Jenkins-Of-Ewelme Web Site

Solar Power in Ewelme

This page has been appropriately included within the 'Technology' section (last update 7/07/12), as an opportunity to convey some of the aspects of the installation of a solar panel array to our house in Ewelme, and to discuss whether such a system can be regarded as a worthwhile investment for generating and selling electricity. It is certainly not such an easy decision in terms of just accepting current advertising hype on the subject, but there are undoubtedly a number of real advantages in proceeding with such a carbon free technologically biased project.

To generate electricity from the Sun, solar radiation needs to be converted to an electrical voltage by means of a panel constructed from an array of silicon semi-conductor based photo-voltaic (PV) 'cells'. This is the same kind of material used to make light emitting diodes (LEDs) and microprocessors. If the panel/s are mounted at an optimum angle and direction to catch as many of the Sun's rays as possible, then the most efficient PV conversion to usable electricity will be achieved. Of course, the rotation and angle of the Earth as it orbits the Sun once a year causes the appearance of the Sun to rise and set on a daily basis, but also its maximum height to vary between it's highest in mid Summer, with longest hours of daylight, to it's lowest in mid Winter, when days are short. So obviously, the Summer months will potentially generate more electricity than in the Winter.

Solar panels generate 'Direct Current' (DC) like a battery, but the kind of electricity we use domestically from the National Grid is 'Alternating Current' (AC). This is because it is easier to transport AC over long distances from the power station using high voltages, which is then transformed down (using transformers!) into the domestic voltages used in the home of around 240 volts. Within the home, we also transform some of that standard voltage to even lower voltages to run our televisions, PCs, chargers, lights etc. Only AC can be easily transformed in this way. Therefore, we need some means of converting the quite high and varying DC voltages produced by the light dependent solar panels, into a usable AC standard 240 volts 50 Hz (cycles per second) supply. This is done with a unit called an inverter. This black box (or red in our case) does this translation, together with additional electronics incorporating safety cut-outs and circuits for synchronization with the mains frequency, and for monitoring and display of the instantaneous and historical electrical Power generated. Electrical power is measured in Watts, where for example, you might need 1000 Watts (1 kW) to power an electric kettle. We pay for electricity by the unit, which is called the kilowatt hour (Kwh). One unit of electricity would be consumed if running that 1 kW kettle for 1 hour, which would then cost about 9p at 2011 prices (OK, we've got a fixed price contract right now!), although this is expected to rise by a double figure percentage this year.

Why are we all being encouraged to consider fitting such a system to a domestic premises? Well, the less electricity a house consumes means that less fossil fuel needs to be burnt to generate it, and where our increasing national demand for energy can then be sustained  using more renewable energy sources such as wind, nuclear, solar, hydro, tide etc. to replace the ageing  (increasingly imported) gas fired and (imported) coal fired power stations. These resources are not only finite, but also produce CO2 (carbon dioxide) emissions, which are said to be one of the causes of global warming. For every unit of electricity generated by solar, saves about 0.7 Kg of CO2 being lost to the atmosphere. Of course, it is also true that ensuring that our houses are well insulated and that we increase our use of low energy light bulbs etc., helps to do the same thing, but will doing both provide an even higher benefit? Well, if just 1 million homes retrofitted solar panels or had them fitted during new building, you could close down Didcot's 2000 MWatt coal fired power station! Is it really potentially spewing out in the order of 1400 tonnes of CO2 per hour??  (See link at end). Apparently, the carbon offset in the manufacturer of PV panels can be achieved in around three years of system operation.

