In this study, two cleantech measures in the production of cow-feed were considered: the reduction of electricity demand by integrating a variable frequency
drive for the electric motor of a centre pivot irrigation system (“VFD”) and the use
of solar electricity for irrigation (“solar”).
To assess the influence of the cleantech on the environmental impact of milk, it
was assumed that cleantech is used in all irrigated feed production, i.e. silage maize,
grain maize (in concentrated feed) and grass irrigated on the farms. For purchased
feed, the share of irrigated feed on total is based on the South African average share
between 2006 and 2013 [17].
Electric motors are most efficient when they are running at their maximum
capacity. Current irrigation systems running at their maximum capacity, regardless
of the current water demand, use more electricity than needed for irrigation.
Variable speed drives allow the regulation of speed and rotational force—or torque
output—of the motor in accordance with the actual demand. The centrifugal pump
on irrigation systems has particularly high potential to save power. A subcategory
of variable speed drives are variable frequency drives: they combine a converter and
an inverter with a control unit in between to allow adjustment of the frequency,
which changes the speed of the motor. A 30% reduction in electricity use of the
water pump [19] was used for this model.
Photovoltaic electricity for irrigation in South Africa was modelled based on a
570 kWp open ground multi-crystalline silicon power plant in the ecoinvent
database [11, p. 3]. The city Welkom, lying in the main maize production region
(Northwest and Free State), was used for the estimation of the photovoltaic yield.
An annual photovoltaic yield of 1770 kWh/kWp is expected for that city according
to PVGIS of the Joint Research Centre [20]. For the calculations, a lifetime of
30 years for the photovoltaic modules was used, with a yield degradation of 0.7%
per year. This corresponds to an average loss of 10% of the yield per year
(1593 kWh/kWp, including degradation). These assumptions correspond to the
recommendations of the IEA [21]. The module (22.1 m
2 ) has an efficiency of
13.6% (module area of 7.4 m
2 /kWp), resulting in an annual yield of 216 kWh/m
2
of module. It was assumed that the total electricity demand for irrigation was met
using solar electricity, replacing grid electricity from South Africa.
4 Life Cycle Impact Assessment
Different breeds (A)
The greenhouse gas emissions associated with the production of raw milk on the
five farms in KZN varied between 1.2 and 2.0 kg CO 2 -eq/kg. A study on milk from
Western Cape supports these findings, with 1.0–1.6 kg CO 2 -eq/kg raw milk [5].
The production mix for raw milk had a carbon footprint of 1.5 kg CO 2 -eq/kg.
120
R. Keller et al.
drive for the electric motor of a centre pivot irrigation system (“VFD”) and the use
of solar electricity for irrigation (“solar”).
To assess the influence of the cleantech on the environmental impact of milk, it
was assumed that cleantech is used in all irrigated feed production, i.e. silage maize,
grain maize (in concentrated feed) and grass irrigated on the farms. For purchased
feed, the share of irrigated feed on total is based on the South African average share
between 2006 and 2013 [17].
Electric motors are most efficient when they are running at their maximum
capacity. Current irrigation systems running at their maximum capacity, regardless
of the current water demand, use more electricity than needed for irrigation.
Variable speed drives allow the regulation of speed and rotational force—or torque
output—of the motor in accordance with the actual demand. The centrifugal pump
on irrigation systems has particularly high potential to save power. A subcategory
of variable speed drives are variable frequency drives: they combine a converter and
an inverter with a control unit in between to allow adjustment of the frequency,
which changes the speed of the motor. A 30% reduction in electricity use of the
water pump [19] was used for this model.
Photovoltaic electricity for irrigation in South Africa was modelled based on a
570 kWp open ground multi-crystalline silicon power plant in the ecoinvent
database [11, p. 3]. The city Welkom, lying in the main maize production region
(Northwest and Free State), was used for the estimation of the photovoltaic yield.
An annual photovoltaic yield of 1770 kWh/kWp is expected for that city according
to PVGIS of the Joint Research Centre [20]. For the calculations, a lifetime of
30 years for the photovoltaic modules was used, with a yield degradation of 0.7%
per year. This corresponds to an average loss of 10% of the yield per year
(1593 kWh/kWp, including degradation). These assumptions correspond to the
recommendations of the IEA [21]. The module (22.1 m
2 ) has an efficiency of
13.6% (module area of 7.4 m
2 /kWp), resulting in an annual yield of 216 kWh/m
2
of module. It was assumed that the total electricity demand for irrigation was met
using solar electricity, replacing grid electricity from South Africa.
4 Life Cycle Impact Assessment
Different breeds (A)
The greenhouse gas emissions associated with the production of raw milk on the
five farms in KZN varied between 1.2 and 2.0 kg CO 2 -eq/kg. A study on milk from
Western Cape supports these findings, with 1.0–1.6 kg CO 2 -eq/kg raw milk [5].
The production mix for raw milk had a carbon footprint of 1.5 kg CO 2 -eq/kg.
120
R. Keller et al.