5.2 Calculations
5.2.4 General approach
Long-term perspectives for balancing fluctuating renewable energy sources 66
Long-term perspectives for balancing fluctuating renewable energy sources 67 As it can be seen, the criterion that has been followed in order to group the months into the different periods is:
x Winter: months with an average temperature lower than or equal to 10 ºC.
x Spring/autumn: months with an average temperature between 10ºC and 20 ºC.
x Summer: months with an average temperature higher than or equal to than 20ºC.
Therefore, the hourly demand curves provided in section 5.2.2 correspond to the average temperatures of 7.8ºC (winter), 14.3ºC (spring/autumn) and 22.3ºC (summer) respectively.
The calculation of the energy demand curves for each month of the year has been carried out as follows:
x Air-conditioning electricity demand: it is obtained taking as a reference the profile of the corresponding period and modifying it proportionally to the difference between the average temperature of the period and the average temperature of the month considered.
This way, the higher the temperature is, the bigger the electricity consumption is. Due to the third assumption, the obtained curves will be the same for all days of the same month.
x Total electricity demand: it has been supposed that the only electricity consumption that varies along the year is the corresponding to the air-conditioning system. Therefore, the electricity demand without taking into account the air-conditioning is the same for all months of the same period. Total electricity demand is calculated adding to these values, the air-conditioning consumption corresponding to each month that is obtained as it was explained in the previous paragraph. The same as previously, all days of the same month have the same curves.
x Gas demand: this demand is due to both space and water heating. It has been considered that gas consumption corresponding to water heating is the same for all months of the year in contrast to space heating, whose consumption depends on the ambient temperature: the lower the temperature, the higher the consumption, because more energy is required to reach the comfort temperature. The calculation of this variable has been carried out taking into account the deviation of the average temperature of each month in relation to the comfort temperature that has been considered to be 20ºC. The obtained differences will be used to modify demand data corresponding to each period in order to obtain the demand curves for each month. For example, the space heating demand for one day of January at a determined time H will be calculated with the following formula:
D SHJanuary = D SHwinter
) º 8 . 7 º 20 (
) º 6 º 20 (
C C
C C
Where D SHwinter is the natural gas demand for one day of winter at time H, and 7.8ºC and 6ºC , the average temperatures of winter and January respectively. Total gas demand will be the addition of space heating and water heating (D WH) demands. As stated previously, the last one is the same for all days of the year:
D TotalJanuary = D SHJanuary + D WH
From these calculations, the following curves for the total electricity demand, air-conditioning electricity demand and natural gas consumption are obtained. These curves represent the hourly demands for one day of each month:
Long-term perspectives for balancing fluctuating renewable energy sources 68
Total Electricity Demand
0 50 100 150 200 250
0:00 6:00 12:00 18:00 0:00
Time
P(KWh)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 5-14: Hourly electricity demand for each month (Conventional installation)
Air-conditioning electricitiy demand
0 2 4 6 8 10 12 14
0:00 6:00 12:00 18:00 0:00
Time
P (kWh)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 5-15: Hourly air-conditioning electricity demand for each month (Conventional installation)
Gas demand
-100 0 100 200 300 400 500 600
0:00 6:00 12:00 18:00 0:00
Time
P (kWh)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 5-16: Hourly gas demand for each month (Conventional installation)
By adding the values for the whole day, total daily demands can be obtained.
These added values are presented in Table 5-9, Figure 5-17 and Figure 5-18.
Long-term perspectives for balancing fluctuating renewable energy sources 69 Table 5-9: Energy demand for each month (Conventional installation)
Energy demand (KWh/day) Month Total Electricity Air-conditioning
electricity Gas
January 2 706.84 0.00 2 760.57
February 2 706.84 0.00 2 579.11
March 2 706.84 0.00 2 216.19
April 2 953.87 33.35 1 782.82
May 2 964.99 44.47 1 001.48
June 3 205.82 71.62 220.13
July 3 220.14 85.94 220.13
August 3 220.14 85.94 220.13
September 3 209.40 75.20 220.13
October 2 962.21 41.69 1 196.81
November 2 706.84 0.00 2 034.73
December 2 706.84 0.00 2 579.11
Figure 5-17: Daily electricity demand for each month (Conventional installation)
Figure 5-18: Daily natural gas demand for each month (Conventional installation)
The next step consisted in calculating the energy demand curves for the whole year, by making use of the third assumption that supposes that all days of the same month have the same demand for electricity and natural gas.
Long-term perspectives for balancing fluctuating renewable energy sources 70
Total electricity demand
0 50 100 150 200 250
jan feb mar apr may jun jul aug sep oct nov dec
Time
P (kW)
Figure 5-19: Total electricity demand for the whole year (Conventional installation)
Air-conditioning electricity demand
0 2 4 6 8 10 12 14
jan feb mar apr may jun jul aug sep oct nov dec
Time
P (kW)
Figure 5-20: Electric demand of the air-conditioning system for the whole year (Conventional installation)
Gas demand
0 100 200 300 400 500 600
jan feb mar apr may jun jul aug sep oct nov dec
Time
P (kW)
Figure 5-21: Natural gas demand for the whole year (Conventional installation)
Finally, in the following table the total amount of energy demanded in the whole year is presented:
Table 5-10: Total Energy demands for the whole year (Conventional installation) Energy demand (KWh/year)
Total Electricity Air-conditioning electricity Gas
1 073 198 13 404 515 977