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Capacity Factor (CF), an indicator for the performance of a power plant, is the ratio of the actual energy generated by the plant in a year to its potential (the product of the rated power of the plant and 8766 hours in a year). The theoretically maximum potential of electricity produced by a 1000MW (or 1000MWe) plant operating non-stop for 24 hours a day for 365 days would be:

(1000MW) x (365 x 24 hours) = (1000MW) x (8760 hours) =8.76 billion kWh

A 1000 MW generating plant that produces half of this figure (4.38 billion kWh) in a year is said to have a CF of 50%. The value of CF is high for conventional energy sources (coal, nuclear, gas, major hydro with dams and oil); - the largest values above 80% are for nuclear and coal plants, which are usually used for based load power generation. On the other hand CF for renewable energy sources is rather low, typically about 12-20% and 20-35% for solar and wind energies respectively.

 

Performance of Hydropower
In Table1 are installed capacities and the corresponding generated electricity of the first five largest hydropower plants in the world. The calculated values of CF are given in the last column of the table; - 73 and 76% are among the highest for hydropower plants.

Table 1: Capacity Factor of the Five Largest Hydropower Plants

Note: The data in the third and fourth columns were extracted from an article on Hydroelectric by PESWiki, sponsored by Pure Energy System, - contact www.peswiki.com

It is also very interesting to study the average CF of hydro-generated electricity for the twelve European countries, specially selected to highlight the conditions that favour hydropower. The installed capacity in the fourth column of Table2 is the total for major plants with dams, micro hydro plants or run-of-river plants and pumped storage plants. The four nations that produce about 50% to almost 100% of their power from hydro are Sweden, Switzerland, Austria and Norway. They are all in the mountainous areas in the coldest part of Europe. Belgium and the UK have negligible contribution from hydro, but in the case of Denmark and the Netherlands (with many canals), generated power from hydro is virtually zero. Note that the average CF for hydro plants in Europe, with better precipitation in the form of rain and snow, and relatively lower evaporation, could be less than 50%.

 

Table 2: Average CF of Hydro-generated Electricity in a Few Selected European Nations

Note: The data in the second, third and fourth columns were extracted from a table in an article in Euro Wasser: Europe’s Hydropower Potential Today and in the Future. The authors were Bernhard Lehner et al. University of Kessel, Germany 



Performance of Wind Power
In Table 3, the average number of Hours of Equivalent Full Power for operating wind-power plants Europe is only 1973 out of the total of 8760 hours in a year. The ratio of these two numbers has been taken as the Estimated CF given in the table. They are
generally higher than the usual calculated values using installed capacity and annual electricity production from many sources. Using such data from the Complete 2001 Energy Resources, by the World Energy Council, CF for wind-power in Ireland, the UK, Denmark and Germany were found to be about 32, 30, 20 and 19% respectively. Similar calculations done for Germany with the data from Renewable Energy Made in Germany, by the German Federal Ministry of Economics and Technology, the CF for wind-power in Germany for in 2005 was only 16.4%.

Table3: Hours of Full Power Equivalent for Wind Plants in Europe

Countries	Installed  Power (MWe)			Production  in 2002 (TWh)	Hours of Full Power  Equivalent	Estimated  Capacity Factor (%)
	2001	2002
Germany	8 754	12 001		19,4	1 869	21.3
Spain	3 337	4 830		7,66	1 875	21.4
Denmark	2 417	2 889		5,92	2 231	25.5
Ireland	125	138		0.30	2 509	28.6
Italy	697	785		1,47	1 983	22.4
Netherlands	493	688		1,2	2 032	23.2
UK	474	552		1,48	2 884	32.9
Europe	17 250	23 059		39,77	1 973	22.5

Note: 

Let us sum up with some comments made by Professor Wolfgang Pfaffenbeger, an expert energy analysts and Director of the Bremen Energy Institute in Germany, from BBC News World Edition, posted on the website on 25-02-05. The professor, apparently skeptical about the potential of the vast number of wind turbines in Germany said: “The specific problem is that you cannot always have the wind when you need the energy”. He added: “That is why at the moment more than 15% of our capacity is wind power, but produces only 3% of our energy”. He also said that an average kilowatt from wind cost about 10 cents, whereas the average cost of electricity on the market is only about one-third of this”.

Capacity Factor of Solar Photovoltaic (PV)
CF for solar power is lower than that of wind power, and it ranges from about 10-20%. According to a paper on Freiburg Solar City, in 2003 the total installed PV capacity of about 3200 kW in the Solar Region Freiburg in south-west Germany produced 3 million kWh in that year. When 3 million kWh is divided by (3200 kW X 8766 hours), we get 0.1070 which corresponds to CF of 10.7%. The first sentence of the last paragraph reads: “Solar PV and other renewables still only provide 2% of the power that Freiburg needs.”


Intermittency of Solar and Wind Power Plants
Beside the fact solar and wind energies are so diffuse that it takes a lot of space and expensive hi-tech materials to harness their energy with a relatively little output, they are also intermittent. Hence solar or wind power can not be used as a dependable, stand-alone power supply for the needy communities in SSA. Any back-up for them makes the already high unit cost of electricity generated from these sources still more expensive. Where the produced electricity has to be stored for use later, one has to be aware that a bank of batteries for that purpose is not only very expensive, it also diminishes the produced energy, - for energy is always lost during charging and discharging of a battery, and it gets worse with time. Handling of old and damaged batteries as well as used chemicals without proper supervision can lead to very serious environmental damages.

