Wednesday, 02 November 2011
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PQS Data I was recently trying to compare PQS data for direct drive refrigerators. Data for two parameters of prime importance are not always given: - Solar radiation reference period - Power consumption: Stable Running Data is also usually given for 43 deg C and sometimes for 32 deg C. Data at 32 deg C is most useful because it is more typical of average daily temperatures in developing countries. I don’t think there is tropical location where 24-hour average temperatures are near 43 deg C. For the HBC-60 the power consumption at stable running was, 1820 watt hours/day for a 6 KWH/m^2/day and the stated array sizing required was 180 watts. A 180 watt array on a 6 KWH/m^2/day could at most generate 1080 watt hours/day. Am I interpreting the data correctly? Do prices in the PQS sheets include solar panels? This is not always clear. If a direct drive unit needs a battery it would be of value to know the size and type of battery. Array Sizing for Direct Drive Systems There are very few places in the world where the minimum average daily solar radiation is 6 KWH/m^2/day. For reliable system sizing it would be better to give the data for 3.5 KWH/m^2/day or the proposed 4.5 KWH/m^2/day. Unfortunately, average daily solar radiation data for direct drive systems does not give enough information for system sizing. It typically takes about 50 watts of solar power to start the compressors in a direct drive refrigerator. The number of hours a compressor operates cannot be calculated from accumulated KWH/m^2/day data. The same KWH/m^2/day can be obtained for uniformly cloudy conditions or partly sunny conditions, however with these two conditions the number of hours per day the compressors operates per day will probably be different. What is needed to properly size a direct drive system is hourly data, which is unfortunately not available for developing countries. Given this situation, more research is needed into how to size the array for direct drive systems.
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