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Climate change concerns, coupled with high oil prices, peak oil, and increasing government support, are driving increasing renewable energy legislation, incentives and commercialization. New government spending, regulation and policies helped the industry weather the global financial crisis better than many other sectors. Renewable energy is energy that comes from natural resources such as sunlight, wind, rain, tides, waves and geothermal heat, which are renewable because they are naturally replenished at a constant rate. About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from hydroelectricity. New renewables (small hydro, modern biomass, wind, solar, geothermal, and biofuels) accounted for another 3% and are growing very rapidly. The share of renewables in electricity generation is around 19%, with 16% of global electricity coming from hydroelectricity and 3% from new renewables. Since its emergence; renewable energy has come a long way.
In was not until the 1970s that environmentalists promoted the development of alternative energy both as a replacement for the eventual depletion of oil, as well as for an escape from dependence on oil; it was at that stage that the first wind turbines appeared. On the other hand, solar had always been used for heating and cooling, but solar panels were too costly to build solar farms, until 1980.
The reason why have chosen the topic of solar heating systems; solar energy for my dissertation is because among the various renewable energy sources, solar energy is one of the crucial energy sources, if not the most crucial. According to a 2011 projection by the International Energy Agency, solar power generators may produce most of the world’s electricity within 50 years, dramatically reducing the emissions of greenhouse gases that harm the environment. Before doing this report, I have to admit that the knowledge that I had regarding solar energy or solar energy systems was minimal. But since starting working on this report, I think, I have come a long way; yet, I have to admit, there has been done so much research in this field, in the past couple of decade that I would still have to go a long way before I would consider myself a specialist. This report should cater towards any individual who had heard of the solar energy, solar energy systems and how they could benefit from it. This report also gives a brief insight into, where solar energy system (solar energy) is headed in the future.
A far as the structure of my report is concerned, I will be looking into the history of solar energy, the solar energy itself, solar energy collectors solar panels; Furthermore, I would also be looking at the benefits of solar energy systems for us and the consequences, if any. On the other hand, I would also be analysing economic issues related to solar energy systems such as: the cost of heating a house or a building by the means of solar energy contra to contemporary means. Last but not the least I would be summarizing the advantages that I have discussed as well as look at some disadvantages, if there are any. I will sum up the whole report with a conclusion, thanks beforehand.
History of solar energy
Before we delve into the discussion of why solar energy is so needed in the world today, we’ll first look into what solar energy really is. By definition, solar energy is that beaming light and heat that is generated from the sun. Solar energy has been used by human beings since time immemorial.
The radiation that comes from solar energy along with the resultant solar energized resources such as wave power, wind, biomass and hydroelectricity all give an explanation for most of the accessible renewable energy that is present on earth. However, only an infinitesimal portion of the existing solar energy is used.
Solar energy has been used by humans for thousands of years. For example, ancient cultures used energy from the sun to keep warm by starting fires with it.
Ancient Egyptians built places to live that allowed stored energy from the sun during the day, and a heat release during the night. This kind of architecture: heated homes at night while keeping the temperature low during the day; buildings were designed so that, walls and floors collected solar heat during the day, that was released at night to keep them warm. If you have ever stood in the sun to get warm then you too have utilized solar thermal energy. Egyptians also used the sun as part of their mummification process, using the sun to dry dead bodies. The Egyptians used a form of passive solar power.
3rd Century B.C., Greek soldiers with the help of Archimedes, focused light on a Roman fleet by using mirrors. The Romans were invading a port city that did not have defenses ready for the attack. The mirrors were used to concentrate the energy of the sun, and cause the fleet’s sails to burn. The Romans retreated and the Greeks were able to prevent the invasion. The Greeks used passive solar power.
100 A.D. a historical writer by the name of Pliny the Younger, built a house in the northern part of Italy that had mica windows in one room. This one particular room demonstrated solar heating in that its mica windows stored heat, and later gave it off. This room was useful because the added heat it generated lessened the amount of wood that had to be burnt, to maintain heat.
Roman bath houses had famous south facing windows that heated the rooms.
Native Americans also built houses that used passive solar power. Houses were built into the side of cliffs or hills to allow storage of heat during the day, and a release of heat at night.
In 1767, the world’s first solar collector was built by Swiss scientist Horace de Saussare.
