August 4th, 2017
by Peter Jones
I had a kitchen contractor over to quote for some work in my house. As he ran a company that specialised in using reclaimed wood, the conversation turned to green issues – and let’s just say he wasn’t averse to sharing his opinions. “Those wind turbines,” he grumbled, “they’re an eyesore and they’re not even carbon neutral.”
For reasons other than his attitude to low carbon energy, he didn’t end up doing the work, but his question stayed with me. The fact that someone who had built a business around resource-efficiency should believe that low carbon energy generation was a waste of time surprised me. If he believed this, how many other people might think the same? Could it be true, either of wind or solar power?
It’s important that we assess energy technologies by the right standard. It’s certainly true that neither wind nor solar energy is “zero carbon”: the construction of a wind turbine or a solar panel requires energy and resources, some of which will at present be derived from fossil sources, as does its maintenance. Whilst each additional gigawatt hour of electricity generated will result in no new emissions, it is fair to spread the initial carbon ‘investment’ embodied in the generator across its lifespan.
But it would be unfair to criticise renewables for failing to meet a “zero carbon” criterion. Nothing could: even if the fabled “over unity” device could be invented, mysteriously pulling free energy from thin air, it wouldn’t be “zero carbon” because of the embodied, fossil-derived energy in the device. Of course, as wind and solar (both of which do pull energy from thin air, but in non-mysterious ways) supply more of our electricity needs, the amount of carbon emissions involved in their production will also decrease – so in theory at least, they could be become close to zero carbon technologies if they succeed in supplanting combustion-based energy sources.
A more common argument is that renewables never generate back the energy – or sometimes, the CO2 cost of the energy – that was invested in their construction. Critics will highlight the substantial tonnage of various materials that goes into a wind turbine, including the rare earths such as neodymium that are required in order to build the sophisticated magnets they contain. It’s also true that solar panels and wind turbines have a limited lifespan.
It’s payback time
However, the academic literature on this topic is pretty conclusive. Technology has been rapidly improving, extending the lifespan of renewables, increasing their efficiency and reducing the production energy costs. Early solar panels and wind turbines were expensive, and may well have taken more energy to construct than they would ever produce. These days things are different – both in carbon and financial terms.
Eunomia monitors the Renewable Energy Planning Database (REPD) on behalf of BEIS, which involves tracking developments in the renewable energy market. One of the most striking recent announcements was that onshore wind is cheap enough now to deliver power to UK consumers without subsidy, and the business case is still improving: for example, MH Vestas recently increased the rated power of their turbines without increasing the rotor diameter It seems that subsidy-free solar is already viable in some countries, and may not be far behind in the UK.
Assessing how much carbon has gone into a renewable technology isn’t simple. You have to decide on the system boundary – what will you factor in? Of course, you want to consider the direct energy costs of producing the item, of producing and transporting the raw materials, and of managing them once their useful life is over. But should you go further, and factor in – say – a share of all of the carbon emissions involved in the decades of development that have gone into the technology? What about a share of the emissions from the offices where the planning decision on a wind farm might be made? Generally, though, there will come a point where all of the major factors have been accounted for, and the remainder are likely to have a negligible impact.
There are also some significant variations which are difficult to get across if you’re aiming to give an overall answer for a particular technology. It matters where a solar panel is produced, for example: if it comes from a country where coal is a big part of the grid mix, its production will be a lot more carbon intensive than if it was made at a facility that generates its own renewable energy. Plans to build a “solar breeder” facility in the Sahara, where local sand and locally generated solar energy can be used, would take this idea to its logical limit.
It also matters where renewables are deployed. A solar panel in the cloudy UK will take longer to repay the initial energy investment than in sunny Southern California. A wind turbine that replaces carbon-intensive coal fired electricity generation will save more emissions than if it replaces more efficient gas. If you have to tear down rainforest or drain a peat bog to prepare your site, it will eat into the carbon benefits.
But we can set aside most of these issues, as the academic studies are clear. The energy case for renewables is now far from marginal, and they have very short energy payback periods: less than a year for a wind turbine, and less than two years for a solar panel. Indeed, it has recently been estimated that solar panels have, collectively, repaid all of the energy put into their development.
Finally, some argue that, while renewables themselves may achieve energy payback, their benefits are undermined by other indirect costs. Most critiques of renewables bring up the issue of ‘intermittency’ – you can only generate wind power when it’s windy, and you receive far less solar power on cloudy days. That necessitates a level of “spinning reserve” – generally fossil fuel power stations that have to be ready to step in if renewables aren’t available. Starting up and shutting down a fossil fuel power station is less carbon-efficient than just running one constantly.
However, this issue has also been the subject of considerable research, and real data indicates that, while the need for a spinning reserve does offset some of the carbon benefits of renewables, the impact is not as large as some theoretical calculations have suggested. UKERC recently reported a study by the National Grid that found that the impact of wind power on gas generation over an 18 month period was an average efficiency loss of 0.081%.
The issue of intermittency might be expected to become more significant as the contribution of renewables increases. However, that assumes that our electricity network and management practices do not gradually adapt to better fit the patterns of renewable energy.
The grid is continually being updated, and there is scope to do this in ways that are tailored to renewables. The Government issued a call for evidence last year on how to move to a smarter and more flexible electricity system, and recently published a summary of the responses and its own position, suggesting that grid policy is moving in a direction that will better suit renewables. Better grid interconnection over wide geographical areas will help to ensure that intermittency’s impacts are minimised: on days when it is less windy and/or sunny than normal across the UK, it’s probably windy or sunny somewhere else in Europe.
We can build more storage capacity into the system, allowing us to save excess generation for when it is needed. Battery storage is advancing, while other new technologies are improving our ability to store electricity: solutions such as Highview’s Liquid Air Energy Storage system could improve grid-scale storage response time and alleviate the need for spinning reserve if proven to be commercially and technically viable.
Eunomia has been analysing opportunities for the deployment of storage technologies, and also finding scope for energy demand management to play a part. Equally important is a continuing focus on energy efficiency, helping to reduce peak demand.
So, while renewables are not ‘zero carbon’, that’s an unreasonable standard by which to judge. They certainly produce more energy than it takes to create them, and their efficiency continues to improve. And in real world operation, the evidence is that they reduce total CO2 emissions, and have the potential to deliver greater benefits as they become increasingly mainstream.