Wind and carbon

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I referred recently to two of the arguments most often used against wind energy.  Another standard response from opponents is to argue that wind turbines actually contribute nothing to reduction of carbon emissions, and indeed one commenter on the previous posts raised that very point.

The argument takes various forms – ‘useless’ is a word frequently bandied about – but the underlying question ‘how much difference do turbines make to total carbon emissions?’ is an entirely valid one to ask.  If it were true that they make no contribution at all, it would indeed be something of a killer argument against turbines.

However, whilst demonstrating the invalidity of the claim (that they save no carbon emissions) is relatively straightforward, putting accurate numbers to the difference they do make is much less so, and is, I guess, the main reason that the argument still gets put forward so often and is so readily believed.

The problem, fundamentally, is a lack of agreement around the assumptions which are used to derive any figures, and in the absence of agreement of those assumptions, there is no chance that any figures produced by using them will be universally agreed.

There is no real dispute about the fact that, once built, the electricity from wind farms is virtually carbon free.  So, taking purely the production costs, each Kwh of electricity produced from wind energy saves the CO2 emissions which would be generated from a conventional power station.

That isn’t the whole story of course.  There’s also a carbon cost from site development, transportation, turbine construction, and eventual decommissioning.  However, even on this score, there is no argument against the proposition that wind energy has a very much lower lifetime CO2 cost than equivalent fossil fuel powered plant.  Because the carbon cost of fuel during use completely dwarfs the carbon cost of construction, the carbon cost during the ‘operational’ phase is hugely more significant.

The debate revolves largely around the question of intermittency and the extent to which fossil fuel powered plant has to be kept running at all times in case the wind drops.  This report claimed that use of wind turbines required “17 new gas-fired power stations simply to provide back-up for all those times when the wind drops …  those 17 dedicated power stations, [which] will be kept running on "spinning reserve", 24 hours a day”.

That same claim, in one form or another, runs through all the arguments that I’ve seen against the efficacy of wind turbines.  And, in fairness, if it were true, then there would be no question about it – there could be no case for building wind turbines.  The truth or otherwise of the proposition becomes critical. 

It is, though, simply not true (and was the subject of one of the previous posts).  It seems, in turn, to be based on the assumption that the wind is so variable that wind farms running at optimum capacity one minute can suddenly and unexpectedly stop, across the whole of the UK.  And that simply is not reality.  Wind speeds in a given locality can change quite dramatically, but over a large enough area any degradation in wind speed is much more predictable and gradual.  The actual need for operational backup is thus very much lower than claimed by opponents.

What is true, though, is the rather more straightforward observation that there are times when there is little or no wind across the UK (or large areas of it), that that situation can pertain for days at a time, and that alternative generating capacity is needed to replace wind on those occasions. 

All of that is true, but it undermines the case for wind only to the extent that that capacity would not need to be there if there was not a single wind turbine in existence, and only to the extent that the carbon cost of building power plant which is only used occasionally outweighs the carbon saving from wind. 

Running a complex operation like the Grid in a way which keeps the lights on requires a great deal of flexibility.  There is always going to be significant ‘surplus’ capacity in the system, some of it operational, some of it available at different periods of notice, to allow for situations where one or more other sources of electricity fail, for whatever reason. 

Thus, the extent of that surplus isn’t just down to the use of wind energy.  Even today, with wind at a very low level of penetration (<5% of generating capacity), there is something over 85GW of generating capacity linked to the Grid, against an expected peak demand during an average cold spell of around 56GW.  That capacity is needed in order to cater for periods of maintenance, breakdown – or even lack of fuel or variations in the relative price and availability of fuels.

It is true that adding more renewable energy to the mix will almost certainly lead to an increase in the difference between expected peak demand and total attached capacity. But that isn’t just because the wind doesn’t always blow, and the increase cannot just be ascribed to backing up wind turbines. 

Other sources of renewable electricity come with similar problems.  PV panels don’t produce electricity at night, tidal flow generators only produce at full capacity when the tidal flow is at peak, and hydro-electric schemes depend on the level of flow in rivers.  It’s why any renewables-based energy policy needs to include a mix of sources, as well as looking at such issues as demand management and storage.

The answer to the question, ‘how much difference do they make?’ will inevitably lie in a range, depending on the assumptions made.  But because the key factor in making the comparison is the carbon emissions during operation, the only basis for claiming that wind turbines produce no overall reduction at all in carbon emissions is to depend on invalid assumptions about the need for backup and for keeping that backup operational at all times.