Callidus Design Consulting Engineers

Designers, engineers, consultants and technical specialists covering a wide range of building and process services.


Renewables - Solar Power

The information below provides a brief summary of the available solar energy technologies which can typically be incorporated within new or existing domestic and non-domestic buildings.

There are then two main ways actively to exploit the sun’s energy in climates such as that of the UK:
• Using thermal collectors, (either flat plate or evacuated tube) to absorb the sun’s radiation to produce hot water or air
• Using photovoltaic cells which utilise the sun’s light to create an electric current and generate electricity

Solar Thermal
Solar water heating systems use the energy from the sun to heat water, most commonly in the UK for hot water needs. The systems use a heat collector, generally mounted on the roof or a south facing façade in which a fluid is heated by the sun. This fluid is used to heat water that is stored in either a separate hot water cylinder or more commonly a twin coil hot water cylinder with the second coil providing top-up heating from a conventional boiler. Ideally the collectors should be mounted in a south-facing location, although south-east/south-west orientations within 45° of south will also function successfully. The panels can be bolted onto the roof or walls or integrated into the roof.

There are two standard types of collectors used: flat plate and evacuated tube. The flat plate collector is the predominant type used in solar domestic hot water systems, as they tend to have a lower cost for each unit of energy saved. Evacuated tube collectors are generally more expensive due to the complex manufacturing process required to achieve the vacuum, but manufacturers generally claim better winter all-round performance.

Photovoltaic (PV) systems convert energy from the sun into electricity through semiconductor cells. Systems consist of semiconductor cells connected together and mounted into modules. Modules are connected to an inverter to convert their direct current (DC) in to alternating current (AC), which is usable in buildings. PV can supply electricity either to the buildings to which they are attached, or when the building demand is insufficient, electricity can be exported to the electricity grid. For PV to work effectively it should ideally face south and at an incline of 30º to the horizontal, although orientations within 45º of south are acceptable and will function successfully. It is essential that the system is unshaded, as even a small shadow may significantly reduce output.

PVs are available in a number of forms including monocrystalline, polycrystalline, amorphous silicon (thin film) or hybrid panels that are mounted on, or integrated into the roof or facades of buildings. Examples of building integrated photovoltaic products that can be incorporated into buildings include:

— rainscreen cladding integrated into the façade
— shading louvres with integrated photovoltaics
— photovoltaics integrated into glazing
— panels bolted on to the roof
— tilted panels on a flat roof
— thin film laid on a standing seam roof
— solar tiles

PV system size is measured in kWp. A 1 kWp polycrystalline system will generate around 750 kWh of electricity a year in the south of England. The size of the PV systems can be varied to match the carbon saving required.

Please get in touch if Callidus Design can be of assistance with the design of your new Solar Thermal or Photovoltaics installation.

(extracted from CIBSE Guide L - Sustainability and CIBSE KS15)