[MUSIC] Hello,the variability of renewable electricity production is often mentioned as the main constrain for their massive integration in the electric network. However, the availability of the resource is not the only source of variations in a power system. The demand for electricity or load, also varies and leads to a wide range of capacity factors for power plants. I will give in this session, few examples and quantitative numbers for standard power units. If we first consider for instance the wind energy in Germany. The media often emphasize on the rapid increase of the install capacity in gigawatt. However, the relation between the install capacity and the annual energy prediction is not direct. If we look at a typical wind turbines, the wind power is highly intermittent. And the wind turbines operate below their nameplate capacity. In 2014, the installed capacity of wind turbines in Germany was about 39 GW, while their annual energy production was about 56 TWh. To quantify the relation between the installed capacity and the energy production, we introduce the capacity factor. Which is the ratio of the annual amount of energy produced by a given power unit, divided by the amount of energy the unit would have produced at full capacity during one year. If we consider all the German wind farms, we get in 2014, a mean capacity factor around 16%. This value is not constant and may change from year to year due to the interannual wind variability. Note that a typical interannual wind fluctuation of 10% will lead to wind power variability of 30%. If now we consider the hydropower generation in comparison with wind and energy. The availability of the resource is high, with a relatively weak variability. What could then be the mean capacity factor of all the hydropower units in France? Try to give a rough estimation. Let's see what is the correct answer. In 2012, the installed hydropower capacity was about 25 GW, and the annual energy production of 67 TWh. Hence the corresponding capacity factor for all the French hydropower units is on average, 30%. If we consider individual hydropower units, the capacity factor may vary from 9 to 50%. And this wide diversity is not related here to the availability of the hydraulic resources, but to the variability of the demand. If now we consider fossil fuel power plant, for instance, the Porcheville thermal power plant which is near Paris. This power plant has four units of 600 MW each, leading to a total power capacity of 2.4 GW. In 2013, the annual energy production was about 139 GW power. Which is very small indeed. If we calculate the capacity factor, we get less than 1%. In fact, the Porcheville plant is a big load power plant, which supplies power only occasionally when there is a high demand in the Paris area. This extreme case shows that the capacity factor of a given power unit is not directly related to the availability of the resource. Other examples of power units could be nuclear reactors. The nuclear power plant of Cruas-Meysse contains 4 reactor of 900 MW each. For a total power capacity of 3.6 GW. The annual production could reach 24TWh, which leads to capacity factor about 76%. Nuclear power plants may take hours or days through change the power output. Hence, they are typical base load plants, they run all times the year. Except in the case of repairs or maintenance. Hence, such units may reach high capacity factors. As far as renewable power plants are concerned, geothermal units could also reach similar capacity factor. The Bouillante geothermal power plant, in the Guadeloupe island, produces 95 GWh per year for a power capacity of only 15 MW. Hence the annual capacity factor reach almost 73%. We have just seen that the variability of the electric pollution could be due to the fluctuation in the resource, but also variation in the demand. If we focus on the electricity demand, it varies both on the daily or a seasonal time scale. The daily cycle follows a regular pattern, with a large variation the course of the day. There is almost 40% of increase in the electricity demand between night time and the daily peak, which is around 7 PM. This significant fluctuation the daily demand induces strong pice situations on the wholesale market of electricity. The price variability is directly correlated to the demand with amplified fluctuations. If the demand increases by 40% the electricity price may double. According to this typical chart, the lowest price could be around 30 euro per megawatt hour in the middle of the night, why? It reaches it's average value during lunch time, and raise up to it's highest value around 80 euro per megawatt hour at the peak demand in the late afternoon. For this example, the peak price is almost three times higher than the lowest price of the day. But in some specific cases, when the demand exceeds the usual capacity production, the peak price could be ten times higher. If now we look at the annual variations of the electricity demand, we can see a clear seasonal cycle, with high demands in winter, and smaller demands during summer months. On the top of this seasonal cycle, we could also detect some smaller fluctuations which are directly linked to banks holidays just such as Easter, the Feast of the Ascension, Whit Monday, or the 15th of August, which is, in France, the day of the year with the lowest economical activity. Almost everyone is in vacation the 15th of August in France. The second low in the demand is related here to Christmas holidays and new year eve. These few examples shows that all the sources of electricity, renewable or not, may experience significant power fluctuations, in order to match the valuable demand. Some specific renewable resource could fuel base load power plants with high capacity factors, and on the other hand, some fossil fuel power plants which are used as peak plant, could have capacity factors much lower than intermittent wind farm.
