Build your dream home with confidence
BOOK YOUR TWO FREE TICKETS HEREEstimate your project costs instantly with Build It's interactive self-build cost calculator
Calculate NowGet an accurate, detailed cost breakdown of your project
Submit plans
Planned changes to building standards and regulations are seeing a rise in policy pressure, shifting solar PV away from a nice-to-have addition towards becoming a must-install technology.
With energy prices showing little sign of falling, many self builders are keen to adhere to tomorrow’s regulations today, and solar PV is a great way to reduce electricity costs and a reliance on the National Grid. You can also sell excess self-generated power back to the grid via your energy provider, via the Smart Export Guarantee.
According to the Energy Saving Trust, you can typically expect to achieve payback on the installation costs within 9-15 years. Panels last 25+ years, so you could essentially net 12-16 years of profit – though there will be a little maintenance throughout that period (the solar inverter typically needs replacing every 10-15 years, at a cost of around £1,000). “Self builders should see solar PV as a long-term infrastructure investment that will reduce running costs, protect against energy price rises and strengthen EPC performance from day one,” says Elizabeth Sinikas, marketing manager at GreenGenUK.
So, what’s involved when specifying and installing a solar pv system? Here, we explain the basics of how solar PV works, before taking a deep dive into solar panel costs, payback periods and what can affect the amount of time it takes for your investment to pay off.
Photovoltaic generation (PV) takes energy from light (photons) and transforms it into electricity (volts). Photovoltaic cells produce very small amounts of power, so they’re grouped into modules. A solar panel consists of several modules linked together. Where multiple units are grouped together this is known as a solar pv array.
The power generated by PV cells is direct current at low voltage. Unless the power is being used solely to run low-voltage, direct current (d/c) appliances, it needs to be converted to 240V alternating current (a/c) – ie normal domestic electricity – by means of an inverter. A cable connects the solar panels to the inverter and the system is then linked to the mains. Any electricity which isn’t immediately used on site can either be stored in a battery or exported to the grid.
This sympathetic one-and-a-half-storey SIPs self build by SIPS@Clays features a range of renewable systems to achieve net zero carbon, including a 6.4kW solar PV array, 3kW wind turbine and an MVHR system
When planning the efficiency and performance of your new home, Building Regulations and energy assessments play a key role. As part of the design and Building Regs compliance phase, you’ll need to arrange a pre-construction SAP (Standard Assessment Procedure) rating, indicating the house’s predicted performance. Once the project is complete, an EPC (Energy Performance Certificate) measures its final as-built performance.
Note that SAP will be replaced by the new Home Energy Model (HEM) as part of implementing the upcoming Future Homes Standard amendments to Building Regulations. “A well-sized domestic PV system can improve a property’s SAP score by several points, and is often enough to move a home up one EPC band,” says Elizabeth Sinikas.
For self builders, prioritising efficiency and integrating solar PV from the outset will reduce running costs from day one, futureproof the property against regulatory change and deliver a good SAP and EPC result – which can be a boon if you come to sell in future. Early planning also enables optimal roof orientation, structural loading allowance, inverter location and cable routing – all of which will maximise the performance of your solar array and help you to fully reap the system’s benefits.
With the introduction of the Future Homes Standard in 2025, new homes are required to produce 75-80% less CO2 emissions in use than those built under 2013 standards (31% less than mandated by 2021 updates to the regs). Generating electricity on site through solar PV can be a cost-effective route to meeting that target, and can even take your home into the next EPC band.
A recent installation by GreenGenUK consists of an 8.6kW solar PV array, made up of 18 x 480-watt panels on a single-phase grid connection, and is predicted to provide annual carbon savings of around two tonnes. This is equivalent to planting 482 trees or avoiding 75,021km of car journeys each year. It is worth noting, however, that production and installation require significant embodied carbon. And while around 90-95% of a panel can technically be recycled, the market for this is still in relative infancy.
Furthermore, as the UK’s grid continues to get greener, the carbon savings made by generating the electricity yourself get lower. “If the grid is already 100% renewable, there are no carbon emissions savings to be made,” says Rhiannon Jones, technical sales manager at GB-Sol. “But the benefits are still there in terms of having an individual source of power and being less reliant on the grid and global energy prices.”
To maximise yield, solar panels should be orientated to face south, though a useful lower yield will still be achieved from solar panels facing southwest to southeast. At east or west orientation the yield starts to fall significantly. At our latitude in the UK, the angle for collectors to be installed to maximise yield is 35° from the horizontal. Fortunately, this is consistent with the most common roof types in this country, so if you have a south-facing pitched roof you can most likely get close to the maximum yield simply by fitting solar panels on the existing structure.
