Solar Panels for Home

Are you curious about how solar panels can provide 'free electricity' for your home? In this comprehensive guide, the experts at NimbleFins dive into the fundamentals of solar PV systems, explaining how they work, what components are involved, and how the electricity generated can be used throughout your house. We'll also explore the financial aspects, including whether solar panels are worth the investment, how long they take to pay back, and the potential downsides to consider. Additionally, we'll address common questions about solar panel efficiency, maintenance, and compatibility with different roof types. By the end of this article, you'll have a clear understanding of how solar energy can be harnessed to power your home and potentially reduce your reliance on the grid.

• How do home solar panel systems work?
• Are solar panels worth it?
  • How long do solar panels take to payback?
  • How much can solar panels save on electric bills?
  • Would solar panels be suitable for my home?
• What can solar power be used for?
• What is the downside of solar panels in UK?
• FAQs

How do home solar panel systems work?

Solar panel are made out of a semiconductor like silicon, glass casings and metal frames. When photons from sunlight hit the semiconductor material, electrons are released, producing an electric charge. This electric charge then travels through an inverter which converts the direct current (DC) generated by the panels into alternating current (AC) which can be safely used in the home.

Solar-generated power can be used immediately, stored in a battery (optional) or sent back to the grid (optional), usually in that order:

What is an inverter? A solar PV system generates direct current (DC) electricity. Because the electricity used in a home is alternating current (AC), an inverter is installed between the rooftop solar panels and the mains Distribution Grid. The inverter converts the DC electricity into AC, then sends that energy via AC cables to your mains distribution board.

Once at your mains distribution board, this electricity can then be used throughout your home (e.g. to run your lights and home appliances, heat your home or hot water, power your EV, etc.), stored in a home battery (for use later in the day) or exported to the grid (in which case you can earn a little bit of money on a SEG tariff).

What is an optimiser? Those with a shade-optimised system may have additional pieces of kit called 'optimisers', which are placed between the panels and the inverter. When used, optimisers are placed on each panel and essentially ensure that the output of the entire system is maximised. How? Without optimisers, if one panel is compromised due to shade, the power output of all of the other panels in the system is dropped to match the lower output of the shade-affected panel. But with optimisers, each panel is free to work independently and produce the maximum amount of power possible at any given moment. So they shaded panels produce less energy while the sunny panels can work at full power.

For example, SolarEdge divides the functions of the classic string inverter into two separate components—optimiser and inverter—to get the most out of a system even if some cells of the panel are shaded (e.g. by a tree or a chimney).

Can you run a house on solar power alone?

Possibly. To run a house on solar power alone, the solar panel system would really require one critical piece of equipment: a home battery (solar panel battery). A home battery is needed to store up extra solar energy generated during the day, for use at night. With a home battery, a home that is powered on solar alone can still have access to solar-generated electricity after the sun goes down in the evening.

Whether or not you can run a house mostly on solar power also depends on factors like the geographic location of the home, the direction of the roof, the number of solar panels that can fit on the roof, the natural electricity consumption of the home, time of year, weather, etc.

And even if all of these factors line up, there may need to be some draw on the grid for electricity even during daylight hours, in particular to power up high-energy appliances like a kettle or toaster. All that said, a home with a good-sized roof facing the right direction (e.g. not North) and a large home battery might be able to run largely on solar power. To find out if your home can run on solar power alone, get a solar panel quote from a specialist.

Are solar panels worth it?

Once installed, solar PV panels can provide essentially free electricity to a home—but is the upfront cost of thousands of pounds worth it? Two of the best ways to think about this question are to 1) calculate how long solar panels take to pay back and 2) calculate much can solar panels save you on electric bills.

At the extremes, if solar panels paid back in just a couple of years, it'd be a no brainer—they'd definitely be worth the upfront cost. But if solar panels took 30 years to pay back, you'd probably be right in thinking they're not worth it (because even the best solar panels aren't guaranteed past 30 years).

