Solar Photovoltaic Systems

What are Solar Photovoltaic (PV)?

Solar photovoltaic cells (PV) enable light to be converted into electricity that can be used to power electrical appliances and lighting. They are already an important part of our lives with simple PV systems providing power for many small everyday items, such as calculators and road traffic signs. More complicated systems provide power for communications satellites and commercial processes. Few power-generation technologies have as little impact on the environment as photovoltaics. The systems quietly generate electricity from light without producing air pollution or hazardous waste. They don't require liquid or gaseous fuels to be transported or combusted and because its energy source, sunlight, is free and abundant, they can significantly reduce the running costs of any building on which they are fitted.

How Does Solar Photovoltaic Work?

There are different types of Solar PV systems, but the principle on which they operate is similar. All Green Energy Doctor systems consist of two main components:

Solar Photovoltaic (PV) Panels
Commonly known as solar cells, individual PV cells convert sunlight into electrical energy using semiconductor materials such as silicon or gallium arsenide. When light shines on the cell it creates an electric field across its layers, causing electricity to flow. This electricity is then conducted away by metal contacts as direct current (DC). The amount of electricity produced will depend on the amount of light that falls on the PV cells. PV does not require direct sunlight, only sunlight to generate electricity, however the output from a PV cell will vary with the intensity of the light. All PV cells operate at a low voltage; therefore they are often connected together in series to form PV modules that may be up to several feet long and a few feet wide. Modules, in turn, can be combined and connected to form PV arrays of different sizes and power output for household or commercial needs.

Inverter
This converts the direct current (DC) electricity generated by the panels into alternating current (AC) electricity that matches the building's mains electrical grid supply. If the building is not grid connected the inverter is usually replaced with a battery bank to store the electricity generated.

Solar PV systems produce electricity, which is conducted away as direct current and converted to alternating current for use within the buildings AC electrical circuit. 1. Sun Rays, 2. Solar Panel/Array, 3. DC/AC Inverter, 4. PV Generation Meter, 5. Mains Electrical Board (Fuse Box), 6. Mains Electricity Meter, 7. Electrical Socket (Or Other Electrical Output e.g. Lighting).

Types of Solar Photovoltaic (PV) Systems

There are two primary types of solar system, dependant on how the outputs are used:

Standalone Systems
These PV solutions are popular in remote areas, where connection to public electric grid is expensive or impossible. Systems that are not connected to the national grid require energy storage facilities to allow for the time lapse between the production of energy and the energy requirement, these usually come in the form of rechargeable batteries. An inverter is then used to convert DC electricity to AC (alternating current - mains electricity).

Grid Connected Systems
Solar PV systems can also be connected to the national electricity grid. A special inverter and controller converts DC electricity to AC at a quality and standard acceptable to the grid. No battery storage is required. Any unused or excess electricity may be able to be exported to the grid and sold to your electricity supplier.

What Are The Benefits?

Reduce Your Electricity Bills by Up to 50%
Solar energy is free and with an on-grid system you can sell electricity back to the grid. So if you have a typical 3 bedroom property with a properly sized and installed 2.5 kWp solar system, you can expect to save 50% off your electricity bill. The only limiting factors to you producing 100% of your electricity and selling the excess, is the budget you have to buy and install the system and the space available for the PV array. Installations on commercial buildings are particularly suitable for PV, as demand for electricity occurs at the same time as generation.

Reduce Your Impact On The Environment
The sun generates solar PV electricity, so it's a clean fuel source. They don't pollute the air like power plants that rely on combustion of fossil fuels, such as coal or natural gas. They don't produce atmospheric emissions that cause acid rain or greenhouse gasses. Therefore, a typical domestic solar PV system will save 450kg of CO2 per year for each 1kWp installed.

Reduce Your Dependency On Fossil Fuel Imports
The sun is a plentiful and free source of energy and is estimated to be secure for the next 4 billion years. This can provide you with the peace of mind that a significant proportion of your energy is under your control and will not increase in price as a result of foreign government actions or the prevailing economic climate.

Sell Surplus Electricity Back To Grid
If your solar PV system is producing more electricity than you require, the excess can be exported back onto the National Grid using an export meter. The rate paid various from company to company but some tariffs offer over 10p per kWh.

Sell Renewable Obligation Certificates (ROC's)
Eligible sustainable generators, including consumers are awarded these digital certificates for every 1000kwh of electricity generated. Energy Companies are required to generate a minimum level of their electricity output from sustainable sources. If they have not managed to produce the required amount of green energy themselves they must buy ROCs on the open market to make up the shortfall. Each certificate can be sold to electricity suppliers for up to £40, this equates to an additional 4p per kWh.

