines, the concentric lens acts as a straight line. If the teeth are arranged in concentric circles, light is concentrated in a central point. However, no object can transmit 100% of incident light. The best lenses can transmit 90% to 95% and, in practice, most transmit less. In addition, concentrators can not focus diffuse sunlight, representing approximately 30% of the available solar radiation on a clear day.
High rate of concentration shows a heat problem. As far as solar radiation is concentrated, so is the amount of heat produced. Cell efficiency decreases as temperature increases. High temperatures threaten long-term stability of solar cells. Therefore, solar cells need to be kept cold in a concentrator system, requiring synchronized cooling systems.
One of the most important objectives in designing concentrator systems is to minimize the electrical resistance where the electrical contacts on the cell carry out current generated by the cell. A model with large grid lines, known as "fingers", is in the contact grid on top of the cell, making it ideal for low resistance, blocking too much light because of their shadow.
A solution to the problems of resistance and shading are coverings. Another solution is a back-contact cell, which differs from conventional cells, where both positive and negative electrical contacts are in the back. Placing all electrical contacts on the back of the cell eliminate power losses from the shade, but it also requires exceptionally good quality silicon material.
Concentrator Photovoltaic Systems
Photovoltaic systems are usually composed of many solar arrays, which in turn are composed of many photovoltaic cells.
System performance depends on the performance of its components.
The reliability of PV systems is an important factor in the cost of photovoltaic systems and consumer acceptance. However, in the building of blocks of modules, photovoltaic cells are regarded as 'solid' parts, with devices without moving components being extremely reliable and long lasting. Therefore, reliability photovoltaic system measurements are focused not on cells, but on modules and entire systems.
Reliability can be improved through a circuit design that involves using various redundant features in the circuit to control the effect of partial failure of overall module efficiency and degradation of the power alignment. Degradation can be controlled by dividing the modules in a number of parallel networks of solar cells called secondary circuits. This type of design can improve the way of loss caused by broken cells and other circuit errors.
Bypass Diodes are also used or other corrective measures to reduce local heating effects cells. However, today, the rates of failure of a component are small enough that, with more cells connected in series / parallel and bypass diodes, it is possible to achieve a high level of reliability.
Performance measurements of modules
PV performance module is measured with a watt rating on top. Measured Watt peak (Wp) is determined by measuring the maximum power of a PV module under laboratory conditions of relatively high light, favorable air mass and low cell temperature. But these conditions are not the same in the real world. Therefore, researchers can use a different procedure, known as COTN operating cell – or operating cells with normal temperature.
In this procedure, the first module balances with a specified sorrounding temperature so that maximum power is measured at a nominal operating temperature of the cell. This COTN rating results in a lower value of nominal watt than the maximum watts rating, but is probably more realistic.
However, none of these methods are designed to show the performance of solar module in realistic operating conditions. Another technique, standard AMPM involves consideration of a entire day, rather than peak solar intensity. This standard, designed to meet the users basically needs, relies on the description of a average solar day of global standard in terms of brightness level, ambient temperature and air mass.
Solar panels are designed to provide specific amounts of electricity under certain conditions.
The following factors are usually taken into account in determining the performance of a panel: a solar cell electrical performance characterization, determination of degradation factors related to the design and assembly of the panel, converting environmental considerations in operating temperature of solar cells and calculation of power output capacity panel.
The amount of power required can be defined by one, or through a combination of performance criteria, by the following:
This is the power (in watts) available to the power regulator, specified either as peak power or average power produced during a day.
Output Energy (watt per hour or Wh). This indicates the amount of energy produced during a certain period of time. Parameters are output per unit area of the panel (Wh/m2), production per unit mass of the panel (Wh / kg) and the unit production cost with a panel change (Wh / $).
This parameter is defined as:
- Production of energy from panel / energy input from the sun x 100%.
It is often given as a power output equal to: power output from the panel / power input from the sun x 100%.
Power is usually given in watt units (W) and energy, typically, in units of watts-hour (Wh).
