Renewable Energy Technologies for St George's Church


PV on a roof

The Technology

Solar generated electricity is created by the technology of photovoltaics (PV) - solid state semi-conductors that convert light into electricity. When a small amount of light (a photon) lands on a PV cell it gives energy to an electron. The electron moves away from the cell into an electrical circuit. The electricity created is direct current (DC). This can either be used to charge batteries or power DC devices, however, in the UK, it would normally be converted to alternating current (AC) via an inverter to meet the electrical demands of the site and be tied into the grid, with any surplus after on-site use, generating an income. We have been using the technology for years to power calculators.

Systems are easily retrofitted and involve attaching standard modules to form an array on to an unshaded roof that faces within 60° of south.

Grid Connection

This operates in the following manner; the PV array feeds electricity into the site buildings, offsetting that imported from the national grid. When electricity demand on site is more than the output from the PV array, the difference is drawn from the grid. Should electricity demand be less than the output from the PV array, electricity can be exported back into the grid.


Educational products/public awareness displays

PV arrays can also be supplied with interactive digital display units and computer software tailored to specific curricula so that they become an educational resource as well as a supplier of power. The information generated by the array can be made available to local primary and secondary schools.

Churches elsewhere with PV arrays

St James Picadilly

In 2005, St James's church in Piccadilly, London (part of the Diocese of London), installed solar panels on its roof. The building is a Christopher Wren design, consecrated in 1684 and is a Grade 1 listed building. This meant that the panels could not be allowed to either damage the fabric of the building or be visible from the ground.

The PV array now harnesses the sun's energy to power lights and electrical appliances, reducing the church's carbon dioxide emissions by nearly two tonnes a year and saving it around £500 annually.

Installation cost £36,000, but the church received a grant of £16,500 from EDF Energy's Green Energy Fund and £12,500 from the Energy Saving Trust, who administered the Governments Low Carbon Buildings Programme at the time of application

St James's presented the work as an educational project - to make visitors and people in the local community think about renewable energy and climate change - and believes that this helped secure the grants. For more information, contact the Revd Dr Charles Hedley of St James's Church.

PV systems on churches in the UK continue to be a rare sight, but this project and a few others are presented below.


Ground Source Heat Pumps

In the UK, the earth at a depth of 1.5 meters and below keeps a constant temperature of around 11-12 ºC throughout the year. Because of the ground's high thermal mass, it stores heat from the sun during the summer. Ground source heat pumps (GSHPS) can pump this heat from the ground into a building to provide space heating and, in some cases pre-heating for hot water. For every unit of electricity used to pump the heat, 3-4 units of heat are produced.

The Technology

There are three important elements to consider for a GSHP

heat pump

For ground loop based installations there are three main options: borehole (see diagram below, left), straight horizontal and spiral horizontal, often called 'slinkys' (below, right). Each has different characteristics allowing you to choose the most suitable for the site. Horizontal trenches can cost less than boreholes, but require greater land area. For a slinky coil, a trench of about 10m length will provide for about 1kW of heating load. Borehole based collectors will be at depths of between 30 - 200m.

borehole diagram   slinkys diagram

Energy is needed to activate the heat pump cycle and to compress the vapour for the production of useful heat. The efficiency of this process is expressed by the ratio between the useful heat delivered and the driving energy used by the compressor. This ratio is called the Coefficient of Performance (COP).

As environmental heat is free and available in very large quantities, it is not included in the COP. That is why the COP is always larger than 1. The COP of the current generation of heat pumps varies from 2.5 to 5. Since the COP shows performance at a steady state only, a second parameter is usually used to show the performance of the heat pump over an entire year. It is called the seasonal performance factor (SPF), which is the ratio of annually delivered useful heat over annually used driving energy. When calculating the SPF, it is common to include the annual electricity requirements of auxiliary equipment, such as circulation pumps, fans, etc.

Therefore, the performance of a heat pump system is affected by several factors, which include:

The performance of heat pumps should be balanced by the fact that the efficiency of electricity generation in the UK is less than 35%. That means that for every unit of electricity used, more than 2.5 units of primary energy (mix of oil, gas, peat, etc.) have been burned. Therefore, a heat pump with a COP of 4 driven by electricity generated by a thermal power plant has a primary energy efficiency of 160%.

That is already better than the 90+% achieved by a modern gas condensing boiler operating at low temperatures for example. But you can increase the primary energy efficiency of your heat pump, and the environmental benefit, by 3 times by driving it with green electricity. It is now possible to switch easily to a green electricity supplier at no extra cost, or to utilise a PV system to generate ‘green' electricity on site.

Case Study - Gamblesby Village Hall, Cumbria

Gamblesby Village Hall Setting: A remote village in the North Pennines off gas mains. The 150 year old village hall had over time fallen into disrepair and with no other local amenities remaining it needed renovation.

Project: The hall's committee knew that to attract funding they needed to be innovative. Therefore plans included environmental measures such as renewable energy heating.

Fuel Supply: During warmer times of the year the sun shines on the ground, storing low level heat beneath the surface. Coiled pipes about 2 meters beneath the surface has a liquid that passes through them collecting up heat at about 5°C. This is returned to the heat pump which ‘steps up' the heat to 30-40°C in a process that is the reverse of refrigeration. This heated liquid then passes into the village hall and used in an under floor heating system.

Fuel: Sun as a heat source, 3kW electricity to run the pump

Capital Cost (total renovation): £42,016

Running Costs: Cost of electricity to run the pump

The Benefits - After the electricity has been paid, free heat!

installation picture Any Issues? - Reliable - no problems to date - low maintenance. The pump needs occasional servicing - keeping costs down - overcome by using volunteers for most of the work. - Brought the community together to raise funds and help with renovation work - Drawing together all the funding, especially through fund-raising initiatives - Low environmental impact, low CO2 emissions

"With oil prices going up all the time, I have received lots of enquiries about our scheme from other village halls interested in this apparent miracle of getting 'free' heat from our car park!."
Eric Mason, Gamblesby Village Hall Committee Chairman

Further examples of GSHP projects

St. Mary's Church, Welwyn -

Roman Catholic Parish Church, Walsingham, Norfolk

Bankfoot Church, Scotland -

For more information go to

Pippa Hughes, TVE