poster - International Conference of Agricultural Engineering

them cover similar percentages. During the highest energy consumption (February-March
and October-November) this percentage increases considerably.
Nevertheless, and according to the results, it can be observed that the use of the cheaper
periods (P3 and P2) could be increased in the studied irrigation station. For this reason, it is
possible to move consumptions from P1 period, and even from P2, to P3 (cheapest period),
what would suppose a decrease in energy costs of about 27%.
A recommended general measure is to study the offers of the different companies annually,
since most of them offer great discounts in the first year.
TABLE 2. Energy consumption for lettuce irrigation in the studied farm (2010-2011 season).
Consumption period
Active Energy
Consumption (kWh)
Reactive Energy
Consumption (kVAr)
Average
Cosine of phi
Monthly Bill (€)
June 2010 9,049 3,982 0.92 1,708.44
July 2010 2,660 2,068 0.79 561.36
August 2010 247 227 0.74 141.63
October 2010 11,670 5,857 0.89 2,032.33
November 2010 10,735 3,491 0.95 1,723.95
December 2010 5,018 0 0.95 1,708.44
January 2011 5,688 7,598 0.60 1,845.23
February 2011 11,816 6,632 0.87 2,071.15
March 2011 10,515 6,947 0.83 2,091.63
TOTAL 67,398 36,802 0.89 12,175.71
Another feature to be taken into account is the correction of the power factor to values over
0.95 in order to decrease the reactive energy consumption. For this purpose, an automatic
capacitor bank is installed in the electric circuit. This way, a low value in the power factor or
cosine of phi (see Table 2) may be due to the next reasons:
Bad design of the automatic capacitor bank, since every month a surcharge depending
on the reactive energy is applied. In this study, the power factor values were under
0.95 except in December of 2010. Concretely, the surcharge for a power factor value
between 0.8 and 0.95 is 0.041554 €·kVArh-1.
Bad system maintenance. In this study, decreases of the power factor, and
consequently an increment of the penalization, were registered in the monthly bills.
This could be caused by the failure of one of the condensers. During January, a power
factor of 0.6 was registered, what involves a penalization of 0.062332 €·kVArh-1. This
supposed a surcharge of 132.3 € in a bill of 1,845.23€.
The budget to repair the automatic capacitor bank is around 125€, whose cost could be
recovered in a month. If a redesign of the automatic capacitor bank is chosen instead, the
return period of the investment can increase up to 18 months. This measure will only
decrease the costs produced by the reactive energy, but not the energy consumption costs.
Maximum values of energy consumption (see Table 3) were registered during October of
2010 (seedling phase in three plots and beginning of rosette formation in one plot), January
of 2011 (beginning of rosette formation in three plots, rosette formation phase in a plot and
seedling phase in two plots), February of 2011 (rosette formation phase in four plots,
beginning of rosette formation phase in two plots and seedling phase in one plot) and March
of 2011 (heart formation phase and harvesting in two plots and rosette formation phase in
five plots). During these months, highest demands of lettuce crops were registered. The total
water volume was estimated for every cited month: 58,630 m 3 (October 2010), 28,724 m 3
(January 2011), 59,671 m 3 (February 2011) and 53,100 m 3 (March 2011).