Quantifying CO2 savings from wind power redux: Ireland 2012

The Sustainability Energy Authority of Ireland (SEAI) have a new report which looks at CO_2 emission savings from wind energy in 2012. The electricity grid is simulated using \frac{1}{2}-hourly system demand, known outages, and inter-connector flows as boundary conditions. One simulation is done using actual wind generation in 2012 while another sets wind generation to zero. The difference in total CO_2 corresponds to emissions savings. The SEAI study was carried out using off-the-shelf PLEXOS dispatch modelling software.

Here is a summary of SEAI’s findings (Table 4 p 31 of the report):

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The savings for RoI is far lower than SEAI’s earlier number 0.49tCO2/MWh. In terms of “effectiveness”, 1 MWh of wind generation displaces the CO_2 equivalent of 0.65MWh of average thermal generation. The earlier SEAI number corresponds to approximately one-for-one displacement. So this is a big change.

SEAI’s simulation findings can be compared to results based on empirical estimates. This method (described here and here) uses the commercially metered generation data from SEMO to calculate grid CO_2 emissions. An ARMA model then relates these emissions to wind generation and other variables. Very good fits to the empirical CO_2 time-series can be obtained.^*

Here are findings using the empirical method for 2011:

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The NI CO_2 savings number is much lower than found by SEAI. In fact, SEAI’s 2012 savings of -0.8tCO_2/MWh is hard to understand, because only \approx \frac{1}{3} of NI generation came from coal.

Simulation and empirical approaches each has advantages and disadvantages. Both are sensitive to imperfections in the wind generation/system demand dataset. However SEAI make a number of claims about the 2011 empirical method results which seem to me to be wrong. Firstly, system constraints and outages are automatically taken into account  in the empirical method. Secondly, despite the absence of pumped storage  and reduced inter-connector flow in 2011, emissions intensity was lower compared to 2012. This is because 2012 fuel prices favoured coal relative to gas. If anything the grid was less flexible in 2012.

^* System demand, tie-in flows between RoI/NI grids and Moyle interconnector flow are included as additional regression variables.

 

4 Comments

  • Joe,

    The table above with the ‘effectiveness’ from your 2011 paper says effectiveness for all Ireland is 65%. But the results in your table for the sophisticated analysis say the effectiveness is 53% (p 3). Your simple, preliminary analysis said 65% (p 2). Am I misunderstanding something?

  • Joe,

    Why does your second table (after this sentence “Here are findings using the empirical method for 2011:”):
    say that wind’s effectiveness in ROI was 61% in 2011 whereas your Energy Policy paper says 53%?

  • Peter,

    Imports and exports of power means that carbon intensity can be expressed in different ways -using domestic generation or domestic demand. The results quoted above are with respect to domestic generation in order to match the SEAI report method, whereas the 53% number quoted in the paper is with respect to domestic demand. There is a short discussion in the paper.

    Of course this ambiguity does not arise in the case of an isolated grid (e.g. Australian NEM).

  • Joe,

    Thank you for your reply (sorry for the long dealy in replying; I’ve only just seen your reply).

    I am still unclear. Domestic demand should be the same as domestic generation plus interconnector transfers plus net energy stored in pumped hydro. Pumped hydro storage is negliginle in Ireland. Net transfers to UK are small too. So, to clarify for me, is the difference between 61% in your post above and 53% in your ‘Energy Policy’ paper explained by:

    1. the interconnector transfers to Northern Ireland, and

    2. different year (SEAI is ansalysis is of 2012 whereas yours is of 2011 data)

    Which estimate of CO2 abatement effectiveness do you believe is more relevant for estimating the CO2 abatement cost with wind power, the 53% or the 61%?

    Regards

    Peter lang

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