http://www.solar-alternatives.net/ Solar power is a clean, renewable energy source for the future. en Copyright 2007 Wed, 28 Mar 2007 05:55:25 +0000 http://www.sixapart.com/movabletype/ http://blogs.law.harvard.edu/tech/rss Having electricity during the day, and then only on clear days, is not a situation that anyone would choose to put themselves in, given a choice. There is a need for energy storage, in short, batteries. Unfortunately, batteries add a lot of cost and maintenance to the PV system. They are currently a necessity if you want to be completely independent. Some people attempt to get around the problem by connecting their house to the utility grid, buying power when they need it. They even sell the excess power when they produce more than they need. This way, the utility acts as a practically infinite storage system. The utility has to agree, of course, and in most cases will buy power from you at a much lower price than their own selling price. You will also need special equipment to make sure that the power you sell to your utility is synchronous with theirs -- that it shares the same sinusoidal waveform and frequency. Safety is an issue as well. The utility has to make sure that if there's a power outage in your neighborhood; your PV system won't try to feed electricity into lines that a lineman may think is dead. This is called islanding. Please keep in mind that when using batteries, they will have to be maintained and then replaced after a certain number of years. The PV modules should last 20 years or more, but batteries just don't have that kind of useful life. Batteries in PV systems need to be in a well-ventilated, non-metallic enclosure for them because they can be very dangerous because of the energy they store and the acidic electrolytes they contain. There are different kinds of batteries commonly used, but one characteristic they should all have in common is that they are deep-cycle batteries. Unlike a car battery, which is a shallow-cycle battery, deep-cycle batteries can maintain a long life but still discharge more of their stored energy. Shallow-cycle batteries discharge a large current for a very short time, for example to start your car, which are then immediately recharged as you drive. PV batteries generally have to discharge a smaller current for a longer period (such as all night), while being charged during the day. Lead-acid batteries are the most commonly used deep-cycle batteries, which can be both sealed and vented, and nickel-cadmium batteries. Though more expensive, Nickel-cadmium batteries last longer and can be discharged more completely without harm. Even deep-cycle lead-acid batteries will have a seriously shortened life expectancy if they are discharged 100 percent. PV systems are designed to discharge lead-acid batteries no more than 40 or 50 percent. A device called a charge controller is needed with the use of batteries. The life of the batteries last a lot longer if care is taken so that they aren't overcharged or drained too much. A charge controller does exactly that. Once the batteries are fully charged, the charge controller will not allow current from the PV modules continue to flow into them. Once the batteries have been drained to a certain predetermined level, controlled by measuring battery voltage, many charge controllers will also not allow more current to be drained from the batteries until they have been recharged. Charge controllers are very important in maintaining a long life for a battery. Another of the problems besides energy storage is that the electricity generated by your PV modules, and the electricity extracted from your batteries should you choose to use them, is not in the form that's used by the electrical appliances in your house. The electricity generated by a solar system is direct current. The electricity supplied by your utility as well as the kind that every appliance in your house uses is alternating current. That means you will need an inverter, a device that converts DC to AC. Some PV modules actually have an inverter already built into each module, called AC modules. These eliminate the need for a large, central inverter, and simplifying wiring issues. Most large inverters will also allow you to automatically control how your system works. In order to have a working system, you will need mounting hardware, wiring, junction boxes, grounding equipment, over current protection, DC and AC disconnects and other accessories. You will also need an inspection to make sure that the electrical codes were followed. There is a section in the National Electrical Code just for PV, and it's highly recommended that a licensed electrician who has experience with PV systems do the installation. But once up and running, a PV system requires very little maintenance, especially if no batteries are used. It will provide electricity cleanly and quietly for 20 years or more. http://www.solar-alternatives.net/2007/03/solving_solar_power_issues.html http://www.solar-alternatives.net/2007/03/solving_solar_power_issues.html Issues Facing Solar Power Wed, 28 Mar 2007 05:55:25 +0000 Governments install incentive policies for PV in order to grow the industry even while the cost of PV is significantly above grid parity, hoping to achieve the economies of scale necessary to reach grid parity. The policies are implemented both for economic and environmental reasons. They will help to promote national energy independence, high tech job creation and reduction of CO2 emissions. There are two types of incentives used: Investment subsidies: the authorities refund part of the cost of installation of the system. Feed in tariffs/net metering: the electricity utility buys PV electricity from the producer under a multiyear contract at a guaranteed rate. These financial burden falls upon the