Solar energy is our oldest and most readily available energy source. It does not belong to anyone. It is reliable, free, and clean. Using solar energy doesn’t cause air pollution or involve damaging the Earth’s surface. It requires no difficult and expensive extraction procedures. Since prehistoric times, humans have used solar energy. When we hang out our clothes to dry in the sun, we use the energy of the sun. In the same way, solar panels absorb the energy of the sun to provide heat for cooking and for heating water. Such systems are available in the market and are being used in homes and factories.
This century we have started to use solar energy more effectively, and it is likely that we’ll increase its use in the future. There is an enormous amount of information; research, study, and application of solar energy are plentiful on the Internet. If you are interested in this alternative method of energy, here is a brief introduction to get you started.
After the 1973 oil embargo, there was a resurgence of interest in solar energy. Faced with a possibility of scarce oil resources, the
Before 1970, some research and development was carried out in a few countries to exploit solar energy more efficiently, but most of this work remained mainly academic. After the dramatic rise in oil prices in the 1970s, several countries began to formulate extensive research and development programs to exploit solar energy.
Consumer demand for clean renewable energy and the deregulation of the utilities industry has also spurred growth in green power—solar, wind, geothermal steam, biomass, and small-scale hydroelectric sources of power. Small commercial solar power plants have begun serving some energy markets. However, zoning laws and ordinances in some communities protects access to unobstructed sunlight for use both in passive solar designs and active systems.
Many people equate solar energy and solar power with hot and sunny climates, however even on a cloudy day there is a great deal of clean, low-cost energy available from the sun. This solar energy can be effectively utilized to provide enough to heat the average household's daily water requirements in summer.
- A typical system includes a roof-mounted solar collector, sometimes referred to as the solar panel. In fact, they can also be made up of tubes. Heat is then pumped inside the building to a hot water store where supplementary heat is often added to make it useful for normal domestic appliances.
- Solar energy can be used to produce electricity with different equipment generally referred to as photovoltaic panels.
- Solar energy is also used to heat rooms directly, like in a greenhouse. This is called passive solar gain.
The Earth is bathed in huge amounts of the sun’s energy. We can use this solar energy directly, simply by capturing sunlight. One of the greatest features of solar energy is the fact that it is likely to continue to exist so far into the future that we can think of it as being unending. It is, therefore, a form of renewable energy. This is a big contrast with non-renewable energy sources, most of which are running out as we use them.
But the main problem is what to do when the sun doesn’t shine. The times when we most need energy – when it is dark or cold – are when sunlight is least available. But there are possible ways around this.
Compared to fossil fuels, sunlight is a weak energy source. Capturing sunlight is not as easy as it sounds. It is a dilute energy source, spread out over time and space. Earth receives 5.6 x 1018 (5,600,000,000,000,000,000) mega joules of solar radiation each year, but to make it worthwhile we need to collect it over many hours and across many square meters of ground. We then need to concentrate it so as to make available the sort of power that modern society needs. Sunlight is not as ‘energy-dense’ as oil but this is made up for by the fact that it is present over such a large area.
By careful design and positioning of houses we can use sunlight to warm our homes and our domestic water. This passive solar can help us reduce fossil fuel use (and save money) but it’s not enough to replace those traditional fuels entirely.
To be most useful, the energy in sunlight must be converted to another form. Light can be changed directly to an electric current by photovoltaic cells. The efficiency with which these convert light to electricity is still too low, and their cost too high, to make them useful for many applications. Furthermore, you need to have a large area of photovoltaic cells to power something like a car – although it can be done.
Unfortunately, we can’t yet power our homes entirely on sunlight. Photovoltaic cells for a house are expensive, and many houses are not in the sunniest part of the world. The solution is to put the sun’s energy into a form that can be stored and moved around, so that we can collect it in those places where most of it falls and move it to where it is needed.
Steam or hydrogen gas are two of the best future conversion options. Solar collectors—best sited in a desert--can concentrate sunlight. Solar collectors focus sunlight from a large area on to a central vessel in which water is heated to become very high temperature steam. The expanding steam can power a turbine and generate electricity on a sufficiently large scale that it can be sent across a power grid.
The greatest challenge for solar energy is to power modern society’s transport and industrial needs. Transport fuels must be light but packed with energy. They must also operate when it’s dark, so photovoltaic cells are out. The answer for the future probably lies in hydrogen gas, derived from water split apart using solar electricity or the sun’s concentrated heat.
Solar water heating, using roof-mounted collectors, is established as the most reliable and accessible way to actively use this free energy supply in our homes.
By collecting both direct and diffused sunshine it is possible to heat over half the annual hot water demand of a normal domestic house, most of this occurring in the summer. In its simplest form it is possible to enjoy a solar heated shower by hanging a black plastic bag outside for a few hours to collect the sunshine. However, to reap the full benefits it is necessary to integrate solar heating with a conventional boiler.