To ensure consistency and quality of the photovoltaic systems and increase consumer confidence in system performance, groups such as the Institute of Electrical and Electronic Engineers and Society for Testing Materials are working on standard and criteria performances for photovoltaic systems.
Concentration of solar power
This solar concentrator shows an antenna with fixed-focus faces in a concentration of about 250 suns. This system can be used for large fields connected to the utility grid, hydrogen generation or water pumping.
Credit: International Science Applications Corporation / PIX 13464
Concentrating solar power technologies use mirrors to reflect and concentrate sunlight that collects solar energy and converts it into heat. This thermal energy can then be used to produce electricity through a steam turbine or heat engine which drives a generator.
Concentrated solar power provides the utility scale, a farm, renewable energy options that can help meet our nation's demand for electricity. These plants produce power by first using mirrors to concentrate sunlight and heat a working fluid. Finally, this high temperature fluid is used to spin a turbine or an engine that drives a generator. The final product is electricity.
Smaller systems can be placed directly on locations if electricity is needed. For example, a single engine can produce 3 to 25 kilowatts of electricity and fits for distributed applications.
There are several types of concentrating solar power systems. Learn more about:
- Concentrator linear systems
- Dish / Engine Systems
- Towers Power Systems
- Thermal storage systems.
Solar energy resources
Solar radiation, often called solar resource is a general term for the electromagnetic radiation emitted by the sun. Solar radiation can be captured and converted into useful forms of energy, such as heat and electricity, using a variety of technologies. However, technical feasibility and economic exploitation of these technologies at a particular location depends on the available solar resources.
The basic principles
Every location on Earth receives sunlight at least one period of the year. The amount of solar radiations reaching at any place on the earth's surface varies according to:
- Geographic Location
- Time of day
- Local landscape
- Local weather
Because the Earth is round, the sun hits the surface at different angles ranging from 0 ° (above the horizon) to 90 ° (overhead). When the sun's rays are vertical, the surface of the Earth receives all the energy possible. The more angled is the sunlight, the more travels through the atmosphere, becoming more dispersed and diffuse. Because the Earth is round, cold polar regions don’t receive large amounts of sunlight and because of the tilted axis of rotation, these areas receive no sun at all throughout the year.
Earth revolves around the Sun in an elliptical orbit and is closer to the sun during certain parts of the year. When the sun is closer to Earth, the Earth's surface receives more energy from the sun. Earth is closer to the sun when it is summer in the southern hemisphere and winter in the northern hemisphere. However, the vast presence of the ocean moderates the hotter summers and colder winters.
23.5 ° in the axis of rotation of the Earth is a more important factor in determining the amount of sunlight that hits the Earth in a certain location. Results are obtained in the longer days in the Northern Hemisphere, in the spring and winter equinox and longer days than in the southern hemisphere during the other six months. Days and nights are exactly 12 hours long in the equinox and this occurs each year around March 23 and September 22.
Earth's rotation is also responsible for hourly variations in sunlight. In the early hours of the morning and late afternoon, the sun is low in the sky Its rays still travel through the atmosphere, more than at noon when the sun is at its highest point. On a clear day, the largest amount of solar energy reaches a solar collector around noon.
Direct and diffuse solar radiations
As sunlight passes through the atmosphere, some of it is absorbed, scattered and reflected by:
- Air molecules
- Water vapor
- Forest fires
This is called diffuse solar radiation.
Solar radiation that reaches the earth's surface without being diffused is called fascicle ofdirect solar radiation. The sum of direct and diffuse solar radiation is called global solar radiation. Atmospheric conditions can reduce direct rays by 10% on clear days and 100% during cloudy days.
Scientists measure the amount of sunlight falling on specific locations at different times of the year. They then estimated the amount of light falling on certain regions of the same latitude, showing similar climates.
Solar energy measurements are typically expressed as total radiation on a horizontal surface, or total radiations traced on a sun surface.
Details of solar radiation for photovoltaic systems are often represented as kilowatt-hour per square meter (kWh/m2). Direct estimates of solar energy may also be expressed as watts per square meter (W/m2).
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