Wednesday, 20 July 2011

Wind and carbon

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.


Unknown said...

John - you appear to imply that conventional power stations can be turned off when the wind is blowing. This is not the case. Gas powered generators can be modulated to some extent but they can't just be turned off and on, because of the temperatures at which they operate.

Although I may come across as hostile to Wind, I am in fact agnostic, and am seeking the truth - I have been unable to find any convincing figures that demonstrate any actual carbon saving.

The Carbon cost of commissioning the turbines is not as negligible as you suggest - the carbon released bu the huge displacement of peat for the bases and the service roads, and the large number of trees that are felled in some cases (Brechfa, for instance) is not usually counted. - ANd the environmental damage cannot be undone by decommissioning.

You are right that PV is pretty useless in northern climates. The only renewables that makes sense to me is Hydro Electric (Including Pump storage) and Tidal lagoons - which can generate reliably and predictably for 22/24 hours a day, are particularly suitable for deployment of the Welsh coast with its large tidal range, and can also be configured as pump storage facilities to balance the grid. These can actually be used to fulfil peak demand, which wind never can.

Boncath said...

This could be becoming an obsession
We are becoming totally dependent on electricity as a power/fuel source to the exclusion of all other forms.
To all intents and purposes it is invisible to consumers and more worrying infinitely available.

Hence the obsession with maximising generation from any source however viable and regardless of impact in the short or long term
No one ever mentions the consumption side
How many read their meters and are aware of the consumption and related costs thereof

We can live without gas but it is difficult to envisage a world without electricity but we have been there before and could do so again

Anonymous said...

Just a small point of correction John. You say "tidal flow generators only produce at full capacity when the tidal flow is at peak". This is not true. Using a lagoon system, tidal flow generators can produce steady output 24/7. This is achieved by "locking" some head of the tide in a lagoon or natural obstruction so that flow is maintained during the turn. This works by using at least two generators spaced apart with apertures reversible according to current/lagoon discharge.

John Dixon said...


"Gas powered generators can be modulated to some extent but they can't just be turned off and on, because of the temperatures at which they operate"

That's another version of the 'must be kept running at all times' argument. But it isn't true. What is true is that it can take up to an hour from a cold start for the temperature to be high enough for the steam part of the cycle, and that prior to that the plant operates as an OCGT rather than a CCGT (with, therefore, reduced thermal efficiency). But the fact that they can be fairly easily turned on and off is one of the reasons why the gas industry is pushing for CCGT alongside renewables - and asking for subsidies for when they're non-operational.

The practicality of turning them on and off brings us back to the basic point about how variable the wind actually is. Only on an assumption of extreme and rapid variability do all the stations need to be kept running. It that were true, I'd accept that I'd lost the argument - but it isn't.

"The Carbon cost of commissioning the turbines is not as negligible as you suggest"

I didn't intend to suggest that it is negligible; merely that any comparison of construction carbon costs between the fossil-fuel and renewable stations is dwarfed by the difference in operating carbon costs.

"Although I may come across as hostile to Wind, I am in fact agnostic, and am seeking the truth - I have been unable to find any convincing figures that demonstrate any actual carbon saving."

I accept that, and understand it. Putting precise figures to it is problematic, but underlying that is the problem of the assumptions being made. There's an interesting paper here. The appendices are very technical, and cover some of the areas you refer to.

"Tidal lagoons - which can generate reliably and predictably for 22/24 hours a day, are particularly suitable for deployment of the Welsh coast with its large tidal range, and can also be configured as pump storage facilities to balance the grid"

Anon made a similar point as well. Point taken; I was thinking more of the barrage approach when I made the comment - the large barrage which has often been mooted would actually produce electricity for only something like 8 hours a day in two four hour periods. Entirely accept that lagoons would improve significantly on that, giving a lower peak production, but an overall more consistent production. And, given a number of them spread around the coast, we could probably achieve some generation at any time of the night or day. I'm not sure whether Anon intended to suggest that individual lagoons could generate 24/7 - I'd disagree with that - but a collection of them could come pretty close to that. There is still, though, a variation in the flow (and therefore the generation) at different phases of the tide. It's more predictable than wind, but still variable to an extent.


"We are becoming totally dependent on electricity as a power/fuel source to the exclusion of all other forms"

And that is likely to continue. Electricity has the advantage of being 'clean' at point of use, which concentrates the question of emissions at the point of production. I think that we have to assume that electricity - whether from mains or from fuel cells - is going to be the fuel of choice at point of use.

"No one ever mentions the consumption side "

Perhaps the reference to 'demand management' in the original post was a little cryptic, but that was a reference to the consumption side. I agree that it needs more attention - reducing demand is the single biggest contribution that we can make to reducing emissions.

Unknown said...

Thank you for the reference - it appears to be just what I am looking for, but you will understand that it will take me time to digest it, which I need to do before I comment.

Tidal lagoons only need a head of 1-2 meters to produce electricity, so they can be used at full tilt for all but just before and just after slack tide, which is Swansea is just over an hour each, I understand. However, as I think Anon referred to, by holding back either the flooding or the emptying of the pond, the rate and timing of the generation can be adjusted to supply power at peak times, and not at other times.

