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| Figure 1. Declining price of solar photovoltaic installaations in the USA |
| Livestock Research for Rural Development 26 (9) 2014 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
A comparison was made of the energy consumption of two types of refrigerator; (i) one operated with 12 volt DC current (imported from China); (ii) a standard 230V AC model produced in Vietnam. The 12V DC power was supplied by 8 solar panels each of 135W capacity, and was stored in 8 deep cycle lead acid batteries each of 80AH capacity. For the 230V refrigerator 4 solar panels were arranged in series to provide 48V which was transformed to 230V AC in an inverter of 1.4 KW capacity. The rated power consumption of each of the two refrigerators was 80W. Power meters were inserted in the input lines to both refrigerators to measure energy consumption.
Electricity consumption was 15% higher for the 230V refrigerator when only the cost of refrigeration was measured and 31% higher when the energy cost of the inverter was also included. Of the electricity required for the 230V refrigerator, 14% was used to invert the current from 12 volts DC to 230 volts AC.
Key words: climate change, decentralization, renewable energy, remore rural areas
Renewable energy derived from solar voltaic panels is an important feature of strategies to reduce global warming and to improve the livelihoods of people living in remote rural areas.
When the second authorof this paper imported solar panels to Vietnam in 1996, the cost was USD 6.00/watt. We recently installed complete solar lighting units for families in the Mekong Delta in Vietnam for an overall price of USD 4.00watt, in which the price of the solar panels was only USD1.2/watt. These costs are in line with recent data from the USA (Figure 1).
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| Figure 1. Declining price of solar photovoltaic installaations in the USA |
The cost of electricity from solar panels could match that from coal within the next few years according to a recent report (Solar to match coal in China by 2016, threatening fossil dominance) , while recent data from Germany shows how solar energy and wind have replaced coal in 2014 compared with the same period in 2013 (Figure 2).
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Figure 2. Solar energy replacing coal in Germany (http://www.renewablesinternational.net/german-power-sector-27-percent-non-hydro-renewable-in-2014/150/537/80072/ |
The current generation of solar panels produces DC (Direct Current) power at 12 volts with varying capacities ranging from 25-50 watts to 500 watts. However, standard electrical appliances use AC (Alternating Current) either at 115V (as in USA and Japan) or 230V as in Europe and Asia. Thus in order to power conventional electrical appliances from solar energy sources the voltage must be inverted to AC current at either 115 or 230V. In order to promote the use of solar electricity there is a need: (i) to develop appliances that use 12V DC current; and (ii) to demonstrate the potential advantages of being able to use 12V DC current directly instead of inverting it to 115 or 230V AC.
The research described in this paper aimed to compare the efficiency of running refrigerators that operated directly on 12V DC current or which used 230V AC current inverted from 12V DC.
The experiment was conducted in the Center for Research and Technology Transfer, Nong Lam University, Thu Duc District, Ho Chi Minh City, Vietnam, from April to August 2014.
The experiment involved a comparison of two refrigerators; (i) one operated with 12 volt DC current (imported from China); (ii) a standard 230V AC model produced in Vietnam.
The 12V DC power was supplied by 8 solar panels each of 135W capacity, and was stored in 8 deep cycle lead acid batteries each of 80AH capacity. For the 230V refrigerator 4 solar panels were arranged in series to provide 48V which was transformed to 230V AC in an inverter of 1.4 KW capacity. The rated power consumption of each of the two refrigerators was 80W. Power meters were inserted in the input lines to both refrigerators (Photos 1 and 2).
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| Photo 1. DC power meter (SkyRC Technology Co., Ltd, China) | Photo 2. AC power meter (Gembird Software Ltd, Netherlands |
The main treatments were the two refrigerators; sub-treatments were L-0: No load in the refrigerator, L-3: 3 kg of fresh bananas; amd L-6: 6 kg of fresh bananas. The bananas were placed in the cool compartment of the refrigerators (10ºC); the freezer section was empty and set at -10ºC. Each treatment was applied over 24h and was repeated three times.
The energy consumption in the two refrigerators was measured with power meters (Photos 1 nd 2). For the 12 volt refrigerator system, the DC power meter was placed in-line between the solar controller and the 12V refrigerator. For the 230V refrigerator system the energy consumed by the whole system was measured by installing the DC power meter in-line between the solar panels and the inverter; while the energy consumed only by the refrigerator was determined with the Energy Saving Power Meter (Gembird Software Ltd, Netherlands) which was set between the inverter and the refrigerator (Photo 3).
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| Photo 3: Location of the power meters in relation to the inverters and charge controllers |
The data for each treatment were recorded for periods of 24h on successive days for each load. The load was changed after 3 days.
The data were analysed by the general linear model (GLM) option of the ANOVA program in the Minitab software (Minitab 2010).
Electricity consumption was 15% higher for the 230V refrigerator when only the cost of refrigeration was measured and 31% higher when the energy cost of the inverter was also included (Table 1; Figures 3 and 4). Of the electricity required for the 230V refrigerator, 14% was used to invert the current from 12 volts DC to 230 volts AC.
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Table 1. Mean values for consumption of electricity (KWh) in 12V and 230V refrigerators with different loads (green bananas of different weights) |
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Voltage |
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Load, kg |
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12V |
230V |
SEM |
p |
0 |
3 |
6 |
SEM |
p |
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Energy consumed, KWh |
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Refrigrator alone |
0.754 |
0.867 |
0.0451 |
0.094 |
0.688 |
0.884 |
0.859 |
0.055 |
0.059 |
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Refrig + Inverter |
0.754 |
0.986 |
0.0485 |
0.04 |
0.738 |
0.937 |
0.934 |
0.059 |
0.061 |
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| Figure 3. Comparison of 12 and 230V refrigerators excluding the energy used by the inverter (for the 230V system) |
Figure 4. Comparison of 12 and 230V refrigerators including the energy used by the inverter (for the 230V system) |
The 31% saving in energy by using a direct current 12V DC refrigerator compared with the 230V AC refrigerator permits a corresponding smaller investment in solar panels used to generate the electricity. Systems employing 12V DC current also have other advantages, including safety from electrical shocks as well as reduced risk of incendieries.
This research is part of the requirement for the PhD of the senior author. Financial support from the Sida-financed project, MEKARN II, is gratefuly acknowledged.
Minitab 2010 Minitab Statistical Software, Release 16.1.1 for Window. (Minitab Inc. State College PA, USA)
Winter, Caroline 2014 "Germany Reaches New Levels of Greendom, Gets 31 Percent of Its Electricity From Renewables", in Business Week, 14 August 2014
Received 25 August 2014; Accepted 30 August 2014; Published 5 September 2014
