Solar PV power

Why install solar PV panels?

2 reasons:

1. Solar power is now the cheapest energy source in the world, after huge drops in panel prices, and being installed at a great rate everywhere. In the UK, this only makes a small difference as the installation labour is the main cost, but at the same time new electricity export tariffs mean that you can make money on solar. A typical 4kW array might cost £6,000 to install, and make/save you £900 a year. It's the "minus" bit that gets your energy from a big cost to net zero. There is no VAT  on solar panels or installation costs.

2. Solar power is super green. It's the major way we get to net zero carbon emissions, and cheaply too. The panels are silent and last for decades, and are practical and affordable for the majority of homes. There are already about 1.5m homes with solar in the UK, and record ongoing installation levels.

 

Can I install solar panels?

If you have a south, east or west facing roof then you can install solar panels - though south and west are the most cost effective, because they generate more power at times of day when power prices are higher.

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Most commonly solar photovoltaic panels are attached to rails which are fixed to the roof. The fixings pass between the tiles, and an array can normally be installed in one day. You will need scaffolding in most cases, though installers may be able to use just a portable tower if installing on a bungalow or garage, which will reduce costs.

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The size of array you can install will depend on your roof size, but the most common array size is around 4-5kW, or 10-12 panels. Note that to achieve net zero, you may need a slightly bigger array than this, eg 6kW. This will be no problem on a larger roof, but might be a tight fit for smaller homes or those with difficult roof lines, dormers, Velux etc. Consider if you can fit extra panels on a garage or in the garden.

A cable runs into the roof and to a vital device called an inverter, which changes the direct current (DC) generated by the panels into alternating current (AC) which is used by the grid and all your house appliances. If you want a battery as well it's a good idea to install this at the same time as the battery and solar array can share the same inverter, and it's a particular type called a hybrid inverter which works for both. If you don't plan a battery but think you might in future, ask about getting a hybrid inverter for your solar to "future-proof" you for a future battery.

 

You don't need planning permission in the UK unless you have a historic listed house, or live in a conservation area. In these cases you may need planning permission, and you may not be able to install on the main house roof if it affects the appearance of a historic house or conservation area. Often however you can install them on a garage or outhouse, or if you have land you can install in a field or big garden, on the ground. This may be cheaper as no scaffolding or roof work is required.

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You can install on a flat roof too, normally using weighted frames which sit steady on the flat roof under their own weight, holding their panels at the right angle to the sun. The panels on many flat roofs may be invisible from the ground if they are behind a parapet, which may help if appearance is a concern, eg in a conservation area.

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What income can I generate?

You make money from solar in two ways: generating free electricity for your own use which you then don't have to pay for. and exporting to the grid, for which you get paid. Which of these is most important for you will depend on how much electricity you consume. If you use most of your PV power yourself, you will save more from the cut in your electricity bill than from exporting. But if you use less electricity then you may well make more from exporting (and you will of course be better off overall). The arrival of high export tariffs, most notably from Octopus Energy, has massively improved the financial returns you can make from solar panels. As they rise and fall in line with electricity import prices, they effectively insulate you against electricity price changes (in fact you may be better off when prices are high!).

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For example, our original 4kW solar array generates about 4000kWh per year. Last year we used about 1000kWh of that ourselves, and paid for another 1100kWh from the grid. We therefore exported 3000kWh which earned us £600, while the grid power only cost us about £330 - net negative! [prices early 2023]. To work out the return on investment, we can add to the £600 the 1000kWh we didn't have to pay for, which would have cost about £300. So we gained £900 per year from an investment of £7000. That's a 7.7 year payback or 13% return on investment. (and installation prices have dropped since then).

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There are no grants or subsidies for solar PV. In the early days they were supported by the Feed-in-Tariff (FiT), which guaranteed a price for all electricity generated. This was intially very generous, reflecting the high early cost of installing PV, but was then scaled back as PV prices fell. It was finally removed in 2019. Following an unfortunate hiatus, it was replaced by the Smart Export Guarantee (SEG) which guarantees that a PV owner gets paid something for export, though these sums were initially very small - a few pence per kWh. Finally, decent export tariff levels (15p/kWh) were introduced by Octopus in 2023, but the rates offered by many other energy companies remain shameful.

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You should also check how much power will be produced from your proposed panel site, especially if it is not south facing, or if there is shading. Some online calculators will do this, including the Energy Saving Trust and Spirit Solar. These will do a good job of working out the solar energy for your geographical location and orientation, but shading is more difficult to assess. The best thing is to look at your chosen roof in the sun at different times of the day/year to see if it is shaded by buildings or trees. You need to check all seasons as the sun is much lower in winter than summer. A little shading for an hour or so is no problem, but if most of the area is shaded in the middle of the day in summer, then you may have to think again. If you can't wait a whole year to check on the sun in the different seasons, you could try an astronomy app like Google Skymap which will show you where the sun will be on different dates/times.