The intermittency of solar and wind energies makes them also less desirable to many utilities that have to guarantee a steady power supply to their customers, especially their supply to hi-tech industries. That is why the share of the most often touted wind and solar energies in global electricity production is still negligibly low as shown in Table4, Fig1 and Table5, all from very competent sources. The share of RES in the power production in the US for the year 2000 is given the third row of Table4. The share of wind and solar in that year was 0.13 and 0.02% respectively.

Wind and solar energies are free and inexhaustible, yet the industrialized countries with the latest technologies and insatiable appetite for energy, do not get much from them. That is why such countries are earnestly engaged in clean-coal technologies of capturing and sequestration of carbon dioxide from fossil-fuelled power plants. Though such untested technologies are expensive, they are still attractive simply because they can provide more reliable and meaningful power than RES.



Table4: The Share of RES in Electricity Production in the US

	TOTAL ELECTRICITY	TOTAL RENEWABLE	HYDRO  ELECTRICITY	BIOMASS	GEO- THERMAL	WIND	SOLAR
Production Million of kWh	3,799,944	362,715	278,633	64,088	14,197	4,953	844
% of Total Electricity	100.00%	9.55%	7.33%	1.69%	0.37%	0.13%	0.02%
% of Total Renewable	-	100.00%	76.82%	17.67%	3.91%	1.37%	0.23%

From the website: August 2001 Testimony of David K. Garman of Energy Efficiency and Renewable Energy, U.S. Department of Energy.

The main message from Table4 is that the share of non-hydro RES such as wind and solar in electricity generation is negligibly low. The message is the same in Fig1 and Table5. Fig1 is on 2003 Renewables in Electricity Production in the world, while Table5 is on Production of Electricity (World 2001). .


Fig 1


Table 5



Comments: It is quite apparent that the annual electricity consumption per capita of 435 kWh given in Table5 is for SSA including South Africa, whose consumption accounts for about two-thirds of electric energy consumed in SSA. So it does not reflect the real situation in SSA where the value for a greater number of countries is far below 100 kWh, and negligible in several cases. The ratio of electricity consumption per capita in several countries in SSA with that in North America could be 1:200. Hence SSA needs a massive injection of a reliable power supply at affordable cost to give the necessary impetus to accelerate poverty eradication in SSA. That will not be achievable when we are limited to mainly RES. That will perpetuate and deepen the already huge imbalance of quality of life between the rich and the poor nations in SSA.





Performance of CES
Unlike RES, whose performance, limited by vagaries of nature, is not dispatch-able, the performance or choice of CES is influenced by external forces such as geo-politics, economics, and in some cases by the industrial actions. So many factors influence the choice of options for power generation. It is interesting to note the combination of energy sources in OECD nations. For Canada and Australia their first choice is hydro and coal respectively, whilst the OECD Europe and Japan that are not endowed with their own indigenous energy sources like the USA and Canada, nuclear is the largest single option.
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Fig 2



CF for hydro, limited by nature is low, but the fact it can be started more quickly than the other options, makes it a suitable the peak load generation that may last for a few hours. a peaking option changes and may have a very low

The data of installed capacity and annual power production in Table 6 was on the Characteristics of Swiss Power Generation Sector. The calculated values of CF in the last column were not part of the original table. The table shows that the installed capacity of nuclear in 2000 was about three times less than hydro, yet its share in the annual power generated was higher than that of hydro, indicating that nuclear produces electricity more abundantly than the other sources, hence CF for nuclear in the table is the highest.


Table 6: Characteristics of Swiss Power Generation Sector in 2000

Swiss Federal Office of Energy, Bern

 

Note that hydropower is in two groups; - run-of-river and the usual hydro plants. The other type used in Switzerland, but not mentioned in the table is Pumped Storage, which is based on recycling of water. Such plants consume more energy than they produce, but they are economically viable in countries, where there is an abundant power supply at affordable cost from preferably clean energy sources such as nuclear energy. In such cases, water is pumped up from a lower reservoir into an upper one in the nights, when power is available at a much lower unit cost. Since hydro responds to changes much faster than the other energy sources, pumped storage, described as peaking plants, are operated only during the high peak periods, when the unit cost is very high.

Base, Intermediate and Peak Load
Electricity in advanced countries is produced under two or three categories, namely base, intermediate and peak load generation. By the rule of thumb, energy sources which are reliable and produce electricity abundantly at affordable cost are suitable for base load generation. In Fig 3 is U.S. Electricity Production Costs for nuclear, coal, gas and oil. Note that in the US coal-fired plants are constructed close to coal mines. Unlike Europe, the US has no carbon tax for fossil fuels.

Figure 3

 

Source: Nuclear Energy Institute
Note: the above data refer to fuel plus operation and maintenance costs only, they exclude capital, since this varies greatly among utilities and states, as well as with the age of the plant

CF for hydro, limited by nature, is low. But the fact that it can be started more quickly than the other options, makes it suitable for the intermediate or peak load generation. The low value of CF for oil and gas means they are sparingly used due their high cost. It is clear that coal and nuclear are the main options for base load generation in the US. The table confirms that the share of electricity production from non-hydro RES is very low.

Table 7: U.S. Capacity and Market Share by Fuel 2000

Energy Information Administration, Washington DC, USA