• Frequently Asked Questions

    If you can't find your answer here, give us a call. We'll be happy to help.

Frequently Asked Questions

You’ll find our most commonly asked questions here. If you have a particular project in mind, or you require more detailed information, simply give us a call. We’ll be happy to help and provide free expert advice.

Solar panels

Can solar panels produce electricity when it's cloudy or raining?

Solar photovoltaic (PV) panels need light to function. They work best in direct sunlight, but they will generate electricity during daylight hours no matter the weather conditions. Our engineers work with customers to ensure that panels are located in positions where they receive as much direct sunlight as possible.

How big a system will I need?

This depends entirely on your requirements and the purpose for the installation. You may want to produce just enough for an off-grid system to supply the electricity you need on site or generate as much as possible to take full advantage of the feed-in tariffs (FiTs). How big a system you install will also depend on the area you have available, whether this is a roof-mounted or ground-mounted system.

What sort of payback will I get?

Payback comes in three forms – two components from income generated through the feed-in tariff (FiT), and one in the reduction of your energy bills:

The FiT consists of two parts:

  • Generation Tariff – where you are paid an amount per unit of electricity that you generate using the solar panels. Even if you use this electricity you still get paid for the generation.
  • Export tariff – which is an additional, and lower, amount paid for every unit of electricity that you export back to the grid.

Pay-back through energy savings:

  • As you use the electricity generated through the solar panels you draw less electricity from the national grid, therefore reducing your electricity bills.

With the current FiT rates for commercial systems, and accounting for these three components, you should see paybacks between 7 and 9 years.

What is the Return On Investment (ROI) on a solar panel system?

The average ROI on commercial solar panel systems is between 6 to 10%, but the rate depends on the size of your system, its location, and your energy usage on site.

Is it best to install as many solar panels as the roof can take?

If you have the funds available, then the rule is generally ‘the bigger the better’. You might see a slightly longer payback period, as you will be exceeding the maximum energy savings that you can make on site and the remaining benefit will be coming entirely from the feed-in tariff (FiT).  But over the lifetime of the panels, and the duration of the FiT, you will likely have earned a larger amount of money (typically between 6-10%), which you would be hard pressed to find in more traditional investments, for the investment required.

The FiT is arranged in bands, giving lower rates over a certain quantity of panels, which does limit the amount of solar panels that would be financially feasible; however, we’ll run through all of the financial options available to you when we quote for your system, allowing you to choose the system that is best for your needs.

Do solar panels work off-grid, or when there is a power cut?

A solar panel system is an excellent off-grid solution, although you will require additional components such as a charge controller, and a battery, or some other form of storage so that energy produced when the sun shines can be used when it is dark.

In the case of a power cut, this also depends on the equipment installed. We can discuss systems designed to allow you to draw power from batteries or the panels themselves during grid failure. The best option for you will depend on your individual requirements and the likelihood of grid failure.

Can you fit solar panels to a flat membrane roof?

We have a range of mounting frames, or console boxes, designed especially for flat roofs. These frames hold the solar panels at the optimum pitch angle and in the optimum direction without penetration of the roof covering. Alternatively, flexible thin film modules can be welded directly onto the roof membrane. If you have a particularly unusual roof covering we can design bespoke systems to fit your building.

Can you fix solar panels to a trapezoidal roof?

Yes, special fixings are available for this type of roof and, in fact, this is the easiest and fastest roof to fix to. However, care must be taken to ensure that installations on insulated trapezoidal roofs do not cause delamination of the roof material.

Will the roof be strong enough for solar panels?

Most roofs are strong enough to support a solar panel installation and we always carry out a structural assessment of every roof to ensure that the additional load can be supported. Occasionally, we may advise that additional reinforcement work is carried out.

We have an east/west facing roof. Will solar panels work? Is it better to install on the east or the west side?

Solar panels will still work well on an east or west facing roof but output will be about 15% less than that of a south facing roof.

Generally speaking, a west facing roof is preferable to an east facing roof as in the UK our afternoons tend to be less cloudy. However, you should also consider your demand profile, for example, if you have greater electricity consumption during the morning, you may want to make the most of the generated electricity and therefore install the panels in the east facing direction.

Do we need planning permission?

