A simple model: solar versus wind

Recently, I learned that that demand response (a change in energy consumption in order to deal with intermittency) would be more problematic for increasing solar capacities and easier for increasing wind capacities. Initially, that seemed a bit contra-intuitive to me. Solar is doing best during the day when most power is needed, so until then I assumed that it would be easier for demand to follow solar power (coinciding with the demand pattern) than wind power (which is more erratic).

However, there are some things that might interfere with that reasoning. For example, sunny weekends or holidays could spell trouble (high production, yet low demand). More, at our latitude, solar produces most power in summer when least power is needed and least in winter when most power is needed. This however allows for building backup during the summer months to be used later when there is a shortage.

The dynamics of wind power is different. At our latitude, there is more wind in winter when we need most power and less in summer when we need least power. It is however not guaranteed to blow when demand is high and then it also requires some kind of backup/storage.

Looking at it over a longer time frame, demand should follow wind better, potentially decreasing the need for demand response. Time to adapt my simple energy model to find out.

Until now, the capacity of both power sources were increased together relative to their current capacity. To find the impact of both energy sources separately, I needed to decouple solar and wind capacity. I forked the model with the unlimited storage to be able to see what is happening in storage. I also wanted the results of solar and wind next to each other, so I also had to tweak the output graphs.

I will stick with the same scenario of the last three posts where there is already some charge in storage at the beginning of the year and a leveled capacity of 3,369.05 MW for solar and of 3,157.185 MW for wind.

At first, I was not sure how to tackle the question. After playing around with the model, I decided to keep solar at zero while increasing wind, following by doing the opposite (keeping wind at zero and increasing solar). Then I could put them side by side for comparison. This is not a scenario that exists in reality, but it will show the differences between solar and wind clearly.

The problem with that approach is that to be comparable, both solar and wind need to produce the same power per year. This is not the case in previous versions of the model, I assumed that both power sources would increase at the same pace. Solar has a lower capacity factor than wind, so I can’t just compare for example 5x solar with 5x wind. At our latitude, the capacity factor of solar is around 12% and that of wind is around 24%, so I would need to double the multiplier of solar compared to wind.

Unfortunately, the capacity factors of solar and wind are not exactly 12% and 24%, so it is not as simple as doubling the multiplier. With some trial and error, I came to 1.904685 times before the production of solar and wind was exactly the same in the reference year.

That being done, this is is the result for 10x current capacity of wind and 19.05x of solar (these capacities produce the same amount of power over one year):

simple energy model (charts007d) - belgium - solar x10 and wind x19.05 - reference year: 2018 - with_unlimited_storage

The blue line is total load and the orange line is renewables load (click on the picture for a bigger view). Where the orange line is visible, there was a shortage at that timeslot. The deeper the orange line, the bigger the shortage. Clearly visible is that solar has issues both at the start and at the end of the year, while wind has problems during the summer/beginning of autumn.

There is a dramatic difference in storage. Solar power storage peaks in summer and then draws empty in a couple months, leaving nothing in storage at the end of the year. Wind power storage stay relatively low over the entire timespan (although 2,000+ GWh is still incredibly high for storage).

Let’s crank it up a notch:

simple energy model (charts007d) - belgium - solar x15 and wind x28.57 - reference year: 2018 - with unlimited storage

Solar still has some problems at the beginning of the year (January until April). Wind has some problems too, but it amounts to just a few hours in January, so wind is very close to the point where enough power is produced to cope with demand over the year when storage is included.

Looking at storage, the same is happening as in previous run. Solar builds up considerably from April until after summer and then power is getting drawn from it, leaving quite a lot in storage for the next year. The needed storage capacity of wind stays again low relative to solar (although almost 11,619 GWh is a shitload of storage).

Let’s look at the numbers, comparing equal production of solar and wind:

Solar Wind
  Production Solar minus total load Storage   Production Wind minus total load Storage
  range (MW) lower limit (MW) upper limit (MW) Minimum needed backup
Maximum in storage
  range (MW) lower limit (MW) upper limit (MW) Minimum needed backup
Maximum in storage
9.52x 25,021.28 -13,310.82 15,475.80 13,310.82 98.72 5x 13,619.28 -13,011.65 4,228.79 13.011.65 107.79
14.29x 37,531.91 -13,310.82 27,808.11 13,310.82 1,351.9 7.5x 20,428.92 -12,862.06 10,672.13 12,862.06 646.24
19.05x 50,042.55 -13,310.82 40,140.43 13,266.46 8,550.5 10x 27,238.55 -12,754.19 17,385.71 12,745.81 2,017.60
23.81x 62,553.19 -13,310.82 52,472.74 13,266.46 19,309.17 12.5x 34,048.19 -12,737.39 24,099.29 11,024.68 5,371.50
28.57x 75,063.83 -13,310.82 64,805.85 13,235.47 31,956.13 15x 40,857.83 -12,720.59 30,812.87 4,357.87 11,618.78

Everything points in the same direction, whether looking solely at production or comparing it with total load or looking what is happening at the storage side. Comparing the same production of solar and wind, solar has more extremes:

  • there is a wider range of production (almost double that of wind)
  • lower limit (deficit side) stays low for longer
  • upper limit (surplus side) is two to three times higher
  • minimum needed backup decreases very slowly
  • more storage is needed (except at smaller multiplication levels).

That is bad news when it comes to demand response. It means that, for it to be effective, more effort will be needed for solar than for wind. The statement that solar will make demand response difficult at higher capacities is correct, but at first glance, wind doesn’t do that much better.


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