Buyers Guide

How Solar PV Works

Solar panels convert sunlight into electrical energy using a thin layer of semi-conducting materials most commonly silicon, encased between a sheet of glass and a polymer resin. Solar panels usually consist of between 60 - 72 solar cells each one generates a small amount of direct current (DC) when exposed to daylight this current is then carried through circuitry to a central inverter which converts it to alternating current (AC) suitable for connection to your mains supply.

What is the feed in tariff

In 2010 the Government introduced a scheme whereby you can get paid for the electricity generated from your solar array whether you use it or not, in addition you will also receive a further payment for the electricity you export. These payments are in addition to the savings made by using the electricity generated by your array instead of that from the national grid. Although the payments you receive are index linked and tax free for 20 years they are subject to the rate at the time of your installation. Current Solar PV Tariffs are:

Solar Array Size Current Tariff p/Kwh Tariff Lifetime
Upto 4Kwp with EPC D or Higher 16p 20 years
Upto 4Kwp with EPC D or Higher 9p 20 years
Export Tariff 4.5p 20 years

Buyer Beware

What can affect the performance of a panel?

Orientation and Tilt: Ideally your roof should face due south at an angle of between 30 and 50 degrees from the horizontal to receive the best annual performance. Installations between due south and East/West are feasible but output will be reduced however installations on North facing roofs are not recommended.

Shading: According to some experts, homeowners could be losing as much as 40 percent of the potential output of their solar PV installation because of shade. And that isn’t because the whole panel is being shaded. Just 10 percent shading of a solar PV panel can result in a 50 percent decline in efficiency according to some reports. And this is due to the way the solar cells are connected.

Solar Panels are connected in a series of parallel ‘strings’. If one panel is affected by shade, then the losses are passed onto the rest in the chain of cells. To prevent all the cells failing completely, the installation usually includes bypass diodes. These then reroute the current, bypassing the underperforming cells. However, despite stopping the array from failing all together – in the same way a set of Christmas tree lights go off when one bulb has gone – it does restrict the energy from the cells and lowers the entire strings voltage.

Any competent installer should be able to give you advice on shading issue’s for example Micro Inverters can greatly reduce the overall effects of shading

Panel Efficiency and Performance: A solar panel is an interconnected assembly of solar cells and is the basic component of a solar pv array. A photovoltaic panel consists of transparent glass front side, encompassing solar cells and a backside. It is usually framed with an aluminum frame, occasionally with a stainless steel or sometimes with a plastic frame. The front side material (superstrate) is usually low-iron, tempered glass. Most common backside materials (substrate) are EVA (ethylene-vinyl-acetate) and PVB (polyvinyl-burial). According to the solar cell technology popular photovoltaic panels are classified as Monocrystalline, Polycrystalline and Amorphous solar panels, and the latter is also known as thin-film panels.

A photovoltaic panels electrical performance depends on environmental conditions such as the temperature, solar irradiance, angle-of-incidence, solar spectral(air mass), and the types of PV cells used. Each PV panel is rated under industrial Standard Test Conditions (STC) of solar irradiance of 1,000 W/m² with zero angle of incidence, solar spectrum of 1.5 air mass and 25°C cell temperature. Electrical characteristics from manufacturers include maximum rated power, open circuit voltage, short circuit current, maximum power voltage, maximum power current, and temperature coefficients

Rated Power Tolerance: The specified range within which a panel will either overperform or underperform its rated power Pm at STC. Power tolerance can vary greatly, from as much as +10% to -10%. A 200 watt panel with ±10% rated power tolerance may produce only 180 Watts or as much as 220 watts out of the box. To ensure expected power output, look for panels with a small negative (or positive only) power tolerance.

Panel Efficiency (%): The ratio of output power to input power from the sunlight, i.e., what percentage of light energy that hits the panel gets converted into electricity. The higher the efficiency value, the more electricity generated in a given space. You must be aware, however, that the solar cell efficiency doesn’t equal the panel efficiency. The panel efficiency is usually 1 to 3% lower than the solar cell efficiency due to glass reflection, frame shadowing or higher temperature coefficients etc.

Price Guide

4 Key Things to look for before investing in Solar PV

  1. Their power rating: The higher the PV solar panel’s rated output in Watts, the more expensive it is liable to be. A higher output means that fewer PV solar panels will be required to generate the desired amount of electricity for your home or business.

  2. Their Efficiency. The greater a PV solar panel’s efficiency at converting light into electricity the more expensive it will be. Greater conversion efficiency means that the solar panel will be effective in a wider range of light conditions. The efficiency of a domestic PV solar panel currently ranges between 11% and 21%.

  3. Technology Used to create the PV solar cells within the panel. Polycrystalline PV solar cells are cheaper than their Monocrystalline equivalents, which in turn are cheaper than high-efficiency ‘Hybrid’ PV solar cells.

  4. Build Quality: Remember the panels will be sited on your rooftop for at least 25 years and they will be subject to all the adverse conditions the British weather has to offer so Wind and Snow loading capabilities are paramount as the panels may bend and flex repeatedly over time. This can cause small micro fractures in the panels which will get worse over time and ultimately cause the panels to fail.

How Much Can I Expect To Pay For Solar PV

There are currently well over 700 different panels on the market but before you invite a company to your premises for a quote make sure that they are MCS registered and that the panels and inverters used are also certified by MCS as this is necessary for you to receive your Feed In Tariff.

Quality 2 Kwp 2.5 Kwp 3 Kwp 3.5 Kwp 4 Kwp
Best £5935 £6400 £7200 £8100 £8900
Mid £4850 £5400 £6350 £6750 £7400
Budget £4500 £5050 £5800 £6200 £6700

Please note the above are to be used as a guide only as many things can affect the price of an installation from the type of inverter used to the complexity of the installation itself.

Closing the door on rogue traders

Dynamic Energies Ltd is helping to ensure that rogue traders are forced out of the marketplace by joining 'No Rogue Traders Here', a network of businesses who have all been checked by Trading Standards.

Customers of Dynamic Energies Ltd can relax safe in the knowledge that in order to achieve membership, we have been checked out on all fronts and most importantly of all, Trading Standards have accepted us as being a wholly legitimate and properly operated business.

The website makes this clear, saying "We feel that if a business is willing to have their membership agreed by Trading Standards, be bankruptcy checked, credit checked, identity checked, provide recent references and have their work rated directly by customers, then they are far more likely to be the type of business you would want to hire."