Crisis, what energy crisis?

Domestic Sustainable Energy, Part 1

Chatting with the UK Microsoft MVP community this week, the opening banter was mostly about the weather (we are British) and not turning on the heating. I mentioned that we had installed solar panels and a battery and that the look on my face was of extreme smugness.

Far from shutting me down and banning me from future video meetings, there was an insistent suggestion that I should share my experiences. Thus, I offer Part 1 of my Supertramp-titled Domestic Sustainable Energy blog.

Way back in early 2011 my wonderful wife found herself providing book-keeping services to one of the alternative energy companies that popped up in response to the government Feed in Tariff programme. The promise of a ‘mates rate’ installation and an interest in all things tech led us to invest in a 3.29kWp rooftop PV system on the main house, above my office in the loft. It cost the not inconsiderable sum of £10,000; a lot of money for us at the time. We benefit from being almost perfectly south facing (10° off), and the roof is at a good angle to the sun, so actual output vs. theoretical peak (kWp) was encouraging. I calculated that the system should pay for itself in under 8 years.

Installation was straightforward, though the required scaffolding was a nuisance while it was up; it was about a week from start to finish and the installer chaps were only busy for two or three days of those.

Some people seem to get hung up on the appearance of PV panels. That’s always puzzled me. I have never been outside a house, looked up at the roof and thought, “ooh, those are lovely tiles!”. I’ll concede that on-roof panels aren’t works of art, but they are pretty cool and what they represent is cooler still. We were the first property in our East Yorkshire village to install PV and it generated almost as much interest as electricity! No one said, “Ooh, they’re ugly!”.

1 kWh is the equivalent of running a 1kW device for 1 hour, or a 3kW kettle for 20 minutes, or a 250 horsepower electric motor flat out for 19 seconds.

Understanding the terminology

At this point it would probably be helpful to clarify the various jargon and units of measurement.

Solar PV. PV stands for photovoltaic and is the clever semiconductor technology that directly converts sunshine into DC electricity.

DC is Direct Current, of course, like you get from a battery. The voltage of a PV system depends on how many panels are linked in series, what their efficiency and size is, and the amount of sunlight they receive at any moment.

Kilowatt (abbr: kW) the Watt is the SI unit of power, so a kilowatt is a 1000 Watts, or 1.34 horsepower if you insist on using outmoded unts. For the geeks and physics nerds, a Watt is equal to 1 Joule per Second. It’s used to measure the power output of a PV panel or system at any given moment; you can think of it as energy in motion if you like. Interesting fact: our roof runs at about 7 horsepower in summer.

Kilowatt hour (abbr: kWh) is a way of expressing how much power is used, or stored. 1kWh is the equivalent of running a 1kW device for 1 hour, or a 3kW kettle for 20 minutes, or a 250 horsepower electric motor flat out for 19 seconds. You can think of kWh as energy at rest – perhaps in an electric car’s battery, or the amount that was used by a device in a period of time. More interesting facts: a house uses about 12 – 20kWh each day. As it happens, a Tesla Model 3 Standard can run, foot-to-the-floor, for 19 seconds on 1 kWh, though I dare not try it.

Inverter This is the bit of kit that converts DC from the solar panels into the mains AC used by your household appliances (240 volts, or weedy 110V if you are in N America). Inverters often support multiple strings – a bunch of daisy-chained solar panels. They often offer smart features so that you can monitor the solar output etc.

Micro-inverters are a relatively recent innovation, where each and every PV panel has its own inverter. This solves a problem with some panels being in shade etc. and which drags the performance of the entire system down. These systems are a little more expensive but give a much better efficiency for the system as a whole.

Efficiency is how much of the incident sunlight gets turned into electricity. Older panels have an efficiency of around 15%, with modern, high efficiency panels hitting 23% (a 50% improvement in the last decade). The semiconductors in panels tend to work at the red end of the visible light spectrum, which is a shame as a ‘blue’ photon carries twice as much energy as a ‘red’ photon. In the lab, panels have hit 47% efficiency by extending the absorption range using exotic semiconductor designs. Hopefully, domestic panels will have even higher outputs in future.

