Switching to a hybrid solar hot water/heat pump system reduces the cost of energy and shows a good return on investment on the capital outlay. Even with heat pumps, Melomed Gatesville used approximately 350,000 kWh per month (11,600kWh per day) at a 2017 cost of R432,000 per month. Any savings of energy therefore make a very significant impact on the bottom line.
After designing a small solar water heating system, Solarex applied for a grant from Soltrain/AEE INTEC, a program of the Austrian Development Agency. This grant makes the economics of such a project very attractive, the only condition being that the plant may be used as a demonstration unit.
Melomed accepted the updated proposal in December 2016, and the AEE INTEC grant was awarded in March 2017. After the final design, equipment was specified and ordered, and construction started in May 2017.
On completion a month later, the equipment and installation were assessed by Rudi Moschik, an expert engineer from AEE INTEC, and was successfully signed off by SOLTRAIN on July 6, 2017.
The thermal performance of one of the hot water plants was monitored by the Centre for Renewable Studies (CRSES) at Stellenbosch University for a period of 12 months to allow for a full analysis of the energy generated, and to indicate where further improvements might be made to optimise the energy efficiency of the entire hot water system.
The following conclusions were reached:
- Hot water consumption is much lower than expected at 3,662 litres per day versus an assumed 15,000 litres per day for the one plant that was monitored. This discrepancy is attributable to city-wide water restrictions imposed during the monitoring period brought on by severe drought.
- In the winter months (May-August), solar thermal is producing 24% of the water heating load
- The summer solar fraction increases to greater than 50%.
- The annual average is approximately 50/50 across both systems. Ideally, the solar fraction should be increased to 80% and it is advisable to implement this system expansion when the older heat pumps are replaced.
- The saving from solar heat was initially R65,000 per annum (3 to 3½ year payback) at the 2017 tariff of R0,69/kWh.
- The current savings are R130,000 per annum at the 2021 tariff average of R1,40/kWh.
- Maximum temperatures from the solar system are about 60 to 80ºC.
- The heat pump is regulated at 60 to 65ºC.
- The ring main losses amount to 99kWh per day.
Download the full report, including graphs and schematics, at this link.