Every day, we talk to people wanting to understand PV panels and the options for their Solar insulations, here we try to explain in depth some of the differences and options you have, when choosing the right PV modules for you.
We have tried to make this guide simple by addressing the questions we are most commonly asked, however please let us know if we have missed anything, as no doubt we have.
PV Panels Solar PV panels are made up of photovoltaic cells, these cells convert the sun’s rays into electricity by exciting the electrons in silicon cells, using the photons of light from the sun. The Solar Panel then generates power, which is a direct current (DC). The power will vary according the intensity of the light and UV radiation levels but better, quality cells are able to produce power more efficiently and will have higher production levels over their life.
The Photovoltaic cells are laminated between glass and a backing membrane and are sealed with silicone in an aluminium frame. Most PV panels have 60 or 72 solar cells in them.
There are also panels where the cells are sealed between two layers of glass and known as glass – glass modules and the added advantage is that they can be mounted without a frame.
Solar PV panels efficiency for domestic panels are typically around 20%, this means they can take around 20% of the light they receive and turn it into electric. This is known as solar efficiency. There are other forms of photovoltaic cells available that are used for commercial and industrial purposes. These cells have an efficiency rating up to 40%, however they are more expensive than domestic models. Solar Panel efficiencies over the last 5 years have risen from 14% to 20% with some of the highest quality now at 22%.
A useful article on Solar Panels to read is on te Energy Saving Trusts website
Energy Saving Trust
There are several options for panels, depending on budgets and availability.
Classic Crystalline Panels
Traditional Monocrystalline and Polycrystalline panels are widely installed on both domestic and commercial solar installations throughout the UK. They represent the most affordable panel and the quickest return on investment, due to the economies of scale achieved on mass manufacturing. They typically are made of silicone cells mounted in silver or black frames. Traditionally, Monocrystalline panels have been seen as the most efficient but in the last few years Polycrystalline has improved to a point where they are almost identical. Polycrystalline has better properties for generation on dull days, whereas Monocrystalline has better production in direct sunlight.
Thin film solar cells are more expensive than traditional modules, however they offer the benefit of being flexible and allows them to bend the to the shape of the installation surface and can be fixed using an adhesive, making them less noticeable on a roof. Thin film Solar cells tend not to be as efficient as traditional Monocrystalline and Polycrystalline modules.
Solar Slates / Tiles
Solar Slates and Tiles, aesthetically are the most eye pleasing installation option, however they are the most expensive option by a distance. Solar slates are installed in place of roof slates or tiles and have solar cells built into the them to give the appearance that no solar array is present.
There are also panels that are made to look more like a tiles and mimic the overlap but to date these have not been popular.
Which PV Cell is better Monocrystalline or Polycrystalline PV Panels?
The difference between these solar cells is the raw material that are used to make them.
Monocrystalline photovoltaic cells are made from single crystalline silicon. Typically the cells are coloured and tend to have a cylindrical shape.
To make solar cells for monocrystalline panels, silicon is formed into bars and cut into wafers, as the cell is composed of a single crystal, the electrons that generate a flow of electricity have more room to move. As a result, monocrystalline panels are more efficient than their polycrystalline counterparts in direct sunlight.
Polycrystalline solar panels are generally cheaper than monocrystalline panels. The aesthetics of polycrystalline panels is different as they tend to have a blue hue instead of a black hue of monocrystalline panels.
Polycrystalline are manufactured from many fragments of silicon to form the wafers for the panel. Polycrystaline panels are also known as “multi crystalline” or many-crystal silicon. Due to the fact there are many crystals in each cell, there is less freedom for the electrons to move. As a result, polycrystalline solar panels can have lower efficiency rating than monocrystalline panels.
What is the maximum and minimum wattage in a PV panel?
Typically, the smallest PV panel you will find on the market is 5 watts, these day 5-200w solar panels are installed on small off-grid applications.
For domestic and commercial Solar PV, you would be looking at a module in the region of 250-420 Watts. The module you have installed will be dependant on the size of the roof available, budget, and mounting equipment used.
Can I choose the colour of the PV Module?
There are a few. If you go for a polycrystalline module you can choose between a blue with a silver frame and an all black PV panel. If your option is for mono you can choose between an all-black or black mono cells, with a white background which is part of the lamination process.
Is there a manufacturer’s warranty on PV modules?
Most PV manufacturers offer a warranty of 10-12 years on the product and in addition manufacturers usually offer a 25 year linear performance warranty.
That means that over the lifetime of the module, they must perform to a predetermined output and failure to do so can see the manufacture have to either compensate the owner of replace the modules.
Which brands are available?
Most Photovoltaic panels in the world are manufactured in China or Taiwan and produce PV panels brands such as JA Solar, Canadian Solar, Trina Solar and Phono Solar.
If you prefer a better known brand LG and Panasonic both manufacture PV panels, which tend to be of a higher and efficiency and a premium price.
Can I trust Chinese modules?
China has been at the forefront of Module production for many years and many of the well known companies have a reputation within the trade of producing a quality product with minimal failure rates.
Are there any quality standards I should look for?
All modules should carry the Microgeneration Certificate Scheme Logo (MCS) as this represents a certificate that all aspects of the module production has been examined including quality, output and production consistency.
Are they safe?
All modules will have undergone rigorous safety checks that will include impact tests, electrical safety, ammonia and salt resistance and strength tests.
Do I need to clean them?
In most cases the rain is sufficient to clean them, however in some circumstances, there can be a build-up of green algae around the frame and this may need cleaning for aesthetic reasons.
Do PV systems perform all year round?
Yes a Photovoltaic panel installation will operate all year round however there are several factors that cause output to be lower in the winter than summer. This is due to shorter days, poorer weather and lower solar activity. It is possible to model system outputs so that you can predict outputs based on local weather records.
Do I need planning permission?
Not for anything that projects less than 200mm off the roof, this is providing the property is not listed or in a special conservation area where they may be conditions where property owners need to seek guidance or permission
How Many PV Panels do I need?
In an ideal world you would match your generation to your consumption. However mitigating factors, such as the roof space available to mount the system and the requirement for systems over 3.68kW to have G99 certification from the District Network Operator (DNO), will dictate the size of your solar array.
Yes, a Photovoltaic panel installation will operate all year round however there are several factors that cause output to be lower in the winter than summer. This is due to shorter days, poorer weather and lower solar activity. It is possible to model system outputs so that you can predict outputs based on local weather records.
Further Reading and Useful Links
If you would like to learn more about Solar Panels please see the links below:
Solar Trade Association
National Energy Foundation
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