Please select your question from the list below:

What areas of the UK do we work in?
What type of system do we install?
Are SEI an independent supplier?
Will we organise the DNO connection (permission to connect to the electricity grid)?
How long will be required from order to installation?
How will the grant application process work?
Are our products certified?
Will we visit you?
What does kWp mean?
How much electricity does a typical PV system generate in a year?
How much roof area is required for a PV system?
What proportion of electricity will a PV system produce?
What is a kWh?
How reliable is a PV system?
How long do PV systems last?
What happens when little or no electricity is being generated e.g. during the night?
What happens if the PV system is generating more electricity than is being used at that time?
Will we make an agreement with your electricity supplier for payment for electricity from the PV system that goes back to the mains?
Can I heat my hot water using a PV system?
What's the difference between a solar water heating (SWH) system and a photovoltaic (PV or solar electric) system?
When should I have a grid-connected system?
What is the optimum roof angle and orientation?
How much CO₂ is mitigated per kWh generated from PV?
What is the payback period of a PV system?

If your question isn't listed here, try searching our website or contact one of our engineers.

What areas of the UK do SEI work in?

SEI cover all of the UK.

What type of system does SEI install?

SEI install photovoltaic systems (solar electricity), wind turbines and hydro systems. 

Are SEI an independent supplier?

SEI are an independent installation company not tied to any particular supplier.  SEI can therefore install whatever system you would like and best suits your building and your needs. If you do not have any specific ideas of the type of system you require, SEI will provide advice and help you to make a selection.  SEI would generally only recommend roof-integrated photovoltaic systems where you are replacing the roof anyway, or on a new building.

Will SEI organise the DNO connection (permission to connect to the electricity grid)?

Yes, SEI will apply on your behalf when you place a confirmed order with us.

How long will be required from order to installation?

This will depend on the system chosen as time for some products to be delivered is longer than others. However, 4-8 weeks should generally be allowed for equipment ordering.

Can I get help with project costs?

There are grants available for most projects, whether they are for domestic, public sector or commercial clients, through the government's Low Carbon Buildings Programme. Some projects are also eligible for additional funding from other sources.  SEI can advise you on the funds available and assist you with the grant application process. Please see our Grants page for more information.

If you have any queries we are of course happy to help. Further details on the grant scheme are available from the Low Carbon Buildings Programme or by calling the grants helpline free on 0800 915 0990.  Please note that SEI is a member of TLCP, a consortium accredited for Phase 2 (public sector) projects.

Are our products certified?

All equipment must be certified to be eligible for the Solar Grants Scheme (i.e. IEC61215 or IEC61646 & G83/1).  As an accredited installer we have signed up to say we will provide this and the DBERR's (incorporating the DTI) grant scheme management team will check a proportion of our installations to ensure that all is of good quality.  SEI is a member of the Renewable Energy Association and as such has signed up to the REAL Code of Practice.

Will SEI visit your site?

SEI will normally provide quotations without a site visit on the basis of drawings, photos and/or measurements provided by the customer. If you decide that our quotation is of interest and place an order, SEI will visit site and talk the installation through with you before commencing the installation.

What does kWp mean?

The power of a PV system is measured in Watts just like all other electrical devices (e.g. 100W lightbulbs).  A kilowatt or kW is a thousand Watts.  However, because the power generated by a PV system is dependent on the weather, 'Standard Test Conditions' (or STC) are defined under which the power is measured.  The power of a PV system is normally quoted at STC and is measured in kWp.

How much electricity does a typical PV system generate in a year?

In optimal conditions i.e. facing south and tilted at an angle of 30 degrees to the horizontal, a typical 1 kWp domestic PV system in the UK will generate 800 kWh per annum. 1kWh is equivalent to 1 unit of electricity on your electricity bill. A standard domestic system can be up to 2 kWp, schools and small offices 5-10 kWp, and larger buildings can have up to 50 kWp or more.

How much roof area is required for a PV system?

A 2 kWp system would typically takes up approximately 16 m²  (4m x 4m) when using crystalline silcone modules. 

What proportion of electricity will a PV system produce?

All buildings consume vastly differing amounts of electricity.  An example is given here for a household. Electricity bills will be lower because often electricity from the PV system will be used instead of taking electricity from the mains.  A typical UK three-bedroom family home built to 2006 Building Regulations uses 3,000-4,000kWh of electricity per year.  A typical 2 kWp PV system would provide almost 50% of electricity needs i.e. 1,600 kWh. This can vary considerably dependent on electricity consumption and how energy efficient the electrical appliances in a house are. It is possible for a 2 kWp PV system to supply all electricity needs if all possible energy saving measures are implemented.

