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Types of Solar Energy

“Solar” means “of or pertaining to the sun”, and comes from the Latin word “sol”, meaning “sun”. Solar energy refers to energy directly originating from the sun. Confusion sometimes arises over the difference between solar thermal and solar electric energy, as the term “solar energy” can be used for either or both forms! Similarly, a “solar collector” may refer to either a solar thermal or a photovoltaic panel. The following explanation clarifies the difference between solar thermal and PV, and will help you understand what someone is referring to when the mention “solar energy”.

Solar Thermal Panel Cross-Section

Solar Thermal Heating

Solar thermal collectors convert the sun’s energy to heat. Inside the collector is an absorber system. The absorber traps the radiation inside, converting it to heat. This absorber is made of a high-conductivity material (copper or aluminium), which increases the amount of heat transferred. It is treated with a selective coating to increase heat absorption. A heat transfer fluid, non-toxic antifreeze (propylene-glycol mixed with water), passes through the absorber. Once warmed, this fluid transfers the heat energy to a hot water tank. A heat exchanger is used to avoid contamination of drinking water. This occurs within a separate closed loop system.

Solar thermal systems can be used all year round. Thermal systems can provide all domestic hot water, and assist your existing heating system as well as providing heating for existing swimming pools.

Photovoltaic Energy

Much attention has been given to photovoltaic (PV) energy in recent years. This has been due to significant advances in the field.

Photovoltaic cells convert sunlight striking its surface into electricity. The sun frees electrons from the surface of the cell, and causes them to migrate to the opposite side. This migration creates a difference in voltage potential across the cell. The voltage difference and electron flow creates electricity.

Multiple PV cells are combined to create a PV panel. The panels can be connected in series or in parallel to create a PV array with the desired voltage and energy output. The DC (direct current) electricity from the PV array is captured and transferred along wires for use or storage. Presently many stand-alone systems utilize batteries for storage. Electricity from PV may either be used directly with special DC appliances, or converted to AC (alternating current) using an inverter for use with common household appliances.

Various jurisdictions are investigating the direct connection of PV energy to the local electricity grid, which would reduce the need for battery back up and increase efficiency. However, due to policy and safety issues, grid-connected PV systems still face considerable roadblocks.

In terms of a cost-comparison, PV systems are considerably more cost-competitive than they were twenty years ago. However, they are still several years, and incentives, away from large-scale implementation. They continue to be the energy-source-of-choice to those keen on environmental sustainability, and to those located far from the electric grid, where the cost of connection is high.

Due to the relative simplicity in design and components, solar thermal systems are presently financially viable alternatives for those wishing to invest in a green future and high economic returns.