There are a large number of applications in which solar energy can be utilized directly by exploiting its heat characteristics. Such technologies are comparatively simple, relatively low cost and easy to adopt. The applications include off and on grid power generation, cooking, heating and cooling of buildings, generation of high temperature steam, heating water for domestic and industrial applications, and drying agricultural products under controlled temperatures.
Solar Thermal power uses direct sunlight, called ‘infrared radiation’ or Direct Normal Irradiation (DNI). This is the sunlight that is not deviated by clouds, fumes or dust in the atmosphere and which reaches the Earth’s surface in parallel beams for concentration.
Suitable sites are those that get a lot of this direct sun – at least 2,000 kilowatt hours (kWh) of sunlight radiation per square meter annually. The best sites receive more than 2,800 kWh / m2 a year. Typical regions for Concentrated Solar Power (CSP) are those without large amounts of atmospheric humidity, dust and fumes. They include steppes, bush, savannas, semi-deserts and true deserts, ideally located within less than 40 degrees of latitude north or south.
The most promising areas of the world include the south-western United States, Central and South America, North and Southern Africa, the Mediterranean countries of Europe, the Near and Middle East, Iran and the desert plains of India, Pakistan, the former Soviet Union, China and Australia. In these regions, 1 sq km of land is enough to generate as much as 100 - 130 GWh (GWh) of solar electricity a year using solar thermal technology. This is the same as the power produced by a 50 MW conventional coal or gas-fired mid-load power plant. Over the total life cycle of a solar thermal power system, its output would be equivalent to the energy contained in more than 5 million barrels of oil.
Like conventional power plants, CSP plants need cooling at the so-called “cold” end of the steam turbine cycles. This can be achieved through evaporative (wet) cooling where water is available or through dry cooling (with air) – both are the conventional technologies. Dry cooling requires higher investment and eventually leads to 5% to 10% higher cost compared to wet cooling.
There is another options which is Hybrid cooling. Hybrid cooling can optimize performance for site conditions and these are under further development. However, the huge solar power potential in these areas by far exceeds local demand. So, solar electricity can be exported to regions with a high demand for power but with less solar resource.
If the sun-belt countries harvest their natural energy in this way, they would be making a big contribution to protecting the global climate. Certain country such as Germany is already seriously considering importing solar electricity from North Africa and Southern Europe as to make their power sector more sustainable. Off course, for any new development, local demand should be met first
HOW IT WORKS – THE TECHNOLOGIES
A range of technologies can be used to concentrate and collect sunlight and to turn it into medium to high temperature heat. This heat is then used to create electricity in a conventional way, for example, using a steam or gas turbine or a Sterling engine.
Solar heat collected during the day can also be stored in liquid or solid media such as molten salts, ceramics; concrete or phase-changing salt mixtures. At night, it can be extracted from the storage medium to keep the turbine running.
Solar thermal power plants with solar - only generation work well to supply the summer noon peak loads in wealthy regions with significant cooling demands, such as Spain and California. With thermal energy storage systems they operate longer and even provide base-load power.
CSP plants produce electricity in a similar way to conventional power stations – using steam to drive a turbine. The difference is that their energy comes from solar radiation converted to high-temperature steam or gas. To harness the solar thermal energy four main elements are required: a concentrator, a receiver, some form of transport media or storage, and power conversion.
Many different types of systems are possible, including combinations with other renewable and non-renewable technologies. So far, plants with both solar output and some fossil fuel co-firing have been favored, particularly in landmark developments in the US and North Africa. Hybrids plants help produce a reliable peak-load supply, even on less sunny days.
FOR DETAIL SOLAR THERMAL:
Solar Thermal power Plant:
SOLAR WATER HEATER
Solar water heating technology is quite mature but its use in Pakistan has been quite limited so far mainly because of inability of market development and absence of governmental support and subsidized gas price. A number of public sector organizations are actively working on the development of low cost solar water heaters that have now started gaining popularity particularly in the northern mountainous regions due to cold weather and limited and difficult supply of natural gas in these areas. With the electricity and natural gas prices registering sharp increases, the use of solar water heaters is bound to increase. The production and commercialization of such heaters has already been started in the private sector.
Solar Water Heating:
SOLAR DRYER (Detail attached in the brochure)
Solar energy can be utilized very effectively in drying agriculture products using solar dryers, and good quality products can be obtained at much less cost due to savings in cost of electricity or other heating fuels that would have been used otherwise for the same purpose. Due to the lack of logistics and basic infrastructure in the northern mountainous regions of Gilgit and Sakardu etc tons of fruit like apricots go waste every year. Solar dryers are now being used to dry large quantities of such fruit, which are transported and sold them later in the urban market, resulting in a positive effect on the economy of this area. Solar dryers could be equally effectively used in the provinces of Punjab and Sindh to dry agriculture products for better market value and generating local employment.
Recent achievement of PCRET in solar Drying, several models of solar dryers have been developed by this council and are being disseminated.
Ø In Public Sector Development Programme, Govt of Pakistan PCRET designed developed and installed 10 unglazed collector type hybrid (Solar + Biomass) dryer having 500 kg capacities for drying of dates in Punjab, Khyber Pakhtoonkhwa.
Ø Designed solar dryer for Pakistan Tobacco Board for Curing of Tobacco.
Ø Designed 500 kg capacity solar tunnel dryer for drying of fruits and vegetables for Govt of Sindh in this project Sindh Govt disseminate 80 solar dryers of 500 kg each in Sindh.
Ø Designed and developed Green House Solar Dryer of 200-300 kg capacity.
Solar Dryer: https://en.wikipedia.org/wiki/Solar_dryer
The unavailability of drinkable water in large parts of Baluchistan, Sindh and Southern Punjab is a critical issue. Underground water exists, but it is highly saline due to the presence mainly of sodium chloride and other salts. Saline water is not only unsuitable for washing and cleaning but also causes many stomach diseases and hypertension. Solar energy can very effectively and economically be used to convert this available saline water into potable water. The solar desalination technology is simple, low cost and low-tech, and therefore, local people can easily adopt it. Furthermore, solar desalinated water is also free from bacteria, which is killed during the process due to high water temperature in the still, Several small plants of capacity 250 gallons per day each in rural areas to convert brackish water into potable water.
Solar Desalination: https://en.wikipedia.org/wiki/Solar_desalination
A number of public sector organizations have worked in the past and are still working on the development of low cost and efficient designs of both box and concentrator type solar cookers. Non-governmental organizations are also active in this field and have supplied a number of such cookers to rural areas. The Pakistan Council for Renewable Energy Technologies (PCRET), which is later described in this paper, routinely organizes training workshops on the use and maintenance of such devices. The numbers of solar cookers in use in Pakistan is more than 10,000, but it is still far less than that being used in China and India (400,000). Pakistan needs to popularize solar cookers to reduce the use of precious forest resources as fuel wood.
Solar cookers come in two types: box types that are more suitable for baking the food, and concentrated (parabolic) type that works at high temperatures. Foods prepared in solar ovens keep their natural flavor and taste and retain their vitamin content. Less oil is required for cooking in the solar oven, therefore, solar oven cooked food is good for weight conscious people.
All Pakistani dishes including prathas and chapatti can be prepared on concentrated type cooker in the same time interval as taken by a conventional single stove gas cooker. The method of cooking is also similar to that of conventional cooker. The cooker emits no harmful smoke to harm eyes and lungs of the cook. The cooking can be done on this cooker from 9.00 am to 3.00 p.m. on all sunny days of the year.