Industry Report: Non-Conventional Solar Energy Technologies

In a future society with limited access to fossil fuels, the availability of technologies for efficient and on demand delivery of renewable energy will be highly desirable. In this regard, methods that allow for solar energy storage and on demand solar driven power generation are particularly relevant, since the sun is the most abundant energy source available. Small solar energy systems can provide electricity for homes, businesses and remote power needs. Additionally, larger solar energy systems provide more electricity for contribution to the national electric power system. Solar energy systems can be divided into two major categories: photovoltaic and thermal. Photovoltaic cells produce electricity directly, while solar thermal systems produce heat for buildings, industrial processes or domestic hot water. Thermal systems can also generate electricity by operating heat engines or by producing steam to spin electric turbines. Solar energy systems have no fuel costs, so most of their cost comes from the original investment in the equipment. How Solar Photovoltaic works Solar Photovoltaics (PV) arrays capture the sun’s energy using photovoltaic cells. These cells do not need direct sunlight to work, as they can still generate some electricity on a cloudy day. The cells convert the sunlight into electricity, which can be used to run household appliances and lighting.

The power of a PV cell is measured in kilowatts peak (kWp). That is the rate at which it generates energy at peak performance in full direct sunlight during the summer. A 4kWp system can generate around 3,800 kilowatt hours of electricity a year in the south of England (the same amount of electricity it takes to turn the London Eye 25 times). A system of this size will save nearly two tonnes of carbon dioxide every year. The average domestic solar PV system is 4kWp and costs £5,000 – 8,000, including VAT at 5 per cent. More information about this solar energy technology can be found here: https://renewableinstitute.org/training-courses/-solar-photovoltaic-courseHow Solar Thermal works

Solar hot water systems (also known as solar thermal) harness heat from sunlight by capturing energy that is radiated by the sun within solar panels or collectors. Solar water heating is not to be confused with solar PV (Photovoltaic), which is designed to generate electricity.

Concentrating solar power (CSP) Technologies Concentrating solar power (CSP) technologies use mirrors to concentrate (focus) the sun’s light energy and convert it into heat, to create steam to drive a turbine that generates electrical power. CSP technology utilises focused sunlight. CSP plants generate electric power by using mirrors to concentrate the sun’s energy and convert it into high-temperature heat. That heat is then channelled through a conventional generator. The plants consist of two parts: one that collects solar energy and converts it to heat, and another that converts the heat energy to electricity. Trough Systems A parabolic trough is a type of solar thermal collector based on the concept of concentrating only direct sunlight, with the aim of heating a thermal fluid, which will be used to generate either electricity or thermal energy to feed industrial processes.

Solar collectors must be fitted with a proper monitoring system that enables them to rotate their position following the path of the sun, to maximize capture of solar energy. Solar energy is reflected from mirrors and concentrated into glass receiver, which is located in the focal line of the mirror. This heats the fluid that flows through the receiver pipe, achieving temperatures of 400ºC with efficiencies between 60 and 70 per cent. The fluid in the pipe can be water, oil or even molten salts. Power Tower Systems Power tower systems, also called central receivers, use many large, flat heliostats (mirrors) to track the sun and focus its rays onto a receiver. The receiver sits on top of a tall tower, in which concentrated sunlight heats a fluid, such as molten salt, as hot as 600 ºC. The hot fluid can be used immediately to make steam for electricity generation or stored for later use. Molten salt retains heat efficiently, so it can be stored for days before being converted into electricity. That means electricity can be produced during periods of peak need on cloudy days or even several hours after sunset.

Dish Stirling Systems These systems use mirrored dishes to focus and concentrate sunlight onto a receiver. The receiver is mounted at the focal point of the dish. To capture the maximum amount of solar energy, the dish assembly tracks the sun across the sky. The receiver is integrated into a high-efficiency external combustion engine. The engine has thin tubes containing hydrogen or helium gas that run along the outside of the engine’s four piston cylinders and open into the cylinders. As concentrated sunlight falls on the receiver, it heats the gas in the tubes to very high temperatures, which causes hot gas to expand inside the cylinders. The expanding gas drives the pistons. The pistons turn a crankshaft, which drives an electric generator. The receiver, engine, and generator comprise a single, integrated assembly mounted at the focus of the mirrored dish.

Fresnel Reflector Systems This technology uses modular, flat mirrors to focus the sun’s heat onto long, elevated receivers, which consist of a system of boiler tubes through which water flows. The concentrated sunlight boils the water in the tubes, generating saturated and super-heated solar steam for use in power generation and industrial steam applications, thereby generating electricity.

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This report was written by Salvador Selva Martí for the Renewable Energy Institute (REI). Salvador is an REI Volunteer and AREI member of the EnergyCPD Global Professional Membership Programme. If you would like to get in touch with Salvador, please email training@renewableinstitute.org References [1] Clean Energy for Future. 2015. Solar energy, solar cells and solar panels. [ONLINE] Available at: http://cleanenergyforfuture.com/solar-energy-solar-cells-and-solar-panels/. [Accessed 23 May 2016]. [2] Belarusian web portal on renewable energy. 2012. Solar energy overview. [ONLINE] Available at: http://re.energybel.by/en/solar-energy-overview/. [Accessed 23 May 2016]. [3] GreenTech Systems. 2012. An introduction to thin film solar PV Cell Panels. [ONLINE] Available at: http://www.green-technology-systems.ie/an-introduction-to-thin-film-solar-pv-cell-panels/. [Accessed 23 May 2016]. [4] The Renewable Energy Hub UK. 2016. Solar Thermal Panel Mounting Methods. [ONLINE] Available at:https://www.renewableenergyhub.co.uk/solar-thermal-panels-mounting-methods.html. [Accessed 23 May 2016]. [5] Ecoideaz. 2016. Concentrated Solar Power in India – Still in Infancy. [ONLINE] Available at: http://www.ecoideaz.com/expert-corner/concentrated-solar-power-in-india-still-in-infancy. [Accessed 23 May 2016]. [6] The Energy Backyard. 2013. CONCENTRATED SOLAR POWER. [ONLINE] Available at:https://theenergybackyard.wordpress.com/2013/03/25/concentrated-solar-power/. [Accessed 23 May 2016]. [7] Shaik Mohasin. 2012. National Solar Energy Summit – 2012. [ONLINE] Available at: https://shaikmohasin.wordpress.com/tag/csp/. [Accessed 23 May 2016]. [8] The Energy Backyard. 2013. CONCENTRATED SOLAR POWER. [ONLINE] Available at:https://theenergybackyard.wordpress.com/2013/03/25/concentrated-solar-power/. [Accessed 23 May 2016].