Anyway, now to talk about whether such a system would be suitable to be installed at a particular location. Ideally, part of the roof ought to point due South. However, within 45 degrees either side (SE to SW) would also be regarded as good. Outside these boundaries, it is still also possible, but will start to become less efficient in terms of  reaching the potential daily collection of direct sunlight between sunrise and sunset. Obviously, a North facing roof will not get the direct sun at all, nor will a roof in any direction that is shaded by trees or an adjacent house. Another consideration even if the roof is South facing, is whether part of it will have a moving 'sun-dial' shadow moving over part of the available surface area, such as from a chimney stack. Since a PV solar panel system is made up of a number of panels, that part of the roof subject to shadowing should be avoided if possible, otherwise panels may 'switch off'. Now, at what angle should the panels be mounted? In most cases, there is no choice, as  the pitch of a roof is fixed, but basically if the roof pitch is between 30-40 degrees, this will be a reasonable all year compromise to get the most out of a fixed system. Other suitability considerations include the disadvantages/negations of thatched/glass/flat roofs, listed buildings, and whether planning permission might be required locally. This last hurdle should be easy to establish just by looking on the local council's web site for guidance, although some authorities require payment just to provide a response!


So, now we come to the all important  aspects of finance. How much will this cost and how long will it take to recover the investment? Such a decision may also depend on some other personal factors such as whether you want to help save the planet, increase the value of your house or to make a long term profitable investment? None of these questions can be fully answered here, although some hopefully useful guidance can be offered. If your house is suitably located but you do nothing about it, your financial status quo may well be preserved, and you may be left with some available capital to spend on something else e.g. a conservatory, a holiday, a car or some other investment etc. But your per unit electricity prices will just continue to rise over the years due to inflation and the cost of generation, which will also include the 'climate change levy' now being charged by the electricity companies to every consumer to help pay for domestic solar and other power generation!

There are two main costs to consider for such a system to be installed. The first depends on the size of your South-ish  facing roof. In other words, the more panels you have, the more it will cost. Most standard domestic houses would be able to manage anything from about a 1.5 kW system to around a 3.5 kW system depending on the un-shadowed roof area. We have a 2.115 kWp array (the p means peak capability)  fitted in the form of 9 adjacent panels (9 x Sanyo HIT N235SE10 modules). We could have had less to keep the price down, but more would have been affected by shadowing, and therefore the system would have been less efficient. This together with a 2kW inverter (SMA SB2000HF-30), makes up the main hardware of our system, at a cost of £6143 + VAT @ 5%.(the saving the planet rate!) The second part of the equation  relates to the cost of supply, installation and commissioning, and this is where the overall result can vary quite a lot depending on your location and supplier. We needed scaffolding to be erected, which is probably required for most installations. This, together with the requirement for a qualified electrician  cost £965 + VAT @ 5% . A structural engineer was initially required to assess the structural suitability of the roof. This cost £278 + VAT @ 5%. A tentative assessment had already had been made, but by involving a professional, provided absolute assurance that the roof was sound. The declared additional cost of managing the overall installation was £1100 + VAT. Had additional planning permission been required, this would have cost another £380 overall. However, this installation was concluded to be what's known as 'permitted development' and that planning permission was not required after all. So, the overall cost was some £8900 inc VAT at the reduced rate. I had previously heard that 'as a rule of thumb' to expect a cost of £5000 per kWp installed. To discover that overall, we had achieved £4213/kWp without even being offered BOGOF panels ('Buy one get one free. I said buy one......!'), was quite satisfying really, and in the end confirmed the project professionalism exhibited by our chosen solar installation specialist (see later). Obviously, the higher the ratio between the cost of the actual electrical generating materials against that of the one off fixed costs of installation, the better.

Worthwhile Investment?
So, how are we going to recover our investment and how long will it take? Well, there are no guarantees of course, and it all depends on the weather to a certain extent. But  some official calculations are used to help potential users make up their minds. The basis of the 'payback' is that my chosen electricity supplier will pay me 43.3p per kWh (unit) generated by the system (45.4p from 1/4/12). It is estimated that our system will generate some 1687 kWh annually (that's 1.7 Mega Watt hours !), yielding £730. In addition, it is assumed (not metered) that 50% of this will be exported back to the grid, which will be bought for 3.1p per kWh (3.2 from 1/4/12), yielding a further £26 per year. In addition it is assumed that a cost saving of £101 per year will be seen from the 'normal' electricity bill. Such a yield on an annual basis, would mean break-even would occur after around 10 years, with cost recovery starting after the first quarter of operation.