They also kept their homes warm through passive solar energy designs
The discovery of photovoltaic happened in 1839 when the French physicist Edmond Becquerel first showed photovoltaic activity. Edmond had found that electrical current in certain materials could be increased when exposed to light. 66 years later, in 1905, we gained an understanding of Edmonds’ work, when the famous physicist Albert Einstein clearly described the photoelectric effect, the principle on which photovoltaic are based. In 1921 Einstein received the Nobel Prize for his theories on the photoelectric effect.
Solar cells of practical use have been available since the mid 1950’s when AT&T Labs first developed 6% efficient silicon solar cells. By 1960 Hoffman Electronics increased commercial solar cell efficiencies to as much as 14% and today, researchers have developed cells with more than 20% efficiencies. 20% efficient means that out of the total energy that hits the surface of a solar cell; about 20% is converted into usable electricity.
The first long-term practical application of PV cells was in satellite systems. In 1958 the Vanguard I, was launched into space. It was the first orbiting vehicle to be powered by solar energy. Photovoltaic silicon solar cells provided the electrical power to the satellite until 1964 when the system was shut down. The solar power system was so successful that PV’s have been a part of world-wide satellite space programs ever since. The sun provides endless nonpolluting energy to the satellite power systems and demand for solar cells has risen as a result of the telecommunications revolution and need for satellites.
The energy crisis and oil embargos of the 1970’s made many nations aware of their dependency on controlled non-renewable energy sources and this fueled exploration of alternative energy sources. This included further research into renewable sources such as solar power, wind power and geothermal power.
An economic breakthrough occurred in the 1970’s when Dr. Elliot Berman was able to design a less expensive solar cell bringing the price down from $100 per watt to $20 per watt. This huge cost savings opened up a large number of applications that were not considered before because of high costs. These applications included railroads, lighthouses, off-shore oil rigs, buoys, and remote homes. For some countries and many applications, solar energy is now considered a primary energy source, not an alternative.
Solar energy is the energy derived from the sun through the form of solar radiation. Solar powered electrical generation relies on photovoltaic and heat engines. A partial list of other solar applications includes space heating and cooling through solar architecture, day lighting, solar hot water, solar cooking, and high temperature process heat for industrial purposes. In my report, I would only be looking into a few of the above mentioned solar power harnessing techniques, due to the fact that there is a limitation towards, how much material I can present in my dissertation.
A solar cell (also called a photovoltaic cell) is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect. It is a form of photoelectric cell (in that its electrical characteristics– e.g. current, voltage, or resistance– vary when light is incident upon it) which, when exposed to light, can generate and support an electric current without being attached to any external voltage source.
Passive solar or active solar
Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute solar energy. Active solar techniques include the use of photovoltaic panels and solar thermal collectors to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate.
The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere .Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. The spectrum of solar light at the Earth’s surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet.
Earth’s land surface, oceans and atmosphere absorb solar radiation, and this raises their temperature. Warm air containing evaporated water from the oceans rises, causing atmospheric circulation or convection. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the Earth’s surface, completing the water cycle. The latent heat of water condensation amplifies convection, producing atmospheric phenomena such as wind, cyclones and anti-cyclones. Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C. By photosynthesis green plants convert solar energy into chemical energy, which produces food, wood and the biomass from which fossil fuels are derived.
Yearly Solar fluxes & Human Energy Consumption
Primary energy use (2005)
The total solar energy absorbed by Earth’s atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year. In 2002, this was more energy in one hour than the world used in one year. Photosynthesis captures approximately 3,000 EJ per year in biomass. The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth’s non-renewable resources of coal, oil, natural gas, and mined uranium combined Solar energy can be harnessed at different levels around the world, mostly depending on distance from the equator.
How solar power works
Light (photons) striking certain compounds, in particular metals, causes the surface of the material to emit electrons. Light striking other compounds causes the material to accept electrons. It is the combination of these two compounds that can be made use of to cause electrons to flow through a conductor, and thereby create electricity. This phenomenon is called the photo-electric effect. Photovoltaic means sunlight converted into a flow of electrons (electricity).
Passive solar heating
In passive solar building design, windows, walls, and floors are made to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design or climatic design because, unlike active solar heating systems, it doesn’t involve the use of mechanical and electrical devices.
The key to designing a passive solar building is to best take advantage of the local climate. Elements to be considered include window placement and glazing type, thermal insulation, thermal mass, and shading. Passive solar design techniques can be applied most easily to new buildings, but existing buildings can be adapted or “retrofitted”.