Low Maintenance Cost
The technology is proven and established. The panels have no moving parts and as such there is very little that can go wrong with them, which means that maintenance costs are kept to a minimum.

Unobtrusive & Scalable
Unlike wind turbines, a Solar PV system is silent and can be integrated into or mounted on an existing roof and so is relatively discreet. The systems are also modular which means they can be added to at any time to increase this saving.

Is It Suitable For My Requirements?

Which system is most suitable for your property or project depends on a number of factors that we will take into account prior to designing a solution. In the meantime, the following gives a good indication of some general principles that should be taken into account when deciding if the technology is suitable, and if so, designing a cost effective Solar Photovoltaic system:

Panel Location
These systems work equally well in any environment (urban or rural) as they can be easily installed on the roof of just about any building and they can be easily connected to a buildings electricity supply. Panels can be roof or ground mounted. Ground panels can be oriented due south, and can easily have snow swept off of it to maximise efficiency, but many buildings lack the ground space needed; in an urban setting, the roof is usually a better option.

Roof Mounting
Green Energy Doctor supplies and fits high quality PV modules in a wide variety of shapes and sizes which can be mounted in the following ways:

• Solar Slates
  Solar slates come in variable sizes and can be installed on the roof in the same manner as roof tiles. Although it is more economical to install these on a new build property, they can be installed on an existing property.
• Above-Roof Solar Panels
  Solar panels are rectangular units. The above-roof mounting system is typically used when retro-fitting to existing properties, whereby rails are fixed over the roof tiles and anchored to the roof beneath. The panel is then attached to the rails.
• In-Roof Integrated Solar Panels
  In roof integrated panels are similar to on roof panels but with the mountings allowing the panels to be fixed directly to the roof flush with the surrounding roof tiles. These can be used on an existing property, but above-roof mounting is usually cheaper than in-roof integrated in this situation.

Orientation of the Panels:
Ideally the collector should be on a roof within 45 degrees of South and with a pitch between 30 degrees and 60 degrees to allow them to absorb the most light.

Shading/Obstructions
Roofs that have any shaded areas for any part of the day would not be suitable for Solar PV systems. A solar shading analysis would be done by Green Energy Doctor to assess the roof's production potential.

Suitable Space:
Both the rectangular panels, and the solar slates, are invariably fitted in multiples and they can be fitted in any configuration, but for the average three-bedroom house wishing to produce 50% of the electricity requirement, you would ideally need 20m2 for the solar array. For a two-bedroom house, this may be smaller, although this will depend on your electrical usage.

Energy Requirement and System Sizing
System sizing is an important question for off-grid electric systems; but is less of a problem for on-grid systems, where the excess electricity can be sold to the electricity company. You can easily estimate the number of solar modules you need by determining your wattage needs from your electricity bills. You can calculate the power production of a system by multiplying the number of hours of sunlight by the number of watts of the solar panel or array. Not to worry though, as Green Energy Doctor can advise on whether a particular solar panel or array is enough to meet your needs.

Please feel free to call us, send us an email or send us a drawing of your specific project.

Typical Outputs and Costs

Solar PV cells, modules and arrays are rated at peak output power. Watts peak (Wp) is the peak power in Watts (W) produced in standard test conditions. These conditions are rarely achieved consistently in practice as the output fluctuates with solar radiation levels, which vary considerably during the day and also during the year. However, below will give you an indication of the typical outputs by system size:

Array Size	1kWp	2kWp	3kWp	4kWp
Applications	Households	Households	Households and small commercial premises	Households, schools, local authority buildings and small industrial units
Annual Output (kWh)	700-800	1,500-1,700	2,500	3,400
A% Of Typical Household Requirement (approx.)	25%	50%	75%	100%
CO2 Saving per Annum	400kg	800kg	1,200kg	1,700kg
Typical Roof Space Required	10m2	20m2	30m2	40m2
Estimated Costs (including installation)	£6,000	£9,000	£12,000	£14,000

• Approximate annual household energy consumption for three bedroom house = 3800kWh

How Much Does It Cost To Install?

The cost of a complete Solar PV system, including installation, can vary dramatically depending on the type of system to be installed (grid-tied or standalone) and the installation method to be used (roof integrated, on roof, flat roof or ground mounted). Solar tiles cost more than conventional panels and panels that are integrated into a roof are more expensive than those that sit on top.

However, as a guide, costs range between £6,000- £8,500 per kWp installed with most domestic systems usually between 1.5 and 3 kWp.

Once the technical survey has been carried out, all Green Energy Doctor prices will be given as fixed prices.

Government grants are available for these technologies; please contact us to find out more information.

How to Get Started...

To organise a no obligation site visit or to start moving your project forward contact the Green Energy Doctor today on:

T: 0845 009 5652
E: info@greenenergydoctor.co.uk