What isn't included in the official calculation is that the FiT (Feed In Tariff) revenue is index linked! This means that at the current rate of inflation, it is likely that this will be increased year by year. This in itself will reduce the payback timescale. There is no doubt that one's electricity bill will be reduced while generating a proportion of previous use. However, one thing is certainly not in the calculations, and that is that some older consumption meters have been seen to go backwards when exporting unused current! I'm sure this won't be the case if/when 'smart meters' become widespread. In the meantime at least, I have witnessed sunny days when my normal daily meter consumption has been near zero, even though we have had electric showers and used the washing machine etc.!! So maybe our normal electricity saving will be even greater?

  Now that the installation is complete, I guess my attitude has been to write the investment off, in the same way as if we had built an extension or had some other building improvements done. It's debateable whether this project will have actually increased the value of the house. Probably not by much, since it only represents less than 2% of the current value anyway, but may make the property a little more attractive if a similar house in the area without this facility was also for sale. A new buyer would also get the advantage of receiving an actual income from electricity generation for up to 25 years, whether or not a premium was paid for the property. So it is also quite likely that anyone having done the same thing previously, would seek another property with similar facilities already installed, perhaps in the same way as having been used to the advantages of double glazing and central heating, and more new properties are providing this facility as standard anyway. Consider maybe also thinking about the investment as a pension annuity. Where else would you get a yield of at least 7% of a pension pot, tax free for a guaranteed 25 years? Most standard personal pensions only guarantee to pay out for 5 years and it usually takes around 15 years of payment to even recover your initial 'pot' back!

Technical Information
Below is a circuit schematic of the system. The inverter is located in the loft of a converted garage. The generation meter and isolation switch is located adjacent to the house consumer unit (fuse box). All these locations are flexible and were initially discussed with the installer.

It should be noted that invertors come in certain defined sizes (and prices) depending on the overall generation capability. In the case of the recommended SMA equipment, the range includes a 2 kW, 2.5 kW and 3 kW unit. It is important to realise that even though the array of panels could potentially generate more energy, a particular inverter can only provide for what it is specified . In other words, our 2.115 kWp array will only ever generate a maximum of 2 kW output. However, for the majority of the year, the peak output of the solar panels will never be reached. On the other hand, it would probably be sensible to link say a 2.8 kWp  array to a 3 kW inverter rather than potentially losing 0.3 kW (a whole panel's worth), during periods of maximum solar radiation. It is also important to understand that an array of panels should all be exposed to the same level of radiation (generate the same voltage). This is why avoidance of partial shading is so important. Also, if the roof orientation is such that the array is divided in two, to say catch first the morning sun and then afternoon sun, it would be necessary in this case to have two inverters fitted.


Using the SMA equipment chosen, the inverter may be mounted in a convenient position in order that its display can be read when required, or as we have it, out of the way in a ground floor loft. In addition, a unit called 'Sunny Beam' is available, which communicates via Bluetooth to provide a variety of data on a portable, desk mounted display, also incorporating a solar panel to keep the internal battery charged.

The Installation
I have had a technological interest in free solar (and wind) power for a number of years now, and constructed a 3 x 15 watt solar panel array on a redundant garden umbrella mechanism. This has, and remains being used to power a dual pump waterfall and lights in the back garden. Together with a sailing boat wind turbine, the DC voltages generated charges a battery ('leisure' type not car), which then feeds a readily available inverter to drive the mains operated pumps and LED lights. Unlike the roof system being described, this does not need to be synchronised with the mains, but it does mean that we don't have to use any 'paid for' electricity to regularly run what we find is an 'interesting' garden feature throughout the whole year! Whilst I have sometimes  been accused of somehow being related to 'Heath Robinson', this high power solar system is not something that could be tackled as a DIY project (worst luck!). This is because the system and installation has to be specifically certified by suitably trained and qualified people in solar technology, and where a long-in-the-tooth technologist has little practical input to offer here!


