ponedjeljak, 11. listopada 2010.
SOLAR SERDAR - ELECTRICITY FROM THE SUN
CROATIAN CENTER of RENEWABLE ENERGY SOURCES
ELECTRICITY FROM THE SUN
Solar water heating can be used for heating hot water or swimming pools at home. One needs about four square meters of direct sunlight on the roof (southeast to south west) for the main part of the day for a domestic home system. Additional space will be required for a water cylinder system.
Choosing a system requires looking into a few factors- where the direct sunlight falls on the roof, the existing hot water system at home and your budget. If one lives in the colder part of North Carolina, there is also an indirect method where a non-toxic anti-freeze liquid is used. The sun warms this liquid which transfer the heat to water that is held in the tank. The heated liquid is brought from the solar collector to the water tank, where the pipes loop around the water heater to transfer their heat to the tank.
Movement of the liquid through either type of system can be either active or passive. An active system uses a pump. A passive system is based on the thermosiphon principle that water rises as it heats. As the solar thermal collector pipes heat up, they draw new liquid into the system. The pipes are laid at such an angle that if there is not enough heat to draw the liquid up, then it drains back down into the house. This prevents liquid from being in the pipes if they freeze.More info at firstname.lastname@example.org
During winter one will want to keep the propane heating system as a backup during mornings, evenings, and the coldest parts of winter. A two- tank system or a one-tank system can be used. In a two-tank system, the solar-heated water is first sent to the solar tank, then sent through the conventional water heater. In a one-tank system, the solar storage and backup heater are combined in one tank. Also, the propane heater should be adjusted so that it heats water only to up to the maximum degree it is required.
Locating A System - Some Tips
If a system is in the shade it will not work effectively, so first and foremost make sure that you have your system in the direct sunlight. This means throughout the day, some systems get great sun in the mid-day and are shaded all afternoon (try to avoid this). Secondly, make sure that your system is facing in the Southern direction for maximum efficiency.
Solar water heating systems usually cost more to purchase and install than conventional water heating systems. However, a solar water heater can usually save you money in the long run, and when installed in a new home can be cash flow positive from day one.More info at email@example.com
How much money you save depends on the following:
The amount of hot water you use
Your system's performance
Your geographic location and solar resource
Available financing and incentives
The cost of conventional fuels (natural gas, oil, and electricity)
The cost of the fuel you use for your backup water heating system, if you have one.
On average, if you install a solar water heater, your water heating bills should drop 50%–80%. Also, because the sun is free, you're protected from future fuel shortages and price hikes.More info at firstname.lastname@example.org
If you're building a new home or refinancing, the economics are even more attractive. Including the price of a solar water heater in a new 30-year mortgage usually amounts to between $13 and $20 per month. The federal income tax deduction for mortgage interest attributable to the solar system reduces that by about $3–$5 per month. So if your fuel savings are more than $15 per month, the solar investment is profitable immediately. On a monthly basis, you're saving more than you're paying.
According to the U.S. Department of Energy, using solar thermal technology will drop your water-heating bill an average of 50 to 80 percent. Additional benefits include protection from fuel shortages and price hikes and the benefit of contributing to the overall environment. In your neighborhood alone, switching to solar water heating will drastically reduce emissions caused by conventional systems.
Solar water heating operates at 80 percent efficiency. What’s more, solar water heating is simple, usually consisting of two or three rooftop collectors that direct sun-heated water to holding tanks that contain anywhere from 66 to 120 gallons of water.
Solar hot water heaters stand out as a reliable and cost effective renewable energy technology with significant near-term potential to meet energy needs in the residential, commercial and industrial sectors.
A typical solar hot water (or solar thermal) system in North Carolina can supply 50-80 percent of a household’s water heating needs using free, radiant energy from the sun. Such systems lead to significant cost savings over time, since homeowners spend on average $300 – or up to 25 percent of their energy bill – every year heating water.
Solar thermal costs more than conventional electric or natural gas-fueled water heaters – around $6,500 depending on whether it is installed in a new or existing home. However, North Carolina’s solar energy tax credits, which are among the most generous of any state in the county, can be used in combination with a federal tax credit to make solar thermal systems much more cost-competitive.More info at email@example.com
In today’s market, up-front costs for solar thermal systems are typically recovered through energy cost savings in about 10 years, a fraction of the system’s 20 to 30-year lifespan. If you include its cost in a 30-year mortgage for a new home, a solar thermal system can be purchased for around $16 per month, an expense that would be offset by the energy savings that the system provides. In addition, the energy savings provide a hedge against future uncertainty of energy prices.
