What significance do the numbers 666.4 and the words Robben Island have? If you thought ‘prison number’ and ‘Nelson Mandela’ you would be close, but wrong. It’s actually the kilowatt peak (kWp) output of a solar PV farm comprising nearly 2 000 high-efficiency modules recently built on the island.
‘It’s sheer coincidence,’ says SOLA Future Energy CEO Dom Wills, commenting on the similarity to Mandela’s Robben Island prison number: 466/64. ‘Our design engineer worked out the best solar output based on cost and size. It just happened to be the perfect fit.’
Surrounded by the chilly Atlantic, the historic island 9 km offshore was heavily reliant on diesel for its energy, supplied by barge, primarily to fuel its desalination plant. That was until SOLA, based in Cape Town, was awarded the R25 million solar PV contract by the Department of Tourism. Besides the needs of the heavy tourist traffic (about 300 000 people visit the island’s former prison a year), more than 100 permanent residents currently depend on the plant as there is no fresh water on the island.
‘The island was a real diesel guzzler – the cost of purchasing and transporting the diesel formed a substantial portion of the island’s operating budget,’ says Wills. The island used to burn more than 600 000 litres of diesel a year, at great cost and causing a great deal of pollution. He adds that over and above the financial considerations, the noise and dust emanating from the generators were not conducive to an environmentally or tourist-friendly space.
The island also tended to suffer from unreliable electricity provision. ‘Previously, the quality of supply had peaks and troughs, meaning that equipment could be affected by unbalanced supply.’
The island’s status as a World Heritage Site as well as a political and historical monument – and a sensitive ecological area – meant the solar project had three times more ‘permanence’ than usual. The island is home to African penguins, an endangered species, and a large colony is situated within 100m of the solar farm.
‘The original environmentalists who consulted on the project wanted the penguins to roam freely around the solar farm,’ says Wills. ‘However, the Department of Environmental Affairs requested that a penguin-proof fence surround the solar farm and go underground to prevent penguins burrowing [underground]. The fence was erected as a safety consideration to prevent penguins nesting in, and biting cables and other equipment.’
Two project team members underwent penguin-handling training at the Southern African Foundation for the Conservation of Coastal Birds in the event of penguins venturing into the PV plant construction area. There were no injuries during the build resulting from the construction activities, but numerous penguin bites were sustained by team members.
Selecting Robben Island for the solar project was the result of a pilot scheme by the Department of Tourism to ‘green’ eight prominent sites through-out the country with solar energy to reduce their carbon footprint. Other locations include the Skukuza and Lower Sabie rest camps, and the Nkuhlu and Tshokwane picnic sites in the Kruger National Park as well as the Free State National Botanical Gardens in Bloemfontein.
‘The first thing that was needed when designing the plant was an assessment of the energy requirements of the island,’ says Wills. From there, the design incorporated several phases, including the replacement of a mini-substation to incorporate PV into Robben Island’s existing grid, as well as the design of the ground-mounted solar farm and its placement, and the battery bank and controls.
The solar farm has 1 960 monocrystalline modules, while the battery bank comprises 2 420 lithium-ion battery cells. It’s able to store 837 kWh. The original diesel generators are still used when no solar or battery storage is available.
Robben Island identified a piece of land that was least historically significant for the build. Wills says that ex-political prisoners had a say in the project and how the land was utilised. ‘Three sites were available for selection – an airfield; a rugby and soccer field used by prisoners; and a cricket pitch used by prison wardens right on the shoreline. The airfield held important historical significance because of Nelson Mandela’s landing after the Rivonia Trials, as did the soccer field, and so the cricket oval was given a thumbs-up for the site.’
Construction began in September 2016 and, by July last year, the farm was live. It was inaugurated by then Minister of Tourism, Tokozile Xasa, in October. Liam May, SOLA operations and maintenance manager, who assisted with project management and took charge of logistical and environmental aspects, says the weather brought its own challenges. ‘Cargo was offloaded at the Robben Island depot at the Cape Town harbour, but the weather often meant that the cargo boat was cancelled, which was challenging in terms of delivery times and building schedules.’
The people working on the project were transported to the island daily using the usual staff and tourist ferries from the Nelson Mandela Gateway to Robben Island. However, one member of the team, SOLA project manager Hlayisani Ngwana, stayed on the island for an extended period, supervising the workforce and construction activities. The logistics alone involved 11 tons of components that were transported via Robben Island’s cargo barge, Blouberg, over 15 trips.
The solar panels are secured to the ground by posts that are screwed 1.5m deep. Pylons are added above ground and, when attached to each other, they form a very solid structure, much like the design of a roof frame.
Solar PV usually powers a building directly by turning its direct current (DC) electricity into alternating current (AC) electricity, through solar inverters. This power is usually supplied in 400 kV size, which is the power that typically supplies plug points and electrical outlets in buildings. However, incorporating it into an energy grid requires a different kind of connection.
‘Robben Island’s energy grid runs off of an 11 kV line. In order to incorporate the PV system into the island’s grid, 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 11 kV,’ according to Wills.
Multinational power group ABB provided the solar inverters. An ABB ability wireless network connects the solar plant to the microgrid. ABB South Africa and Southern Africa MD Leon Viljoen told Engineering News: ‘The communication used here is a wireless system that communicates between the control system and the solar plant that’s on the other side of the island. So there are no cables laid between the two for communication.’
He added that the information goes into the cloud, and the control and monitoring of the system is done from Cape Town.
According to Wills, 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 a 30% state of charge [SOC],’ he says. ‘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.’
The new plant, which Wills says will power the entire island for at least nine months of the year, will save around 235 000 litres of diesel annually and reduce C02 emissions by 820 tons.
‘Technically, the island could make use of a bigger battery,’ says Wills. ‘But before this happens, the island wants to be more efficient in terms of energy usage. There is enough energy being produced by the solar panels currently, and although the plant is 50% energy efficient, the island plans to run on 90% to 100% solar energy in the future.’
The plant has allowed this precious World Heritage Site to go greener, improving its image and function, which is key, especially since it is the gateway to South Africa’s heritage.
‘It was such a great honour and a privilege. It’s an astounding achievement to have succeeded in completing the construction of this renewable energy project,’ says Ngwana. ‘The prison and the World War II ruins were my private escape during my own stay there. I felt connected to the soil.’
OVERALL PROJECT DESIGN