Passive energy gain
Passive solar technologies use sunlight without active mechanical systems (as contrasted to active solar). Such technologies convert sunlight into usable heat (water, air, and thermal mass), cause air-movement for ventilating, or future use, with little use of other energy sources. A common example is a solarium on the equator-side of a building. Passive cooling is the use of the same design principles to reduce summer cooling requirements.
Some passive systems use a small amount of conventional energy to control dampers, shutters, night insulation, and other devices that enhance solar energy collection, storage, and use, and reduce undesirable heat transfer.
Passive solar technologies include direct and indirect solar gain for space heating, solar water heating systems based on the thermo siphon or geyser pump, use of thermal mass and phase-change materials for slowing indoor air temperature swings, solar cookers, the solar chimney for enhancing natural ventilation, and earth sheltering.
More widely, passive solar technologies include the solar furnace and solar forge, but these typically require some external energy for aligning their concentrating mirrors or receivers, and historically have not proven to be practical or cost effective for widespread use. ‘Low-grade’ energy needs, such as space and water heating, have proven, over time, to be better applications for passive use of solar energy.
Pragmatic approach to a productive passive solar energy
Many detached suburban houses can achieve reductions in heating expense without obvious changes to their appearance, comfort or usability. This is done using good siting and window positioning, small amounts of thermal mass, with good-but-conventional insulation, weatherization, and an occasional supplementary heat source, such as a central radiator connected to a (solar) water heater. Sunrays may fall on a wall during the daytime and raise the temperature of its thermal mass. This will then radiate heat into the building in the evening. This can be a problem in the summer, especially on western walls in areas with high degree day cooling requirements. External shading, or a radiant barrier plus air gap, may be used to reduce undesirable summer solar gain.
Active solar heating systems
Active solar technologies are employed to convert solar energy into another more useful form of energy. This would normally be a conversion to heat or electrical energy. Inside a building this energy would be used for heating, cooling, or off-setting other energy use or costs. Active solar uses electrical or mechanical equipment for this conversion. Solar energy collection and utilization systems that do not use external energy, such as a solar chimney, are classified as passive solar technologies. Passive solar relies on the inherent thermo-dynamic properties of the system or materials to operate. They do not need external energy sources.
Solar hot water systems, except those based on the thermo siphon, use pumps or fans to circulate fluid (often a mixture of water and glycol to prevent freezing during winter periods) or air, through solar collectors, and are therefore classified under active solar technology.
The basic benefit of active systems is that controls (usually electrical) can be used to maximize their effectiveness. For example a passive solar thermal array which does not rely on pumps and sensors will only start circulating when a certain amount of internal energy has built up in the system. Using sensors and pumps, a relatively small amount of energy (i.e. that used to power a pump and controller) can harvest a far larger amount of available thermal energy by switching on as soon as a useful temperature differential becomes present. Controls also allow a greater variety of choices for utilizing the energy that becomes available. For example a solar thermal array could heat a swimming pool on a relatively cool morning where heating a domestic hot water cylinder was impractical due to the different stored water temperatures. Later in the day as the temperature rises the controls could be used to switch the solar heated water over to the cylinder instead.
The downside to Active Solar systems is that the external power sources can fail (probably rendering them useless), and the controls need maintenance.
How to buy solar panels solar water heating
Solar water heating can meet about a third of your hot water needs, research conducted by a UK research magazine.
A solar water heating system (also known as solar thermal system) uses panels fitted to your roof to heat water for use around the home.
A typical solar hot water system is able to meet around a third of a household’s hot water needs – a saving of £55 to £80 on your annual water-heating bills, based on a three-bedroom semi-detached house.
Householders installing solar water heating systems can get £300 through the government’s Renewable Heat Incentive Premium Payment scheme.
Choosing a solar water heating system
When choosing a solar water heating system, you’ll need to consider four major factors:
your average hot water use
the area of south-facing roof available
your existing water heating system
You’ll need roughly one square meter of collector area per person in the household. Each metre of panel area will need between 30 and 60 litres of water tank volume.
If you use a less efficient collector (such as flat-plate solar water heating panels), you’ll need to cover a larger area than if you use a more efficient collector (such as evacuated tubes).
You’ll also need to select system components (such as a hot water cylinder, controls and pipe work) and choose the location for your solar panels, considering shade, pipe runs, roof pitch and future access.
Solar water heating installation
There are plenty of solar panel installers out there, so I recommend that you always collect a range of quotes to compare.
