solar thermal systems

02/05/2023 IEC-803 ENERGY BASICS BY DR N R KIDWAI, INTEGRAL UNIVERSITY 1

Heating Applications & other Solar Applications of Solar Energy

SOLAR THERMAL ENERGY, CONCENTRATING SOLAR, APPLICATIONS AND PERFORMANCE; SOLAR THERMAL POWER PLANTS, THERMAL ENERGY STORAGE FOR SOLAR HEATING AND COOLING, L IMITATIONS, AIR AND WATER HEATING SYSTEMS, SOLAR PUMPS, SOLAR LIGHTING SYSTEMS, SOLAR COOKERS, SOLAR DRYING OF GRAINS.


Solar Thermal EnergySolar thermal technology uses the sun’s energy,, to generate low-cost, environmentally friendly thermal energy. This energy is used to heat water or other fluids, which can be used to generate electricity. Solar thermal systems differ from solar PV systems, which generate electricity directlySolar thermal collectors on a roof, shade structure or other location absorb solar energy.Solar fluid circulated through the collectors by a pump delivers heat to a water storage tank.For hot water use, solar-heated water in the storage tank feeds the water-heating system thereby reducing energy bill for heating


Solar Thermal Energy Thermal Energy Needs Residential Buildings : Hot water for bathing Hotels & Hospitals : Steam for Laundry & Cooking,

Hot water for bathing, washing, cleaning etc

Commercial Buildings: Office & Retail Air-conditioning Steam for canteen cooking Industries / Factories Process Heating


Solar Thermal Energy

Solar Thermal Collectors

Non ConcentratingEvacuated tube Collector (ETC)

Flat Plate Collector (FPC)Solar Pond

Concentrating

Heliostat Field Collector

Parabolic Dish Reflector

Single axis tracking

Non tracking

Two axis tracking

Compound Parabolic Collector

Parabolic Trough Collector

Linear Fresnel Collector

Compound Parabolic Collector


Concentrating Solar Technologies

Concentrating solar thermal power (CSP) turns sunlight into electricity indirectly

Concentrated solar thermal power provides firm, peak, intermediate or base load capacities due to thermal storage and/or fuel back-up.

The building of CSP plant creates eight to ten jobs per megawatt of equivalent electrical solar capacity in the construction and manufacturing of components

There are four main technologies. Troughs and Fresnel reflectors track the sun on one axis, while dishes and towers track the sun on two axes

Trough plants, linear Fresnel reflectors and most tower designs can be completed with heat storage and/or fuel back-up. The current reference technology for storage is based on molten salts.



Troughs or parabolic cylinders accounts for more than 90% of the installed CSP capacity. It is based on parabolic mirrors that concentrate the sun’s rays on heat receivers (i.e. steel tubes) placed on the focal line. Receivers have a special coating to maximise energy absorption and minimise infrared re-irradiation and work in an evacuated glass envelope to avoid convection heat losses.

The solar heat is removed by a heat transfer fluid (e.g. synthetic oil, molten salt) flowing in the receiver tube and transferred to a steam generator to produce the super-heated steam that runs the turbine. Mirrors and receivers (i.e. the solar collectors) track the sun’s path along a single axis (usually East to West). An array of mirrors can be up to 100 metres long with a aperture of 5-6 metres. Most PT plants have capacities between 14-80 MW, efficiencies of around 14-16% and maximum operating temperatures of 390°C



Linear Fresnel reflectors (LFR) FR plants are similar to PT plants but use a series of ground-based, flat or slightly curved mirrors placed at different angles to concentrate the sunlight onto a fixed receiver located several meters above the mirror field. Each line of mirrors is equipped with a single axis tracking system to concentrate the sunlight onto the fixed receiver. The receiver consists of a long, selectively-coated tube where flowing water is converted into saturated steam (DSG or Direct Steam Generation). Since the focal line in the FR plant can be distorted by astigmatism, a secondary mirror is placed above the receiver to refocus the sun’s rays..

The main advantages of FR compared to PT systems are the lower cost of ground-based mirrors and solar collectors In addition, as FR systems use direct steam generation, thermal energy storage is likely to be more challenging and expensive.



Towers or central receiver systems (CRS), In the ST plants a large number of computer assisted mirrors (heliostats) track the sun individually over two axes and concentrate the solar irradiation onto a single receiver mounted on top of a central tower where the solar heat drives a thermodynamic cycle and generates electricity. The ST plants use water-steam (DSG), synthetic oil or molten salt or high temperature gas as the heat transfer fluid. Maximum operating temperatures may range from 250-300°C (water-steam) to 390°C (synthetic oil) and up to 565°C (molten salt), above 800°C (gases).

ST plants can be equipped with thermal storage systems whose operating temperatures also depend on the primary heat transfer fluid. High-temperature ST plants offer potential advantages over other CSP technologies in terms of efficiency, heat storage, performance, capacity factors and costs.



Parabolic dishes or solar dishes The SD system consists of a parabolic dish shaped concentrator (like a satellite dish) that reflects sunlight into a receiver placed at the focal point of the dish. The receiver may be a Stirling engine (i.e. kinematic and free-piston variants) or a micro-turbine. SD systems require two-axis sun tracking systems and offer very high concentration factors and operating temperatures.

