## CO2 equivalent savings – is there an accurate calculation for renewables?

One of the most useful tools in the solar industry is a calculation for CO2 equivalent savings when you switch from a typical grid supply. The figure is obtained through a very simple calculation but just how accurate is this method of working out your carbon footprint reductions?

Why are we interested in CO2 savings?

It’s no secret that climate change is one of the greatest global threats we face today and that these changes are most likely driven by an unprecedented rate of greenhouse gas emissions from human activities. The greatest proportion of greenhouse gas emissions are comprised of CO2 and CO2 has become a benchmark for calculating the global warming potential of other greenhouse gases like methane (CH4) and nitrous oxide (N2O). This is expressed as a carbon dioxide equivalent in kg CO2e – the equivalent quantity of CO2 that would be needed to give the same greenhouse effect.

CO2 equivalent conversions are also useful for working out the global warming potential of activities for energy production and transportation. In order to standardise these calculations DECC have created a document of energy conversion factors that can be used to compare different methods of energy production. The most useful is their conversion factor for UK grid electricity, which represents the electricity used at the final point of consumption. Since the fuel mix consumed in UK power stations changes from year to year the figure is presented as a five year rolling average.

The math…

According to DECC every kWh of electricity consumed from the grid emits 0.541 kgCO2e

For on-site renewable energy generation DECC advise that a factor of zero may be used

Therefore, we can assume that for every kWh of electricity generated from on-site renewables there is an equivalent saving of 0.541 kg of CO2.

Simple! If not a little too simple…

An earlier article examined the carbon footprint of solar panels, because even though electricity production from renewables does not directly emit greenhouse gases, there are indirect emissions associated with manufacturing and maintenance. Where renewable energy is used to power the manufacturing process of the panel itself then the CO2 equivalent emissions may be as little as 0.021 kg CO2e per kWh. The ‘energy payback’ can be as little as one year, depending on where in the world the panel is located.

The actual CO2 savings of a renewable energy system will vary between technologies. It will even vary between products within the same technology depending on their performance, quality, degradation, manufacturing processes and transportation. For this reason there isn’t really a simple yet accurate calculation that can be applied across the board.

If you are interested in calculating specific CO2 equivalent savings of a particular renewable energy system or your overall CO2 equivalent emissions then DECC offer a number of useful guides and spreadsheets, which allow you to input your own data. Many renewable technology manufacturers are also pretty good at assessing the total Lifecycle Analysis of their products so you should be able to apply a slightly more accurate figure to your calculations.

There are always going to be assumptions and margins for error when calculating CO2 equivalent savings but for the sake of keeping our estimates simple and easily comparable it is a good idea to follow the DECC guidance whilst bearing in mind some important points:

1. The savings are expressed as an equivalent in CO2 emissions that may represent a variety of greenhouse gases
2. Savings from renewables are calculated by the amount of electricity produced from a system – a renewable energy system still requires back-up power from the grid.
3. It is important not to confuse direct and indirect emissions – DECC’s conversion factor of zero for renewables does not include indirect emissions, which will vary between systems, technologies, products.
4. The figures are approximate
5. The calculations can only be applied to systems located in the UK