Insolation is the amount of energy of sunlit as it falls on the Earth. At the equator at midday our friendly neighbourhood star, Sol, provides 1 kW per square metre. That’s quite a bit. In Yorkshire, that number is much lower since the Sun is 60° from the horizon in summer (the solar elevation angle), rather than overhead; it’s down to less than 20° in December. You can do the trigonometry if you wish, but it ends up looking something like 600-800 Watts per square metre of panels at best.

Feed In Tariff (FIT) is a government grant that encouraged early adopters to invest in solar PV. It is no longer available, but remains linked to the UK Retail Price index for those of us that got aboard early on, and pays about £2000 per year for most systems (rates are here).

Smart Export Guarantee (SEG) FIT has been replaced by the Smart Export Guarantee in the UK, which ensures your electricity company pay you for every kilowatt hour you export.

On roof/In roof. Most solar panels sit on brackets above your roof tiles, so are On Roof; these are pretty easy to retrofit, with most installed in 1 – 2 days for the panels (and a few more for the electrics and inverter commissioning). The installers will usually need to put up scaffolding (for health and safety), but there is no need to remove your roof tiles etc. This is what we have on our main roof. In Roof panels don’t; sit on the roof, they are the roof. Instead of tiles, the panels provide the weatherproofing; they also look very slick. These are generally installed at the time of building or renovating a roof and require a bit more planning as the roof and panels sizes need to work out. We have in roof panels on our conservatory and had to increase the roof size to make it all work – it looks great though, especially with the fully integrated Velux window.

District Network Operator (DNO) is the organisation who manages your regional electricity grid. There are 14 regions in the UK, operated by 6 groups. They are responsible for making the grid work and need to approve any system that exports energy to the grid.

Back to the story

We initially installed 14 panels on the main roof (with an area of 1.3m² each for 18.5m² in total). It attracted the Feed in Tariff, which paid us 41.3p per kWh (officially it’s a ‘Retrofit 0-4kW’ system for FIT purposes), with ‘deemed’ export); 11 years on that has risen to 56.03p (2022 figures, Sheet April 2011, cell E28) and earned us £2295 for 2022.

Our 3.29kWp primary system has generated 37MWh of electricity in 11½ years, about 3200kWh per year.

Technical details

• Nominal system output:  3.29kWp
  • 14 x LDK 235 Watt panels, rated at ~16.59% efficiency.
  • Size: 1642 x 992mm each
  • Nominal panel output: 235Wp per panel

More importantly for readers of this blog, in that time this system has generated 37MWh of electricity, about 3200kWh per year.

The panels and FIT are guaranteed for 25 years, so we are looking at over £50k Return on our investment. We are rather pleased with that; it massively outperforms most of the investment decisions I have made!

Panel performance does degrade over time. Ours are guaranteed to provide 80% of their design output after 25 years. In reality they will be closer to 90% given engineering tolerances, as long as you give them a clean every year or two. I use a cheap pressure washer and a sponge, I access them from my Velux; there are dedicated companies who will do it for you, though whether that makes financial sense is up for some debate. Note that they will continue to function long after that, so it’s an even better long-term investment despite the FIT ending 13 years from now for us. There is a chance the inverter will need to be replaced before then, which will be £600 – £1000.

In parallel with all this we did a lot of stuff to improve the insulation in our house (we also have an air source heat pump – that’s yet another blog – so became a bit fanatical about keeping the heat we produce), plus we started tracking our energy consumption and changing our kit and habits to optimise our use. Most houses have a ‘standby’ consumption of about 600 Watts (overnight, when things are mostly meant to be turned off); we got ours down to between 200W and 300W (it’s the fridge and freezers that push it up and down) by switching to LED lighting everywhere and using smart devices (Alexa, smart sockets and smart bulbs) to switch things on and off as needed/to a schedule. Echo Dots and other smart devices use less than 2W, so it’s worth having a bunch of them controlling stuff.