Of course, you need to avoid overshading, as trees or nearby buildings on the southern aspect of the installation will sharply reduce the output of your solar pv system. PV can also be fitted on flat roofs by using suitably angled mounting brackets. In independent installations, yield can be increased by using a solar tracker which turns the panels to follow the sun, so the array is always angled towards it.
Solar electric panels are rated according to their performance in optimum conditions (i.e. direct sunlight during summertime, or – to get technical –under full solar radiation). This is expressed as kilowatts peak (kWp).
A typical domestic setup (for a two to three-bedroom house) will be rated somewhere between 3.5kWp and 4kWp – but the exact specification will depend on a variety of factors, such as the size of the house, number of occupants and current/future electricity needs.
Depending on the system you use, you can expect to require around 8m² of roof space per kWp. As a rule, 1kWp of solar PV panels installed on a south-facing roof at a good pitch will provide around 800-1,000kWh of electricity per year. This will vary according to your home’s location in the UK – a well-oriented roof in the Devon countryside is likely to get more sun than an inner-city equivalent in Liverpool, for example.
On average, a 3.5kWp setup might deliver 2,800 to 3,500kWh of electricity – which equates to the majority of an average household’s annual electricity requirement. But don’t expect to rely on the panels all year round.
Carolyn Copperwheat built a stylish Passivhaus home in East Sussex using a timber frame superstructure from MBC Timber Frame. The airtight house features a solar PV array on the roof, from PDP Services, and high-performance alu-clad glazing from ecoHaus Windows & Doors.Photo: Mary Gaudin
Most domestic solar photovoltaic panels (on-roof solar panels) are fitted to the property’s roof, ideally one that’s on a south-facing elevation and offers a 30 to 40° pitch to maximise the array’s exposure to light. Fitting the PV units is a fairly painless process, and most jobs can be completed in two or three days.
If you’re building a home from scratch, then you can make allowances for the above in your architectural brief. Considering solar PV when you’re in the early design phases makes most sense, as you can make sure your solar electric panels are orientated and fitted as efficiently as possible.
The government’s bid to reduce carbon emissions means that homeowners are now free to install solar panels on a house or outbuilding under permitted development (PD) rights, meaning the majority of UK homeowners will not require formal planning permission. The installation must meet these conditions to qualify for PD:
Any works completed under permitted development rights should be signed off with a certificate of lawful development, to prove that the works were permitted at the time. If you are unsure whether or not your installation qualifies under permitted development, you should speak to your local council.
permitted development (PD) guide
There are two main options for installing the panels. The first is an ‘on-roof’ solar PV system, where the modules are fitted in a mount that’s anchored to the rafters. This method is particularly suited to retrofits, as it involves minimal disruption.
Vincent Denecker’s old brick house proved difficult and expensive to heat, so after years of contemplating a project, he replaced it with a contemporary, energy-efficient timber home. The sustainable home benefits from rooftop solar panels from Solarwatt and a heat pump ventilation (HPV) system that provides space heating and fresh air thanks to integral mechanical ventilation and heat recovery (MVHR), plus hot water via a second heat pump unit. Photo: David Stewart
If your roof is already tiled, these will need to be lifted, the anchors fixed and the tiles replaced before the mount is attached. With some slate roofs, it’s preferable to leave the covering in situ and drill through to provide a fixing. In both cases, the panels sit slightly proud of the covering to provide a ventilation gap.
The second option is an ‘in-roof’ or integrated system, which is often preferred for self builds or big renovation projects where the structure is already being re-roofed. With this method, the solar panels are fitted on the same plane as the covering for a sleeker finish, with a flashing kit used to provide waterproofing.
In-roof panels need to be specified early on in the design process to avoid problems down the line. “While an architect can reach out to a manufacturer to get dimensions, many don’t realise that there also needs to be flashing (a tray for the panels),” says Yen Dai, solar expert and former director at Eco Energy Environment. “Even if this is highlighted to them, no one then explains that there should be a buffer around the edges – one and a half tiles on the sides, and two rows on the top and bottom of the array.”
“When we come in late and see that there physically isn’t the space to allow for the flashing or minimum row of tiles, it means the client will have to lose some panels – so people get very disappointed,” says Yen.
You can even choose to install individual solar tiles or slates, available from suppliers such as Solex. As with any solar PV system, ventilation is important, so your installer may counter-batten to provide good airflow.
Solar tiles are an interesting alternative to panels, having the advantage that they are virtually invisible, and can even pass muster in conservation areas. This comes at a greater cost, though – perhaps 50% more than a panel system.