The economics of solar thermal for commercial and institutional buildings is quite positive. A solar water heating system with 30 collectors would cost about $110,000. With federal tax credits, state tax credits, and depreciation, the net cost would only be about $18,500. The annual energy savings would be about $3,600. The energy savings would provide about a 19% annual return on investment.
The aggregate impact of widespread solar thermal adoption can be significant. If North Carolina’s solar thermal companies installed 35,000 residential systems and 500 commercial systems each year, the energy savings generated would be about 130 million kWh -- $11 million of savings annually. Assuming this level of installation could continue for 10 years, the energy savings would be approximately $110 million each year, a savings that would escalate over time as energy prices rise. The savings would be equivalent to avoiding combustion of 550,000 tons of coal each year.
Photovoltaic comes from the words photo meaning light and volt, a measurement of electricity. First used in about 1890, the word has two parts: photo, a stem derived from the Greek phos, which means light, and volt, a measurement unit named for Alessandro Volta (1745-1827), a pioneer in the study of electricity. Therefore, photovoltaic could literally be translated as light-electricity. That is exactly what photovoltaic materials and devices do; they convert light energy to electricity, as Edmond Becquerel and others discovered in the 18th Century.
Photovoltaic (PV), is a technology that converts light directly into electricity. Photovoltaic is the technology that uses light to convert it into electricity. A photovoltaic cell converts solar energy into electricity by the photovoltaic effect. More info at firstname.lastname@example.org
How can we get electricity from the sun?
A: When certain semiconducting materials, such as certain kinds of silicon, are exposed to sunlight, they release small amounts of electricity. This process is known as the photoelectric effect. The photoelectric effect refers to the emission, or ejection, of electrons from the surface of a metal in response to light. It is the basic physical process in which a solar electric or photovoltaic (PV) cell converts sunlight to electricity.
Sunlight is made up of photons, or particles of solar energy. Photons contain various amounts of energy, corresponding to the different wavelengths of the solar spectrum. When photons strike a PV cell, they may be reflected or absorbed, or they may pass right through. Only the absorbed photons generate electricity. When this happens, the energy of the photon is transferred to an electron in an atom of the PV cell (which is actually a semiconductor).
With its newfound energy, the electron escapes from its normal position in an atom of the semiconductor material and becomes part of the current in an electrical circuit. By leaving its position, the electron causes a hole to form. Special electrical properties of the PV cell—a built-in electric field—provide the voltage needed to drive the current through an external load (such as a light bulb).More info at email@example.com
How long do photovoltaic (PV) systems last?
A: A PV system that is designed, installed, and maintained well will operate for more than 20 years. The basic PV module (interconnected, enclosed panel of PV cells) has no moving parts and can last more than 30 years. The best way to ensure and extend the life and effectiveness of your PV system is by having it installed and maintained properly.
Experience has shown that most problems occur because of poor or sloppy system installation. Failed connections, insufficient wire size, components not rated for dc application, and so on, are the main culprits. The next most common cause of problems is the failure of the electronic parts in the balance of systems (BOS): the controller, inverter, and protection components. Batteries fail quickly if they're used outside their operating specification. For most applications (uses), batteries should be fully recharged shortly after use. In many PV systems, batteries are discharged AND recharged slowly, perhaps over a period of days or weeks. Some batteries quickly fail under these conditions. Be sure the batteries specified for your system are appropriate for the application.More info at firstname.lastname@example.org
How much electricity does a photovoltaic (PV) system generate?
A: A 10% efficient PV system in most areas of the United States will generate about 180 kilowatt-hours per square meter. A PV system rated at 1 kilowatt will produce about 1800 kilowatt-hours a year. Most PV panels are warranted to last 20 years or more (perhaps as many as 30 years) and to degrade (lose efficiency) at a rate of less than 1% per year. Under these conditions, a PV system could generate close to 36,000 kilowatt-hours of electricity over 20 years and close to 54,000 kilowatt-hours over 30 years. This means that a PV system generates more than $10,000 worth of electricity over 30 years.
( Source: US department of energy: http://www.eere.energy.gov/solar/cfm/faqs/)
As sun’s waves hit a photovoltaic cell it hits the electrons within layers of the cell. The electrons jump back and forth, creating electricity. This electricity is captured by wires running through the PV cells and sends out electricity. The electric current generated by PV cells is direct current (DC), and is the same current used in batteries. Most of the appliances in the United States run off of alternating current (AC), or the type of current that comes over power lines.More info at email@example.com
Why use a Photovoltaic system?
A residential PV power system enables a homeowner to generate some or all of their daily electrical energy demand on their own roof, exchanging daytime excess power for future energy needs (i.e. nighttime usage). The house remains connected to the electric utility at all times, so any power needed above what the solar system can produce is simply drawn from the utility.
