Mining company Vedanta Zinc International, which owns Black Mountain Mining (BMM) in South Africa, appointed consulting firm WSP in Africa’s sustainability specialist consultants to assist in achieving a Net Zero Carbon level rating for the mine’s white office.

''BMM wanted to use our services for the net-zero initiative, as we are very experienced in sustainability ratings in South Africa," WSP in Africa regional director Alison Groves says.

BMM had a goal of achieving a Net Zero Carbon Level 2 rating. This stringent certification is based on actual measured values, as opposed to modelled values, as required for the Level 1 certification. 

“The Green Building Council of South Africa (GBCSA) offers two approaches at present. Under Level 1, Net Zero Carbon is calculated on the base building energy demand which is generated through energy modelling of the building. Where Level 2 encompasses the actual modelled renewable energy that is manufactured and consumed.  

“The energy consumption takes account of both the base building needs and the tenant's operational needs. This is a more accurate reflection of whether the building is performing as a Net Zero entity,” Groves explains.

To achieve this, WSP began by assessing the types of air conditioning, lighting and water systems that were installed throughout the building. A key finding of the assessment was that the consumption of utility services was not being measured, and that the energy costs for the town were being settled by BMM, without passing any of the cost on to their employees.

There was also no monitoring of consumption through municipal meters, so the company did not know how much power was being consumed.

“Since you cannot manage what you cannot measure, the first step towards achieving net zero in the offices was to install a metering system and gain an understanding of how much energy was being used by the office and residential units. This enabled us to calculate the benefit of the solar installation,” Groves says.

The 422 m² office complex consists of a collection of single-storey buildings housing 22 private offices, a reception and waiting area, a large meeting/conference room, a training room, kitchen and bathrooms. Additionally, each office has air conditioning.

The next step was to install a 99 kW ground-mounted solar photovoltaic (PV) solar system, tied to the grid without a battery backup. 

Groves notes that, at the time, 99 kW was the maximum permitted installation without having to undergo an onerous licensing procedure. The legislation has since changed.

“Because there is no battery storage installed as part of the PV system, the sizing of PV installation was designed to exceed the annual energy demand of the office complex. As the energy is not stored, the system is designed to continue to generate electricity, over and above the needs of the office.

“This generated a unique opportunity to continue to serve the community in which it operates, by feeding the balance of the renewable energy to the nearby residences and create an energy bank of sorts. This surplus energy that is accrued by the residential buildings, could then be claimed by the office complex when solar production does not meet the office’s energy needs,” Groves explains.

To see how well the solution worked and as a requirement for attaining the Level 2 certification, WSP monitored how much renewable energy was generated over 12 months and compared it to the energy requirements of the office complex.

This analysis, performed from May last year up to April this year, showed that while the total yearly energy consumption of the office complex was 193 008 kg of carbon dioxide (CO₂)/kWh, the total yearly output of the solar PV plant exceeded that, producing 251 065 kg CO₂/kWh. This meant that the solar plant was generating enough renewable energy to offset 130% of the office complex’s yearly carbon emissions.

It also exceeded the 5% required by the Green Star Net Carbon rating to demonstrate that the building is now net positive.

“The Green Star Net Zero Carbon rating is especially important in our world where buildings are striving to reduce their energy consumption and source 100% of the electricity requirements from renewable energy.

“This is an important use case and benchmark in the local market, as it bodes well for other mine operators that want to serve both the environment and the communities in which they operate, with a future ready approach to their environment, social and governance commitments and sustainable business practices,” Groves says.