During the technical and financial pros and cons assessment prior to reaching a decision as to the worthiness of such a project, I became annoyed with the increasing amount of unsolicited postal advertising we were starting to receive, and also noticed TV adverts promoting 'free electricity', including well known double glazing companies ('you didn't expect this high level company to be doing this, now did you?'!). I hated the idea of inviting a 'salesman' into the house possibly representing a company located in some remote town or city. I shouldn't have worried. I did a search of 'PV' in Google and came across a site enabling the further search for  local companies ONLY dealing with solar installations. Without this specialist attribute, it brought up plenty of plumbing, boiler and double glazing companies, who all professed to be able to fit solar panels to the required standard.  However, one company stood out, since they were located in Wallingford, some 5 miles away, and was no doubt the sought out specialist, since it was called 'Sims Solar' ('you can't expect to get more specialist than that now, can you?'!). An email enquiry produced a rapid response leading to an early visit to discuss the possibilities. Paul Sims is not a salesman as such, but a consultant engineer who sympathetically conveyed his opinions as to the options available to us considering the direction and size of our roof.  Within a couple of weeks, we received a professional proposal, to a standard not unlike the type I used to have to prepare in an effort to win large company contracts!  This provided all the reasoning behind the choice of proposed equipment, a full breakdown of the costs, and standardized calculations as to what power was expected to be generated, and an estimate of the annual energy export and payback period. On the other hand, it also acted as a draft contract detailing required deposit, installation payment and final handover payment. Following some further technical queries, to which Paul provided emailed manuals and links to manufactures' web sites, we decided to proceed. I have no connection with Sims Solar, but I would highly recommend the company and its associated contractors for performing a thoroughly professional service, and even for just finding out more about what solar power is all about.

Monitoring and Data-logging
Apart from filling in a form every quarter and looking at your bank statements to see the money rolling in, there is no need to take any more interest in the technological aspects of solar power generation than you do when just glancing at your quarterly electricity bill. On the other hand, you don't necessarily need to be an anorak-wearing geek to wonder how much power you are personally producing, and what the difference is between the energy generated on a nice Summer's day (instant and over the day) and that possible during a dull week in Winter. I can only talk about SMA inverter equipment, but all other manufactures will at least provide you with a display on the front panel, with possibly graphical means to show various aspects of generation. That may be enough, but if the inverter is installed in the garage or loft, you (and others) may like to be able to see such information in the house. Desk mounted displays are available (e.g. SMA's 'Sunny Beam'), which will take the data stored (logged) in the inverter via 'Bluetooth' wireless technology, and display it in various forms. This unit can also be connected to a PC and the logged data can be stored again for display by say a spreadsheet program in tabular or graphical form if you really want to! However, SMA provide lots of free downloadable PC applications (and manuals) as well, the most useful of which in my opinion is called 'Sunny Explorer'. Without the necessity to actually use the Sunny Beam at all, a Bluetooth enabled PC can interrogate the inverter in real time and display just basic or historically logged data for instant monitoring or further publication (see below). The Explorer will also enable logged data to be exported to a PC file (in .csv comma de-limited format), for use by spreadsheets etc. Personally, I would like to regularly publish such results on this web site should anyone else (dear reader) be interested.

The charts above were extracted using Sunny Explorer, via a Bluetooth connection between a PC and the inverter.

First Quarter Results (July - Sept 2011)
The electricity generated from PV over a 13 week period amounted to 662 kWh (units).
At 43.3p Feed In Tariff per unit = £285.65
Plus half that generated, 331 at 3.1p = £10.26
Value of electricity bought by Eon = £295.91
Consumer meter reading over quarter = 15734 to 16432 = 698 units compared with 1546 units July-Sept 2010
Saving in consumption of 1546 - 698 = 848 units at current rate of 9.62p per unit = £81.57
Total recovery of investment so far is 295.91 + 81.57 = +£377.48.