A PV system reduces, or can completely eliminate, the amount of electricity you have to purchase from your utility or electric service provider. A PV system can save you money on your electricity bill and act as a hedge against future price increases. The electricity generated by your PV system is clean, renewable and reliable. You help your community by reducing the electricity demand and provide additional electricity for the grid when you generate more than you use during the day, when this demand is highest.
Solar heating is an affordable and cost-effective alternative for heating or cooling water or space in commercial and industrial buildings. More info at firstname.lastname@example.org
General Solar Heating Information
Solar process-heating systems are designed to meet the need for large quantities of hot water or space heating at commercial, industrial, and institutional buildings. A typical system consists of several thousand square feet of ground-mounted collectors, combined with pumps, heat exchangers, controls, and one or more large-volume storage tanks. Solar process-heating systems have successfully developed niche markets in federal and state governments. Such facilities might include schools, military bases, office buildings, and prisons that provide hot water for bathing, cooking, laundry, and space heating.More info at email@example.com
What does solar water heating look like?
The roof collectors look like skylights that integrate well with rooflines. Flat plate collectors are most common, available in sleek black colors.
Solar Water Heating
One of the most cost-effective ways to include renewable technologies into a building is by incorporating solar hot water. The Housing and Urban Development’s Partnership for Advancing Technology in Housing Program named solar water heating one of the top 10 technologies for 2007!
A typical residential solar water-heating system reduces the need for conventional water heating by about two-thirds. It minimizes the expense of electricity or fossil fuel to heat the water and reduces the associated environmental impacts.
Solar Water Heating for Buildings
Most solar water-heating systems for buildings have two main parts: (1) a solar collector and (2) a storage tank. The most common collector used in solar hot water systems is the flat-plate collector.
Solar water heaters use the sun to heat either water or a heat-transfer fluid in the collector. Heated water is then held in the storage tank ready for use, with a conventional system providing additional heating as necessary. The tank can be a modified standard water heater, but it is usually larger and very well insulated. Solar water heating systems can be either active or passive, but the most common are active systems.
Active solar water heaters
Active solar water heaters rely on electric pumps, and controllers to circulate water, or other heat-transfer fluids through the collectors. These are the three types of active solar water-heating systems:
Direct-circulation systems use pumps to circulate pressurized potable water directly through the collectors. These systems are appropriate in areas that do not freeze for long periods and do not have hard or acidic water. These systems are not approved by the Solar Rating & Certification Corporation (SRCC) if they use recirculation freeze protection (circulating warm tank water during freeze conditions) because that requires electrical power for the protection to be effective.
Indirect-circulation systems pump heat-transfer fluids through collectors. Heat exchangers transfer the heat from the fluid to the potable water. Some indirect systems have "overheat protection," which is a means to protect the collector and the glycol fluid from becoming super-heated when the load is low and the intensity of incoming solar radiation is high. The two most common indirect systems are:
Antifreeze. The heat transfer fluid is usually a glycol-water mixture with the glycol concentration depending on the expected minimum temperature. The glycol is usually food-grade propylene glycol because it is non-toxic.
Drainback systems are a type of indirect system that uses pumps to circulate water through the collectors. The water in the collector loop drains into a reservoir tank when the pumps stop. This makes drainback systems a good choice in colder climates. Drainback systems must be carefully installed to assure that the piping always slopes downward, so that the water will completely drain from the piping. This can be difficult to achieve in some circumstances.
Passive solar water heaters
Passive solar water heaters rely on gravity and the tendency for water to naturally circulate as it is heated. Because they contain no electrical components, passive systems are generally more reliable, easier to maintain, and possibly have a longer work life than active systems. The two most popular types of passive systems are:
Integral-collector storage systems consist of one or more storage tanks placed in an insulated box with a glazed side facing the sun. These solar collectors are suited for areas where temperatures rarely go below freezing. They are also good in households with significant daytime and evening hot-water needs; but they do not work well in households with predominantly morning draws because they lose most of the collected energy overnight.
Thermosyphon systems are an economical and reliable choice, especially in new homes. These systems rely on the natural convection of warm water rising to circulate water through the collectors and to the tank (located above the collector). As water in the solar collector heats, it becomes lighter and rises naturally into the tank above. Meanwhile, the cooler water flows down the pipes to the bottom of the collector, enhancing the circulation. Some manufacturers place the storage tank in the house's attic, concealing it from view. Indirect thermosyphons (that use a glycol fluid in the collector loop) can be installed in freeze-prone climates if the piping in the unconditioned space is adequately protected.
CROATIAN CENTER of RENEWABLE ENERGY SOURCES ( CCRES )