During sunny summer days it is possible to switch off the conventional boiler and rely on solar heating alone, whereas during the rest of the year the conventional boiler tops up any shortfall. Although possible to use solar energy for space heating of rooms, i.e., central heating, this can only be done with difficulty and requires special low temperature heat emitters such as under-floor tubing set in insulated concrete.
For a competent, skillful person it is possible to install a solar heating system; however specialist professional installers are worth considering especially if the solar collectors are to be mounted on a roof. At the very least, it is worth finding a supplier of parts who will encourage and support your project perhaps designing the plumbing and electrical layout for you. There are resources at the end of this article that can assist you.
Typically, solar water heating is principally comprised of collectors, usually mounted on the roof, facing as near south as permits and (fortuitously!) at the same angle as a typical pitched roof. These collectors can take various forms, the most advanced, efficient, and expensive being the evacuated glass tube heat-pipe type which are grouped, 20 to 30, into manifolds, looking very much like roof windows from a distance. The tubes are highly insulated, due to a vacuum inside the glass, and use alcohol as a transfer fluid instead of water hence they are quick to respond to changing weather and are automatically temperature regulated.
Commercially manufactured flat plate types consist of specially coated black metal surfaces, boxed behind glass or plastic, in which water flows in pipes soldered onto the plates. Despite their lower performance, the payback is often as good as the advanced type due to reduced material costs. These can be assembled from reclaimed materials, however, the resulting low performance and longevity makes this a questionable exercise for the extra work involved especially considering the harsh environment they receive on a normal roof.
The solar hot water from all these collectors is normally pumped down to a well insulated copper storage cylinder, controlled by an electronic temperature sensing switch to avoid unnecessary pumping, where the heat is indirectly exchanged to the domestic hot-water via a coil allowing use of special anti-freeze in the collector.
There are a number of options for the exact plumbing arrangements depending on budget, space, and appearance--perhaps most important being the ability of the existing boiler to accurately respond to preheated water. The opportunity to update existing heating controls should never be missed along with increasing pipe insulation.
A solar water heating system could pay for itself after eight years, although this would depend heavily on the hot water usage and upon the fuel that is being displaced by the sun. Fifteen years is more likely for a professional installation supplying water for two or three people. Many people use solar heating as their contribution to reducing pollution, as well as it being a fascinating subject which ultimately can pay for its cost many times over.
The choice of solar collector influences the appearance, temperatures, and efficiency of the system. However, the following points are equally as important:
- Where to position the storage cylinder
- Insulation on pipes and cylinders
- The way the solar system connects to your existing hot water supply
- Type of pump controller
In the next few years it is expected that millions of households in the world will be using solar energy as the trends in the
Solar energy can also be used to meet our electricity requirements. Through Solar Photovoltaic cells, solar radiation gets converted into DC electricity directly. This electricity can either be used as it is or can be stored in the battery. This stored electrical energy then can be used at night. SPV can be used for a number of applications such as:
- Domestic lighting
- Street lighting
- Village electrification
- Water pumping
- Desalination of salty water
- Powering of remote telecommunication repeater stations
- Railway stations
Everything we build is solar. When we ignore solar energy during the design stages we end up with a building that may benefit from solar, though it is just as likely to be beat up by solar energy.
Passive solar designs will not only lower your utility bills, it will be comfortable, and comfort is priceless.
The following guidelines are drawn from research and practical application, from successes and failures, and from our ancestors who lived in caves to computer generated engineering studies.
Orientation: The longest wall of the home should face south. The winter sun rises south of east and sets south of west. Placing more glass on the south wall will ensure that your home receives free solar energy.
This same orientation helps to prevent the high summer sun from entering the home. A compass will point to magnetic North/South, but a solar home or collector works best when it faces TRUE SOUTH.
Passive Solar and Energy Efficient Home Design
More basic information about solar is also available.
Photovoltaics (PV)
Photovoltaic solar cells, which directly convert sunlight into electricity, are made of semiconducting materials. The simplest cells power watches and calculators and the like, while more complex systems can light houses and provide power to the electric grid.
Passive Solar Heating, Cooling and Daylighting
Concentrating Solar Power
Concentrating solar power technologies use reflective materials such as mirrors to concentrate the sun's energy. This concentrated heat energy is then converted into electricity.
Solar Hot Water and Space Heating and Cooling
Solar hot water heaters use the sun to heat either water or a heat-transfer fluid in collectors. A typical system will reduce the need for conventional water heating by about two-thirds. High-temperature solar water heaters can provide energy-efficient hot water and hot water heat for large commercial and industrial facilities.
The Future of Solar Energy
The success of solar power will depend on the answer to the following question: 'What do you do when the sun goes down?'
The simple answer is to build an auxiliary system that will store energy when the sun is out. However, the problem is that such storage systems are unavailable today. Simple systems, like water pipes surrounded by vacuum, do exist. It is based on the concept that provided the pipes are insulated, the water will store thermal energy.