Cost effectiveness of solar water heating systems
In my opinion developing common industry standards and offering public incentives is important. He emphasizes that creating public awareness programs is the key to having success in this industry, including a cleaner environment and more jobs as a consequence.
It is clear that installing the application is easy for households since the technology is less complicated and cheaper than PV. According to The Solar Guide, the payback period for an investment in a solar water heating system is 3 to 5 years, although it may vary a lot in different countries due to national standards and differences in manufacturing quality.
The return of investment depends on the system and the current fuel source that is being used to heat the water. It makes more sense to install a combi-system (hot water+space heating) whereby a 12-20 sq-m would completely cover a household’s water heating demand and a substantial part of its space heating demand in spring and in autumn.
Solar trackers may be driven by active or passive solar technology
Most solar collectors are fixed in their array position mounting, but can have a higher performance if they track the path of the sun through the sky (however it is unusual for thermal collectors to be mounted in this way). Solar trackers, used to orient solar arrays may be driven by either passive or active technology, and can have a significant gain in energy yield over the course of a year when compared to a fixed array. Again passive solar tracking would rely on the inherent thermo-dynamic properties of the materials used in the system rather than an external power source to generate its tracking movement. Active Solar Tracking would utilize sensors and motors track the path of the sun across the sky. This action can be caused by geographical and time data being programmed into the controls. However, some systems actually track the brightest point in the sky using light sensors, and manufacturers claim this can add a significant extra yield over and above geographical tracking.
How does Solar Thermal work?
The basic mechanism of solar thermal energy is to collect the solar radiation and transfer the heat directly or indirectly to its final destination via a heat transfer medium – usually a fluid.
The most commonly used applications are Domestic Hot water (DHW), Combined DHW and Space Heating, District Heating, Solar Cooling and Air-Conditioning. High Temperature Solar Thermal Electricity Generation is also among solar thermal applications. (e.g. solar tower and parabolic through applications).
The key component of the solar thermal systems is the collectors which can be divided into two groups:
Unglazed collectors have been used in the industry for a long time, mainly for heating open-air swimming pools. There is no heat exchanger in the system, and the water is flowing directly through long thin tubes. It is cheap and easy to install. Due to the simplicity of unglazed collectors, they cannot fulfill the needs for delivering full-time energy. Unglazed collectors are mainly used in the USA and in Australia.
Glazed collectors are much more efficient in supplying continuous heating and achieving higher temperatures than unglazed ones. Glazed collectors are usually rectangular boxes covered by glass, containing little pipes and tubes and a heat absorbing material inside. There are different types of collectors for different means of use. Glazed collectors are commonly used in China, Europe and the Middle East.
Solar thermal collector
A solar thermal collector is a solar collector designed to collect heat by absorbing sunlight. The term is applied to solar hot water panels, but may also be used to denote more complex installations such as solar parabolic, solar trough and solar towers or simpler installations such as solar air heat. The more complex collectors are generally used in solar power plants where solar heat is used to generate electricity by heating water to produce steam which drives a turbine connected to an electrical generator. The simpler collectors are typically used for supplemental space heating in residential and commercial buildings. A collector is a device for converting the energy in solar radiation into a more usable or storable form. The energy in sunlight is in the form of electromagnetic radiation from the infrared (long) to the ultraviolet (short) wavelengths. The solar energy striking the Earth’s surface depends on weather conditions, as well as location and orientation of the surface, but overall, it averages about 1,000 watts per square meter under clear skies with the surface directly perpendicular to the sun’s rays.
A solar collector works to convert and concentrate solar energy into a more usable form. For example, a thermal collector may use a parabolic array of mirrors to focus, direct, and reflect the light of the sun to a smaller point where the heat can be used to drive some sort of turbine engine by heating the driving fluid. Another type of collector may use a flat panel array of solar photovoltaic cells to convert solar energy directly into electricity. Some metals exhibit a photoelectric property whereby when the metal is exposed to light, it causes electrons to be emitted. These metals may be arranged in a valence-covalence band configuration which generates the actual voltage within the array.
Types of solar collectors for heat
Solar collectors fall into two general categories: non-concentrating and concentrating. In the non-concentrating type, the collector area (i.e., the area that intercepts the solar radiation) is the same as the absorber area (i.e., the area absorbing the radiation). In these types the whole solar panel absorbs the light.
Flat-plate and evacuated-tube solar collectors are used to collect heat for space heating, domestic hot water or cooling with an absorption chiller.
