Commercial Building Roof Top Solar Case Study

Project Cardiff 1

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Project Cardiff 1 – Background

The Solvo Energy team were appointed by a commercial building owner to undertake the design and specification of the Engineering, Procurement and Construction (EPC) works for a rooftop solar PV installation located on their building in Cardiff.


System Size


Total System Price


Estimated Annual Electricity Bill Savings

182,451 kWh

Annual Electricity Generation

The installation of this system will save the client approximately £21,818 in electricity per annum and will pay for itself in just under 7 years. Excluding O&M, this will lead to a net saving through on-site electricity generation over the systems 25-year life cycle of £545,466.

The design displayed above represented the render of the site’s preliminary system design before the initial site visit, construction design, equipment procurement and installation.

System Functionality

The installed system will function under three primary operational scenarios:

Generating Excess Solar

During daytime hours the system may produce more energy than required on site, and so excess energy is sold to the grid.

Partially Offset Usage

During daytime hours the system may not produce enough energy required to fully power the site. In this case excess energy is purchased from the grid to supply the deficit.


As solar PV does not generate electricity outside of sunlight hours, no power is generated, and all electricity must be drawn from the grid.

Solar PV generates electricity savings and reduces carbon consumption on-site when generating excess solar and partially offsetting usage. The installation of a Battery Energy Storage System (BESS) can allow for utilisation of the system overnight, but as the client only operates during regular business hours a BESS would not produce any significant benefit.

Environmental Benefits

Solar PV produces no CO2 emissions when generating electricity, creating a completely clean source of energy. The table below demonstrates the estimated benefits provided by this system over its 25-year life cycle.


Estimated tonnes avoided CO2


Car miles avoided


Trees planted


Long haul flights avoided

Environmental benefits generated by commercial rooftop solar PV systems are key to reducing the UK’s energy mix carbon intensity, a measure critical to combat global warming and creating more sustainable businesses.

System Technical Evaluation

PV Array Parameters

The solar panel array is divided into three separate areas called sub-arrays. Each sub-array supplies their own inverter.
The inverters convert the DC current produced by the solar panels into AC current suitable for supply to the client or export to the grid.

Normalised Production at Nominal Power: 164 kWp

The system will produce a maximum average of 5.15 kWh/ kWp/ day in June, and a minimum average of 0.81 kWh/ kWp/ day during December. This is because production is correlated to irradiance from the sun, which is highest during the summer in the UK.

Table of Main Results

The system will produce a total of 186,191 kWh per annum, achieving an overall performance ratio of 0.882.

System Losses

System based losses (a completely normal characteristic for any energy generation system) will reduce the energy available to be consumer or exported to the grid creating a final usable production value of 182,451 kWh per annum. This is the final value provided to the client and used for detailed modelling.

Single Line Diagram

A single line diagram provides a simple representation of the electrical system. This forms part of the design which is shared with the DNO (District Network Operator).

Final Design

After the team has established the building specifics via a site visit, the detailed redesign is finalised allowing the installation to begin.