Many interesting stories can be written about the pioneering and highly energy efficient CoolTek Home (2005), designed by Harry Boswell and Stephanie Bacon for their retirement in Malaysia. This article, however, will focus on their roof solar photovoltaic system, which was installed in 2007 and was the first solar system in Malaysia to come under the Feed-In Tariff (FiT) in 2012; an economic subsidy scheme to make solar photovoltaic installation economically attractive.
Stephanie Bacon has kindly shared her meticulous energy recordings of the solar photovoltaic system (PV), namely monthly solar electricity production readings as well as written records of when the solar panels were manually cleaned. There's great value and lessons to be learned from this unique and complete 14-year record for this pioneering domestic solar photovoltaic installation in Malaysia.
Solar Photovoltaic System
The 4.8 kWp (kilowatt peak) grid-connected solar system used 40 solar photovoltaic panels from Mitshubishi Electric. The panels were installed on white metal roof with 15 degree tilt from horizontal. The panels were distributed equally on the roof surfaces facing North and South, respectively.
The CoolTek house is located along the golf course inside the Tiara Melaka Golf & Country Club. The exact location of the CoolTek house at latitude and longitude, 2.279832 and 102.316711 degrees, respectively; the Google Map location of the house is: https://maps.app.goo.gl/CrBpES72bxfRkwxK8
The Measurements
Below are the two tables with monthly and annual records that the owners' of the CoolTek house have been keeping for the solar photovoltaic system since its installation in 2007:
In the section below has closer analysis of the data. Moreover, the data is made publicly available in csv format to the benefit of students / researchers / the industry and the public at large. The two data-sets from CoolTek solar system can be downloaded here:
When presenting / posting / publishing the data, please give credit to: Harry Boswell and Stephanie Bacon, CoolTek, Melaka, Malaysia, www.cooltek.org
Analysis
The key metric of a solar photovoltaic system is how much electricity that it is able to produce across the year (kWh/year) compared to the maximum production capacity (kWp) of the solar panels. Thus, the unit for this yearly performance metric of solar systems is expressed as kWh/kWp/year. It is this crucial performance metric that is illustrated (bold black line) in the graph below:
The above graph shows that for the first nine years, the CoolTek solar system produced about 1,200 kWh / kWp / year with a bit of variation typically ascribed to the annual variation in solar radiation, which, for example, can be caused by weeks long air pollution events such as the blanket of smoke ('the haze') from the slash-and-burn agricultural practices in this part of the World.
From year 2017 onwards, however, dramatic variations are observed in the annual yield of the solar photovoltaic system. According to the manual records, the solar panels were observed to be 'very dirty' in year 2018, which explains why the measured power production yield this year dropped 22% below normal. For the next three years (2019, 2020 and 2021), an annual cleaning of the solar panels resumed. As a result, the measured power production yield almost bounced back to normal, only under-performing by 5% (year 2020).
Once again, the regular solar panel cleaning stopped, which explains why the measured power production yield reached it's lowest point in 2023, where it under-performed by 25.5%.
During both periods without solar panel cleaning, aka 2017-2018 and 2022-2023, the performance was seen to drop about 10% per year, which is about 10-fold higher than the natural efficiency drop of solar photovoltaic panels, typically set to 1% reduction per year. From the FiT projected production data, the annual efficiency drop is set to about 0.8% per year.
Conclusion
This article analyses 16-years of measured data from the CoolTek house, which is one of earliest domestic roof solar photovoltaic systems in Malaysia. The key findings from the analysis are:
During the period where the solar panels were regularly cleaned (2008-2016), the following annual solar photovoltaic performance was measured: a) 1,202 kWh / kWp / year [average annual electric yield, years 2008 - 2016] with a standard deviation of 19.6 kWh / kWp / year b) 1,171 kWh / kWp / year [minimum annual electric yield, year 2013] c) 1,228 kWh / kWp / year [maximum annual electric yield, year 2009]
Annual cleaning of the solar panels is important. a) For each year that the solar panels are not cleaned, the annual yield was measured to drop about 10%. b) Once cleaned, the yield of the solar panels got back to nearly the expected performance level
The data is available for download; see link above under "The Measurements" section
Additional resources:
Official webpage of the CoolTek house: https://www.cooltek.org/
Download conference paper on the CoolTek house undergound thermal air-intake system, pertaining to another interesting energy system of the house:
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