As part of the Zimbabwe National Road Agency’s (Zinara’s) roads rehabilita- tion project, the Zinara toll plaza near Bulawayo, in Zimbabwe, has been designed and commissioned by engineering consultancy Arup, making it the world’s first solar-powered off-grid toll plaza.

The project is part of Arup’s appointment with diversified construction company Group Five International – Zimbabwe branch – for the 822 km Plumtree to Mutare roads upgrade. The plazas will be operated by Intertoll, a subsidiary of Group Five.

The toll plaza’s source of power is derived from solar panels installed on the roof over the plaza lanes and the collection booths. The project is part of the Zimbabwe government’s initiative to upgrade the logistics network and support expected growth, which will result in eight toll plazas being constructed and operated across the country.

The road rehabilitation project has a capital cost value of $205-million, which includes the cost of the additional seven toll stations currently under construction and the rehabilitation of 822 km of existing roads.

“The viability of solar power was identified, owing to the high cost of providing national grid electricity connection for the plazas. The financial balance between connection costs and generator running costs in the event of possible power outages, specifically considering fuel and maintenance, swung the balance in favour of solar photovoltaic (PV) generation,” explains Arup senior electrical design engineer Paul Trewartha.

Arup developed a design based on reliable equipment used on other solar PV instal- lations. The company opted for chemical light-emitting diode lighting instead of con- ventional lighting, which resulted in a reduction of about 50% in the amount of energy used for lighting. Arup was also tasked with providing archi- tectural, civil, structural, mechanical, elec-trical, public health and infrastructure engi-neering services.

To demonstrate the viability of the scheme, Arup developed a unique model to simulate expected seasonal generation and daily load trends. This established that solar panels could supply more than 80% of the load needed to power the plaza, with diesel generation provided as backup.

The plaza operates independently of the electricity grid, reducing its carbon footprint. The reduction of the total electrical load of the plazas was critical to the success of the off-grid system and was achieved using energy efficient, state-of-the-art lighting technology and implementing an innovative electrical load management system.

“Sustainable traffic management solutions will heavily influence our future, so this was the perfect opportunity to develop a concept that would help save valuable energy and reduce energy costs. We are also thrilled to be involved in a project that will aid growth and support Zimbabwe’s economy,” says Trewartha.

The PV generation system at Ntabazinduna Plaza took about three weeks to install. The system was commissioned on March 7.