taxpayer, the extra cost of feed in tariffs is distributed across the utilities' customer base. While the investment subsidy may be simpler to administer, the main reason given for feed in tariffs is the encouragement of quality. Investment subsidies are paid out as a function of the nameplate capacity of the installed system and are independent of its actual power yield over time. This causes a reward overstatement of power, and toleration of poor durability and maintenance. Feed in tariffs reward the number of kWh produced over a long period of time. The price paid per kWh under a feed in tariff is more than the price of grid electricity. "Net metering" refers to the case where the price paid by the utility is the same as the price charged. In Japan, the government (through its Ministry of International Trade and Industry) ran a successful programme of subsidies from 1994 to 2003. By the end of 2004, Japan was leading the world in installed PV capacity with over 1.1 GW. The German government introduced the first large scale feed in tariff system in 2004. A law known as the 'EEG' resulted in explosive growth of PV installations in Germany. The principle behind the German system is a 20 year flat rate contract. The value of new contracts is programmed to decrease each year, in order to encourage the industry to pass on lower costs to the end users. Spain, Italy, Greece and France have also introduced feed in tariffs. None have replicated the programmed decrease of FIT in new contracts though, so the German incentive relatively less and less attractive compared to other countries. The French FIT offers a uniquely high premium for building integrated systems. In 2006 California approved the 'California Solar Initiative', offering a choice of investment subsidies or FIT for small and medium systems and a FIT for large systems. Incentives are scheduled to decrease in future depending as a function of the amount of PV capacity installed. The price/kWh or kWp of the FIT or investment subsidies in stimulating the installation of PV is only one of three factors. The other two are insolation (the more sunshine, the less money is needed) and administrative ease of obtaining permits and contracts. http://www.solar-alternatives.net/2007/03/financial_incentives.html http://www.solar-alternatives.net/2007/03/financial_incentives.html Issues Facing Solar Power Wed, 28 Mar 2007 05:55:23 +0000 Grid parity Grid parity means photovoltaic power is equal to or cheaper than grid power. Grid parity is already reached in some regions. Grid parity has been reached in Hawaii and many other islands that use diesel fuel to produce electricity. In Italy PV power has been cheaper than grid electricity since 2006. One kWh costs 21.08 -€cent/kWh. Italy has an average of 1,600 kWh/m2 (Sicily even 1,800 kWh/m2) sun power/year. At 4 % costs of capital, 25 years of depreciation and costs (including installation) of 4,600 €/kWp PV current costs are 20.91 €-cent/kWh. At large scale plants with 3,900 €/kWp the costs reduces to 17.75 €-cent/kWh and is 15 % cheaper. To reach a 19% PV power coverage in Italy, 34,000 MWp power must be installed. This means 0.09 % of the size of Italy. 9 % of the size of Sicily could produce 25 % of the power of the complete European Union (ca. 2,100 TWh/year). ]]> http://www.solar-alternatives.net/2007/03/energy_return_on_investment.html http://www.solar-alternatives.net/2007/03/energy_return_on_investment.html Issues Facing Solar Power Wed, 28 Mar 2007 05:55:22 +0000 Professional Application Ocean navigation aids: many lighthouses and most buoys are now powered by solar cells. Telecommunication systems: radio transceivers on mountain tops or telephone boxes in the country can often be solar powered. Remote monitoring and control: scientific research stations, seismic recording, weather stations, etc. use very little power which, in combination with a dependable battery, is provided reliably by a small PV module. Cathodic protection: this is a method for shielding metalwork from corrosion, for example, pipelines and other metal structures. A PV system is well suited to this application since a DC source of power is required in remote locations along the path of a pipeline. Electric power generation in space The best choice for providing electrical power to satellites in an orbit around the Earth has been and will remain photovoltaic solar generators. Solar cells on the U.S. satellite Vanguard I in 1958 demonstrated the first practical application of photovoltaics. Since then, the satellite power requirements have grown from a few Watts to several kilowatts. Arrays approaching 100 kW are being planned for a future space station. In the adverse conditions of space environment, a space solar array must be extremely reliable. It is very expensive to lift every kilogram of weight into the orbit, so the space array should also have a high power-to-weight ratio. Solar-powered vehicles Solar-powered vehicles and the technology is developing rapidly due to large research interest. Solar-powered cars are becoming common at solar races like the World Solar Challenge and at car and technology shows. Solar boats have also made an appearance. Cars can use a variety of solar cell technologies, but they usually use polycrystalline silicon, monocrystalline silicon, or gallium arsenide. The cells are wired together into strings while strings are often wired together to form a panel. Panels normally have voltages close to the nominal battery voltage. The main aim is to get as many cells in as small a space as possible. These cells are encapsulated to protect them from the weather and breakage. It is more difficult to design a solar array than to just stringing bunch of cells together. A solar array acts like a lot of very small batteries all hooked together in series. The