Photovoltaic Questions and Answers
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In November 2005 a Photo-Voltaic array was installed on the roof of St James's Church, Piccadilly, London.

The PV system generates non-polluting electricity and feeds it into the church where we can use it for lighting and other electrical equipment.

There has been a lot of interest in the installation so we have put these web-pages together to provide some information. This page lists some answers to the common questions we are getting (through this website) from people who want to install PVs on their own buildings. The other page ( Photovoltaic Systems at St James's Church, Piccadilly) shows a set of photographs of the various components of the PV system..

This web site is still under construction, and we will be adding new bits over the next few weeks. If you have any questions in the meantime please feel free to contact me.

Simon Dawson

1. What do the panels loook like, are where are they installed in the church?

There is a set of pictures of the entire installation on a separate web-page - Photovoltaic Systems at St James's Church, Piccadilly.

2. I have seen the article about St James's photovoltaic installation. I am sure all parish churches could benefit from such a system, but how much does it cost?

Photovoltaic systems are not currently cost effective if you simply balance the financial benefit from the power generated against their full capital cost. But the Government and other bodies recognise this and offer grants for system installation to prime the developing market. As the number of installations goes up the prices hopefully will fall until we reach the stage where PV systems are financially self supporting.

Also, electricity prices are likely to go up in future years due to the rising wholesale price of gas and other fuels, and that will help to improve the relative cost effectiveness of PV installations year by year.

Our system cost thirty six thousand pounds (36K). We obtained two grants, 16.5K from the EDF Energy Green Energy Fund, and 12.5K from the DTI's Energy Saving Trust. The balance paid from church funds was 7K. At current energy prices the system reduces our electricity bills by about 340 pounds per year, so for us it pays for itself in financial terms, and will be profitable if electricity prices rise year on year.

The reduction of 1.8 tons of CO2 per year, and our ability to use the system for educational purposes, are the bonus that makes it worth doing.

3. We are at a very early stage but already our architect has turned pale and our English Heritage case officer gave a knowing smile. I wonder how you dealt with the statutory bodies who so often tell us what we may not do?

When we started talking to the planners and English Heritage etc there was a lot of nervousness initially about the idea of a PV system on a grade I listed historic building, such as our Christopher Wren designed church. The main concerns stated were that there should be no damage to the historic fabric of a listed building, and that the PV system should not be visible to "spoil" any view of the structure.

Because we at St James's will be replacing our copper roof in a couple of years we found that by going for the system we used, resting on (not bolted to) a flat roof behind a parapet, we could get a system which would be easily dismountable for the roof repair, did not entail any major engineering to a historic structure, and conformed to the planners aesthetic demands.

Our main learning point about PV is how simple it is. It is not big engineering. The installers bring some panels along, wire them up, and plug them into the mains. Simple as that. Even if the panels need to be bolted to a sloping roof there will be little more drilling holes or altering the historic structure than there would be for simply replacing roof tiles.

Once we had demonstrated this to the regulatory authorities we found we were able to obtain consent. The London Diocesan Advisory Board told us "It was commented that your proposal was much to be praised in environmental terms, and should be treated as an exemplar for other churches! The presumption should always be to employ solar panels unless there is good reason not to." (This may be a helpful statement for churches to quote to their own Diocesan Advisory Committee.

The one compromise we were forced to make was to accept a system design which is a bit smaller than we would have liked, in order to meet the invisibility requirements. Learning to install green technology in churches is a step by step process, however. Hopefully we have made one step by showing that you can fit green technology to a grade 1 listed building without affecting its historic fabric. It would be good if the next team to try can take it a step further by successfully challenging the visibility restrictions and getting a bigger system approved.

4. Which installer did you use, and why did you chose them?

After obtaining proposals from three companies we chose an installer called PV Systems Ltd, primarily because of they offered the non roof penetrating "console" system mentioned above.

Main Office

P V Systems Ltd
Unit 2
Glan-y-Llyn Industrial Estate
Cardiff Road, Taffs Well
CF15 7M
T - 029 20820910

London Representative

Amolak Hunjan
12, Scarle Road
T - 0208 903 0175

5. What are the benefits of the System, and why did you go for Photovoltaics?

The idea of a PV installation came out of a full church environmental audit, where the benefits of a PV installation was integrated with other environmental measures to reduce energy usage. We felt that such a system was in line with our church Mission Statement, part of which called on us to "Cherish Creation"

We chose photovoltaics because we were a city centre church, in the wind shadow of larger buildings (which excluded the possibility wind generation), and because our major energy need was electricity for use in the church and parish offices during daylight (office) hours. Each church will need to decide what technology is best for its own needs. For example an organisation with a primary need for hot water (perhaps for a school kitchen or shower block) might do better with a solar water heating system, or a parish church in the countryside might benefit from a wind turbine on the tower.

PV systems are not fully cost effective yet - a fact recognised by grant giving bodies who subsidise installations to prime the market. We calculated that a PV system would just about break even when looking at cost grounds alone. However we benefit from being a city centre church with about 5000 visitors a week, either to participate in the various spiritual and cultural activities on site, or tourists to visit the Christpher Wren building. Being able to use the system as an educational/promotional tool for green techology in historic buildings was the "added value" factor that made it worth while for us.

