Wednesday, 28 October 2015

Storing The Wind

Would storing wind power sort out the intermittency problem ?

One of the solutions offered for wind intermittency is storage. Let's take the recent calm spell, which was interspersed with very high winds, to see if storing wind would balance out the variances and lead to a more stable predictable electricity supply.

Let's remind ourselves of what the recent wind output looked like (Figure 1) :

Figure 1: Raw wind power which is what we have at present

We can see from the 23rd to 30th September, there was some very high wind output, and again at 4th till 7th October. This was interspersed with a very calm spell lasting a couple of days. After the 4th, there was a long period of poor winds lasting about 12 days.

So what would happen if we balanced out this wind variation to provide more stable constant output ?


There are a number of storage options - pumped storage, battery or compressed air. For this study, I assume a 500MW storage device is built and 1MW of stored power produces 1MW output when needed at all times. As far as I know, only pumped storage can provide this type of reliable storage. My understanding is that a battery produces less output when it's stored power is running low than it does at full charge i.e. the 1MW you put in does not produce 1MW 20 days later.

The other assumption made is that once wind power goes above 500MW, the surplus power is stored. When wind goes below 500MW, the storage device makes up the difference to bring output back to 500MW. Only wind power is stored.


In a perfect world, this would result in a constant wind plus storage output of 500MW. However, as you can see below (Figure 2), there is a blip in the storage output at around 3 days in on the 25th September. But output really hits a brick wall on the 1st October, at 9 days in.

Figure 2: Output from a storage unit powered solely from wind

At this point, there is a sudden drop in power from 500MW to 335MW and then to 11MW that lasts a full day as stored power runs out. Then we get reliable output for the next four days but the battery runs out again on the 6th October (two weeks in) and we are once again at the mercy of the wind. At one point it reaches 5MW. This lull in wind and storage power lasts for 12 days.

On the 18th we get good winds again and the battery begins re-charging but the problem is you can't use this power when it was most needed i.e. a couple of weeks prior. 

Figure 3 shows the contribution of the wind plus storage unit towards demand. The storage unit actually comprises 2,500MW of wind and 500MW storage, so 3,000MW in total. For 3,000MW of capacity, as you can see, you only get very small amounts of power out - about one seventh or 15% of peak demand - when the unit is running at full output i.e. 500MW. This compares very badly with gas powered stations (or indeed coal, biomass or any dispatchable plant) which could power 85% of peak demand for the same amounts of capacity.

Figure 3: Contribution from the storage unit towards demand

To add further insult to injury, you still get unreliable and intermittent amounts of power for large portions of the month - 43% of the time in this scenario. So we are back to square 1. 


Storage doesn't work. There are simply too many calm days to make it a reliable worthwhile solution. It's no wonder the Spirit of Ireland proposal, now dropped, intended to use grid power to move water uphill, rather than raw wind power.


  1. See my you tube video No 9 Storage. Google Val Martin You Tube ans select No 9.

  2. Deutsche Asset & Wealth Management are explained by the below:

    They have written an excellent analysis, posted on the website of the German Employers' Association:

    Put it into google translate, although it would be very nice to have a formal translation, but unfortunately I don't have time.

    It is a damming criticism of the German cloud in the sky cuckoo home energy policy. The article starts of with why nobody wants to invest in Germany's energy programme. It then explains in very good detail exactly why. Indeed, one cannot criticise the factual issues raised.

    For instance I liked how they rubbished all this super grid nonsense, as they point out weather systems for wind energy are the same over approximately a 600 km distance, so if you wanted to get this fantasy grid to work, it would have to reach from Portugal to Chad and over to Azerbaijan before you would get equalisation of the regional variations in wind energy input.

    If you wanted to do pumped storage for Germany to level out the fluctuations in weather systems and wind energy, you would have to construct a second Lake Constance and shove it up 600 meters above the existing one (that's the very big lake in South West Germany bordering Austria and Switzerland, also called Bodensee).

    Of course, you could do the same thing with lithium batteries, but this would cost 5 to 10 times that of the €100 per kWh for a 'cost effective' pumped storage. Even the mighty Germany couldn't afford the €8,000 billion required for all of this Green Energy storage systems.

    1. Thanks for that Pat.

      One of the things I learned from doing the above analysis was that the capacity of the storage unit is largely irrelevant when you dont have enough wind to keep the battery fully charged or the lake full of water. So you end up, as in the above example, with idle storage capacity for significant periods.

      Basically, you transfer the intermittency of wind on the grid to the storage unit. As you say, you would need to cover vast distances to smooth out the intermittencies to make it worthwhile.

  3. An interesting side issue is how costs in money terms effect the use of fossil fuels and co2 emissions. If a single income family has Dad as a taxi driver, their disposable income (after paying for essentials) is 50 euros per week, if that disposable income decreases to zero, Dad will have to do an extra 3 hours work per week to recoup this income. In doing so, he will have to use more fuel in his taxi. If that family live in a modest house and you suddenly re- house them in their own version of Windsor Castle, they will not be able to afford the maintenance, heating and lighting costs and will end up shutting off a few rooms to live in. Like wise if the Irish people are to have their electricity generation system changed from an adequate one to a glittering super extravagant one, then they either have to forego their disposable income, ration their use of electricity or try earn more income. Earning more income necessitates burning more fuel in their respective work place. My own domestic electricity bill rose by 5.08% in the first half of 2015.