THE ECO CENTRE SOLAR ROOF

The ECO Centre's grid connected photovoltaic system

Lifting the Solar Pannel The West Wales ECO Centre, based in Newport, Pembrokeshire, is an environmental centre committed to educating the public about energy conservation and energy use, and their associated impacts on the environment. Within the ECO Centre there is an Energy Efficiency Advice Centre and an Eco House which includes a Visitor Centre and offices. The Eco House was renovated to maximise it's energy efficiency and in 1995 Wind & Sun were approached to supply a demonstration PV system to power computer equipment and lighting. Since the majority of visitors to the ECO Centre would be grid connected, it was felt that a grid linked system would demonstrate the feasibility of such a system.

Project details

The photovoltaic array, made up of six Siemens M-75 modules connected in alt text here series, has a peak output of 450 watts. The panels are sited on the south facing slate roof of the Eco House and their output is fed into an SWR-700 'Sunny Boy' inverter, located in the loft. This inverter changes the d.c power from the panels to 230volts a.c and matches the characteristics of the grid electricity coming into the house. Generated power is supplied to the Eco House loads via the distribution and fuse box reducing the electricity demand from the grid. Any extra power needed is imported from the grid as normal. Any surplus power generated can be exported to the grid, although for nearly all of the time, power requirements exceed power being produced. Metering is by two standard mechanical meters with backstops.

Communication with the inverter is via a modem linked PC using the 'Sunny Data' software supplied with the inverter. This provides a graphical display in the Visitor Centre which can display many parameters including system voltage, current and accumulated power output. The ECO Centre's PV system was designed by Steve Wade of Wind & Sun and installed in one day in February 1996 with the help of Martin Cottrell of Sundog. Commissioning, however, took another eight months.

Cost

The cost of the system was around £4000 with the costs of negotiation and testing donated kindly by Wind & Sun and Econnect. SWALEC kindly donated the extra metering needed. The system was funded by Preseli Pembs District Council and the Welsh Office.

Performance

Since commissioning, the PV array has generated 305kWh (11/8/97), offsetting the emission of 0.3 tonnes of CO2, and is well on line for exceeding the predicted 315 kWh annual output. Because the Eco House acts as office space for the ECO Centre there is a large electricity demand from computers, printers etc, so the PV array actually only satisfies about 40% of the centre's needs on a sunny day. Over the course of a year the system should generate around 15 - 20% of the Centre's needs with export only occurring during sunny weekend days when the centre is closed. Because most demand occurs during daylight hours the maximum benefit is gained from the system as it offsets otherwise imported electricity. Any electricity exported to the grid is purchased by SWALEC for 2.7p per unit(kWh) whereas imported electricity is charged at 8p per unit. Obviously the more power that can be used directly on- site, the better.

The problems of grid connection

Fitting the Solar Pannel Although the Regional Electricity Companies (REC's) are required by law to purchase electricity from small scale generators there are presently no UK standards for PV grid connected inverters which meant that SWALEC (the local electricity utility) had no standards to refer to in order to satisfy safety concerns regarding the equipment. They proposed the inclusion of dedicated protection equipment which conformed to UK standards but this would have added approx. 20% of the cost of the system and it was felt that the German inverter contained all the necessary 'state of the art' protection equipment needed. After a long period of negotiation, it was agreed to conduct in-situ tests on the inverter to show that the inverter would shut down within the limits of the present G59/1 standard. These tests were carried out by Econnect to the satisfaction of the SWALEC engineers and the system was finally commissioned on the 11th October 1996 as a demonstration project. SWALEC are keen to point out that this is only a demonstration project and further such connections would have to undergo the same scrutiny as this one. So the terms of connection are still very much at the discretion of the RECs. Hundreds of similar grid linked systems are in use all over Germany using the exact same inverter and BP Solar are now marketing the inverter in a different format. Pressure is now mounting in the UK for specific guidelines to be drawn up which will make it far easier to install such systems in the future. Other countries around the world are embarking upon ambitious and exciting solar programmes. Japan is aiming to install 70,000 solar electric roofs by the year 2000 and there are already thousands of grid connected systems in Europe. The potential for use as cladding on office and commercial buildings is enormous and it will only take a small shift in political policy to enable the utilisation of this resource to begin to achieve what is theoretically possible.