This quarter is possibly the best one for solar generation of the year. Time will tell, but it would be a mistake to expect each quarter within a year to yield the same. However, with annual index linking of FIT and increasing electricity prices, it will be interesting to compare the yield at the same time next year.

Second Quarter Results (Oct - Dec 2011)
The electricity generated from PV over a 13 week period amounted to 830 - 662 = 168 kWh (units).
At 43.3p Feed In Tariff per unit = £72.74
Plus half that generated, 84 at 3.1p = £2.60
Value of electricity bought by Eon = £75.34
Consumer meter reading over quarter = 16432 to 17534 = 1102 units compared with 1702 units Oct-Dec 2010
Saving in consumption of 1702 - 1102 = 600 units at current rate of 9.62p per unit = £57.72
Total recovery of investment this month is 75.34 + 57.72 = +£133.06

Third Quarter Results (Jan - Mar 2012)
The electricity generated from PV over a 13 week period amounted to1080 - 830 = 250 kWh (units).
At 43.3p Feed In Tariff per unit = £108.25
Plus half that generated,125 at 3.1p = £3.86
Value of electricity bought by Eon = £112.11
Consumer meter reading over quarter = 17534 to 18714 = 1180 units compared with 1412 units Jan-Mar 2011
Saving in consumption of 1412 - 1180 = 232 units at current rate of 9.62p per unit = £22.31
Total recovery of investment this month is 112.11 + 22.31 = +£134.42

Fourth Quarter Results (Apl - Jun 2012)
The electricity generated from PV over a 13 week period amounted to 1790 -1080 = 710 kWh (units).
At 45.4p Feed In Tariff per unit (increase of 2.1p) = £322.34
Plus half that generated, 355 at 3.2p (increase of 0.1p) = £11.36
Value of electricity bought by Eon = £333.70
Consumer meter reading over quarter = 18714 to 19492 = 778 units compared with 752 units Apr-Jun 2011
Saving in consumption of 778 - 752 = 26 units at current rate of 9.62p per unit = £2.50
Total recovery of investment this quarter is 333.70 + 2.50 = +£336.20

July-Sept 2012
2463-1790 = 673 kWh @ 45.4p = £305.54 + half exported @ 3.2p = £10.77. Total qtr income £316.31
Consumer meter reading over quarter 20173 - 19625 = 448 units compared with 1546 Jul - Sept 2010.
Saving in consumption = 1098 units @ 9.62 per unit = + £105.63 (12.1p/unit next qtr for 3 years)
Total recovery of investment this quarter is 316.31 + 105.63 = +£421.94

Oct-Dec 2012
2622-2463 = 159 kWh @ 45.4p = £72.19 + half exported @ 3.2p = £2.54. Total qtr income £74.73
Consumer meter reading over quarter 21720 - 20173  = 1547 units compared with 1702 Oct - Dec 2010.
Saving in consumption = 155 units @ 12.1 per unit = + £18.76
Total recovery of investment this quarter is 74.73 + 18.76 = +£93.49

Jan-Mar 2013
2824-2622 = 202 kWh @ 45.4p = £91.71 + half exported @ 3.2p = £3.23. Total qtr income £94.94
Consumer meter reading over quarter 23073 - 21720 = 1353 units compared with 1412 Jan - Mar 2011.
Saving in consumption = 59 units @12.1 per unit = + £7.14
Total recovery of investment this quarter is 94.94 + 7.14 = +£102.08

April -July 2013
680 kWh generated . Total qtr income £322.11
Meter reading consumption compared with April-July 2011 - 752-639= 113@ 12.1 = £13.67
Total recovery - £335.78

Total recovery of investment so far (1.75 years) is 377.48 + 133.06 + 134.42 + 336.20 + 421.94 + 93.49 +102.08 + 335.78= +£1935 (17.96%)
Extrapolating this, would mean that full recovery will take another (8900/ (1935/2)) - 2 = 7.2 years.