For most roof-mounted solar panels systems, you will not require planning permission, the exceptions are if your building is in a conservation area or within the curtilage of a listed building. Most ground-mounted panels do require planning permission. For information on planning permission, and other government and local authority policies and regulations, see our government policy page.

What's the lifespan of a solar module?

All our modules have a 5-year manufacturer’s guarantee and a 20-year performance warranty. The modules normally last for at least 20 years.

With a 20-year performance warranty, the manufacturers expect their panel to last 20 years and still produce at least 80% of their initial rated peak output, an average efficiency decrease of no more than 1% per year.

What does Wp mean in relation to solar panels?

Wp means peak Watts: A 120 Wp panel will generate a maximum of 120 W in peak conditions. Peak conditions are considered as 1 kW/m2 solar irradiation falling on the surface.

What is an inverter?

A solar inverter takes the DC (direct current) from the solar panel and creates a useable form of AC (alternating current). Today, most inverters come with inbuilt protection that enables you to connect directly to the grid. If you are running an off-grid system or powering batteries, then a charge controller will also be required.

What does a standard solar power system comprise of?

A grid connected solar panel system consists of the following main components:

  • Solar panel generator (array
  • Direct current (DC) isolator switch
  • DC cabling
  • Solar Inverter
  • Alternating current (AC) cabling
  • AC isolator switch
  • kWh meter


What size biomass boiler will I need?

Your biomass installation will be sized to suit the space and water heating requirements of the building. We will take various measurements and carry out heat load calculations to assess the optimum boiler size. We always go back to first principles and calculate heat loads from scratch, as often existing boiler size is not a good indicator of optimum biomass boiler size. Visit the biomass boiler technology pages for further details.

Can I claim the Renewable Heat Incentive with a biomass boiler?

If this is a commercial biomass installation, then yes. You’ll be able to apply for the renewable heat incentive (RHI) tariff system, which is similar to the to the renewable electricity feed-in tariff (FiT) scheme. For more information on applying for the scheme and the details of this incentive visit our RHI pages.

What is the return on investment for a biomass boiler?

The return on investment (ROI) can vary depending on the type of fuel that the biomass boiler is replacing. The more expensive the fuel that is being replaced the larger the ROI. If you are able to use your own fuel source (e.g. wood sourced from your own land), then the payback period is even less. For installations replacing LPG or oil, where the commercial renewable heat incentive (RHI) applies, you can expect payback periods from 4 to 8 years.

Should I keep my old boiler as a back-up system?

In most situations, it isn’t necessary to have a back-up boiler in place but it is perfectly fine to keep the old system functional as long as space isn’t limited, the boiler is safe to run and the new boiler doesn’t need to occupy the exact same spot as the old one. The heat produced by your biomass boiler will be metered and you will receive payments under the renewable heat incentive (RHI) for this heat. Obviously, any heat generated from your old back-up boiler will not be eligible for RHI payments and there will be a cost associated with integrating the old boiler into the new system.

What kind of payback figures can I expect?

This depends on the size of the system you install and on the type of fuel that the biomass boiler is replacing, but a smaller system of 20 kW in size can pay back your investment within 8 years; a larger system of 250 kW can payback in as little as 5 years. Once the investment is paid back, the money received from incentives and fuel cost savings translates to a direct income.

How much refilling or maintenance time is required?

The fuel refill frequency depends on how much heat your site needs and how automated you want to make the system. For most of our biomass boilers, we give you the option to add automatic fill equipment. This equipment works by transporting fuel from your fuel store and automatically feeding it into the boiler hopper. This feature is particularly useful for large systems and it removes the need for you to have to top up the boiler manually.

Biomass boilers are easy to maintain, with minimal cleaning required. Most manufacturers recommend a service every 6 – 12 months to check all of the components and to ensure that the boiler continues to work safely.

Do biomass boilers smell?

Biomass boilers are very efficient and release very little odour and most of the boilers we supply are Clean Air Act exempt.

What is the carbon footprint of a biomass boiler?

Whichever fuel you are switching from, a biomass boiler will lower your carbon footprint; the amount it can be reduced depends on which fuel you currently use, but savings can be as great as 7.5 tonnes of carbon per year if switching from coal or electric heaters.

Is biomass really sustainable?