Types of solar collectors for electricity generation
Parabolic troughs, dishes and towers described in this section are used almost exclusively in solar power generating stations or for research purposes. Although simple, these solar concentrators are quite far from the theoretical maximum concentration. For example, the parabolic trough concentration is about 1/3 of the theoretical maximum for the same acceptance angle, that is, for the same overall tolerances for the system. Approaching the theoretical maximum may be achieved by using more elaborate concentrators based on non-imaging optics.
This type of collector is generally used in solar power plants. A trough-shaped parabolic reflector is used to concentrate sunlight on an insulated tube (Dewar tube) or heat pipe, placed at the focal point, containing coolant which transfers heat from the collectors to the boilers in the power station.
Solar Parabolic dish
It is the most powerful type of collector. One or more parabolic dishes concentrate solar energy at a single focal point, -similar to a reflecting telescope which focuses starlight, or to a dish antenna used to focus radio waves. This geometry may be used in solar furnaces and solar power plants.
There are two key phenomena to understand in order to comprehend the design of a parabolic dish. One is that the shape of a parabola is defined such that incoming rays which are parallel to the dish’s axis will be reflected toward the focus, no matter where on the dish they arrive. The second key is that the light rays from the sun arriving at the Earth’s surface are almost completely parallel. So if the dish can be aligned with its axis pointing at the sun, almost all of the incoming radiation will be reflected towards the focal point of the dish-most losses are due to imperfections in the parabolic shape and imperfect reflection.
Losses due to atmosphere between the dish and its focal point are minimal, as the dish is generally designed specifically to be small enough that this factor is insignificant on a clear, sunny day. Compare this though with some other designs, and you will see that this could be an important factor, and if the local weather is hazy, or foggy, it may reduce the efficiency of a parabolic dish significantly.
In dish-stirling power plant designs, a Stirling engine coupled to a dynamo is placed at the focus of the dish, which absorbs the heat of the incident solar radiation, and converts it into electricity.
(Solar) Power tower
A power tower is a large tower surrounded by tracking mirrors called heliostats. These mirrors align themselves and focus sunlight on the receiver at the top of tower, collected heat is transferred to a power station below.
Very high temperatures reached. High temperatures are suitable for electricity generation using conventional methods like steam turbine or some direct high temperature chemical reaction.
Good efficiency. By concentrating sunlight current systems can get better efficiency than simple solar cells.
A larger area can be covered by using relatively inexpensive mirrors rather than using expensive.
Concentrated light can be redirected to a suitable location via. For example illuminating buildings.
Heat storage for power production during cloudy and overnight conditions can be accomplished, often by underground tank storage of heated fluids. Molten salts have been used to good effect.
Concentrating systems require sun tracking to maintain Sunlight focus at the collector.
Inability to provide power in diffused light conditions. Solar Cells are able to provide some output even if the sky becomes a little bit cloudy, but power output from concentrating systems drop drastically in cloudy conditions as diffused light cannot be concentrated passively.
A solar panel (also solar module, photovoltaic module or photovoltaic panel) is a packaged, connected assembly of photovoltaic cells. The solar panel can be used as a component of a larger photovoltaic system to generate and supply electricity in commercial and residential applications. Each panel is rated by its DC output power under standard test conditions, and typically ranges from 100 to 320 watts. The efficiency of a panel determines the area of a panel given the same rated output – an 8% efficient 230 watt panel will have twice the area of a 16% efficient 230 watt panel. Because a single solar panel can produce only a limited amount of power, most installations contain multiple panels. A photovoltaic system typically includes an array of solar panels, an inverter, and sometimes a battery and or solar tracker and interconnection wiring.
Theory and construction
Solar panels use light energy (photons) from the sun to generate electricity through the photovoltaic effect. The majority of modules use wafer-based crystalline silicon cells or thin-film cells based on cadmium telluride or silicon. The structural (load carrying) member of a module can either be the top layer or the back layer. Cells must also be protected from mechanical damage and moisture. Most solar panels are rigid, but semi-flexible ones are available, based on thin-film cells.
Electrical connections are made in series to achieve a desired output voltage and/or in parallel to provide a desired current capability. The conducting wires that take the current off the panels may contain silver, copper or other non-magnetic conductive transition metals. The cells must be connected electrically to one another and to the rest of the system. Externally, popular terrestrial usage photovoltaic panels use MC3 (older) or MC4 connectors to facilitate easy weatherproof connections to the rest of the system.
Bypass diodes may be incorporated or used externally, in case of partial panel shading, to
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