6. You said that the peak output of the panels is 5kW. Does this mean that it's maximum output is 5kw, which presumably is about midday in high summer?

Not quite. "Peak Power" (KWPeak) is a nominal measure of a system's output under a set of standard conditions (defined as an Irradiance of 1000 W/m2, Air Mass 1.5 (AM 1.5 Spectrum), and a cell junction temperature of 25 degrees C).

In real life a number of variables mean that the system output will be very different.

The main variable is the power of the sun's radiation striking the PV array, and this will vary with the time of day, the season, and the angle of tilt at which the panels are mounted. In practise, PV panels are positioned at the best compromise angle to get maximum power generation from the sun's varying elevation through the seasons. Other important variables are the weather, the amount of shading from trees or buildings, the way the panels are connected together and the operating temperature of the system (output falls with raised temperatures).

Even when the PV array has generated it's power, there are likely to be further losses in the inverters, and the cabling carrying the power from the roof into the church's electical systems.

Our 5kw peak system generates between 0.8 kw (winter sun) and almost 3 kw (very hot summer noon) and is normally producing between 1.0 and 2.5 kw. Our church has a large office staff and Courtyard Market so we easily use this power most of the time. We are grid connected, with the PV floating on the grid, so any excess power goes back into the grid. If we were generating huge amounts of surplus power it might be worth paying the capital cost of installing meters to measure and sell this excess. In our case it is currently more cost effective to write off the very occasional small surplus.

Because of these variables most manufacturers will not quote typical output in kw for any given system because the performance and losses are so variable, but they will give you a kw hour per year figure, an estimate of the system's total annual output averaged over a few years.

If you want to look into this aspect further there are two useful web resources:

Photovoltaics in Buildings - a Design Handbook for Architects and Engineers. A 72 page technical handbook in pdf format published by the International Energy Agency.

PV Potential Estimation Utility A set of web utilities showing the variation of solar radiation across the world, and allowing you to estimate the output of a PV system by inputting its location and design parameters.

7. How can I find out more about Solar power and green energy?

The best single souce of information on solar power generation, especially when you get into the more technical aspects, is probably the Centre For Alternative Technology. Their online shop offers a wide range of books on the subject, and their downloadable factsheets are a quick, cheap and fast way of getting good information on a wide range of subjects.

Christian Aid have put together some useful ethical living advice pages on their Surefish website. (Surefish is a fundraising, ethically run, internet service, run by Christain Aid, which benefits from the money it raises). One of their pages gives some more information about our own project (see The Heat is On).

If you want to look at the bigger picture, how to help make the entire life of your Church and her congregation more environmentally friendly, ECOcongregation is "an ecumenical programme helping churches make the link between environmental issues and Christian faith, and respond in practical action in the church, in the lives of individuals, and in the local and global community." Their website contains a superb set of resources for any church to use, such as a Church Check-up, an audit questionnaire to help you look at your own buildings and comunity life, to find what you do well, and discover what you could do better. Look for more stuff in the "Free Resources" link on their website.

If you want to explore all the green energy options, not just photovioltaics, then the Low Impact Living Initiative run a series of courses through the year, including some on green and sustainable energy. Although most courses are about power systems for domestic properties not churches the lessons learnt can easily be transferred to a bigger property.

A good book on sustainable building design is Architecture in a Climate of Change by Peter Smith. The book is more concerned with the design of new buildings rather than backfitting systems to historic properties. Nevertheless for those who want a good technical primer on the underlying theory and practice of green energy (with case studies) then this book is well worth a look.

8. Your system seems to be generating about 3350 KW hours per year, but on the display panel wording it says that the system is expected to generate 4100 KW hours annually. Why the discrepancy?

Yes we noticed this, and obviously we investigated. The two possible reasons were that the installed system was not operating correctly, or that the manufacturer's prediction of system output (the source of the 4100 KW hour figure) was a bit optimistic.

The system has been checked out and is working correctly. On further investigation we have found various sources that quote a rule of thumb that says typical Southern UK PV installations should generate 700-750 KWh per year for every 5 KWPeak installed. Using this rule of thumb our 5 KWPeak system should produce 3500-3750 KWh annually. Allowing for a bit of loss due to shading that we know about, then our achieved output of 3350 KWh seems about in line.

We say the installer was being over-optimistic in his prediction of output. The installer says that the figure of 4100 was ouput directly from the from the PV panels, and we should have known to reduce that figure to allow for innefficiencies, and inverter losses, and shading.

Whatever the reason (possibly a bit of both) it is a good learning point. Make sure you understand exactly what assumptions and allowances are being used in these prediced output calculations. Where do the figures come from, and is the quoted output the output from the system on the roof, or the actual energy delivered into the grid (which may be a lot less)? Ask some hard questions, and if the quoted output is a lot different from about 725 KWh per year per KWPeak installed, ask harder questions still.

If you have any other questions you think we can help you with then please feel free to contact me at the above address. It is also possible (given notice) to arrange guided tours of our PV system for representatives of organisations who may be contemplating their own PV installation.