So where's the sweet spot? It's hard to say and will vary from situation to situation. Is 8 years good enough for you? 12 years? Keep in mind that once they 'pay back' (that is, once you've save more in energy costs than you paid for the panels to begin with), you essentially get free electricity from that point going forward (until the system needs replacing or reinvestment...).

With that in mind, let's look at some solar panel payback examples, using a real-life quote we recently received from a national installer.

How long do solar panels take to payback?

According to a simple back-of-the-envelope calculation by our solar experts, it can take around 8-12 years to pay back a solar panel system producing 3,100kWh of electricity per year, assuming all of this energy is used by the home (in place of energy bought from the grid).

Let's compare two solar panel systems: one without a home battery and one with a 5.8kWh home battery.

Note, for this analysis we used the EPC cost of electricity for April - June 2024 of 24.5p/kWh and a real-life solar panel system quote from a national installer for a size that would suit the typical household.

At first glance, it appears that the solar panel system without a home battery has a better pay back time of 8.6 years, however, there is more to the story.

The pay back times above are only valid if the home can use all of the solar-generated power. And since this is much more likely to be achieved in a system with a battery, we think the safer payback time of a solar panel system is around 12 years. But if a household is home all day and can use the solar energy as it's produced, that household may achieve the shorter payback period of 8-9 years. Let's walk through the two scenarios and explain further.

Also, whether or not your home can produce as much as other homes depends on factors like location, aspect and even how much you're home. To learn more about how these factors affect repayment, read our further analysis on Solar Panel Repayment.

Note, we have not included the SEG payments you can earn by selling energy back to the grid in this example, nor have we included benefits of having a home battery such as being able to buy cheaper grid electricity during the night that can be stored in the battery. As you can see, payback calculations are not necessarily simple!

Solar panel payback time, no battery

We were recently quoted for a solar panel system (without a home battery) costing £6,500 for 3.9 kW of total solar power—a system expected to produce 3,100 kWh of electricity per year.

Given the current cost of electricity of 24.5p/kWh, 3,100 kWh of electricity would cost £760 if purchased from the grid. That implies the solar panel system would pay itself off in 8.6 years (£6,500 divided by £760).

BUT this math assumes the home actively consumes every bit of solar power as it's generated (since the system doesn't include a home battery). If it's not possible to use all of the solar energy as it's generated during the day (and it's probably not...), the pay back time would be longer than 8.6 years.

Two solutions would be to sell some energy back to the grid on a SEG tariff or to install a home battery to store the energy for later use.

SEG export tariffs for selling energy back to the grid are pretty low at around 3-4p/kWh, so let's set that aside.

Installing a home battery for solar is an effective way to ensure all solar-generated power is used by the home, but batteries come at a cost. How does the pay back time look if you add in battery cost?

Solar panel payback time, with home battery

We were also quoted for the same solar panel system (3.9 kW of total solar power, expected to produce 3,100 kWh of electricity per year)—this time WITH a 5.8 kWh home battery—for an all-in cost of £9,300. The battery added £2,800 to the cost, in this case.

The addition of the home battery helps ensure that the solar-generated power can actually be used by the home, not wasted.

As before, the current cost of electricity is 24.5p/kWh and the 3,100 kWh system could potentially save £760 in electricity purchased from the grid. That implies the solar panel system including battery would pay itself off in 12.2 years (£9,300 divided by £760).

This setup could theoretically store 5.8 kWh of energy per day (although batteries will lose some energy when charging and discharging—they're not 100% efficient). Is this enough to ensure a home actually uses all of the solar-generated energy (making the 12.2 year pay back time realistic)?

A quick calculation: the average home uses 2,900 kWh of electricity per year, or 7.9 kWh of electricity per day. Theoretically, a home consuming 7.9 kWh of electricity a day should be able to make the most of their solar panels using a 5.8 kWh home battery. While the storage capacity of the battery is less than the daily usage, keep in mind that some of the solar energy will be used as it's generated, so not all of the energy needs to be stored for nighttime use. Even if people are out during the day, a home continues to draw on electricity to run the refrigerator, other appliances and even possibly heating (e.g. water heating).

