Case study

Here comes the sun – a small-scale domestic solar installation case study

Share content

The case for solar

This article by NCS supporter Ian Runeckles is based on his experience of having solar photo-voltaic (PV) in a domestic setting for ten years. In 2010 he had a 2.1kWp system installed which was followed in 2017 with an additional 1.7kWp system. 

Some pointers and lessons learned:

  • Buy local. If possible find nearby installers with proven track records. Ask for references, see if they’ll put you in touch with a satisfied customer.
  • Expect a site survey. If the installer won’t visit the site prior to quoting then I’d avoid.
  • You might need planning permission and, if you’re going to install over 4kWp, you’ll need Distribution Network Operator (DNO) approval. The installer should be able to help.
  • Check the quotes. Any good installer will estimate an expected kWh output/annum, provide a fixed price and specify the equipment, warranties etc
  • Check online for reviews of the equipment.
  • Monitor and record your output. I found that my first system over-performs the expected output by about 10% and the second system under-performs by 10%.
  • It will probably take longer than you think to payback. I’d anticipated about 10 years: it’s actually going to be around 14.
  • Try to use the electricity as it’s produced. Sounds daft, but if you are out at work all day then the majority of the power will be exported to the grid which you’ll be paid for through the Smart Export Guarantee (SEG) scheme. But using it will save you more by avoiding importing grid electricity. A battery can store it and then use it when needed but is expensive.
  • PV is pretty much fit and forget. My inverters are in the loft and I’ve not looked at them once. Cleaning panels is generally not required, rainwater does the job in the UK. Panels are estimated to have a 25 year lifespan although will probably last longer without much degradation. Inverters are normally expected to last at least 10 years.


Being long-time supporters of green causes and wanting to reduce our environmental impact where possible, having the ability to generate some of our own power through installing PV was appealing. In late 2009, after some basic research, I contacted the Heat Project who were at that time still administering government grants towards PV system installs. I obtained a couple of quotes following site surveys by companies local to us just east of Norwich.. By the skin of my teeth I managed to successfully apply on the deadline day for a £2,500 grant before they were discontinued. At the start of March 2010 a 2.1kWp system was supplied and installed by Green Home Energy Solutions – and has been working ever since.

In 2017, as costs had significantly dropped and I wanted to increase our generation, I decided to add a 1.7kWp system which has a separate inverter. The installer was Green Solar Footprint of Postwick.

Geography and site conditions

The panels are on a standard pitched tiled roof and face approximately south east. Two large beech trees shade the panels first thing in the morning reducing the ability of the PV to generate. Cloudy mornings are better for generation than clear skies as the shadows on the panels are lighter. Micro inverters would help in this regard as any shading affects the whole of the installation (system 2 is less affected) which micro inverters counter. One criticism I have of the original installation is that it would have been better sited on the left side of the roof (where the second system is now) as this is clear of the shading earlier in the day.


System 1 – Ten Sanyo 215 watt panels, SMA Sunny Boy SB2500 inverter and Sunny Beam generation monitoring unit.

System 2 – Six SolarWorld 285 watt panels, Solis mini 1.5kw inverter. Wireless logging to Solis, remotely accessible through website and smartphone app..

Generation output

For system 1 the generation is steady at about 1,500kWh per annum which is around 10% higher than was estimated at site survey. System 2 generates around 1,400kWh per annum, so total production is about 2,900kWh/annum. A good day will produce about 17kWh; June is the best month with the combined system producing an average of 12.5kWh/day and December is the worst producing 2.3kWh/day. Over the year, the average daily production is around 7.1kWh.


The cost of the first system was, after the grant payment, £10,562. I qualified for the Feed In Tariff (FIT) which paid for every kWh produced – currently I receive 54.17p/kWh plus an export payment of 3.82/kWh for 50% of the total generation. After 10 years, I have received £7411 in quarterly payments from npower who I registered with – they were supplying my energy at the time. If you assume that 50% of electricity produced by the panels has been consumed thereby effectively replacing grid energy then the saving has been about £1,125. I estimate after another four years, it will have paid for itself. By the end of the 20 year FIT, assuming some slight panel degradation, I should be about £5,000 in profit.

System 2 cost £2,600 in March 2017. Assuming that I use 700kWh per annum from the system then it will take around 25 years to payback as I receive no FIT or export payments.


