In South Africa, most people tend to think of solar energy when they think of renewable energy sources, and certainly photovoltaic (PV) power is on the rise - the public is becoming more aware of both on-ground solar farms as well as the increase in individual businesses and homes that are installing solar panels to reduce their dependence on the grid. But what about wind, and where are we in South Africa with this interesting renewable option?

Florian Vögerl, head of sales and operations at DEHN Africa,  says, “In 2016, a study by the Council for Scientific and Industrial Research (CSIR) noted that the capacity to produce electricity from wind turbines in South Africa was more widely spread than initially thought, and was in fact on a par with solar energy. Since then, wind energy is becoming an increasingly important part of this renewable landscape. Here at DEHN Africa, we play a critical role in protecting wind turbines that are used in renewable energy production from the destructive effects of lightning and power surges.”

Renewable energy in South Africa

Locally, the energy landscape is in a certain state of upheaval, best summed up around the ongoing uncertainties and delays related to the Department of Energy’s latest draft Integrated Resource Plan for electricity (Draft IRP 2018). The draft IRP walks a delicate tightrope among a number of different stakeholders, including the government, labour, business and communities, and issues at stake include (but are not limited to) those who want to continue for as long as possible with coal-fired energy production, largely because of job continuity; a small number voting for nuclear; and an ever-growing voice clamouring for the final green light for renewable energy sources.

Vögerl comments, “When you think that, as per the CSIR, the cost of new wind generation is 40 percent cheaper than that of coal, it does make enormous sense to explore wind energy as a renewable energy option in South Africa. This is especially true as we have vast areas of the country that are very windy, such as the Eastern and Western Cape provinces, and parts of the interior. Additionally, the average time for construction to completion of renewable energy projects is only 1.9 years, which obviously allows a new source of energy to be connected to the grid very quickly.

“At DEHN Africa, we are obviously aware that legislative issues still need to be enacted around the implementation of different energy sources in the grid overall. But I think it remains a certainty, amidst all the noise, that more wind turbines will be required in South Africa, and they need to be protected against lightning strikes and electricity power surges – quite literally, one turbine at a time.”

Protecting renewable energy equipment from lightning strikes

Lightning strikes to renewable energy equipment, such as that used on wind or solar farms, or rooftop solar panels, will cause damage at the strike point, as well as surge damage to any equipment that is connected downstream. While external lightning protection helps avoid damage at the strike point itself, surge protection devices help prevent downstream damage because of conducted and induced surges from the strike, while further allowing the renewable energy system to stay online.

In addition to the damage that an individual lightning strike can do, it must also be considered that South Africa is a country where many areas have a very high lightning ground flash density (a measurement of the number of lightning strikes to the ground over a period of one year). There are, in fact, areas where the country’s ground flash density is comparable to, or higher than, the lightning hot spots of north and south America, Asia and northern Australia.

“South Africa’s lightning conditions,” says Vögerl, “are in general more frequent than those found in many parts of Europe, where much of the world’s renewable energy sources and technology are developed and implemented. We therefore have even more reason, arguably, to look after our renewable energy equipment than our colleagues in Europe do. Therefore, it is critically important to protect our renewable equipment in South Africa from lightning strikes. The results of a lightning strike to an unprotected renewable energy source will include physical repairs or replacement – not to mention potential reputational damage.”

He clarifies that, in some cases, wind turbines are imported into South Africa with the lightning protection equipment already pre-assembled, and that DEHN Africa’s work requests are mostly around the earthing of the turbines.

Appropriate earthing for wind turbines

In this vein, says Vögerl, the earth termination system for onshore wind turbines has the following tasks:

• Protective earthing, which safely connects electrical equipment to the ground and protects people and property in the event of an electric fault;

• Functional earthing, which needs to ensure safe and efficient operation of the electrical and electronic equipment;

• Lightning protection earthing, which must safely conduct the lightning current from the down conductors to the ground.

DEHN advises in a white paper on the earth termination of on-shore wind turbines that, as regards lightning protection earthing, it is advantageous to have a single, common earth-termination system for all purposes (medium-voltage system, low-voltage supply, lightning protection, electromagnetic compatibility, telecommunication and control systems).

The white paper notes further that the reinforced concrete foundations of wind turbines should primarily be as a foundation earth electrode, as these provide a low earth resistance and represent an excellent basis for equipotential bonding. As a medium-voltage transformer is also installed in the wind turbine, the earth-termination system must be designed according to international standard IEC 61936-1, which describes all types of earth electrodes. Foundation earth electrodes are defined as the most effective earth electrodes.

When working out the dimensions of the earth termination system, it is important to factor in the composition of the surrounding ground, and the type of neutral point treatment and the resulting short circuit currents in case of a fault.

Moving forward

“We believe that South Africa is on the verge of seeing a tremendous increase in the use of renewable wind energy production. When the green light is given for even more investment in the renewables space and the finalisation of the draft Integrated Resource Plan for electricity, companies will want to move quickly with their wind energy production plans. With this in mind, the time for planning is now, and it should be remembered that each wind turbine needs to be earthed properly and individually,” concludes Vögerl.