Last week, the Minister of Tourism opened the Robben Island solar PV microgrid, designed and constructed by SOLA Future Energy. This system, incorporating one of the southern Hemisphere’s largest battery banks, is made of 1960 mono crystalline solar modules, ready to produce 666.4 kW of power and 2420 lithium-ion battery cells, able to store 837 kWh worth of electricity and supply 500 kW worth of peak power.
Designing a smart grid
SOLA Future Energy designed Robben Island’s Microgrid over the course of two months. Designing the PV plant incorporated several phases, including the replacement of a mini-substation to adequately incorporate PV into Robben Island’s existing grid, designing of the ground-mounted solar farm and placement, the battery bank and controls.
Phase 1 – Understanding the island’s energy requirements and solar resource
The first phase of the designing a solar PV microgrid was to understand the energy requirements of the island – and what solar resource is available. With thousands of tourists visiting Robben Island each day, as well as 100 staff living permanently on the island, a lighthouse and a desalination plant, the island’s energy requirements are quite significant. Understanding these requirements was the first phase to knowing what type and size of system to design.
Typically, when designing rooftop solar systems, it is important to consider shading from other buildings or large trees, but with Robben Island’s placement and shrubby vegetation, the solar resource is excellent and relatively undisturbed. In addition, the ability to place the modules at a fixed-tilt axis in a north facing area, made them ideal for solar penetration, right into the late afternoon.
Phase 2 – Understanding the existing grid and how to incorporate into it
Solar PV usually powers a building directly by turning its Direct Current electricity (DC) into Alternating Current electricity (AC), through solar inverters. This power is usually supplied in 400kV size, which is the power that typically supplies plug-points and electric outlets in buildings. However, incorporating into an energy grid requires a different kind of connection.
Robben Island’s energy grid runs off of a historically-erected 11kV line. In order to incorporate the PV system into the island’s grid (as opposed to, for example, a single building), a mini-substation needed to be designed and built in order to convert the PV plant’s supply of 400 kV to the grid’s 11kV. This substation replaced one of the island’s existing, but too small, substations. Once erected, it allowed the PV farm to feed into the island’s grid.
Phase 3 – Modelling and simulating the PV and battery resource
Once the solar farm was designed, based on the energy needs of the island, the design needed to incorporate the battery system to store excess solar power, taking into account the scope of the project. The battery bank is made up of 2420 lithium-ion battery cells. Like cell phone or laptop batteries, lithium-ion batteries have a long life and have a higher threshold to discharge and charge with larger power. Unlike their lead acid counterparts, lithium-ion batteries can use up to 96% of their capacity, making them a highly efficient choice to support the longevity of the solar PV farm, which will last over 25 years.
A large part of designing the battery system to incorporate fully with PV is the programming of the actual microgrid. The programming consists of scheduling the generators to switch off when the batteries reach 30% State of Charge (SOC). When the batteries reach 15% SOC, the generators are scheduled to switch on, making sure that there is a continuous source of power on the island. The wireless system between the three different components allows the batteries to “talk” to the PV. This decision-making ability, and intelligent control in each device, makes the microgrid a smart grid that ensures seamless power to the island.
Helping not only the efficiency, but the quality, of energy supply
One of the unexpected outcomes for Robben Island is a better quality energy supply for the island’s operations. Previously, the quality of supply had peaks and troughs, meaning that equipment could be affected by unbalanced supply. However, the new battery inverters are able to stabilise the grid, making the power better quality overall, and in turn affect equipment and machinery less.
Although the microgrid contains diesel generators, the Robben Island microgrid is unique because it does not rely on the diesel generators to function. Usually, solar PV works by attaching to an existing grid – or diesel generators. However, with a special inverter, the microgrid contains a virtual generator machine (VGM), which allows the PV to run without any generators at all.
SOLA Future Energy has carried out the design and construction over the last year and a half on Robben Island. Although the design of the system took about two months of non-stop design time, there were several other considerations in working on the World Heritage Site. The video of the Robben Island Solar Project tells the story of the island’s symbolic transformation and its relevance as a microcosm of South Africa. The future of Africa is powered by the sun, and we’re there to make it happen.