I have had virtually no problems with the systems – system 1 stopped generating for a few hours shortly after installation, I suspect some kind of inverter issue, but recovered without intervention. Views differ on whether cleaning is necessary, generally rainwater does the job but in 2019 I had all the panels cleaned (by MRH ) for the first time as two panels in system 1 were spotted with lichen. However, I don’t think it has made much difference to the generation. I haven’t seen any real evidence of panel degradation; output has remained fairly stable despite a large ever growing beech tree which shades first thing in the morning. The Sunny Boy inverter is now out of its expected 10 year lifespan so may need replacing but so far has shown no sign of failing. The replacement cost of this would be significantly lower than in 2010.

A small Sunny Beam unit showing daily output

Logging and reporting

System 1 logs to a small Sunny Beam unit which shows daily and monthly outputs and a graphical representation of the day’s generation. This slightly over records so that the total generation on the gen meter is lower than that shown on the Sunny Beam. I use these figures to compare from month to month and year to year so they are a little over the actual output figures. System 2 logs to the Solis app or website via the internet but can be a bit flaky.

I record monthly figures for generation and payments on a spreadsheet since the system(s) were installed so I can calculate annual figures, average monthlies, identify highs and lows. 

Energy consumption

Currently we consume around 2600kWh per annum from the grid supplied by So Energy using 100% renewable electricity. This is for a two-person household and includes the usual household appliances (electric oven but no dishwasher or tumble drier) and also a Renault electric car (purchased 2017) which does around 4,500 miles/annum.

We have a gas combi boiler for heating and hot water, using about 15,000kWh per annum. A woodburner in a single-storey dining area at the end of the house also supplies some heat in colder months. The car is charged as much as possible when the sun shines to take advantage of the solar energy, but we do not have a charge point which can prioritise this such as a MyEnergi Zappi .

Future developments – batteries and smart chargers

I have considered for some time the pros and cons of battery storage but the costs make little sense, even though prices have started to fall. Whilst it can seem galling that the systems are generating more than we are consuming and then having to draw from the grid when the panels aren’t active or we’re using more than they can supply, I figure that the electricity is being consumed by someone on the grid. If battery prices dropped considerably then it could be worthwhile but I don’t see it as a priority. Of course an argument could be that if you have a spare £5000 sitting in a savings account earning next to nothing (effectively depreciating) something that reduces your energy bill slightly could be a good thing. But I estimate that it would take me 30 odd years to pay back and the batteries are usually only guaranteed for 10 years (but may last much longer). I’m watching vehicle to grid (V2G) technologies with interest – the car’s battery works with the house and also helps to balance the local grid  – but V2G is currently only supported for Nissan cars (although Renault have been trialling it in France).

In addition I have thought about replacing my current car charge (PodPoint) with a smart charger such as a Zappi which can be set in various ways one of which is only to draw from the PV which would make more of the solar energy. But again the costs don’t make much sense, it would cost around £1000 to replace my 3 year old PodPoint (there is no OLEV grant available for replacement units) and it would take many years to reap the benefits.

Would I do it now?

I’m advised by Green Solar Footprint that a basic 4kWp system today costs around £4000 (although I could now probably get a higher output from the latest panels which are rated at 310 – 360 watts). On my roof a 4kWp system would produce about the same as I’m getting now, so say 3,000kWh per annum. Currently the Smart Export Guarantee (SEG ) pays around 5p/kWh. Assuming I’m exporting 1,500kWh that’s £75/annum. The remaining 1,500kWh is being used and therefore offsetting grid electricity which at my current rate of 13p/kWh is a further £195/annum. Which gives a payback period of 14 years, which is pretty well exactly the same as for my initial system. So, yes, I would!

Why support community solar initiatives?

Even on the windiest and sunniest days in the UK there is still a significant amount of gas (and occasionally coal) being burnt to generate electricity. To my mind, the more renewable infrastructure there is, the better. There are thousands of roofs in the UK – be they houses, warehouse, schools, public buildings – which could be producing energy and reducing the amount of electricity required from fossil fuel sources. As an advocate of renewable energy – and small scale investor – I welcome and support initiatives such as NCS. My hope is where suitable sites can be found – and negotiations concluded successfully! – that owners, landlords, investors, suppliers and installers can be brought together to enable the UK to move forward to a cleaner greener future for energy.

Ian Runeckles, May 2020