However, this doesn't consider that the FIT rate is increased every year.
Also, at the end of September 2012 the cost of electricity changed from the last 3 years at 9.62p  per unit to a further 3 years at 12p. This will have the effect of also increasing the equivalent savings on standard consumption if panels had never been fitted.
It is encouraging to find that the initial two theoretical estimates of annual generation have both been exceeded, i.e. 1660 kWh and 1687 kWh, as opposed to the actual of 1790 kWh. What makes this even more amazing is that we had the highest rainfall on record during the final quarter!

Having now had a complete year's results to analyse, I'm pleased to conclude that after having had some investment capital available, also a scientific interest in such matters, and having initially estimated that the cost would all be recovered over not an unreasonable period, I honestly believe that this has been an excellent scheme to have taken up, and recommendable to others similarly placed or inclined. But since installation, things have drastically changed! In the latter quarter of last year, the government announced that forthwith, FITs rates would be significantly reduced. This created a bit of a panic within the quite new and evolving solar system industry, where uncertainty regarding the resultant economic attraction for such domestic systems, caused household to reconsider their positions. The industry reacted by taking the government to court! All this did really was to delay the cut off date of the old scheme to April 2012. Indeed, the government have given notice that after August 2012, the scheme will be cut even further, not only with a further reduction of the FIT rate, but also reducing the term of payments from 25 to 20 years.

Maybe as a reaction to this UK situation or increasing demand, manufacturers of panels have steadily reduced their prices. However, labour and other installation costs stay the same. If the powers-that-be had stuck to their initial reduction, one could maybe make a case that the installation of a domestic system was still (until August), an economic proposition due to falling material costs. It is only a personal opinion, but with the post August FIT rate and the shrinking of the payment term, I'm really not sure I would not have taken up the offer, except for perhaps 'green' or scientific reasons, since it will now take more like 15 or more years to recover the investment, and then only 5 or less years to produce a real 'profit'.

For those who have already had systems fitted in the first phase, it may well be that there might be more of an effect on house prices than first thought. When comparing like for like, and considering that such conversions will be rarer or non-existent in future, a buyer may feel that a more efficient house as far as electricity consumption is concerned, PLUS and additional income of say £1000 a year tax free for the remaining part of the 25 year period is worth paying a little extra for!?

Unlike our garden system, where daytime power generation can be stored so that the waterfall pumps and lights can also be used during the hours of darkness, it might be realised that it is actually in the householder's interests to immediately use as much of the power generated internally rather than it being exported. Unless your consumption meter goes backwards, this ensures that the paid-for units on the consumer electricity meter are reduced as much as possible. However, life starts to become a little inconvenient if you patiently wait until midday (or 1 o'clock British Summer Time) to take your daily 10 kW electric shower at the peak altitude of the Sun. But if you heat water with an emersion heater, you could possibly arrange to power it for middle day use only with an appropriate timer. Most appliances involving heating, now incorporate delay timers, which could also be usefully employed to operate while the sun is shinning. On the other hand, if you are going to be so pedantic about the whole issue, you had better remember to use your LED torch for reading your book at bedtime, and you can just forget about using the electric blanket!

I do hope that at some point in time when the economy has recovered, the government re-instates a more attractive tariff system than that about to commence. Perhaps community solar systems (e.g solar farms, or rent-a-roof projects) will continue to attract personal share investments, in order to keep this form of environmentally friendly electricity generation continuing  to evolve.

Roofs for rent: Panels on council houses in Nottingham following a deal with an energy company (Picture by  EON).

Useful Links

Sims Solar

SMA Inverters

Sanyo Solar Panels

Energy Saving Trust

CO2 from Power Stations

Energy Efficient Windows