ICB (Projects) installed a 36kWp solar PV system of thin-film modules on the conference centre at the National Farmers Union HQ at Stoneleigh Park, Warwickshire, built by Thomas Vale Construction in 2012
An understanding of the various types of solar PV technology can enable specifiers to benefit their clients financially as well as helping the environment. Rob Jackson explains.
Most specifiers will be familiar with the basic principle of photovoltaic (PV) panels being used on a rooftop to convert solar light radiation into electricity for use in the building or to be fed into the National Grid. They will also be familiar with the various reasons why promoting renewable energy can be a good idea: from helping the environment to the fact that their clients will benefit financially from the installation as a result of the government-backed feed-in tariff scheme.
Some, however, may not fully understand the various types of solar PV technology that are available to fit on roofs or the factors that should be considered when choosing a system.
PV technology has made dramatic progress in a relatively short period of time, with efficiencies improving greatly, which is just as well as there is an ever-increasing need to tackle the effects of climate change.
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In January 2015, the European Council – the heads of state of the EU member states – reached agreement over its 2030 climate and energy policy framework, and the implications will be challenging. The Council has agreed a binding EU target of at least a 40% reduction in greenhouse gas emissions by 2030 compared to 1990 levels. This target will be delivered collectively by the EU, with all member states involved in the effort. Also the EU target for each member state to reach a minimum of 27% renewable energy by 2030 will be binding.
Although some felt that the Council should have been more ambitious with its targets, there is little doubt that renewables, and in particular photovoltaic energy, will play an increasing role in the construction of our buildings.
Finding the right PV solution
Photons from sunlight strike the PV array and excite electrons within a semiconductor material, freeing them to flow in conductive materials, thus generating electricity through what is known as the photovoltaic effect. Photovoltaic panels produce their highest outputs when sunlight is at its maximum, and obviously none at night. The orientation of the roof, together with shading factors, will have a big influence on determining the best system.
PV arrays are made up of cells that typically comprise silicon crystals doped with phosphorous and boron to stimulate the movement of free electrons and subsequent power generation. Polycrystalline and monocrystalline are the most common types of PV cell, accounting for over 90% of the market. Thin film panels on the other hand are made from various semi-conductor materials and perform better when less than ideal conditions exist, i.e. when heavy cloud or shade issues come into play.
“Traditional” crystalline panels that can achieve efficiencies of up to 17% – which is defined as the electrical energy output divided by the solar energy incident upon the active surface of the PV array – are common.
Polycrystalline cells were historically cheaper, but also less efficient, than monocrystalline cells. However, in today’s market all modern panels have a similar efficiency and price point. Some manufacturers combine crystalline and thin film technologies to create panels that are up to 19.4% efficient and some premium manufacturers now have monocrystalline panels available which push this efficiency up to 21.5%.