Another benefit of having a home battery is that you can sign up for a Time of Use tariff, enabling you to buy cheap electricity at night that you store in the battery. For example, we quoted a Time of Use tariff from Octopus (called Octopus Flux) for our area and found that the rate during most of the day was pretty typical right now at 25.7p/kWh. But the rate was 40% higher for three hours in the late afternoon/evening (4pm - 7pm) and 40% lower for three hours in the middle of the night (2am - 5am). On this type of tariff you can load up your home battery during the night for cheaper (e.g. 15.4p/kWh vs 25.7p/kWh), and use this during the day if your solar panels don't produce enough. This also affects your pay back calculations.

How much can solar panels save on electric bills?

At the current Energy Price Cap (24.5p/kWh), a household with median electricity consumption (2,900kWh/year) could save around £711 a year with 'free' solar energy. Here's how we calculated that figure:

The amount of money one can save on electric bills with solar depends primarily on three factors:

To keep things simple, let's first assume that all of the solar power generated by the PV panels is consumed by the home (i.e., none is unused or sold back to the grid).

From there, it's a simple math exercise to calculate the grid-equivalent cost of the solar electricity. We've run the numbers in the following table, for a range of electricity costs and solar generation figures to see how much you can potentially save on electric bills with solar.

As you can see in the table below, at the current Energy Price Cap (24.5p/kWh), a household with median electricity consumption (2,900kWh/year) could save roughly £711 a year with 'free' solar energy.

Will solar panels work for my home?

The best way to find out if solar panels will work for your home is to have an installer carry out a survey (online or in person). A professional will be able to figure out how much energy you ideally would want to produce (taking into account your typical annual usage) and figure out how much solar energy your home is capable of producing.

To calculate your home's potential solar energy production, the installer will factor in how many solar panels can fit on your roof, the power output of the specific equipment proposed, how much you're home during the day (to use the solar energy as it's produced) and the 'sunniness' of your area. As we illustrate in our article 'Would solar panels be suitable for my home?', the amount of direct sunlight (as determined by geographic location, roof direction and amount of shade) and even how much you're home during the day make a big difference to solar generation potential.

The installer should produce a financial model for you that estimates your energy production and usage, thereby determining how much money you can save with solar each year and the potential payback period. Once you have that information, you can decide how well solar panels will work for your home.

What can solar power be used for?

Solar power generated by solar panels can be converted (using an inverter) into AC electricity to power a home's electrical energy needs. This electricity can be used immediately to power at-the-moment electrical draws or stored in a home battery for use later.

Whether used immediately when the sun ins shining or drawn later from a home battery, solar power can be used for:

What is the downside of solar panels in UK?

The biggest downside of solar panels in the UK is the initial upfront cost, which typically starts from around £6,000 and rises with the size of the system (plus additional costs for a home battery, if one is desired).

Once a solar panel system is in place, electricity generated by solar is essentially free. Given the high cost of electricity, and the low maintenance requirements, there aren't too many downsides to solar panels beyond the expensive initial investment, in our opinion. Perhaps keep in mind that they add an element of difficulty when it comes time to replace the roof, although you might not need to worry about this for decades (your solar panel installer should inspect your roof and give you a time frame for this).

Also, solar panels in the UK certainly produce less energy at certain times of the year, especially those dark and rainy days. When solar panels aren't enough, you'll need to rely on grid electricity (and a solar panel battery can help, too).

FAQs

How long do solar panels last?

Experts we've spoken to in the market currently think solar panels should last around 25 to 30 years. But what's the proof, given some of the technology is relatively now? Let's look at it in a roundabout way.

Current solar panels warranties in the UK are a minimum of 10-12 years, implying that the current technology should last at least that long. But we'd expect them to last a lot longer, because consumer goods usually last for many years more than the length of the warranty.

Consider that a washing machine warranty is around 2 years and a typical car warranty is around 3 years. For reference, the NimbleFins team found that the average age of cars operating in the UK to be around 8.6 years and we have personally found our washing machines to last for ten years and running—manufacturers are naturally incentivised to produce goods that last much longer than than the warranty period, to avoid paying repair costs for goods that fail during the warranty period.

