PHOTOVOLTAIC PANELS

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CAT, PV panels within roof lights (Bagnall, 2015)

WHAT ARE PHOTOVOLTAIC PANELS?

Photovoltaic (PV) panels (otherwise referred to as Solar Panels) are a growing trend across the world in a bid to adapt to using sustainable technologies. While at CAT, a lecture was presented to us from Arthur Butler on the practical uses of PV Panels and how variations in design and weather can affect the electrical output of them.

PV panels are typically made from a silicon base (covalently bonded together), with boron and phosphorus diffused either side of the silicon. It is the electron displacement caused by the solar radiation (gamma) upon the panel, which creates the electricity. This electrical output (form of a DC current) is then sent through an inverter which turns the electricity to an AC current, this can either be used directly in the property or sent into the mains grid. There are positive and negatives to how you use the electricity; if electricity is sent into the mains grid (also known as a UK Feed-in-Tariff), the government will pay for the electricity you supply into the grid. If the electricity is kept, batteries for these systems have low-efficiency and you will lose a lot of the outputted electricity (through various energy transfers), therefore it is recommended that when you have the panels installed you sign up for the Feed-in-Tariff.

HOW DO THEY WORK?

Example of PV panels (Bagnall, 2015)

The solar radiation from the Sun is a vast renewable source, however particularly in the UK, due to the weather system we cannot always efficiently harness all of this energy. As people well know, the UK is not always known for its clear, blue skies and is often cloud covered. This results in a different form of radiation which provides the input to the PV panels;

Direct Radiation

When there is little-to-no cloud cover between the Sun and the PV panel, and the solar radiation hits the panel DIRECTLY. This allows for a higher output of electrical energy from the panel.

Diffuse Radiation

Diffuse radiation relates to when there is medium to high cloud coverage between the panel and the Sun, meaning that the panel will have a smaller input of solar radiation (radiation has DIFFUSED through the clouds, small part of radiation will be absorbed).

As well as cloud coverage (weather), there are various different aspects location and surrounding which need to be considered before installing a photovoltaic panel.

Air pollution
Solar geometry
Diurnal variation
Wind direction

APPLICATION OF PV PANELS IN THE UK

In the UK, standardising tests have been performed with panels to judge how to maximise the efficiency of them when used on both domestic and non-domestic properties. These standardising tests have shown that a panel should be at UK average roof pitch of 35 degrees to provide the best efficiency of the panel. Furthermore the tests shown that the placement of the panels upon the roof plane needs to be calculated carefully to stop any damage to the panels; standard measurements state that a 500mm gap on domestic and a 1000mm gap on non-domestic should be left around the panels to prevent wind lift/damage.

When you see PV panels on roofs, there are mostly static panel which are attached to the roof and do not move; this results in a varying efficiency throughout the day due to the sun path across the sky. This has results in the creation of different panel framing.

Static – does not move (attached to roof plane)
Solar Tracking – allows panel to move on a single axis to follow the sun path
Dual-Axis – allows panel to move on two axes, increasing its position to increase efficiency.

Even though it can be easily accepted that a dual-axis system is better, it is a lot more expensive than a standard static fixing and requires greater room to accommodate its rotation.

TYPES OF PV PANELS

PV panels come in different configurations and sizes, however the generic type of panel can be categorised into three types;

· Mono-crystalline

Single crystalline silicon made from a silicon ingot (pure silicon); can be identified by its black colour. Efficiency of this panel is approximately 22% (at standard testing)

· Poly-crystalline

Multi-crystalline silicon/polysilicon; this panel can be identified with its medium-dark blue colour. This panel is cheaper to make that the mono-crystalline, which also results in a lower efficiency.

· Amorphus

Also known as Thin Film. Sprayed silicon panel with an efficiency of approximate 12%.

APPLICATION TO PROJECT

In terms of applying this technology to my project, I would agree that this form of technology would be ideal. Geographical, the site allows for PV panels to be used, however the weather which the site experiences will need to be considered as well as surrounding context (shading from surrounding building and trees). Nevertheless, the range of photovoltaic panels which are available will provide ways around problems the site brings and makes the use of PV panels (mostly likely mono-crystalline due to higher efficiency) very viable on this project.

COMPANIES/SUPPLIERS

SolarWorld UK - http://www.solarworld-uk.co.uk/products/solar-modules/overview/

EvoEnergy - http://www.evoenergy.co.uk/solar-panels/
Sharp - http://www.sharp.co.uk/cps/rde/xchg/gb/hs.xsl/-/html/photovoltaic.htm

ADDITIONAL LINKS

British Photovoltaic Association - http://bpva.org.uk/
Bristish Gas - http://www.britishgas.co.uk/products-and-services/solar-panels/solar-pv.html
Energy Saving Trust - http://www.energysavingtrust.org.uk/domestic/content/solar-panels

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