Page 46 - Energize May 2021

TECHNICAL

process could include separate charges
for grid energy, solar energy, and stored
energy, and would depend on who owns
and operates the solar and storage
systems. Where an onsite IPP operates
the system, the IPP would consolidate the
energy bills.

Example of a solar hybrid microgrid:
Malachite Mews, Gauteng
Malachite Mews is a 216-unit residential
complex in the suburb of Boksburg in
Gauteng. The microgrid, connected to the
local electricity grid, comprises 500 kW of
rooftop solar PV capacity, from 1533 solar
panels, and 672 kWh of battery storage,
Figure 6: Metering and control network. with a projected annual production of 873
MWh. The microgrid can island from the
Smart meters are capable of more than just unidirectional AC energy management, and could distribution grid, as well as supply surplus
be used for load management, providing valuable information on consumption patterns and power to the grid.
power quality. The billing of residents could be a complicated process. In a sectional title The system uses nine solar inverters
complex, there are two methods of billing. and 27 Victron Quattro 15 hybrid inverters.
• Each unit may either be billed separately by the utility, or owners pay a proportional Twelve km of DC cabling were used to
amount to the body corporate for common property energy usage. carry the power from the panels to the
• More commonly, electricity is managed by the body corporate or property manager and inverters, and 750 m of below-ground
incorporated with the levy account. In this case there is one bulk electricity meter for the trenching was dug for the cabling. In
entire complex registered with the utility. Each unit would then have its own sub-meter addition, 9,8 km of data cabling was used
from which readings are taken. for IoT equipment such as cameras, load
management devices and energy meters.
This becomes complicated when a residential microgrid is installed and billing and payment The ESS includes the largest battery
have to incorporate the reduction in grid usage due to the common solar PV/ESS system. system in South Africa’s residential sector.
The most effective system would be a form of reselling, where the owner of the system, (body Designed and installed by Cenfura,
corporate or IPP) purchases bulk energy from the utility and resells a combination of grid the system was completed in August
energy and PV/ESS to residents, based on their consumption. 2020, and has successfully undergone an
The basic charges would comprise individual energy use as well as a proportional eight-hour grid power interruption test. The
common energy use (for outdoor lighting, security, etc.). The process by which renewable project was a joint venture between DNA
energy is incorporated in the individual bills would depend on the system. A complex charging Global Energy and Cenfura. The group
intends installing 14 such projects across
the country. n

References
1. A Raji: “Modelling and optimisation of
community microgrid components”,
Energy Procedia, 156.
2. N Singh: “Smart communities -
embedded residential microgrids”,
Eskom RTD.
3. E Palacios-Garcia, et al: “Using smart
meters data for energy management
operations and power quality
monitoring in a microgrid”, ISIE 2017.
4. M Rycroft: “Hybrid systems: The key to
managing grid connected PV systems”,
Energize, November 2015.

Figure 7: Malachite mews microgrid in Boksburg (Cenfura). Send your comments to rogerl@nowmedia.co.za

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