To put this into context:

• An old fashioned 60W incandescent bulb, which you may have as an outside light, will use about £200 of electricity if left on 24×7. This drops to ~£14 with a 4W LED bulb, and to about £3.5 if you have a smart bulb that only comes on for 6 hours in the evening.
• Our pond pump was using £100 a year, now it’s about £40 (smart plug turns it off at dusk and on at breakfast time).
• I have a batch file that gives me a one-click standby on my Windows workstation
  • Three monitors using ~40W when active and <1W on standby,
  • A PC running at >100W, but <5W in deep standby.
  • Routers and Wi-Fi need to stay on 24×7 I’m afraid, but only pull a few Watts.

Over the course of a couple of years, we dropped our daily consumption by ~10kWh, excluding heating from the heat pump and our EV, which pushed it back up. However, even including those we averaged 16kWh/day in October, and around 12kWh/day over summer. That’s over £1000 per year at current prices.

New installations

Do it. Do it now. As much as you can.

Here is my quick rule of thumb for anyone thinking of getting Solar PV.

1. Do it. Do it now (if you have/can borrow the capital).
2. Put on as many panels as you can reasonably fit. Panels are the cheaper bit, the inverter, scaffolding, fitting and application to the DNO don’t go up much with extra panels. In summer you will have more electricity than you need (until you buy an EV); in winter you will be glad you have the extra generation for those short, dull days when the sun is reluctant to shine. Aim for at least 5kWp of panels if you can.
3. Add as many other sustainable elements you can at the same time – your first installation is zero rated for VAT, so you will save 20% on everything you cover with the project invoice. I strongly recommend putting in an EV smart charger (see the future EV blog) that can divert excess energy to a car, and a solar diverter (these are great) that can divert energy to your immersion heater (if you have a hot water cylinder, which we don’t. Yet.) If you still have money, get a battery (see the later blog).
4. If your house is mostly south facing, terrific. Cover your south roof, don’t bother with the north (the sun doesn’t shine there). If your house is East-West facing, terrific, you won’t get as much peak output, but you will get the early morning sun from the East (often the brightest part of the day before clouds form) and the evening sun in the west and thereby generate at least as much as a south facing roof overall. You will need an inverter able to handle two ‘strings’ of panels (most do).
5. As a rough guide, for every kWp you have on a south facing roof you will get about 1MWh of electricity per year.
6. Don’t be surprised if it takes weeks to get a reply from the installers and months to get it fitted – installers, the DNOs, the panel importers – are all incredibly busy.
7. Do an energy audit and figure out where you can replace /switch off/ manage all your power consuming devices.
8. Switch to a decent tariff that rewards you for exporting. We are with Octopus (feel free to ask for my referral code – it’s good for us both).

Prerequisites:

• You need a smart meter
• You expect to stay in the current house for at least 7 years.
• You have a reasonably open roof, without shadows
• Check that you are not subject to conservation or deed restrictions.

For new installations you won’t get the FIT, I’m afraid; instead, you get the Smart Export Guarantee (SEG). A good estimate is that you will export 50% of the electricity you produce, mostly in summer (unless you have a battery to capture the excess and use it later. More on that in a later blog).

A 3.5kWp system like ours might export 1600kWh over the course of a year, with the SEG paying 5p to 15p depending on your contract and the state of the market. That’s worth just £80 – £240 ☹. On the other hand you would be avoiding buying 1600kWh of electricity at ~40p per day, so that is another £640, for a combined saving of £900 per year. A new system costs more like £6500 than our £10k, so you have a payback period of around 7 years. Over 10 years you should have made a £2.5k profit.

Conclusion

We got lucky with our timing; solar PV has not only been a great investment, but also has gone a long way to mitigate the impact of the current energy crisis for us. Even more when we take into account our second solar array, battery storage and EV. However, the economics still make sense if you have capital or can borrow the money. It’s unlikely energy will become as cheap as it was before the crisis and the move to Electric Vehicles will make you very glad you have your own means of generating power.

It is currently unclear what the benefit of solar PV will have on the value of your property. Estate Agents are being cagey about it; for myself, I wouldn’t buy any property that doesn’t have solar or is at least suitable for a straightforward installation.

Next time, adding more panels and energy impacts.