Taking all of this into account, our takeaway conclusion is that one could expect solar panels to last for much longer than the warranty. And while some panels are only guaranteed for 10-12 years, some of the best solar panels have warranties of 25-30 years, or even more. So will panels last for 25 years? 30 years? Time will tell for the latest technology, but 25 years seems to be a reasonable expectation, in our opinion, but it will depend on the panels.

That said, the inverter (a key piece of equipment in a solar panel system that converts solar DC energy in AC electricity for the home) may fail and require replacement sooner.

Does solar work with shade?

Solar panels can work with in some shady environments, with specialist equipment.

Shade can come in many forms, such as moving clouds, overcast skies, rain, fallen leaves, nearby trees, bird droppings, dirt and chimneys. When shade is cast over a solar panel, the amount of sunlight reaching the surface is reduced and the power output of the PV modules drops.

Without "shade optimisation" in place, solar panels can be pretty ineffective. This is because if one cell is shaded and its output drops, all other cells in the series will mirror the low output of that shaded cell. As a result, the output of the entire system drops to that of the lowest output cell. For example, if one cell is temporarily shaded by a chimney shadow and its output drops by 50%, the power output of the entire system will fall by 50%. This 'series' setup is similar to some Christmas tree lights—if one goes out, they all go out.

But there are some solutions to help solar panels work in shaded situations. For example, a DC power optimiser placed on each solar panel can help to maintain maximum solar power even in the presence of shade. In a shade-optimised system, the non-shaded cells in the sun can still operate on their own, independently, at full power—even if some cells are completely shaded. Not all inverters are compatible with DC power optimisers, so ask your installer about this.

In short, while solar won't work very well in a heavily-shaded environment, it can work in areas where the the shade is intermittent or light—especially with some specialist equipment like DC power optimisation.

Is it harder to sell a house with solar panels in UK?

It should be easier to sell a house with solar panels in the UK, since the home will generate some of its own energy. Given the high cost of electricity these days, a home that can be powered at a fraction of the cost should appeal to most people. Plus, the home will have a smaller carbon footprint, and an improved energy performance certificate (EPC) rating. Not to mention the ability to sell energy back to the grid (see our article on SEG tariffs).

On the flip side, if the panels and/or the roof are quite old, a buyer might not want to deal with replacing them.

Also, if they are not placed aesthetically, a potential buyer might be put off by the look of them. For example, a bunch of solar panels jammed unsymmetrically on the roof on the front of the house might be a problem. Also, some people might be uncomfortable with the new technology and how to use it, instead preferring to use the grid for electricity as they have for years—especially if a potential buyer doesn't understand the potential cost savings.

The only real potential problem to selling a home with solar panels occurs if the previous owner leased their roof to a solar panel company. This is pretty rare these days, but could cause problems such as in obtaining a mortgage. But again, this is rare.

In short, we think that solar panels should make it easier to sell a house, although there will be exceptions. And while we'd expect the majority of potential buyers to be attracted by solar panels, they may put some people off. But so might the colour of your kitchen cabinets...

How much space do you need for solar?

The amount of space required for solar depends on the size and number of solar panels in the whole system.

Solar panel sizes vary, but are commonly around 1.4m² - 2.0m² per solar panel. For example, the Longi 3.87kW solar panel preferred by at least one national UK installer is 1.7 metres x 1.2 metres (on the larger size).

Here are some rough figures illustrating the roof size needed for varying numbers of solar panels. When deciding how much roof space you have available for solar, keep in mind that installers typically have a minimum required 0.3 metre gap between the edge of the roof and the solar panels—meaning, the solar panels can't bump up against the edge of the roof or a roof hip (this helps prevent uplift during high wind conditions).

A 'typical' PV installation with 8 solar panels would take around 11-16m² of roof space, plus the required space around the panels. See the estimated space your solar panel installation could require in the table below:

Your solar panel installer will look at your roof (in person or using tools like Google Maps) to estimated how many panels can fit on your roof.

Can you install solar on an older roof?

