Power demand and supply Daily load curves

In the British system covering England, Wales and Scotland, the total daily power demand varies between a minimum summer load of about 22.4 giga-watts (GW) and a winter peak above 59.4GW (National Grid, 2006). Figure 1.8 illustrates the demands during the two days, with minimum and maximum demands, respectively, over the 12-month period of 1 July 2005 to 30 June 2006, the areas under the curves representing daily energy demands/supplies and the heights of the curves representing the average half-hourly power demands. Here, the annual base load can be seen to be of the order of 22GW; but, with peak load occurring during the winter, the daily base loads would have higher values over the periods during the winter months.

To meet the continuously changing power demands, a mixture of different types of generation plant with varying degrees of responsiveness is needed to meet the base load, mid range and peak loads. Large predictable daily changes in demand or variable output from renewable generation plant are met by scheduling and contracting the conventional generation as appropriate. However, the load also fluctuates continuously in a random manner on a much smaller scale within a few percentage of the expected value. Generation of power, including all the variability of the power output of renewable sources, has to equal load plus losses at all times. As a result, balancing generation from spare plant has to be brought in and out of the system by the National Grid as required. Some of this spare capacity would be on 'hot standby' (i.e. connected to the network and operating at part load to ensure a stability of connection, as in the case of steam plant) or available for instant start-up and connection (as is the case for hydro, gas turbine and standby diesel plant).

Source: www.nationalgrid.com/uk/Electricity/Data

Figure 1.8 Daily load variation on the UK National Grid system showing maximum and minimum demand days from 1 July 2005 to 30 June 2006

Source: www.nationalgrid.com/uk/Electricity/Data

Figure 1.8 Daily load variation on the UK National Grid system showing maximum and minimum demand days from 1 July 2005 to 30 June 2006

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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