The ocean is a natural reservoir of solar power and could be used as a source for thermal energy. If we can draw warm water from the surface and cold water from the depths, an ocean thermal plant could operate 24 hours a day. This hypothesis was tested as early as 1930 in
There are also the hybrid systems.
Research on photovoltaic cells will continue. Compared to the other options, the majority of the resources will probably flow into research for developing better and more efficient solar cells. Parallel to that, more research will be undertaken to develop rechargeable batteries that will last longer hours.
Definitions
Alternative energy sources--Energy sources different from those in widespread use at the moment (which are referred to as conventional). Alternative energy usually includes solar, wind, wave, tidal, hydroelectric and geothermal energy. Although they each have their own drawbacks, none of these energy sources produces significant air pollution, unlike conventional sources.
Fossil fuels--Carbon or hydrocarbon fuels, derived from what was living material, and found underground or beneath the sea. The most common forms are coal, oil and natural gas. They take millions of years to form. Their energy is only released upon burning, when the carbon and hydrogen within them combine with the oxygen in air to form carbon dioxide (CO2 ), or carbon monoxide (CO) and water (H2 O). Other elements within the fuels (such as sulfur or nitrogen) are also released into the air after combining with oxygen, causing further pollution with SO2 and nitrogen oxide gases. In the case of coal, ash particles are also a problem.
Non-renewable energy--Used to describe energy sources that exist in a limited amount on Earth. Thus all available material could eventually be completely used up. Coal, oil and gas (see fossil fuels) are considered as non-renewable energy sources because the rate of their formation is so slow on human timescales that they we are using them without them being replaced. Uranium (used in nuclear power) is also non-renewable, although its reserves are very large compared to its rate of use.
Passive solar heating--Buildings designed for passive solar and daylighting incorporate design features such as large south-facing windows and building materials that absorb and slowly release the sun's heat. No mechanical means are employed in passive solar heating. Incorporating passive solar designs can reduce heating bills as much as 50 percent. Passive solar designs can also include natural ventilation for cooling. This energy is used for: cooking/heating, drying/timber seasoning, distillation, electricity/power generation, cooling, refrigeration, and cold storage.
Photovoltaic (PV) cells (Also known as solar cells)--A photovoltaic cell is made of thin wafers of two slightly different types of silicon. One, doped with tiny quantities of boron, is called P-type (P for positive) and contains positively charged 'holes', which are missing electrons. (Electrons are negatively charged particles that orbit the nuclei of atoms.) The other type of silicon is doped with small amounts of phosphorus and is called N-type (N for negative). It contains extra electrons. Putting these two thin P and N materials together produces a junction which, when exposed to light, will produce a movement of electrons – and that constitutes an electric current. Photovoltaic cells thus convert light energy into electrical energy. The simplest cells power watches and calculators and the like, while more complex systems can light houses and provide power to the electric grid.
Renewable energy--Used to describe energy sources that are replenished by natural processes on a sufficiently rapid time-scale so that humans can use them more or less indefinitely, provided the quantity taken per unit of time is not too great. Examples are animal dung, ethanol (derived from plant sugars), wood, wind, falling water and sunlight. Compare non-renewable.
Solar collectors--Devices for capturing the sun’s energy over a large area and focusing it on a small area, thereby concentrating it. In this way it can be made to provide extremely high temperatures, used to generate steam that will expand, or to carry out a chemical reaction to produce a portable fuel such as hydrogen. Solar collectors may be curved dishes - like satellite receiving dishes – coated with reflective material, or can consist of an array of reflectors, arranged like flower petals, focusing onto a central point. Usually the dish or the individual reflectors can be steered to follow the sun across the sky.
Solar energy--Energy derived ultimately from the sun. It can be divided into direct and indirect categories. Most energy sources on Earth are forms of indirect solar energy, although we usually don’t think of them in that way. Coal, oil, and natural gas derive from ancient biological material which took its energy from the sun (via plant photosynthesis) millions of years ago. All the energy in wood and foodstuffs also comes from the sun. Movement of the wind (which causes waves at sea), and the evaporation of water to form rainfall which accumulates in rivers and lakes, are also powered by the sun. Therefore, hydroelectric power and wind and wave power are forms of indirect solar energy. Direct solar energy is what we usually mean when we speak of solar power – it is the use of sunlight for heating or generating electricity.
For more information on solar energy and how to harness it for your home link to:
· www.eren.doe.gov/erec/factsheets/solar.html
· The American Solar Energy Society http://www.ases.org/
· Solar Energy International http://www.solarenergy.org/
· The International Solar Energy Society http://www.ises.org/ises.nsf!Open
· The Solar Energy Industries Association http://www.seia.org/
· Home Energy Magazine http://homeenergy.org/hewebsite/