Solex’s solar roof tiles function as electricity generators, as well as providing a roof covering that blends seamlessly with the design of the house. The tiles can be fitted to cover the whole roof covering from edge to edge, all the way from the eaves to the ridge and out to the verge and hips/valleys. They also interlock seamlessly with natural slate roof tiles if you only want to install solar panels on one section of the roof
Alternatives include ground-mounted panels (which literally sit in a frame in your garden) or flat roof installations. In the latter case, the modules are usually fitted at a greater pitch than the roof to maximise the amount of strong daylight to which they’re exposed. New ground-mounted products that move to track the sun’s path can deliver an efficiency advantage over static systems.
Bifacial solar PV panels form the roof of this property’s carport in Wiltshire. Pure Energy UK also installed battery storage and an EV charger as part of the setup
The next step is to think about whether installing a battery storage system would be the right move for your project – bearing in mind the upfront cost can be significant. “You’re looking at roughly £5,000 to £10,000 for a battery system, depending on the size and specification,” says Rhiannon.
The potential payback on battery systems is hard to quantify – but it’s worth thinking towards the future and factoring in that electricity prices may continue to be subject to rises and volatility. “Rather than focusing solely on a five- or seven-year payback, it’s more meaningful to model performance over 15-25 years, using realistic energy inflation assumptions,” says Mark Millar, CEO and founder of Puredrive Energy.
Adding battery storage makes sense when a solar PV system is expected to generate more electricity during the day than can be used in real time. This would mean you’re exporting electricity at a lower rate than the cost of importing grid power later in the evening. A battery therefore reduces reliance on peak-rate electricity, which is particularly valuable for households on time-of-use tariffs, where off-peak and peak pricing differs significantly.
Energy efficiency was important to Adrian Evans, who prioritised a sustainable heating setup powered by renewables when self building a new home on the Cornish coast. This requires a suite of the latest technology. The property’s flat roof boasts 20kW of solar PV panels, facing east and west. These feed into a Tesla PowerWall battery and the two EV chargers. Photos: Simon Burt
On the other hand, a battery may be less compelling where occupants are home throughout the day and consume most of the PV energy on site. “Prioritising a well-sized solar array, with the option to add storage later, can be a more proportionate approach,” says Mark.
It is also important to bear in mind that tariffs are likely to change in the payback period. “With solar export tariffs now reaching 20p/kWh – up from 5p a few years ago – battery owners who based their calculations on much lower export rates may have overestimated their annual savings by hundreds of pounds,” says Rhiannon.
More affordable battery options have entered the market recently, including those from longstanding manufacturers, such as Fox ESS. “It’s still too early to accurately compare the performance, lifespan and value of these systems versus premium products, as most offer a 10-year warranty but have not yet been fitted for 10 years,” says Rhiannon.
Roof size, layout and constraints such as shading will usually determine how many panels you can install – and therefore how much clean electricity you can generate. Getting expert input at the design stage can flag any issues, streamline the process and enable the best the PV design.
A south-facing roof pitch typically delivers the strongest overall performance. East- and west-facing arrays can also work well – particularly if your household uses more energy in the morning (east) or afternoon/evening (west).
In-roof (integrated) PV panels sit flush with your roofing materials for a streamlined look, and double up as the covering (so you don’t need tiles, for instance, on that section). Various mounting systems are available for on-roof installs, flat or low pitches and ground-level installations.
Standard panels typically deliver 300-450W each, while premium models can exceed 500W – potentially maximising output from smaller roofs, for instance.
If you have ample roof space, you may not need to cover it all. Estimate how much electricity a full array could generate annually and compare this with your projected yearly energy use. Then decide how closely you want supply to match demand.
Solar PV systems are measured in terms of kWp – kilowatts peak. This is the amount of energy that a solar PV system can generate when operating at full power, ie in the middle of a sunny day. Costs are normally expressed in £/kWp. So, if a typical domestic solar PV system was 4kWp and cost £7,000, we’d say the cost is £1,750 per kWp. This includes not just the collectors, but the inverter, controls, wiring and installation, too.
Surprisingly, it’s quite difficult to nail down average costs of a solar PV system. They seem to have risen in recent years before falling back a little recently – but data is sparse. Market data suggests that a 4kWp system is likely to cost between £5,500 and £8,000. This works out to around £1,400-£1,900 per kWp for a typical home install.
It’s good to note that smaller solar PV systems tend to have a higher cost per kWp than larger setups due to installation costs such as scaffolding and electrical work remaining the same, regardless of the quantity of panels.
In theory, it should cost less to install a solar pv system if you’re building a new house than if you’re retrofitting the panels on an existing one, as scaffolding is already in place and you have ready access to wiring routes etc. Built-in solar PV systems (BIPV), where the collectors form part of the roof covering, should offer a small saving in deducted roof finish materials to offset the capital cost of the system.
