Sunday, 28 August 2011

What's the plan Stan?

On the 23 September 2010, First Minister Alex Salmond announced a new renewable energy target for Scotland. On that day, he announced that "80% of Scottish electricity consumption was to come from renewables by 2020". This was an increase from the original target of 50% announced in 2007. However, more recently the 80% target has been increased to 100%. So, by 2020, Scotland is expected to be generating the equivalent of 100% of its electricity consumption through renewable sources. This sounds lauadable (in principle) but rather ambitious. Perhaps had this been announced by Jim Hacker in an episode of 'Yes Minister', Sir Humphrey would have raised an eyebrow and suggested to the hapless Jim Hacker that the policy was indeed - 'bold'.

With such a major policy shift, I think it is perfectly natural to expect someone (anyone?) to have a plan; how are we going to get from where we are now to where our incumbent First Minister wants us to be? What specific steps will enable such a transition? What will be the energy mix?

As of the time of posting, there is no real plan telling how we get to 100% or what the energy mix will be. However, there was 'a plan' for the 80% target, and if we look at that, perhaps we can learn something. First of all, I would like to make reference to an independent report published in 2008 by the Scottish Council for Development and Industry. In this, the authors Wood Mackenzie forecast that in 2020, the consumption of electricity would be 45.9 TerraWatt hours (p28 refers). We need to remember that figure, as I will make reference to it at the end of this post.

Next, I need to introduce a term you may be familiar with. Load factor. This is the difference (usually a percentage) between a turbine's rated output capacity and what it can actually output in real world scenarios. There is a significant difference between these two figures, since wind turbines need 'the right sort of wind' - get 'the wrong sort of wind' (ie, too little or too much) and there will be no electricity generated.

Now, onto 'the plan'. The first stop is to get some data, and the Scottish government has provided this very usefully in their Draft Electricity Generation Policy Statement 2010. At the end of the report, there are two tables of exceptionally useful data. I have combined the two tables, and reproduced them here:

Table 1Table 2
CapacityOutput
2008
(MW)
2015
(MW)
2020
(MW)
2030
(MW)
2008
(TWh)
2015
(TWh)
2020
(TWh)
2030
(TWh)
CCGT1,5241,5241,52412006.78.46.93.2
Pumped Storage7407401040134011.11.62.1
Biomass1231503005000.91.12.23.7
CHP2753133684781.922.93.8
Coal345623042304120014.86.35.33.1
Hydro13401361140714072.92.732.9
OCGT555555550000
Other924949490.60.40.40.4
Offshore Wind05001500300001.85.410.6
Onshore Wind1915500065007500513.417.119.8
Nuclear232212001200014.38.57.80
Tidal00200400000.50.9
Wave00300600000.71.4
Total11,85213,19716,74817,73048.245.853.651.9
Renewables as % of total installed capacity/consumption29%53%61%76%25%52%76-80%94-100%
TWh = TerraWatt hour MW = MegaWatt
Data reproduced from Draft Electricity Generation Policy Statement 2010 © Crown Copyright 2010

Table 1 (the left hand side of the data labelled Capacity) shows us the mix of energy types expected to get us to 2020 and beyond that to 2030. The right hand side of the table (labeled Output) shows us how the different types of generational capacity will produce the required output leading to 2020 and beyond. The first thing to note is the scales for the data sets. Table 2 is in TerraWatt hours, and table 1 in MegaWatts (don't mix them up, since 1 TerraWatt hour = 1,000,000 MegaWatt hours). Also note that both tables assume that the 80% target was still applicable. Finally, the generational types in green are those that count towards our 2020 targets and are my addition to the table.

How can we relate Table 1 to Table 2? Well, it's pretty easy and the relationship is primarily governed by the load factor. I took a complete guess at what load factor had been used, and got it right first time; what do you think it is?

If we look along the Onshore Wind row of Table 1 and read off the installed target capacity for 2020, we get 6500 MW. Now we turn this into an output figure, by multiplying it by 24 (number of hours per day) and then 365.25 (number of days per year). We get 56,979,000 MWh. Thats a lot of electricity. However, we now need to apply the load factor, how about we use 30%? Taking 30% of 56,979,000 MWh, we get 17,093,700 MWh. Now, we need to turn this MWh figure into a TWh figure. We do this by moving the decimal place to the right 6 places, and end up with 17.093700 TWh. If we now round this to 1 decimal place, we get 17.1 TWh.

If we now read off the anticipated 2020 output covered by Onshore Wind (Table 2), we see that it is the same, 17.1 TWh. So what? I hear you ask. Well, primarily the calculation we just performed demonstrates that a load factor of 30% has been applied to the expected ouput figure to estimate the installed onshore wind capacity required to achieve the 80% 2020 target - and the significance of that will now be explained.

In March 2011, The John Muir Trust published an absolutely fascinating report they had commissioned into the efficiency of windfarms. All but two of the locations surveyed were Scottish and onshore. One of the main conclusions drawn from the report is that the output from the surveyed wind farms was well below 30% of their maximum rated output, when averaged out over the survey period. Yes, there were instances when 30% was achieved, and on a few occasions exceeded, but such events were most certainly the exception not the rule. Page 9 of the report shows that the output, averaged over the survey period was 24.08%. Clearly, wind farm output is not what was promised, expected and planned for.

Below is a graph showing what the onshore windfarm installed capacity would need to be be to achieve the 17.1TWh total output figure for 2020 for a range of load factors:


If the wind farms continue to only manage a 24.08% output in relation to their installed capacity, we would need an installed capacity of 8098 MW to reach an output of 17.1TWh. Comparing this number to the planned installed capacity of 6500 MW, we see an enormous jump of 1598 MW. To be totally accurate, I should have plotted the net output from the windfarms rather than their metered output, which would reduce their overall contribution since they do consume some electricity in their operation. Unfortunately, I cannot find the necessary data to do this in the public domain and I don't know if the Scottish Governments forecasts allow for this consumption.

The real problem however, comes when we consider that we now have an even higher target to meet. Remember that the calculation we just went through was for the 80% target and that we now need to generate the equivalent of 100% of our electricity through renewable resources by 2020 (that's an extra 25% of the 80% target). Now, I could do a rough (and it would be rough) estimate of the onshore wind generational capacity required to achieve our new 100% 2020 target based upon percentages, but I would be making far too many assumptions. So I won't. Instead, I will leave you with the following thoughts: wind farms would need to hit a load factor of 30% to make the 80% 2020 target, using the equivalent of 6500 1 MW turbines, and that the Scottish Government actually expects (para 5) us to exceed our new 100% target by implementing an as yet unpublished plan. Let us not forget that there is in reality no published plan beyond the Draft Electricity Generation Policy Statement 2010, and that really is just a statement of policy or intent. The actual locations and sizes of onshore wind farms are, as far as we can tell, being dictated by commercial considerations and aren't being coordinated by a central authority to a publicly available plan or timescale.

Finally, remember that figure we extracted from the SCDI report of 2008? Why is there a difference of 7.7TWh between the Scottish Government's 2020 ouput forecast (53.6 TWh - Table 2 refers) and that consumption figure provided by Wood Mackenzie? Somebody seems to have got their forecasts rather wrong - which one was it? The answer could make a massive difference to just how many turbines will eventually be required - or there could be a far more interesting reason: does the difference between these two figures represent electricity destined for export, for example?

It will be interesting to see the 'new 100% plan'; doubtless it will be another great work of creative genius.