From pv magazine Global
A group of scientists at the University of Cordoba, in Spain, has developed a photovoltaic system design for hot water production that is claimed to use around 95% of the available energy it can generate.
The system consists of a 300-litre water tank with electric resistance, connected to a 1.6 kW photovoltaic system by means of a low-cost, experimental electronic conversion system. “It is a model that is versatile, sustainable and economical, which only produces a 5% energy loss,” said the research’s main author, Luis Cámara-Díaz.
The system is equipped with maximum power point tracking (MPPT) as it must constantly operate at the maximum power point. “Without using inverters or batteries, which are more common in traditional solar photovoltaic installations, we have developed a low-cost electronic system capable of acting as an MPPT device,” the researchers explained. “Keeping a fixed reference voltage is the MPPT tracking method used.”
A microcontroller board keeps the reference voltage at the required levels and a metal-oxide-semiconductor field-effect transistor (MOSFET) conducts or cuts the current, depending on the voltage. “The reference voltage, determined by the control system, is equivalent to the maximum power point’s voltage resulting from the grouping of photovoltaic modules,” the academics further explained.
The proposed approach was tested on a PV system built with five JinkoSolar JKM330PP modules with a power output of 330 W each. The electrical heater to produce hot water has a nominal power of 3 kW and heating electrical resistance of 37.8 V. The solar panels were connected in series to reach a nominal operating voltage close to the electrical network voltage.
The system was found to reach water temperatures above 70 degrees Celsius and to cover around 85% of the annual sanitary hot water consumption of a household with six people. “The novelty introduced by this low-cost electronic system is that it is possible to convert the available photovoltaic energy into heat, regardless of whether the existing solar radiation level is high or low,” Cámara-Díaz stated.
The tested system also includes a water recirculation system to allow the input of cold water in the DHW tank, and simulated water consumption and water renovation inside the tank. It was presented in the paper A Cost-Effective and Efficient Electronic Design for Photovoltaic Systems for Solar Hot Water Production, published in Sustainability.
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A variation on conventional practice of using DHW energy storage. Yes, the $$ gain is in the differential between power tariff and FIT. However, if the thermal efficiency of the “system” is be considered for insolation hours as -say- 20% [PV] x 95% with a net electrical te of 19%.[ resistive water heating]; ignoring storage losses], it appears capable of improvement. As an alternative “system”; consider coupling the PV to a transcritical R744 HW heatpump. The narrative changes to -say- 20% x 450% with a net electrical te of 90%. In nominating the R744 transcritical HWHP, although preset to 65 C, the technology can be reconfigured to 90 C for sanitising or increasing thermal mass stored. To validate this claim, I refer to the Mayekawa UNIMO commercial R744 unit which is switchable between 60 C and 90 C. I have installed both Sanden residential HW and UNIMO commercial systems. Other manufacturers also employ the ECOCUTE technology.
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