problem is that if a single cell is in shadow it acts like a diode, blocking the flow of current for the entire string of cells. Array designers try to correct this by using by-pass diodes in parallel with smaller segments of the string of cells, allowing current to flow around the non-functioning cell or cells. Another consideration is that the battery itself can force current backwards through the array unless there are blocking diodes put at the end of each panel. The weather conditions, the position of the sun and the capacity of the array all effect the amount of energy one array can collect. At noon on a bright day, a good array can produce over 2 kilowatts (2.6 hp). ]]> http://www.solar-alternatives.net/2007/03/special_applications_of_solar.html http://www.solar-alternatives.net/2007/03/special_applications_of_solar.html Applications Wed, 28 Mar 2007 05:55:20 +0000 Solar panel Solar-thermal panels or photovoltaic (PV) modules are often arrayed as panels which can be connected either in parallel or series depending upon the design objective. They are typically found in use in residential, commercial, institutional, and light industrial applications. PV modules recently have been a surging upwards toward large scale production. In places difficult to reach or very isolated, PV output and their economics are enhanced. PV modules are the primary component of most small-scale solar-electric power generating facilities. Solar power plants typically contain an array of reflectors (concentrators), a receiver, and a thermodynamic power cycle, and thus use solar-thermal rather than PV. Now under construction, the largest solar panel in the world will be built in the south of Portugal. It is a 116-megawatt facility covering a 250-hectare south-facing hillside in the southern Alentejo region. It should be able to produce electricity for 21,000 households Solar Cell in buildings Solar arrays being seen in use more often in new domestic and industrial buildings as a principal or ancillary source of electrical power. Often, an array is incorporated into the roof or walls of a building, roof tiles, which is visually more attractive than some of the older and larger panels. They can now even be purchased with an integrated PV cell (B.I.P.V.- Building Integrated PhotoVoltaics) . Arrays can also be retrofitted into existing buildings; in this case they are usually fitted on top of the existing roof structure. Alternatively, an array can be located separately from the building but connected by cable to supply power for the building. Public electricity supply is called the grid. In remote or mountainous areas where the grid cannot be reached, PV may be the only possibility for generating electricity, or PV may be used together with wind and/or hydroelectric power. Batteries are usually used to store collected energy in these off-grid situations. However, the largest installations are grid-connected systems through a direct current to alternating current (DC-AC) inverter. When the load required in the building is more than that supplied by the PV array then electricity will be drawn from the grid. The reverse also applies; when the PV array is generating more power than is needed in the building then electricity will be exported to the grid. Batteries are not required and standard AC electrical equipment may be used. The average lowest retail cost of a large PV module declined from USD 7.50 to USD 4 per watt between 1990 and 2004. Recent prices have gone up 15-20% due to increased demand and silicon shortages. With many jurisdictions now giving tax and rebate incentives, and/or net metering solar electric power can now pay for itself in ten to twenty years in a few places. ]]> http://www.solar-alternatives.net/2007/03/typical_applications_of_solar.html http://www.solar-alternatives.net/2007/03/typical_applications_of_solar.html Applications Wed, 28 Mar 2007 05:55:18 +0000 Solar cells and energy payback A common misconception is that solar cells never produce more energy than it takes to make them. The usual working lifetime is around 40 years, while the energy payback time of a solar panel is from 1 to 20 years, but usually under five. This depends on the type and where it is used. This means solar cells can be net energy producers, making enough energy to "reproduce" themselves (from just over once to more than 30 times) over their lifetime. *Please not that some researchers dispute the above findings. They object that such analysis doesn't take into account waste, inefficiency, and related energy costs that would come with a real-world solar cell. ]]> http://www.solar-alternatives.net/2007/03/comparison_of_energy_conversio.html http://www.solar-alternatives.net/2007/03/comparison_of_energy_conversio.html Applications Wed, 28 Mar 2007 05:55:17 +0000 Silicon Known as "solar grade silicon", crystalline silicon is by far the most prevalent bulk material for solar cells. Bulk silicon is separated into multiple categories according to crystallinity and crystal size in the resulting ingot, ribbon, or wafer. Thin films One problem is the amount or mass of light absorbing material required in creating a solar cell. Various thin-film technologies currently being developed reduce that mass. This can lead to reduced processing costs from that of bulk materials (in the case of silicon thin films) but also tends to reduce efficiency. Organic/polymer solar cells Organic solar cells and Polymer solar cells are built from thin films (typically 100 nm) of organic semiconductors. Examples of these include polymers and small-molecule compounds like polyphenylene vinyl, copper phthalocyanine (a blue or green organic pigment) and carbon fullerenes. Energy conversion efficiencies achieved to date using conductive polymers are low. The best cells to date are at 