Abstract:
In recent years, concern over environmental problems, such as the increase of
atmospheric temperatures and destruction of the ozone layer, have amplified on a global
scale. In the future, increased efficiency of energy systems and reduced end-use energy
demand will be significant in attaining the 6% curtailment of greenhouse gases, targeted by
the Kyoto Protocol. Although the energy research and development has been known over
an extended period in large buildings, it has recently been applied at household level.
In South Africa, there are approximately 9 million homes that have access to electricity.
Approximately 27% of the generated energy in South Africa was consumed by the
residential sector in 2015. This making the residential sector the second largest energy
consumer in the economy.
In South Africa, electricity is solely supplied by Eskom, a state-owned enterprise. For
the last decade, Eskom have experienced challenges in meeting the national demand. The
issue of the supply being less than the demand, has led to the requirement of additional
fossil fuel plants, which resulted in financial challenges. These financial challenges have
resulted in harsh tariff increases for consumers. With the aim to reduce the load-demand
of the grid during peak periods, the electricity supply commission (ESKOM), implemented
the time-of-use (TOU) tariff structure, billing consumers at a higher tariff rate during
certain periods of the day. These tariff increases are compelling consumers to search for
alternative ways in meeting their energy demand. Currently, many countries are permitting
residential consumers to install renewable forms of energy sources.
With Eskom contending to meet the load demand, load shedding was introduced, in
order to reduce the load demand during certain periods of the day. If load shedding was
never introduced, the load demand may have resulted in the grid collapsing. As a result of
the electricity challenge in South Africa, a few municipalities have begun revising the
regulations on small scale embedded generators, permitting consumers, under strict
regulations, to feed-back excess energy into the grid. This study used a solar photovoltaic
(PV) system, combined with battery storage. The mathematical modelling of the gridinteractive
PV, with battery storage system, has been developed to allow for optimal energy
storage and sales, while ensuring that the consumer load demand is met at all times, considering variable time-of-use (TOU) tariffs and load demand uncertainties, that may
take place in real-time context.
The aim is to develop a model for optimal operation of a residential grid-interactive PV
system with battery storage, operating under TOU and FIT tariffs. The research will further
assess the potential of energy cost saving and cost effectiveness that the system may
achieve, under the new residential feed-in tariff; along with the impact the battery storage
system will have on the profitability of the grid-interactive solar PV system.
Additionally, the second aim is to maximize the energy sales into the grid, if the system is
grid-interactive. The MATLAB optimization toolbox was used to evaluate the cost
effectiveness of the grid-interactive system, in terms of money spent.
The baseline system was established, consisting solely of energy supplied by the grid. The
optimal operation of the proposed system was simulated and compared to the baseline
system.
A life cycle cost (LCC) analysis was conducted for a period of 20 years, for both the
baseline and the optimally controlled grid-interactive PV with battery storage system
scheme. Results from the analysis indicated that the proposed system would break-even
in 11.5 years, with an approximate saving of 35%, translating into savings of R 270 022.83.
The results clearly illustrated that the consumer could save a significant amount if the
system is implemented correctly, including the parameters of the desired system. The
model showed that it could be used for different operating conditions, as long as the user
incorporates the new environment. The model clearly shows that managing the power flow
in a proposed system could be beneficial for electricity consumers in South Africa and not
merely for residential consumers.