What is a kWh?

kWh stands for Kilo-Watt Hour, and this is a measure of energy (in this case electricity) used or generated.

1 kWh is the same as 1 unit on your electricity bill, and is enough power to light a 100W light bulb for ten hours (or fifty hours for a typical 20W low-energy light bulb). 1 kWh costs approximately 7p for domestic customers.

How reliable is a PV system?

PV systems are very reliable.  PV systems have no mechanical moving parts so mimimising potential faults.

How long do PV systems last?

The PV modules typically carry a 25 year power output warranty. After this time the system would be expected to continue to function, but power output may be reduced. Inverter design lifetimes are typically around 20 years.

What happens when little or no electricity is being generated e.g. during the night?

When little or no electricity is being generated by the PV system, electricity is automatically taken from the National Grid.  You will not need to turn the system on or off - the service will be seamless.

What happens if the PV system is generating more electricity than is being used at that time?

SEI generally installs grid-connected PV systems, so the electricity will be fed back to the mains. Grid-connected systems use an electrical inverter to connect to the mains. There are no batteries.

Will SEI make an agreement with your electricity supplier for payment for electricity from the PV system that goes back to the mains?

No, we leave the choice of supplier up to you.  SEI is independent of all electricity suppliers.  Different electricity suppliers have different arrangements for billing, and these arrangements often change.  SEI will give you up-to-date information on the different electricity suppliers to help you make your choice.  Even without making a specific payment agreement with an electricity supplier, your electricity bill will be lower because you will not be using as much electricity from the mains.

Can I heat my hot water using a PV system?

A PV system is not the most efficient method of heating water. The electricity generated can be used for this purpose but it is unlikely to supply all your hot water needs.

What's the difference between a solar water heating (SWH) system and a photovoltaic (PV or solar electric) system?

Solar water heating panels or solar collectors are completely different to solar photovoltaic panels.  In a solar water heating system, water runs through pipes in the solar collector, and is heated up by the sun.  A SWH system will only produce hot water, and installation may involve some changes to your plumbing system. In contrast, photovoltaic panels generate electricity, which can be used by a wide variety of appliances in your home.  PV panels are based on the semiconductors used in the electronics industry.  During installation of a PV system, there is little disruption to your home - all the components are on your roof or in your loft, apart from a meter and switch which can be installed by your main fusebox.

When should I have a grid-connected system?

In the majority of installations, it makes sense to connect to the electricity grid and operate the PV system in parallel with it. There are a number of reasons for this, which include the following:

• In most circumstances, it is both expensive and space-demanding to size a system that will be able to provide sufficient power through all months of the year
• Batteries currently require a lot of space, are heavy and expensive, and require a lot of maintenance
• You can use the grid in a similar way to a near-infinite battery: You can often sell unused power to your provider, and buy it back when you need it most

In general, unless the site is to be extremely remote and away from a grid connection, it is almost always cheaper to have a grid-connected system. Please see our article on grid connection for more information.

What is the optimum roof angle and orientation?

In the UK, the optimum roof pitch is at an angle of 30° above horizontal, facing due South. However, this is rarely the angle available on the roof of the building; the diagram below shows the percentage of the 'standard figure' (see How much electricity does a typical PV system generate in a year?) that might be generated at given angles and orientations.

For example, a school building with a pitch of 40° facing South-East would generate around 96% of its potential (equating to around 3,840kWh/yr for a typical 5kWp system). There are mounting systems available to increase the incident angle for flat roofs.

Source: Guide to the Installation of Photovoltaic Systems, 2nd Edition

How much CO₂ is mitigated per kWh generated from PV?

The exact amount of CO₂ mitigated by a PV system is hard to measure, as the mix and efficiency of fuels used to generated grid electricity changes constantly. However, the standard figure used for the Building Regulations is 0.568kgCO₂/kWh.

What is the payback period of a PV system?

PV systems require capital-intensive equipment as PV cells are expensive to manufacturer, and this means that the financial payback period for a given system can typical exceed 20 years. While grant schemes do help reduce the burden, a PV system is unlikely to pay back financially as the inverters designed life is less than this. Since future energy price rises cannot be forecast accurately, SEI would not recommend installing a PV system as a financial investment.

Meanwhile, it must be stated that contrary to a circulating urban myth the environmental payback period is much shorter. A PV system can expect to have offset the carbon released during its manufacture within 2-5 years in European conditions. Beyond this a PV system would be expected to be offsetting emissions made by other energy users.

* (Alsema and Niewlaar)