Modern Mining June 2018

POWER SUPPLY AND ENERGY EFFICIENCY

its HFO generators during day-time based on algorithms monitoring irradiance, cloud cover and PV penetration,” he states. “This not only allows us to save HFO but also reduces the operating hours on our large HFO gensets.” Looking to the future, Roos says B2Gold Corporate is considering two further phases of development for the Otjikoto solar project. “Phase 2 envisages Otjikoto being connecting to the national power grid, which could see up to 45 % of the mine’s power requirements being supplied by Nampower on an off-peak tariff, while Phase 3 contemplates the expansion of the solar farm, which would be easily achieved given the modular nature of the installation. We may also, at some point in the future, even look at the possibility of energy storage, allowing the solar energy generated by the solar farm to be used at night-time or at times – for example, when there is cloud cover – when conditions for generating solar energy are unfavourable. Caterpillar and other vendors already have proven systems that could be used.” The operation of the project has thus far met all of B2Gold’s expectations, with 468 155 litres of fuel having been saved from the first day of recording solar energy at the HFO plant (8 March 2018) through to 27 May. Over the nine-year modelling period for the project (effective 1 April 2018), it is anticipated that approximately 26,3 million litres of HFO will be saved resulting in operational savings of an estimated US$16 million. On this basis, the payback period of the project is estimated at 4,5 to 5 years. Photos by Arthur Tassell (unless otherwise acknowledged)

115-W Cat-branded thin-film solar panels, manufactured by its joint venture partner First Solar, Inc, which has its headquarters in Arizona. The panels are mounted on a PiA single-axis tracking system. The DC power is converted to AC power through Sunny tri-power three-phase SMA string inverters and is then distributed to the HFO plant via Schneider switchgear in the PV control build- ing through a 3,5 km overhead powerline. According to Roos, the Cat-branded thin- film panels have a specific yield advantage over traditional polycrystalline panels in hot condi- tions and have a superior shading response. The solar farm has a modular design, allowing PV energy to be added to (or removed from) the Otjikoto microgrid in 1 MW increments.

One of the open pits at the Otjikoto mine.

In integrating the solar farm with the HFO plant to create a hybrid power system, the MMC works in conjunction with the HFO plant’s SCADA system, developed in a collaborative effort between the Barloworld/ Caterpillar technical team and Namibian-owned IAE, which specialises in industrial auto- mation and engineering. Explaining how the MMC works, Roos says it not only regulates the energy being fed to the HFO plant but allows for the seamless selection of the mine’s two energy sources (HFO or solar), choosing the most economically viable option at any point in time. “Most importantly, the MMC enables the mine to switch off one of

June 2018  MODERN MINING  29