The main advantages of SD systems include high efficiency (i.e. up to 30%) and modularity (i.e. 5-50 kW), which is suitable for distributed generation. Unlike other CSP options, SD systems do not need cooling systems for the exhaust heat. This makes SDs suitable for use in water-constrained regions, though at relatively high electricity generation costs compared to other CSP options. The Big Dish technology uses an ammonia-based thermo- chemical storage system.


Solar thermal power plantsSolar thermal power uses solar energy instead of combustionSolar thermal power plants use the sun's rays to heat a fluid to high temperatures. The fluid is then circulated through pipes so that it can transfer its heat to water and produce steam. The steam is converted into mechanical energy in a turbine, which powers a generator to produce electricity.Parabolic trough power plant Solar thermal power generation works essentially the same as power generation using fossil fuels, but instead of using steam produced from the combustion of fossil fuels, the steam is produced by heat collected from sunlight. Solar thermal technologies use concentrator systems to achieve the high temperatures needed to produce steam


Solar thermal power plants


Solar thermal power plants

Schematic of solar thermal tower power plant, with pressurized receiver combined gas & steam turbine cycle


Air and Water heating systems, Over 70% of the household’s energy use goes into space and water heating/ cooling. Covering a big part with a solar system leads to energy as well as financial savings. Solar heating/ cooling is a well established renewable energy source and applied in numerous projects worldwide. Solar thermal systems consist of a solar collector, a heat exchanger, storage, a backup system and a load. This system may serve for both, space heating and tap water heating, known as combi system.

Typical solar heating application Flat plate collector

Evacuated tube collector


Solar Thermal Cooling Systems, There are three thermal driven systems: • Absorption cooling with chilled water • Adsorption cooling with chilled water • Desiccant cooling for air based cooling systems Solar assisted cooling systems involve solar thermal collectors connected to thermally driven cooling devices. They consist of several components: the solar collectors, heat buffer storage, the air conditioning subsystem, including various forms of cold distribution, and auxiliary subsystems

Advantages of thermal Cooling systemsThe availability of high solar radiation during the time when cooling is needed the applicability of thermal energy as driving energy low operating costs and low electrical power rating, Durability and environmental compatibility The disadvantage of solar cooling systems are the still high installation costs, the space needed for heat storage and the additional backup system necessary


Solar Thermal Cooling Systems,

Solar assisted cooling systems: Thermally driven chillers coupled to solar thermal system, cooling water loop and chilled water loop


solar pumps, A protected hole is drilled down into the earth to reach a water source. A solar panel made of photovoltaic modules powers an electric motor - which in turn powers an underground water pump. This pump can draw clean, fresh water, every day.


solar lighting systems, Standalone street light

Solar-powered lighting consists of a solar panel or photovoltaic cell that collects the sun's energy during the day and stores it in a rechargeable gel cell battery.

The intelligent controller senses when there is no longer any energy from the sun and automatically turns the LED light on using a portion of the stored energy in the rechargeable battery.

Solar Street Light


solar cookers, A solar cooker is a device which uses the heat energy of sunlight to heat, cook or pasteurize food or drink. Solar cookers presently in use are relatively inexpensive, low-tech devices. large-scale solar cookers can cook for hundreds of people. Because they use no fuel and cost nothing to operate, thereby reduce fuel costs air pollution, and slow down the deforestation and desertification caused by firewood for cooking. Solar cooking is a form of outdoor cooking and is often used in situations where minimal fuel consumption is important, or the danger of accidental fires is high, and the health and environmental consequences of alternatives are severe. Many types of solar cookers exist, including curved concentrator solar cookers, solar ovens, and panel cookers, among others.

Solar Oven

Parabolic Solar Cooker


solar drying of grains.Solar energy is an excellent alternative source of supplemental heat for low-temperature grain drying systems. Because these systems require only a few degrees additional temperature rise 5-10 F, they are well adapted to the moderate heat increases that solar energy can economically generate. Also, if the temperature rise during midday is substantially above this, the grain will store the excess heat and release it during the night, allowing no drying process to continue.


Solar pondSolar pond collect solar thermal energy and used it for direct heating, water heating, electrical power generation etc.Hence, a solar pond refers to a device which collects and stores the solar radiation energy.It consist of an expanse of water about a meter or two in depth in which salts like sodium or magnesium chloride are dissolved.The concentration of the salt is more at the bottom and less at the top. Because of this, the bottom layers of water are denser than the surface layers even if they are hotter and natural convention does not occur.Thus, the heat from the sun’s rays absorbed at the bottom of the pond is retained in the lower depths, and the upper layers of water, act like a thermal insulation.


Solar pondThe solar pond is large shallow reservoir of salt water. The water gets heated by the sunlight and bottom of pond is painted with black color to absorb heat. Due to convention of water, heat passes through salt waters (different concentrations). The solar pond acts like a thermal collector with large surfaces and large volume.

solar thermal systems

Engineering