You can theoretically install solar on an older roof, as long as it's in a good state of repair. But keep in mind that most solar panel mounting systems involve screwing brackets into the roof frame, so it's not exactly easy to take off solar panels at a later date to replace the tiles underneath, then reattach the solar panels. And solar panels are estimated to last up to 25 - 30 years now. For example, if your roof needs replacing in 5 years, you probably wouldn't want to install solar panels today. Also of note, we've been advised by solar panel companies that solar panels can actually help protect roof tiles, so PV panels could theoretically extend the life of your roof.

Ideally, solar PV systems are installed on a roof that is in good condition. At the beginning of your solar panel installation, the team should do roof check to assess its condition. They'll also need to check that the joists are strong enough to support the added weight of solar panels.

What's the best angle for solar panels UK?

Typically, solar panel companies say that the ideal angle is 20 - 50 degrees. For roofs that are less steep (15-20 degrees), and that don’t exceed 10 degrees to the north from perfect east or perfect west, solar is possible but the panels will generate less energy than if they were facing south.

Solar PV panels produce the most energy when they're perpendicular to the sunlight. But the sun is always in a different place in the sky, from hour to hour, day to day, and season to season. In summer, a flatter position is better (because the sun is directly overhead), but in winter, a steeper angle can be better (because the sun is positioned at a low angle). But given we can get the most from solar panels in the summer, it makes sense to positions panels to optimise summer sun—this would ensure the most energy production over the course of an entire year.

In addition to performance, the angle of solar panels can also impact cleaning. Solar panels are generally self-cleaning at an angle of 15 degrees or more, when rain can wash away dirt and debris. At flatter angles, you won't get help from gravity to help wash away debris.

Note: we've found that most of the larger installers won't install solar panels on flat roofs. If you want solar panels for flat roofs, you might have better luck with a smaller, local installer. We did receive a quote from Pure Energy, who install nationally, for a solar panel system that included both pitched and flat roof installations.

Solar panel cleaning

Solar panels that are clean are more efficient, because the sunlight is not blocked by dirt, dust, leaves, bird droppings and other debris. Power spraying, as well as water and a soft brush, can be an effective method for cleaning solar panels from the ground, but ask the installer for their recommended cleaning methods to ensure the warranty is not voided.

How to bird proof solar panels

Nesting birds can leave droppings, feathers and nesting debris on the surface of solar panels, reducing the power output of the panels. In some cases, birds can also cause a problem with system cabling.

Where there is concern about birds nesting under or next to solar panels, the popular and practical solution is to install a wire mesh system around the perimeter of the panels. A solar panel installation company (or some roofers) can do this, and the mesh can either be fixed to the panels using retaining bolts (check, but this should not impact the solar panel product warranty) or special clips that don't required any drilling or glue.

Solar panels that are installed close to the roof should naturally keep birds out from nesting underneath, simply because there isn't enough room for birds to nest underneath. But even so, birds could cosy up and nest next to the panels, depositing problematic droppings, feathers and debris. And birds tend to return to where they were born, so we'd say you're better off bird proofing your panels right off the bat, rather than trying to fix a bird problem after it's started.

Some solar panel installations may leave a larger gap or may intentionally be set away from the roof. For example, a solar panel installation on a flat roof will be tilted to face the sun at an angle. While 30 to 40 degrees is ideal, flat roof systems don't angle up that much to avoid wind lift issues but even the 12 degree or so tilt on flat roof solar panels can leave room for birds to nest underneath.

Can solar power can help reduce current home gas usage?

Possibly, if some gas-powered appliances or systems are swapped for electricity-powered. For example, water heating can be done with gas (e.g. a boiler) or electric (e.g. an immersion heater or an air source heat pump). An air source pump uses electricity (e.g. solar-powered electricity) to heat water for water-filled radiators (the same kind you use with boiler-heated water).

Historically, it's more expensive to heat water with electric than with gas—if the electric is from the grid at average prices. However, the variable cost of heating with electric can be cheaper if it's done with solar power and/or via off-peak grid energy during the night on a Time of Use tariff (where discounts can be found from 40% to 75% off average electricity tariffs).