Photo Voltaic Cells or PV solar panels are nothing new. 
If you have time to spare go through half century old DIY
publications you would encounter various gadgetry like radios, toys etc. powered by PV cells.
It appears that even after over a half a century PV panels still remain
almost a novelty for average householders.
The Solar Thermal Panels (commonly called solar Water heater panels)
on the other hand are simple devices widely used in domestic
applications and many are therefore familiar with them.
How do they differ?
PV panels convert solar energy directly to Electrical energy. The solar energy incident on the PV panels is converted to electrical energy through the photovoltaic action of the material used to manufacture the panels. At best the conversion efficiency does not exceed 15% in practice though under laboratory conditions efficiencies around 20 % have been obtained.
The resultant energy form off PV panels is direct current and storage is possible with lead acid batteries (as in your car).Unfortunately still storing electrical energy in storage batteries is neither efficient nor economical in the long run.
Solar Panels (also called solar water heaters) in comparison are used for your houses’ hot water needs. While they do work in any climatic condition they are also cost effective. An insulated tank is all that you require for the storage of thermal energy.
Types of Solar Water Heaters
You have the choice to decide on two main different types. viz;
• Active design- which uses circulating pumps and controls
• Passive design – which don’t use any of them
Both however incorporate solar collectors and storage tanks.
Storage tanks
Unlike many other alternative energy sources and electrical energy solar energy can be easily stored as hot water in well insulated water tanks. This means even when the sun has set your hot water will be at hand. The storage tank generally has additional inlet and outlet connections for connection to the collector.
In the installations where two tanks are employed the solar water heater pre-heats the water before it enters the conventional water heater. On the other hand where a single storage tank is employed the back up heater is incorporated within the single storage tank itself.
Solar Heat collectors for domestic applications
There are three types, namely;
• Flat –plate collectors-These Glazed flat plate collectors are weather resistant thickly insulated black plated boxes to retain the collected energy having a top cover of transparent glass or Polymer plate. A variation is the type used for swimming pool heating where the enclosure and the transparent tops are absent and has only dark colored metal or Polymer absorber plates
• Integral Collector –storage systems (aka ICS or Batch Systems)-These comprise of insulated glazed enclosure containing one or more blackened tanks or tubes within. In this technique cold water is pre heated by passing through the solar collector which is then sent to the conventional back up water heater. This is a very reliable system but has some limitations. For example if used in extreme cold climates the outdoor pipes could freeze up.
• Evacuated Solar collectors- These employ several rows of glass tubes in “tube in tube” arrangement with additional absorber metal tube in each. The metal tube has a fin which collects the solar energy and a coating on it absorbs energy but inhibits radiant heat loss. Generally this type is used in commercial water heater applications.
What ever the type of collector or what ever the design, solar energy is free for you. When you consider even in an energy efficient home the share of water heating cost is about 29% you can imagine what your annual savings would be.
Thanks the Techstore Team