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Be aware that shading just a small part of the PV array can shut down most of the output - that's just the way the electronics work. If you're likely to have part of the array shaded then talk to your installer about fitting optimisers or string inverters which can make PV work better with partial shading. These will increase costs though.

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How much should I invest?

How big is your roof?! As long as solar is generating returns above 10% as in the example above, you may want to install the biggest array you can. The limits are of course the physical  - eg your roof size - and the financial, in particular your cost of capital. If you need to borrow the money this will reduce your returns. But solar PV is likely to be the best earner of all the measures we discuss on this site, and relatively simple and non-disruptive in practical terms, so where possible go large*.

* of course, make sure you check the latest export tariffs available so you know what your earnings may be, and realise that these tariffs are not guaranteed and could be withdrawn. As we've seen, import and export tariffs can change unexpectedly, but if you have solar, and especially if you are a net exporter, you will be more protected from high electricity prices than if you don't.

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Impact on house value

So - would you pay more for a house with solar panels, or think them an eyesore? This question was asked a lot in the early days of solar in the 2010s, before PV became more common, and new power tariffs enabled solar to make serious money for the homeowner. With solar panels able to make you around £1000 per year better off, they have clear value when you sell.

That said, it's always good to do the best for your house's appearance. Pay attention to the panel layout on the roof - some approaches look more attractive than others. Normally, a symmetrical layout looks better, and you'll be able to choose which you prefer from a range of different panel designs.

Panels are of course normally rectangular, and this does not always fit beautifully if you have a hipped roof with diagonals. Triangular panels are available, but expensive, and may not match your house angles - they are very rare in practice.

In the end if you had a weird potential buyer who didn't like solar, it would only cost about £1000 to remove them, which is trivial in a house sale.

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Climate impact of solar

Every kWh you generate with solar displaces a kWh from the grid (at least, so long as you don't increase your consumption just because you have solar). So as long as we still have gas and coal power you will be reducing greenhouse gas emissions by installing solar, and each kW you generate will displace the coal or (most often) gas, as that is what is switched off as wind and solar generation rises. In fact your carbon footprint from electricity may well be net negative as in our example above - in other words the world is better off than if you and your home didn't exist at all!

There is of course a climate impact in manufacturing PV panels. One common and simple way of working out the carbon costs and benefits is through the carbon payback calculation - what is the impact of producing a panel, and how long does it take to displace enough fossil electricity to make up for this? This calculation has been done for many panel types and markets - it varies depending on the local grid, for example. The numbers vary quite widely and some of them online are for obsolete panel types (today's panels are infinitely more advanced from those from the noughties). But to use our Sunpower panels as examples, their production impact is quoted at 300g/W  in Table 3 here. Our 3.9kW of panels therefore involved 1.17t CO2e. They generate 4000kWh pa displacing gas generation which would otherwise emit 360g/kWh, so that saves 1.4t CO2e pa. The panels therefore make up for their manufacture in 10 months. (even quicker if you assume coal generation displaced, though the last UK coal plant is due for closure).

There are of course other ways of working it out, and other panels and locations may be better or worse, but hopefully this simple example shows how solar PV is worthwhile. Also, manufacturing impact is improving all the time, especially as the PV factories themselves use PV.

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Other kinds of solar panel

You are probably aware of solar thermal panels which generate hot water directly. An installation of this kind is much smaller than PV, often only a couple of panels worth, and needs plumbing and hot water storage. Solar thermal has been available longer than PV, but has lost out to PV in popularity as it is more complex and generates more modest savings. In particular, a PV array can heat your water very easily using an immersion controller like iBoost or, more efficiently, via a heat pump, so why bother with solar thermal?

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You may also come across a thermodynamic panel. This is a kind of hybrid of heat pump and solar thermal, used only for hot water. It collects solar warmth on a smallish panel and this is then shifted with a compressor heat pump style to your hot water tank. It may therefore be more effective than solar thermal alone, but with a price tag of several thousand pounds it's hard to see the advantage over a proper PV array which may not cost much more. These thermodynamic panels have also been, in our experience, the subject of doorstep hard selling tactics, which is offputting. However, we don't have first hand experience of them and would love to hear from any of you who have.

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Other renewables: it is technically possible to install a wind turbine or hydro, but these are rare and normally only for big land owners. Small micro wind turbines have been found to work poorly on houses due to turbulent wind currents,  and are no longer recommended.