UCT GOES THE RENEWABLES ROUTE TO LOWER ENERGY COSTS

The University of Cape Town (UCT) is phasing in rooftop solar photovoltaic (PV) systems across 30 of its campus buildings as a power saving solution. Alastair Currie speaks to Omaira Jajbhay, graduate engineer: Power and Energy, SMEC South Africa, about the firm’s innovative design approach in developing optimal electrical engineering building services for the client.

UCT was established in 1829 as the South African College and was granted full university status in 1918. This makes it the oldest university in South Africa, and the longest existing institution of its kind in sub-Saharan Africa, ranking 226th globally according to the Quacquarelli Symonds (QS) World University Rankings 2022. Put another way, this means that UCT is in the top 18% of all universities worldwide, underscoring its vital role in championing research and tertiary education in Africa. However, sustaining this focus requires dedicated energy, which has become an increasingly scarce commodity in South

Africa given the ongoing load-shedding experienced across the country as national utility, Eskom, implements a daily round of rolling power cuts to protect a constrained grid. In addition to being a major impediment to society in general, rising Eskom tariffs have also made electricity increasingly costly, motivating the need for alternatives like renewable energy.

In UCT’s case, the decision was made to go the solar PV rooftop route as a complementary power source for the existing standby diesel generator (genset) backup systems, with the solution designed and project managed by SMEC. As Jajbhay explains, it’s a model intended to achieve operational and financial efficiencies.

Buildings earmarked for solar PV

The 30 buildings selected on UCT’s main and allied campuses will now be progressively equipped with rooftop systems. Those selected in the first phase comprise the Baxter Theatre, UCT Graduate School of Business, the Molecular and Cell Biology building, and UCT’s Meulenhof administration facility. Their combined PV outputs will equate to around 500 kWp; in all instances, the PV panels installed will be Tier 1, which is the highest industry standard globally.

“What makes this solar project distinctive is that it’s a grid-tied system. In other words, battery storage is intentionally not part of the design. When load-shedding occurs, the solar PV system will automatically sync with the gensets and run in parallel, thereby contributing towards lower diesel consumption costs,” says Jajbhay, who is the lead design engineer and project manager responsible for all implementation phases.

Baxter Theatre, the largest of the four buildings, will be installed with a 151 kWp system. This will also be the first installation to be fully commissioned before successively moving on to the other three buildings in Phase 1, with the overall project costs valued at around R8 million for scheduled completion by the end of 2023.

“For these projects, we use an ideal DC (power of the modules) to AC (power of the inverter) ratio of 1.2, which provides an excellent yield. For the Baxter Theatre, for example, the inverter will be 125 kW to cater for the 151 kWp solar PV output,” says Jajbhay.

The groundwork

Following an in-depth analysis of UCT’s peak and off-peak demand, the first step in the design process was to carry out a detailed structural inspection on each of the four buildings’ roofs.

“We needed to perform individual weight calculations to determine their capability to handle a solar installation. We also needed to factor in Cape Town’s seasonally high wind conditions. Plus, in most cases, there were existing HVAC installations, water tanks and transformer installations to consider, so each of the four buildings presented a different set of scenarios. Provision has also been made for walking space for routine maintenance,” Jajbhay continues.

Buildings with a flat concrete roof like the Molecular and Cell Biology building can support larger 660 W panels fixed to a ballast mounting system to counter wind loads, with the roof also being able to withstand the weight of the mounting structure. In contrast, the Meulenhof building will have a flush-mount installation since the tiled roof itself has a 30-degree tilt, while the Graduate School of Business will feature a standard fixed-tilt mounting system supporting 660 W panels.

Additionally, the Baxter Theatre will have a flush-mount installation consisting of 420 W panels due to the roof’s original tilt, orientation configuration and the building’s heritage grading. The panels are smaller because the roof is made of corrugated sheet, and its structural integrity must be considered.

“The benchmark for rooftop solar PV in South Africa is to position the panels in a north-facing orientation and to set them at a tilt of 0 to 30 degrees. However, the greater the tilt, the greater the weight and wind impacts, so that always needs to be considered. For the concrete roof system and the Graduate School of Business, we’ve managed to get this down to a 10-degree tilt to achieve the best result given the wind factor,” Jajbhay explains.

Grid connectivity

The solar system will be connected to the City of Cape Town’s grid, following its voltage frequency at the point of connection. When a power outage occurs, and the city’s grid is shut off, UCT’s generators will kick in as normal, and the solar system will then automatically follow the frequency of the generators via a genset controller.

From a monitoring perspective, all solar PV installations with an output greater than 100 kWp require a Scada system in terms of City of Cape Town regulations. However, for systems lower than this, performance can still be monitored in real time via the OEM app supplied with the inverters. This will aid SMEC in refining UCT’s evolving solar PV footprint. And if, at a latter stage, load-shedding becomes a thing of the past, then SMEC’s design caters for the possibility of selling, or wheeling surplus power back to the city.

“For any solar PV installation, a professional design methodology is essential. It’s definitely not an add-on system. Each project needs a dedicated approach that meets the end-user requirements. For UCT, it’s a tailormade solution that reduces their carbon footprint, cuts their energy bill, and keeps the university operational and connected with its approximately 30 000 students,” Jajbhay concludes.