Admin Note - There are a lot of diagrams in this blogpost once again but I believe they tell an interesting story so please bear with me. Apologies if you experience formatting problems - these are not intentional !
However, it is an unfortunate fact that the contribution to adequacy of additional amounts of wind decreases progressively and tends towards zero [ESB 2004].
|Diagram 1 - All Ireland average wind penetration levels (Eirgrid)|
We can see from the above diagram that average wind penetration for the month of March has nearly doubled since 2012. Let's see what impact this has had on the running of our electricity system.
|Diagram 2: Fuel Mix March 2012 (wind penetration 13%)|
Diagram 2 shows the fuel mix for March 2012. Black represents coal, gas is yellow and green is wind.
Gas is acting as back up to the intermittent wind. Given Ireland's generation capacity, this is the most
efficient and cleanest form of back up. Hardly any oil generation was used.
Diagram 3 - Fuel Mix March 2013 (wind penetration 17%)
Diagram 3 shows a similar fuel mix as 2012 but with some oil generation (red shading at top)
Diagram 4: Fuel Mix 2014 (wind penetration 21%)
Diagram 4 again shows a similar fuel mix for 2014 but with small amounts of distillate
(i.e. diesel) oil generation (light green shading at top) and heavy fuel oil (red).
Now we come to March 2015:
Diagram 5: Fuel Mix 2015 (wind penetration 24%)
You probably have noted that gas generation has become comparatively less and less
each year as wind penetration increases. But what we see now in 2015, with average and
maximum wind penetrations of 24% and 61% respectively, is significantly more distillate and
conventional oil generation. This meant that emissions from conventional generators
increased as "dirtier" inefficient oil replaced "cleaner" more efficient gas generation.
Why did this happen ? Well, if we take a look at forecast and actual wind generation
for a period in March 2015 it will give us a clue :
Diagram 6: Wind forecast and generation March 2015
The intermittent nature of wind is evident in Diagram 6. The red line shows forecast wind and
it is clear that actual wind (blue line) failed to meet forecast wind on numerous occasions
during this period.
Oil generators have a unique characteristic in that they are very fast acting, in Ireland it
typically take eight minutes for them to reach full capacity, compared to say a gas generator
which can take up to eight hours to start. But there is a trade off - oil produces more emissions
due to its energy dense nature while gas, once the generator is up and running, produces about
30% less nitrogen oxide and carbon dioxide than oil. Gas plants are also much more efficient
in terms of fuel consumption. So what has happened is that fast acting oil generators are
stepping in to meet loss of supply due to unforeseen drops in wind power.
If we take a system with lower levels of wind penetration, like in 2012 / 13, we can see that
gas generators can cope with these wind levels as sudden loss in supply from wind generators does
not cause a major problem to the system. But we can see in Diagram 6 losses in wind generation
of up to 400MW, which is akin to the loss of the largest power plant in Ireland. One might ask,
but surely, there is reserve there for such a loss of power - well there is, but in my opinion,
this would be reserved for the loss of a power plant rather than loss of wind power.
The conclusion from this is that the system can cope with wind penetration of circa 20% but as
you go above this level, the benefits from wind energy diminish, as you have to back it up with
fast acting higher emitting plant. I have long believed that we have reached saturation
point with wind energy and this data confirms this. It is clear that an all wind strategy does
not make sense.
While nuclear should be an option but requires a long term plan of itself, there is a simpler
solution, that does not require back up oil plants, new pylon infrastructure or a new expensive
Grid Code to accommodate high levels of unstable wind energy, to meeting our renewable
targets - biomass.
The below presentation gives a good summary of the benefits of this option :
While wind provides non dispatchable generation (incapable of been switched on when
required), biomass provides dispatchable generation (can be switched on as required).
This means that biomass generation can replace an existing power station (eg Moneypoint
coal power station) and utilize existing grid structure.
For completeness sake, the below diagram shows March demand for the years 2012 - 2015.
You can see that there was a couple of days where peak demand was higher in 2015
(and also lower) but in general, demand was roughly the same and therefore does not
account for the increased use of oil generation.