If you have more than one pond within a lagoon, you can actual generate electricity at slack tide, by having one pond flooded, the other empty, and streaming water from the one to the other though generators. Of course, such methods will reduce the theoretical load capacity of the lagoon, but that really doesn't matter as what we need is peak power.

Also, the lagoons can be used to store over capacity electricity at quiet times to pump water in or out of the lagoon depending won when the need is anticipated and the known state of the tides at that time.

The other advantage of lagoons is that they actually create rather than destroy habitat, so the RSPB and friends of the earth are all for them while being against barrages.

There are many other advantages, - including protection against tide surges in places like Conwy and Tywyn - but this is not the place to list them.

The way that Andrew davies, under instructions from the DTI treated Tidal Electric,who own all the patents for lagoons, and had a fully developed and funded (£80Million) plan for a 60MW impoundment (the official title for lagoon) in Swansea was disgraceful. They have gone to concentrate on more welcome regimes in Canada and china (and, I think, Mexico) though I understand that they would love to come back here.

It would be a great talismanic renewable for Plaid to espouse, as it is a 'no brainier' - no downside.

Carwyn Jones opposed it because it would reduce the size of the waves in his constituency, which is true, but the amount is calculated as less than 1mm. Hardly likely to have a detrimental effect on his beloved Porthcawl surfing.

Unknown said...

Can I make an off the wall suggestion about energy conservation?

In Wales, we need to insulate as many older homes as necessary. That much is known, and I believe it was Plaid policy in the last election.

My suggestion is that we in Wales use Wool as the insulator. It has many advantages, though I believe a bit expensive, and using it could act as a big philip to our Sheep industry,as well as providing semi-skilled employment in areas where high unemployment and an older housing stock coincide - the valleys.

Boncath said...


It costs more to shear a sheep than the wool is worth
A better plan would be for us to start insulating ourselves with woolen clothing rather than use ultra cheap or is it really imported man made fibre garments with zero insulation value
Must close now as my thermostat has just cut out at its permanent pre set of 75 Fahrenheit and I am feeling cold and its July!!

Unknown said...

Yes we should all start wearing wool again, but to achieve that you have to influence millions of individual decisions. If the Assembly were to adopt woolen insulation as the standard in a mass program, that would be just one decision, and it would undoubtedly have a positive effect on fleece prices at the farm gate. A far more realistic ambition.

John Dixon said...


Glad that the reference was of some use. It won't give you the definitive numbers that you're looking for, I know. 'Answers' in this context are only ever going to be as good as the base data and assumptions used.

I agree that lagoons are a virtual no-brainer, but I wouldn't go far as saying that there is 'no downside'. There's no such thing as a free lunch; and no such thing as electricity generation with absolutely no environmental cost.

All decisions boil down to a question of judging the benefits against the costs, including the environmental costs. Lagoons would still need pylons and sub-stations, for instance, and I don't know what studies have been done on the effect on fish. But, from what is known, I'd agree that they look like one of the best technologies to be using as part of an overall renewables-based approach.

Unknown said...

At least there is a basis of discussion in the document,

I have been taking an interest in the lagoon project for about 5 years now, and I have yet to find a downside that hasn't been addressed. Perhaps you can see one? It got scuppered by the DTI, the reason being, it appears, because they were gunning for more wind (massive lobbying from big business) and the Severn Barrage even more influential and powerful lobbying - and as we know big projects bring knighthoods all round They went all out to disseminate lies and disinformation about lagoons which our Welsh politicians didn't see fit to question. It is a disgrace (it would have been generating for 2 year now had it had the go-ahead when first mooted)

I am writing a piece on it, and I will let you know when I have finished.

John Dixon said...


I mentioned a couple of possible downsides in the comment.

The 'final straw' which led to the mid-Wales protests recently wasn't about the wind farms themselves but about the substation and pylons. But those are objections which apply to any generation scheme.

Earlier this week, we received - perhaps you did too - a document from RWE about the proposed Atlantic Array. This proposes a major off-shore wind farm, which will connect to the Grid near Bideford. The document specifically states that the landfall cannot be on the South Wales side because the South Wales transmission system is currently unable to take the load.

My point here is that any significant additional generating capacity off the South Wales coast (e.g. lagoons) may well require pylons not just to connect to the Grid, but also to strengthen and reinforce the Grid, as well as suitable sub-stations. I don't see that as a reason to oppose such development (although no doubt some will!), but as an illustration that there are always likely to be some environmental costs of even the greenest of schemes.

Unknown said...

I am surprised that it is considered that the SW grid cannot take the load - when I looked into this originally the lagoon electric was planned to come ashore at the Baglan energy park, which had plenty of over capacity, and would not require any new pylons to be built.

I suspect that the planned incinerators ( an environmental disaster) are responsible for filling this capacity - even though they are not built yet.

There is an 8-13 year lead time to connection to the grid at the moment, so I guess that bideford is under capacity at the moment.

I haven't received the document you mention.