The future of solar could be over our highways and up our walls

Rooftop solar installations continue to soar across the globe, and utility-scale solar installations remain a dominant source of new energy generation, but two new studies have posited new options for expanding solar generation – up the walls and over our highways.

A pair of studies published in the last month has highlighted the myriad ways in which solar can be used across our built world and the potential secondary benefits beyond the production of clean energy.

With many of our cities’ rooftops already being plastered with solar panels, attention has spread to whether and how solar could be used on the sides of buildings.

Though not a new idea in and of itself, an international team of researchers modelled the impact of deploying “innovative bifacial photovoltaic systems … on a large-scale disruptive scenario” as against simply aiming to deploy solar PV systems with “optimal” orientation and tilt.

The study considered “the potential of novel deployment practices for PV to quickly reshape the European electricity sector” in the form of “vertical bifacial PV” which they believe could extend the production time of PV electricity to periods where it is more valuable to the consumers and easier to be dispatched.

For example, the researchers demonstrated how east-west oriented vertical solar PV panels are able to extend solar generation time to include sunrise and sunset – periods of the day which are more valuable to consumers than during the middle of the day.

“Such setup typically produces 30% in the 3 midday hours in contrast to the South facing PV that produce nearly 70% of its output in the midday … This difference is higher than the one between off-shore and on-shore wind systems, indicating the potential role vertical systems can play.”

The researchers believe that such a deployment of vertical solar systems offers “a fast, no regret option that decreases land use competition and mitigates PV system integration issues.”

They added that “Bifacial module requires negligible added cost compared to usual PV modules (by replacing the back cover to transparent one) extending the range of PV applications to options that minimise land use changes and can produce electricity in a strikingly different pattern.”

Many models of solar penetration and demand fail to take into consideration the role of vertical solar, leading the researchers to ask, “to what extent conventional generation, including gas, coal and nuclear, is impacted by the integration of a more diversified PV portfolio, including both standard and vertical bifacial modules.”

According to the study’s modelling, the potential of vertical solar becomes apparent, revealing “a substantial increase in the electricity injected into the grid” with increased vertical solar PV utilisation that leads to a concurrent decline in the need for gas and nuclear generation.

The modelling similarly showed that more vertical solar PV could boost the economic value of solar production, reduce wholesale electricity prices, and allow more energy flows between neighbouring countries.”

Overall, it would lead to a significant reduction in the total cost of the power system.

“In the 2040 Reference PV scenario, there is a decrease of 3 billion Euros when increasing the vertical module share to 50%. In the 2040 High PV scenario, the decrease is more significant, amounting to 3.8 billion Euros,” the report says.

“Over the longer-term, the European power system becomes more sustainable both economically and environmentally,” the authors conclude.

The second study demonstrating the role of solar in society, however, posits a relatively new idea – installing solar PV roofs over the world’s major highways.

Two researchers from the Chinese Academy of Sciences recently published research which calculated the costs and benefits of installing solar roofs over highways around the globe.

There are 3.2 million kilometres of highways currently stretching across the planet, and the researchers found that not only could worldwide solar highway roofs meet over 60 per cent of global energy needs each year, but the panels could produce enough electricity to replace 28 per cent of the world’s carbon emissions.

“There are some highway photovoltaic roof pilot programs, but not to the scale that we have imagined,” said Ling Yao, a remote sensing scientist at the Chinese Academy of Sciences and the study’s lead author.

“Covering Earth’s highways with solar roofs could generate 17.58 petawatt hours of electricity per year, equivalent to more than 60% of the world’s total electricity consumption in 2023.”

The inspiration for Yao’s study came to him as he drove across an overpass during his evening commute.

“I suddenly looked down at the road, and thought, ‘The roads are connected to each other. It’s just like a network – the cars can move freely from one place to another,’” he said. “I thought, ‘Why don’t we turn our roads into a network of photovoltaics?’”

Building out a network of solar roofs over highways offers a range of benefits, such as utilising already-developed land for electricity generation, decreasing demand for greenhouse gas-producing energy, resulting in a reduction to overall carbon emissions.

Basing their analyses on polysilicon photovoltaic panels with 250 watts of maximum power generation, placed at a 10-degree tilt toward the outer lanes of the highway, the researchers concluded that covering the world’s highways and major arterial roads would use 52.3 billion solar panels and generate up to 17,578 terawatt-hours per year.

Installing solar roofs over major arterial roads would generate an additional 13,570 terawatt-hours per year.

The researchers determined that solar highway roofs could also help to reduce global traffic deaths by as much as 10.8 per cent in regions with high precipitation due to the extra protection from rain and snow. Improved highway safety would also subsequently reduce economic costs of traffic accidents.