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Lasswade Road, Edinburgh

Solar PV feasibility study for homes in the City of Edinburgh

Overview

This study identifies the feasibility of installing photovoltaic (PV) panels on the roof of apartment buildings in Lasswade Road. The complex on Lasswade Road is comprised of three buildings, each with 10 rented apartments, which were built in 2006. The buildings are four storeys tall and are arranged in an L-shape. Currently, two wood pellet biomass boilers provide heating and hot water for 20 of the flats. It is hoped that electricity produced by the PV installation would minimise the energy needs of the boiler house.

Approach

The Scottish Energy Centre, part of the Institute for Sustainable Construction at Edinburgh Napier University were selected by CIC Start Online on behalf of Malcolm Homes Ltd to conduct the feasibility study for the installation of PV panels at their properties in Edinburgh. The Lasswade Road buildings were selected due to their optimum roof shape and orientation. Both technical and economic feasibility have been considered. The approach taken in the study was as follows:

  • Discuss and evaluate the technical constraints of the building and site, and demonstrate best practice in terms of location, orientation and azimuth – in the Northern hemisphere, PV panels should ideally face between south-east and south-west, in Scotland the most efficient tilt angle is ±2° of 40°. Panels should also be located so that they are not shaded throughout the day.
  • Discuss and identify potential constraints of the energy suppliers requirements – as the UK electricity network has traditionally had centralised generators, distributing energy to domestic and commercial customers.
  • Identify the FIT (feed in tariff) benefits that may be gained – FIT are dependent on installation size (kWp) and rates are set by OFGEM for generation and export.
  • Identify the economic payback of equipment – based on capital cost, maintenance requirements, energy produced and FIT available
  • Explore the rent a roof scheme – where roof space is leased to allow a PV installation, where the householder gains the electricity produced and the installer the FIT (full details on page 27 of the case study).  

 

A design tool, PVSyst, was used to establish the economic and technical feasibility of PV installations. The tool needs the following information to obtain accurate results:

  • Tilt of pitched roof
  • Orientation of roof
  • The amount of output power required
  • The type of PV panels to be used

 

Other considerations include potential shading of the PV panels, FIT restraints and possible issues with grid connections.

A full explanation of how solar PV panels work is included on page 7 of the pdf download (see right).

Performance

The boiler house currently requires a large amount of energy to reach required temperatures. More than 8,000kWh of electricity were used over the winter period, and more than 6,000kWh were used in the summer. The average annual consumption is 29,000kWh. This was reflected in high electricity bills; more than £1,000 for the winter quarter, and £4,300 in total for the year.

The roof at Lasswade Road which provides the best feasibility for installing PV panels is next to the boiler house. It has an ideal southern orientation (5°), but the inclination is too low at 5°, so angle props would be required.

The roof area is 118.5m2. However, there is a corner area which has difficult access and also a maintenance walkway which would need to be maintained. There is also a parapet on the roof which may cause shading, therefore the useful area for PV panels is around 70m2.

The options examined for the roof at Lasswade Road are shown in the table below.

 

Option 1

Option 2

Option 3

Solar Panel Technology

Polycrystalline

Monocrystalline

Monocrystalline

Phases

Single

Single

Single

Number of Modules

36

36

36

Power (wp) per Module

230

250

240

Total Power (kW)

8.3

9.0

8.6

Number of Invertors

1

1

1

Size

8.0kW

8.0kW

8.0kW

Strings

3 x 12

3 x 12

3 x 12

Produced Energy (kWh/yr)

6,542

7,216

7,051

Specific Production (kWh/kWp/yr)

790

802

816

Lessons

Option 2 was considered for further economic analysis, as it provided the highest capacity and annual output. The initial capital cost of this system is estimated to be around £30,000. Capital investment payback is expected sometime in the eighth year of service – when FIT, energy savings and maintenance costs are considered. The PV system would be expected to reduce energy bills by about 25%.

 

Before considering a renewable energy installation, it is imperative that the building is energy efficient, either through recent construction to current building standards or retrofit of an older building to meet these same performance levels. Otherwise, poor energy performance will counteract the effectiveness of the renewable technologies. It was understood before the feasibility study that the buildings at Lasswade Road met these requirements. 

A structural analysis should also be undertaken before installing PV panels to ensure that the roof can withstand the additional loads.

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