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58 Restalrig Circus, Edinburgh

58 Restalrig Circus, Edinburgh

Solar Photovoltaic (PV) Feasibility Study for Housing Association Homes

Overview

This case study examines the possibility of retrofitting solar PVs to an existing property on Restalrig Circus, which is located in the Leith area of the City of Edinburgh. Benefits of this low & zero carbon technology include reducing electricity costs for the tenants, tackling fuel poverty, whilst at the same time reducing the carbon dioxide emissions. 

This study investigated the potential for PV panels and assessed the following:

  • Location and type(s) of PV panels to maximise solar gain, including output and returns
  • Benefits of Feed-in Tariff in relation to provision of solar PVs
  • Restrictions on PV placement on buildings in conservation area
  • Changes to the government’s Feed-in Tariff scheme, and introduced stipulations

Approach

Technical scope of study

The property at 58 Restalrig Circus is a modern addition to the Restalrig Circus estate. It was designed in 1998, and has a distinctive stepped design due to the sloping site, with a two-storey block and a four-storey block joined by a communal area.

This unusual form provides approximately 120m² of south facing roof area which could be utilised for a PV panel installation. The central section has been excluded as it is shaded by the taller of the connecting buildings. A portion of the roof of the two-storey block is also shaded, and this should be considered in the layout design.

The energy consumption in the communal areas has been calculated as 8,300kWh. This is based on utility bills provided by Port of Leith Housing Association.

 

Cost Analysis

The cost analysis of the solar PV systems in this report takes into consideration and evaluates the following information: 

  • Capital cost of materials
  • Labour to install such panels
  • VAT on labour & materials
  • Yearly estimated maintenance fee
  • Estimated inverter replacement (once every 20 years)
  • Decrease in solar panel efficiency
  • Feed in Tariff rate and its yearly increase in line with the Retail Price Index (RPI)
  • Savings made on electricity bill, based upon electricity price per kWh and its estimated increase with inflation
  • Electricity export at £0.31/kWh (if applicable)

A full breakdown of energy and income generation, cost of systems, and carbon dioxide savings are detailed in feasibility report.

Performance

The analysis process included modelling a number of PV panel sizes and technologies along with inverter size options for the building. The modelling mechanism takes influence from the buildings orientation, roof tilt, size of available roof area and any shading that impacts upon the roof. Each PV and inverter option was simulated to obtain a yearly output of electricity and the number of panels required to achieve different output levels. The selection of the ‘best fit’ PV system was based upon the annual kilowatt/hour output to cost ratio.

For 58 Restalrig Circus, three options were analysed.

  Option 1 Option 2 Option 3
Solar Panel Technology Monocrystalline Monocrystalline Polycrystalline
Number of Modules 39 42 42
Power (wp) per Module 250 235 230
Total Power (kWp) 9.8 9.9 9.7
Number of Inverters 1 1 1
Size (kW) 7.7 9.0 9.0
Number of Strings 3 3 3
Produced Energy (kWh/y) 7,613 8,089 7,496
Specific Production (kWh/kWp/y) 781 820 776

 

Option 2 was the preferred solution. This option could contribute 97% of the buildings annual communal electricity consumption. The PV installation has an estimated cost of around £30,000, with payback expected in year 12 or 13.

Lessons

One of the main drivers for making the investment for PV panels is the Feed in Tariff. Without this incentive for the production and export of energy, the pay back of such installations would rely only on the energy savings from the installation. It is for this reason that any changes to these tariffs can substantially affect any decision to invest. This is further discussed in the report (downloadable on the right of this page).

PV systems are often sized or specified based on the amount of modelled or simulated energy required over the course of a year. It is important to appreciate that the PV system without a storage capacity i.e. batteries, will only generate power during daylight hours. Therefore, the calculation comparing the PV energy generation and the buildings energy demand should be granular enough to differentiate the day and night time energy demand profile.

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Case Study

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