There is a lot of focus on “net zero carbon” or “net carbon neutral” or similar in the sustainability world. This is mainly a corporate or building issue with most companies wanted to make an effort to eliminate their CO2 emissions and therefore their contribution to man-made climate change. This is of course admirable and the organisations making these commitments are spending a great deal of money and investing in energy efficiency, renewable energy (directly or indirectly) and often spending a lot of money on offsets to account for any remaining emissions.
But, as the name suggests, “net zero carbon” is not the same as “zero carbon” even though the terms are often used interchangeably. The “net” element essentially treats CO2 emissions like a balance. If, you emit 1,000 tonnes of CO2 from gas boilers, say, you can account for them by generating energy from solar power or by buying off-site generation to give a reduction of a 1,000 tonnes and then you are “net zero carbon”. The issue is that this is not how our energy system works; however much solar power you generate or off-site generation you buy it doesn’t actually eliminate the emissions you generated, they are still out there and that is why you are “Net Zero Carbon” rather than “Zero Carbon”.
Up until recently it was fair to say that the net approach, despite its limitations was still a good way forward and the simplifications made it easier for us all to demonstrate progress and do the accounting. The changes that have been occurring in our energy system over the last decade have now reached a point where that may no longer be the case and it may even lead to perverse outcomes.
If we use a warehouse as an example, (this will apply equally to other buildings, companies and whole countries), it is reasonably easy to achieve “net zero carbon” by putting a large solar system on the roof to generate as much energy as you use over a year. I have put a few examples of the kind of issues this causes us for those of us that want a true zero carbon energy system:
- The solar power generated will be in the middle of the day in the summer when power demand is already low in the country, the energy system is already lower carbon. The carbon intensity of the grid varies daily, seasonally and annually. (For those interested in some more depth on CO2 intensity variation. my colleague Sabbir and I wrote a technical paper on this last year that can be seen here, or see image) So the savings will be much lower in reality.
- Everyone agrees that energy storage is crucial and playing an important role in reducing CO2 emissions and allowing intermittent renewables (solar and wind) to be the dominant source of energy. It allows buildings and companies to absorb energy at low demand/carbon times and then use it at high demand/carbon times. With a net calculation though energy storage actually shows as an increase in CO2 emissions. This is because no energy storage is 100% efficient and therefore if you put 100 units of energy in you will get less out and that will increase the net energy you require over a year.
- Our entire energy system is electrifying, buildings and vehicles and even some industry. This is putting a strain on our electrical system at peak times. This is why energy storage and shifting demand to low use periods is really helpful for reducing the cost of our decarbonisation but a “net” calculation doesn’t take account of when you use energy, just the overall amount. This is despite it probably being true that when you use power is as important as how much
All of the above may seem an esoteric, technical issue but it is fundamental if we going to move to an ultra-low carbon economy and I urge policy makers and companies to work with us to develop a “True zero carbon” standard so that we can all play our part.
This article is written by Barny Evans, Technical Director at WSP
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Journal article can be accessed here.