Done in the right way, yes it is. Burning wood-based biomass does release carbon dioxide, but it is only the amount that is absorbed by the tree in its lifetime. The biomass fuel is sustainable if it is replaced by new plants and trees which are not cut down too quickly, giving them a chance to absorb more carbon dioxide from the air. Carbon emissions result from the transport of biomass but, provided the fuel is sourced locally, this is much less than the carbon emitted by burning fossil fuels to generate power.

Ground and water source heat pumps

Will a heat pump supply all of our hot water needs?

This depends on the temperature of hot water required. A heat pump can only heat the water to a certain temperature using the latent heat of the air, water or ground and the temperatures do not usually reach that required for standard domestic hot water supply. A heat pump can; however, be combined with another supplementary technology to reach these higher temperatures. Contact us to discuss your hot water use in more detail and we can run through the potential solutions available.

Can a heat pump replace a boiler?

Possibly. A correctly sized Ground Source Heat Pump (GSHP) can be combined with a Solar Thermal system to produce a large percentage of your hot water and heating needs, perhaps for an office building, school, historic house or barn supply, but you may want some form of backup system to top up your hot water needs on cloudy days. This could be provided by an electric immersion heater rather than a conventional boiler.

If you require large amounts of hot water or heating for an industrial application then a biomass boiler would likely be a more suitable solution.

Can a heat pump be connected to a traditional heating pipework?

Generally, heat pumps work best when producing hot water at a temperature lower than that which traditional heating systems (radiators) use. Heat pumps work best with underfloor heating and as a result are often installed as part of new build development.

How much electricity does a heat pump need?

A heat pump will typically have a coefficient of performance (CoP) of 3 – 4, which means that for every unit of electricity used, it will deliver 3-4 units of heat. The amount of electricity required will depend on the size of the heat pump and the heat that it is generating.

Does a heat pump need to be switched on all the time?

Ideally yes, although it can be switched off during summer months or during a shut-down period.

How does a heat pump work?

A heat pump works like a refrigerator in reverse. A refrigerant contained within the heat pump system absorbs heat from the source (air, ground, or water). A compressor, powered by electricity, greatly increases the pressure and temperature of this refrigerant, which is then used to heat up the air or water in your buildings.

The heating pipework also contains the refrigerant and it is preferred to water as its properties enable it to transfer much more heat.

Is planning permission required?

Usually, planning permission is not required for a Ground Source Heat Pump (GSHP) or Water Sourced Heat Pump (WSHP); however, other permits are required from bodies such as the planning authority, the British Geological Survey, and the Environment Agency. For more information see our planning permission page.

How much maintenance is required?

Very little. Routine maintenance checks may be recommended by the manufacturer to maintain the warranty on the equipment.

Ground source heat pumps

How many bore holes will be required?

This very much depends on your heating requirements: the more heat required, the more boreholes the system will require. There are limits to the number that can be placed within a certain land area to ensure that the amount of energy extracted from the ground is sustainable.

Horizontal loop systems may be preferable to bore holes, especially if you have plenty of accessible surrounding land.

How much land is required?

This depends on whether bore holes or horizontal loops are used. A horizontal loop system would require around 500 m2 to supply a small 10 kW boiler.

Will the ground freeze?

If the system is designed and installed correctly, then this won’t happen. The ground will only freeze if a Ground Source Heat Pump extracts too much energy from the ground, which a well-designed system will not do.

Can the extraction pipework be installed under a car park?

Yes. Installing the pipework under a carpark can be a good way to make use of the available land. However, as with most heat pump systems, heat pumps are best installed when the car park is built, rather than as a retrofit option.

Water source heat pumps

Can pipework be laid in water?

Yes, but consideration must be given to how the pipes will be sunk, and what other uses there are for the body of water. If the water is tidal, the pipes will need to be secured. If the water is navigable, care must be taken to prevent hazards to shipping.

Will the system cause the surrounding water to freeze?

If the system is designed correctly this will not happen. Water Source Heat Pumps are the trickiest heat pump system to design as a small change of temperature in the water can change the biodiversity and ecology of the water source. All of these factors must be taken into account in the system design and it is important to use competent and experienced engineers to ensure that the system does not impact the surrounding area.

Air source heat pumps

Contact Promo


Keep up-to-date with clean energy 
Get our newsletter
Clean energy is a rapdily changing sector. Our newsletter keeps you up to date with the latest developments and opportunities in an easy-to-read format.
Give it a try, you can unsubscribe anytime.