SOLAR THERMAL ENERGY

Solar thermal is a type of technology that is used for utilizing solar energy to get thermal energy. Solar thermal energy is a form of energy in which the sun is used to produce heat that can be used in a variety of ways. This technology has been used for generations and has been constantly improved by modern technology to expand it’s applications.
SOLAR THERMAL GENERATION
Solar thermal energy is a renewable energy source that converts the heat from solar rays into electricity by indirect means, using steam cycles. Several types of technologies can be used to generate solar thermal energy. Different designs are used as described below;
Parabolic trough designs
This design uses a curved mirrored trough that reflects the solar radiation directly to a glass tube containing the fluid which runs along the length of the trough. The trough is made to tilt in an east to west direction in order to maintain direct focus of the radiation on the pipe. To reduce convective heat loss, the receiver may be enclosed in a glass vacuum chamber. This design is suitable for operation within an average temperature range from 125º C to 400º C.
Power tower designs
In this design, flat mirrors are used to concentrate the light on top of a tower. This method is also called the Rankine cycle and it has the advantage of achieving higher temperatures.
Dish designs
In this design, a solar dish is used to concentrate the sun’s rays on the heating element that is placed above the dish. High temperatures are achieved. This design has the advantage of higher conversion efficiency.
Fresnel reflectors
A series of long narrow mirrors are used to focus light onto receivers which are placed on top of the mirror. This is a cheaper alternative as several mirrors can be used to focus on one receiver. This design is also easier to design as the receiver is not supported by the mirrors.
Fresnel lenses
Prototypes of Fresnel lens concentrators have been produced for the collection of thermal energy by International Automated Systems. No full-scale thermal systems using Fresnel lenses are known to be in operation, although products incorporating Fresnel lenses in conjunction with photovoltaic cells are already available.
The advantage of this design is that lenses are cheaper than mirrors. Furthermore, if a material is chosen that has some flexibility, then a less rigid frame is required to withstand wind load. A new concept of a lightweight, 'non-disruptive' solar concentrator technology using asymmetric Fresnel lenses that occupies minimal ground surface area and allows for large amounts of concentrated solar energy per concentrator is seen in the 'Desert Blooms' project, though a prototype has yet to be made.
HEAT COLLECTION AND EXCHANGE
Heat in the thermal systems is governed by five basic principles. Heat here is a measure of the quantity of energy that an object contains These principles are 1. Heat gain: this is the amount of heat that is accumulated from the sun in the system. The ability of the reflective surface to transmit short wave reflection and reflect long wave radiation enables the system to trap solar thermal heat. 2. Heat transfer: this is done either through conduction or convection 3. Heat storage: this enables solar thermal plants to produce electricity during hours without sunlight. Heat is transferred to a thermal storage medium in an insulated reservoir during hours with sunlight, and is withdrawn for power generation during hours lacking sunlight. Heat storage media include molten salts, pressurized steam, concrete, graphite and phase change materials. 4. Heat transport: this refers to the activity in which heat from a solar collector is transported to the heat storage vault 5. Heat insulation: this prevents heat loss, which in turn relates to energy loss, or decrease in the efficiency of the system.
USES OF SOLAR THERMAL
Solar process heating
These systems are designed to provide large quantities of hot water or space heating for nonresidential buildings. Evaporation ponds
These are shallow ponds that concentrate dissolved solids through evaporation. The use of evaporation ponds to obtain salt from sea water is one of the oldest applications of solar energy. Modern uses include concentrating brine solutions used in leach mining and removing dissolved solids from waste streams. Altogether, evaporation ponds represent one of the largest commercial applications of solar energy in use today.
Solar drying
Solar thermal energy can be useful for drying wood for construction and wood fuels such as wood chips for combustion. Solar is also used for food products such as fruits, grains, and fish. Crop drying by solar means is environmentally friendly as well as cost effective while improving the quality. The less money it takes to make a product, the less it can be sold for, pleasing both the buyers and the sellers. Technologies in solar drying include ultra low cost pumped transpired plate air collectors based on black fabrics. Solar thermal energy is helpful in the process of drying products such as wood chips and other forms of biomass by raising the heat while allowing air to pass through and get rid of the moisture
Cooking
Solar cookers use sunlight for cooking, drying and pasteurization. Solar cooking offsets fuel costs, reduces demand for fuel or firewood, and improves air quality by reducing or removing a source of smoke.
The simplest type of solar cooker is the box cooker first built by Horace de Saussure in 1767. A basic box cooker consists of an insulated container with a transparent lid. These cookers can be used effectively with partially overcast skies and will typically reach temperatures of 50–100 °C.
Concentrating solar cookers use reflectors to concentrate solar energy onto a cooking container. The most common reflector geometries are flat plate, disc and parabolic trough type. These designs cook faster and at higher temperatures (up to 350 °C) but require direct light to function properly.
Distillation
Solar stills can be used to make drinking water in areas where clean water is not common. Solar distillation is necessary in these situations to provide people with purified water. Solar energy heats up the water in the still. The water then evaporates and condenses on the bottom of the covering glass.

Solar wax melter
Industries that utilize wax normally require that the wax is in melted form for processing. Solar thermal technologies give a viable option that may lead to reduction of cost that would be incurred to generate heat using different methods.