How a building's energy performance is affected by renewable energy and load shedding
16 Aug 2021

By Frikkie Malan, head of sustainability at Remote Metering Solutions

While most people instinctively expect that a building with solar PV plant will have a better EPC rating than a building that does not rely on any form of renewable energy, this is not the case.

According to the SANS 1544 (Energy performance certificates for buildings) all energy carriers into a building must be included in the calculation of a building’s energy performance. An energy carrier is defined in the standard as an “energy form or system, including but not limited to, electricity, gas, fossil fuels, and renewable energy”. While it is obvious that grid supplied electricity consumed in a building should count towards the energy performance, some of the other carriers need closer examination.

Let us start with the way “renewable energy” is treated in the calculation of a building’s energy performance rating. The inclusion of renewable energy in the definition of energy carriers implies that the energy performance and consequently the Energy Performance Certificate (EPC) rating of a building will not improve should the property owner invest in, say, a solar PV plant that provides some, or even all, of the electricity consumed in the building. It might be argued that this is incorrect – that a building’s EPC rating should reflect the fact that renewable energy is used in the building, moving the building closer towards the “net zero” ideal. However, the purpose of an EPC is to determine the energy performance of a building, not the carbon emission performance thereof.

An example should explain this a bit better: Consider a building that is terribly inefficient, with the worst possible EPC rating of G. This very same building is now upgraded with a solar PV plant and battery storage, and for all intents the building can go “off the grid”, yet nothing was done to improve the efficiency of the building. Therefore, the same amount of kWh will be consumed in the building, despite the PV plant and storage upgrade. Has the building’s energy performance improved? In terms of efficiency and therefore its EPC rating, certainly not. In terms of carbon emissions, it undeniably has. But reporting on the carbon emissions of a building is not the purpose of EPCs (at least not in its current format).

The next energy carrier that we consider is the supply of back-up power to a building with a generator. Thanks to load shedding, most building owners in South Africa have no option but to make provision for some form of back-up power, usually in the form of a standby generator.

For this example, we are not considering a PV plant with battery storage as a back-up power solution. According to the standard, the energy value of the fuel consumed by generators that provide power to a building must be used to determine that building’s EPC rating, and not the energy value of the electricity supplied by the generator. Since generators are not terribly efficient at converting fuel to electricity, the use of the fuel energy value instead of the delivered energy value will have an adverse impact on a building’s energy performance. As an estimate, let us assume that for every kWh of electricity provided by a generator, approximately 3.3 kWh of fuel is consumed (this is based on an assumed average generator efficiency of 30%). So, the more a building relies on back-up power (for instance due to load shedding) the worse that building’s energy performance becomes!

And this has nothing to do with the inherent efficiency of the building, but rather with the unavoidable use of back-up power to maintain building services, comfort, security, and safety for the occupants.

A simple example calculation will demonstrate how load shedding, which necessitates the use of standby generators, has an adverse effect on a building’s EPC rating:


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