dr Lars Schernikau, energy economist and commodity trader, Switzerland/Singapore, https://www.linkedin.com/in/larsschernikau/
It’s time to talk about “capacity factors”.
In power generation capacity factor, utilization and load factor are not the same.
There is much confusion in the press and certainly in politics and even among “energy experts” about the use of the term “capacity factor”. Apologies, as the distinction made in this article only became relevant with the encroachment of variable “renewable” energies such as wind and solar into our energy systems.
- The world average natural capacity factor (CF) of the sun reaches about ~11-13%. The best locations in California, Australia, South Africa and the Sahara can have over 25% but are rare. (see www.globalsolaratlas.info, set direct normal solar radiation)
- World average natural wind capacity factors (CF) reach around ~21-24%. The best offshore locations in Northern Europe can reach over 40%. Most of Asia and Africa has little usable wind and the average CF would be below 15%, except for small areas on parts of the coasts of South Africa and Vietnam. (see www.globalwindatlas.info, medium power density setting)
Natural capacity factors in Europe tend to be higher for wind than for solar. Wind installations in Northern Europe can average over 30% (higher for more expensive offshore, lower onshore) but less than 15% in India and less than 8% in Indonesia. On average, and the emphasis is on the average, annual solar PV capacity factors reach around ~10-11% in Germany, ~17% in Spain, ~25% in California and can reach 14-19% in India, but they reach less than 15% in the populated areas of Indonesia. Carbajales-Dale et al. 2014 confirm higher capacity factors for wind than for solar; They estimate global average wind capacity factors to be around 21-24% and solar capacity to be around 11-13% (see figure above).
The figure below shows a two week period in May 2022 (when I was writing this chapter of our book on capacity factors) when the average wind capacity factor for ALL German wind turbines (onshore and offshore) only reached ~5%.
To avoid confusion, I try to use the “natural capacity factor” in my writing wherever possible
- That “natural capacity factor (CF)” is the percentage of the maximum possible output of the “power plant” (coal, gas, nuclear, solar, wind, water, etc.) that will be achieved under the natural conditions of the site, provided that there are no operational or technological failures or failures.
- I define “recovery” is the annual average used percentage of the power plant’s usable capacity that is reduced only due to technological, operational, economic failures or limitations … completely independent of the CF
- That “net load factor“ – in my definition – is then the product of the natural capacity factor x utilization
So when we speak of the natural capacity factor, we are only referring to that derived from nature capacity factor, not the technologically or operationally driven “recovery‘ (often referred to as uptime, plant load factor or PLF). In other words, if technology fails or a power plant is intentionally shut down, it reduces utilization but not the natural capacity factor.
As mentioned earlier, the natural capacity factor is due to the location, not the PV array. Thus, even a perfect PV material still has to cope with natural capacity factors of 10-25% annual mean, without considering other losses from conditioning, transmission, balancing or storage of highly intermittent power sources (Schernikau and Smith 2021). .
The press has mentioned several times that have coal or gas capacity factors averaging 60% or less. This is misleading at best, knowingly wrong for political reasons. However, such a number is not the inherent capacity factor; it’s the recovery which decreases with increasing wind and solar penetration and contributes to an increase in electricity system costs.
Utilization can and should never be compared to natural capacity factors, they vary greatly. Conventional power plants have almost 100% natural capacity factors, but their operational and technological utilization is often well below 90%, also but not only because of the priority of wind and sun in the system. Due to their high CF, the net load factor is only slightly lower than recovery for a conventional power plant.
Since the use of wind and sun is often close to 100%, their net load factor is often only slightly lower than theirs natural capacity factor.
Figure: Germany’s wind generation from April 25 to May 10, 2022 during a 2-week wind calm
Source: Agora 2022, Figure 10 in book The Unpopular Truth… about Electricity and the Future of Energy, www.unpopular-truth.com
Of course, the natural capacity factor of wind and sun (even for hydropower due to natural river flows) cannot be predicted or guaranteed for any specific time frame. The natural capacity factor can be estimated on an annual basis, but also fluctuates greatly annually (see Europe in 2021) and is very erratic, sometimes for days and weeks, reaching almost 0% for wind and solar even in top locations.
Hence, natural capacity factors worldwide result directly from the location of the wind or solar system; they are in no way dependent on the technology used and cannot be influenced by it. The last point is important…no advance in technology can change the natural availability of wind, solar or river power and therefore affect the natural capacity factor for any given facility. Technology CAN and WILL improve how much usable electricity you get from the natural input product (wind, sun, river flow, gas, coal, uranium, etc.). This is called conversion efficiency and its limitations are discussed below.
As the easy sites are already “depleted,” average natural capacity factors are expected to decline over time…unlike what Net Zero plans assume (see International Energy Agency (IEA), McKinsey & Company, or International Renewable Energy Agency). (IRENA)).
- For a photovoltaic (PV) park, the natural capacity factor CF depends entirely on the intensity and duration of sunlight, which is affected by the season and cloudiness day and night, and the ability to maintain transparency of the PV module surface, e.g. B. dust in the Sahara or snow in winter.
- The natural capacity factors of wind farms depend on the wind speed distribution of the site and the saturation speed of the wind turbine. The CF of a wind turbine is determined by the number of hours per year that the wind farm operates at or above the saturation wind speed (Smith and Schernikau 2022). If the design wind saturation speed is set low, e.g. B. 4-5 m / s, the wind farm produces little energy even with high capacity factors. Typical wind saturation speeds are 12-15 m/s.
Now it becomes clear why the installed capacity for wind and sun has to be much larger than for available energy such as nuclear energy, coal, gas or hydroelectric power. This significant relative increase in power generation capacity to produce the same available but unpredictable power output is coupled with a significantly higher feedstock input and energy input factor for variable “renewable” energy, which must be offset against any fuel savings.
#Germany is a good example: the total installed capacity has more than doubled in the last 20 years and consists essentially exclusively of wind and sun (see figure below).
- The installed wind and solar capacity is now over 125 GW, more than 150% above the peak electricity demand in Germany of around 80 GW
- Germany’s conventionally installed capacity from coal, gas and nuclear energy still barely covers the peak electricity demand
- With all this capacity growth in Germany, in 2021 wind and solar accounted for less than 30% of total electricity generation and about 5% of total energy consumption
Figure: German installed capacity, power generation and primary energy
Source: Schernikau Research and Analysis based on Fraunhofer 2022, AGE 2021, Agora 2022
Figure 7 in book The Unpopular Truth…about Electricity and the Future of Energy, www.unpopular-truth.com
The low natural capacity factor of wind and solar systems is undoubtedly one of the main reasons for their low net energy efficiency (https://dx.doi.org/10.2139/ssrn.4000800).
For conversion efficiency
The figure below summarizes the energy conversion efficiencies for wind and solar and the laws they follow. Conversion efficiency measures the ratio between the usable output of a power conversion machine and the energetic input, i.e. after accounting for the capacity factor.
Figure: Laws of physics limit technological improvements for wind and solar
Source: Schernikau and Smith Research and Analysis, Figure 11 in book The Unpopular Truth… about Electricity and the Future of Energy, www.unpopular-truth.com
More details can be found in our book “The Unpopular Truth… About Electricity and the Future of Energy“ (on Amazon)… or www.unpopular-truth.com
This article is also available at
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