4-5% efficiency, but these cells could be beneficial for some applications where mechanical flexibility and disposability are important. Nano-crystalline solar cells Making use of some of the same thin-film light absorbing materials, these structures are overlain as an extremely thin absorber on a supporting matrix of conductive polymer or mesoporous metal oxide having a very high surface area to increase internal reflections (and hence increase the probability of light absorption) ]]> http://www.solar-alternatives.net/2007/03/solar_cell_materials.html http://www.solar-alternatives.net/2007/03/solar_cell_materials.html Solar Cell Technology Wed, 28 Mar 2007 05:55:15 +0000 Simple explanation Photons in sunlight hit the solar panel and are absorbed by semiconducting materials, usually silicon. Electrons (negatively charged) are then knocked loose from their atoms, allowing them to flow through the material to produce electricity. The complementary positive charges that are also created (like bubbles) are called holes and flow in the direction opposite of the electrons in a silicon solar panel. Finally, an array of solar panels converts solar energy into a usable amount of direct current (DC) electricity. Charge carrier separation There are two main modes for charge carrier separation in a solar cell: drift of carriers, driven by an electrostatic field established across the device diffusion of carriers from zones of high carrier concentration to zones of low carrier concentration (following a gradient of electrochemical potential). In the widely used p-n junction designed solar cells, the dominant mode of charge carrier separation is by drift. However, in non-p-n junction designed solar cells (typical of the third generation of solar cell research such as dye and polymer thin-film solar cells), a general electrostatic field has been confirmed to be absent, and the dominant mode of separation is via charge carrier diffusion. The p-n junction The most commonly known solar cell is configured as a large-area p-n junction made from silicon. As a simplification, one can imagine bringing a layer of n-type silicon into direct contact with a layer of p-type silicon. In practice, p-n junctions of silicon solar cells are not made in this way, but rather, by diffusing an n-type dopant into one side of a p-type wafer (or vice versa). If a piece of p-type silicon is placed in intimate contact with a piece of n-type silicon, then a diffusion of electrons occurs from the region of high electron concentration (the n-type side of the junction) into the region of low electron concentration (p-type side of the junction). When the electrons diffuse across the p-n junction, they recombine with holes on the p-type side. The diffusion of carriers does not happen indefinitely however, because of an electric field which is created by the imbalance of charge immediately either side of the junction which this diffusion creates. The electric field established across the p-n junction creates a diode that promotes current to flow in only one direction across the junction. Electrons may pass from the n-type side into the p-type side, and holes may pass from the p-type side to the n-type side. This region where electrons have diffused across the junction is called the depletion region because it no longer contains any mobile charge carriers ]]> http://www.solar-alternatives.net/2007/03/anatomy_of_a_solar_cell.html http://www.solar-alternatives.net/2007/03/anatomy_of_a_solar_cell.html Solar Cell Technology Wed, 28 Mar 2007 05:55:13 +0000 Four generations of development: First Consisting of a large-area, the first generation photovoltaic is single layer p-n junction diodes, that is capable of generating usable electrical energy from light sources with the wavelengths of sunlight and are typically made using a silicon wafer. First generation photovoltaic cells are also known as silicon wafer-based solar cells, the dominant technology in the commercial production of solar cells, accounting for more than 86% of the solar cell market. Second Based on the use of thin-film deposits of semiconductors, the second generations of photovoltaic materials were initially designed to be high-efficiency, multiple junction photovoltaic cells. Later, the advantage of using a thin-film of material was noted, reducing the mass of material required for cell design. This contributed to a prediction of greatly reduced costs for thin film solar cells. Currently (2007) there are different technologies/semiconductor materials under investigation or in mass production, such as amorphous silicon, poly-crystalline silicon, micro-crystalline silicon, cadmium telluride, copper indium selenide/sulfide. Typically, the efficiencies of thin-film solar cells are lower compared with silicon (=wafer-based) solar cells, but manufacturing costs are also lower, so that a lower price in terms of $/watt of electrical output can be achieved. Another advantage of the reduced mass is that less support is needed when placing panels on rooftops and it allows fitting panels on light materials or flexible materials, even textiles. Third Third generation photovoltaics are unlike the previous two, broadly defined as semiconductor devices which do not rely on a traditional p-n junction to separate photogenerated charge carriers and include photoelectrochemical cells, Polymer solar cells, and nanocrystal solar cells. Fourth The fourth generation of photovoltaic cells is altogether very different from the other three. Utilizing biological organisms, such as bacteria like P. Argenellus Flavus, to create the biopolymers needed to generate a standing field. ]]> http://www.solar-alternatives.net/2007/03/about_solar_cells.html http://www.solar-alternatives.net/2007/03/about_solar_cells.html Solar Cell Technology Wed, 28 Mar 2007 05:53:05 +0000