| dc.description.abstract | With an increase in both loadshedding and the price of electricity, homeowners are looking to
reduce their dependence on the national electricity grid, both for reliability and financial benefit.
While water heating with an electric resistance heater accounts for approximately 40% of the
total power consumption in a normal household, appliances like lightbulbs and a refrigerator
consume relatively little power. Therefore, a PV system that can save money with water
heating while providing reliable emergency power during grid loadshedding will benefit any
homeowner. In this study, a combined PV system which can provide simultaneous water
heating and emergency power is under techno-economic review.
A simulation model was developed to evaluate the proposed PV system. A single-diode model
(SDM), which uses five parameters from a solar PV cell circuit, was used to model the power
generation of a solar PV array. The model uses hourly solar radiation data from a climatic
design year as input. The generated PV power is then used as input for the water heating and
emergency power simulation. The water heating model uses thermodynamic conservation
laws to determine the change in temperature within the geyser, taking into account a standard
household water consumption profile, standing loss, and energy input from the PV system.
The national grid is only used as an auxiliary power source to heat the water, should the water
not be up to temperature after PV heating. Simultaneously, as the water is heated, the battery
is also charged to be used as emergency power during loadshedding. Again, the grid is only
used to charge the battery when the PV system is not sufficient. The model was verified with
external literature and validated through experimental testing and hand calculations. The study
focused on a side-by-side comparison of the different PV systems, defined in the study.
Therefore, the model was not the main focus of the study, but rather means to compare the
different systems.
Three different PV systems were simulated, each having the same water heating capacity and
PV array, but with different battery capacities. The smallest system included a 12V, 20Ah
battery, only used for lightbulbs and a Wi-Fi router during a 4-hour loadshedding period. The
second system used a 12V, 80Ah battery to also power a refrigerator. Lastly, the third system
used a 12V, 120Ah battery, which is capable of powering all the previously mentioned
appliances as well as a microwave and hairdryer, albeit not at the same time. The system
inverters were sized according to the load requirements of the systems. The simulation was
performed for all three systems in four different locations over South-Africa, including two
coastal cities and two in-land cities.
The study found that the PV systems generated around 2000 kWh for water heating in in-land
cities, while only producing 1400 kWh for water-heating power in coastal cities. The savings,
with regard to emergency power, for each system increased as the system size increased.
The PV system saved, on average, 195 kWh/year for emergency power with system C (largest
system), while system A (smallest system) only saved 37 kWh/year. The cost savings for the
system were calculated by comparing the grid electricity bill without the PV system to the grid
electricity bill after the system was implemented.
The smallest system performed the best financially with a payback period of 6 years for inland
cities and levelised cost of energy of 1.73 ZAR, while the largest system, with its large
battery capacity, saved the most kWh and provided more backup hours and capacity during
loadshedding. The study concluded that: Firstly, the proposed combined system worked,
providing reliable emergency power and financial benefit through savings in water heating.
Secondly, the factors which the homeowner values more, convenience through emergency
power or financial benefit through water heating, determine which system is better suited to
the household. | en_US |