It’s also worth bearing in mind that the inverter is expected to need replacing at least once during the solar PV system’s lifetime. Again, data is sparse but it’s wise to factor in this additional cost from the outset.
The government’s Feed-in Tariff, which paid out to homeowners both for the generation and for the excess electricity their solar PV systems produced, closed to new applicants on 31 March 2019.
Its replacement, the Smart Export Guarantee (SEG), was rolled out on 1 January 2020 and is delivered via licensed electricity suppliers. Under the Smart Export Guarantee, homeowners get paid for electricity exported to the grid from SEG-eligible technologies, such as solar PV. It’s important to note that suppliers set their own export rates, contract terms and tariffs, which means the SEG payments can vary from provider to provider, and with different tariff types.
Many suppliers now offer a range of fixed, variable and time-of-use export tariffs. Some of the highest export rates are only available to customers who also buy electricity from the same supplier or who installed their solar PV and battery system through an approved installer.
To qualify for payments under the Smart Export Guarantee, installations must usually:
Solar Energy UK, formerly the Solar Trade Association, which publishes guidance and information on export tariffs.
Designed by Stanley Bragg Architects, this bio-based, Passivhaus Plus home generates more energy than it consumes. Key features include a super-insulated EcoCocon Kit H straw panel superstructure, high-performance glazing from ecoHaus Windows & Doors, and an 8.1kWp solar array with 10.4kWh home battery system. Photo: Matthew Smith
The amount of time it takes for an investment in a solar PV system to pay back through reductions in energy bills is known as the payback period, or breaking even. Of course, there’s a difference between cash spent now and money saved in the future – you’d rather have £1 now than £1 in 10 years’ time, because that money will go further today.
Future savings should therefore be discounted to arrive at the present value to compare them with capital cost. Using the Treasury’s current Green Book rate of 3.5%, £1 in a decade’s time should be treated as the equivalent of 70p now. So, the value of future payments will gradually diminish over time. After 20 years, the value is less than half. However, electricity prices are expected to rise gradually, so this might well offset the interest rate.
As such, payback times are normally expressed in terms of simple payback – cost divided by savings based on the current price of electricity. This sum is dependent on:
If you’re out most of the day and don’t have battery storage to store the electricity generated by your solar PV system, the bulk of the energy produced is exported to the grid. It’s not straightforward to say how much you’ll be paid for this, as the Smart Export Guarantee scheme only stipulates the rate should be above zero. To get the best tariffs there are many conditions attached, and rates can vary according to time of day. Generally, the export rate is much lower than what you pay to buy your electricity in.
So, in the example (below), with no allowance for the cost of inverter replacement, the payback period would be about 15 years. After that, you start to see a net return against your initial outlay. This can be compared to the average life of a PV system, commonly quoted as 25 years. Therefore, you can expect the system to pay back within its lifetime. Factor in inverter replacement and the payback would be only just within the expected lifetime.
| EXAMPLE PAYBACK PERIOD | |
|---|---|
| Size of system | 4kWp |
| Cost of system | £7,000 |
| Output per kWp | 800kWh/kWp |
| Total annual generation | 3,200kWh |
| Cost of electricity displaced | 20p/kWh |
| Percentage used on site | 50% |
| Annual saving (3,200 kWh x £0.2 x 0.5) | £320 pa |
| Percentage exported | 50% |
| Export payment | 10p/kWh |
| Annual value of exports | £160 pa |
| Total saving | £480 pa |
| Payback period (£7,000 / £480) | 15 years |
The power output generated by any solar pv system falls slightly each year, but this drop is thought to be less than 1% per annum. The rate of degradation may differ between manufacturers and solar panels, so it’s essential to check independently verified data on long term performance before deciding which solar PV solution best suits your home. At 0.8% per annum, the fall in output would only be 18% by year 25, but this still has a modest impact on the payback equation.
It’s always best engage with a specialist solar panel company right at the very beginning of your project – whether you’re retrofitting or building a new house. If you’re self building or reconfiguring the roof, put the solar expert in contact with your house designer to collaborate.
If a specialist solar installer can only suggest solutions, such as moving roof windows, once the planning design is already finalised, some architects can be reluctant because they feel it might spoil their vision for the aesthetics.
In general, solar panels fall under permitted development (PD) rights, so you don’t need planning. However, if you’re in an area of outstanding natural beauty, conservation area, are working on a listed building or installing a ground mount, you will need planning permission.
We now have a UK recycling facility and this is set to get bigger as installs start to come to the end of their life. Components are broken down into their constituent parts and most of the material is then reused. There is a significant energy component to this process and for thin film application there are concerns about the use of cadmium, but it’s possible for polycrystalline panels (the majority of systems) to be recycled safely.
Login/register to save Article for later
Comments are closed.