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Andrew J Ball

On Construction Domestic Energy Assessor (OCDEA) for new-build home energy SAP ratings, providing On Construction Energy Performance Certificates (OCEPCs)

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Photovoltaics for Dwellings


Photovoltaic technology generates electricity from light.  


Most photovoltaic installations for dwellings are grid connected meaning that the system is connected to the local electricity network allowing any excess solar generated electricity to be exported and sold.


The power of the sun is normally harnessed either by use of add on solar PV panels which are normally retro fitted to existing roofs, or by the installation of a new roof covering with integral tiles or slates that also capture solar energy in a similar way.


In order to work efficiently and economically the solar installation must receive as much light as possible. Physical factors that influence this include the pitch and orientation of the solar collectors together with the amount of overshading.


The type of photovoltaic technology also influences efficiency and there are several different types of collector.


Despite having fairly significant capital costs for initial purchase and installation a PV system is relatively simple and low maintenance and many systems come with a guarantee of 20 years or more.


Installation will include the collectors themselves together with an inverter which is required to convert the DC electricity generated to AC which can then be used by normal household appliances and can be exported to the national grid.


As a rule of thumb, in the UK, with optimum positioning of the solar collectors

1m2 of monocrystalline or polycrystalline array will create a useful output of around 100 kWh per annum.

1m2 of amorphous thin film array will create a useful output of around 50 kWh per annum.


Modules are rated in kWp, representing peak watts, which is the maximum output of power that an array will generate at noon on a sunny day. What is achievable over a typical year in the British Isles, therefore, is somewhat less!


A monocrystalline or polycrystalline system with a PV array pointed to the South in the UK will generate 750 kWh per kWp installed, or 100 kWh / m2 per annum.


Is it worth installing a PV system? 


Using the National Homes Energy Rating (NHER) Plan Assessor software it is possible to undertake an NHER calculation to assess the energy performance of an existing or a proposed new dwelling.


This goes beyond a normal Standard Assessment Procedure(SAP) calculation and takes into account additional factors such as energy used for appliances and cooking. Furthermore it is possible to use data on actual current fuel tariffs in use, together with occupancy patterns to produce an excellent understanding of the annual cost and consumption of energy for a dwelling.


Using this baseline data it is then possible to determine whether a proposed photovoltaic system is feasible both in terms of energy produced and cost savings made. Such a calculation is totally independent of suppliers of PV systems.


Please contact us to discuss this NHER Assessment process.