Using sunshine twice: Is agrivoltaics a win-win for Australian farmers?

Agricultural and solar farming could increasingly cohabit the same patch of land – supporting industry growth, efficient land use, increased sustainability and providing a supply of clean power to farming businesses and their communities. Now, researchers at the University of Melbourne are exploring how agrivoltaics could benefit viticulture and horticulture production systems in our uniquely Australian environment.

Using the sun twice: A 20 kW agrivoltaics system integrated into a vineyard at the University of Melbourne’s Dookie Campus between Shepparton and Benalla in Victoria. With an area of ~270m2 it’s 2024 installation comes just in time for the annual growth cycle of grapevines to start.

The Australian agricultural sector has big ambitions. According to the National Farmers Federation, the industry has plans to exceed $100 billion in farm gate output by 2030. At the same time, it’s working to cut its carbon emissions to net-zero by 2050. All this, in the face of mounting challenges such as climate change, droughts, and growing demand for food that is socially and environmentally responsible.

For the agricultural industry in Australia to keep growing, while also becoming more sustainable, will take transformational change. And agrivoltaics could be one way to meet this challenge.

International studies have demonstrated that agrivoltaics – where food and energy are co-generated on the same area of land rather than competing for land – can boost agricultural productivity, increase efficiency in land and water use, and improve soil health.

- Camporese and Abou Najm, 2022

Overseas, mostly in Europe and North America, co-locating solar photovoltaic arrays with a range of different crops has shown benefits for both plants and panels.

But exactly what this means for the Australian agricultural and energy sectors is still up for debate.

Now, researchers at the University of Melbourne are embarking on new research and test cases, here in Victoria, which consider the benefits of photovoltaics specific to Australian environmental conditions.

“The research, funded by AgriFutures, comprises a review of existing studies here and overseas, engagement with industry, an agrivoltaics pilot study set in the university’s vineyard at the Dookie Campus, and knowledge sharing, nationally,” said Dr Sabine Tausz-Posch, Senior Lecturer in Agricultural Food Sciences from the University of Melbourne.

"Our project, titled Agrivoltaics: A Win-Win for Farmers?, is expected to find and share how different farms with different crops can use agrivoltaics and strike the right balance of crop solar exposure throughout the day and season, to improve the environment in which plants grow. All the while, generating clean power from the sun," said Dr Tausz-Posch.

The research will provide answers on the benefits of photovoltaics for viticulture and horticulture production systems, considering the Australian environmental conditions, which, in many cases, are tougher than those elsewhere.

Agrivoltaics means better use of the sun, land and water

The great promise of agrivoltaics is its capacity to create transformational benefits at the nexus of food, energy and water. But how?

To start, solar panels placed on the same area of land where crops are grown means we can effectively harvest energy from the sun, twice: once with the photovoltaics, and once with the plants growing around them.

Then, the solar panels can improve water use, with the micro-climatic environment created by the solar arrays reducing evaporative water losses. This is especially the case in harsh climatic conditions, like those in many Australian agro-ecosystems.

And finally, solar panels may protect crops from heat stress and severe weather events such as hail, benefitting yields and profitability.

Meanwhile, the solar panels operate more efficiently because of the cooling effect of the crops growing underneath them.

So let’s break down all these benefits, in more detail.

1. Solar panels protect crops from excess light.

Crops need sunlight to drive photosynthesis. But for the key physiological process underpinning crop growth and productivity, light saturation is reached at around 800 to 1000  μmol m^-2 s^-1 of photosynthetic photon flux density (= PPFD, Figure 1, yellow area). The majority of crops do not continue to do increasingly well with more light.

In fact, photosynthesis plateaus out above light saturation and crops become light stressed and can develop oxidative stress after light saturation is reached.

On most days, plants harvest more light energy than they can use in photosynthesis.

This excess is particularly true for Australian conditions; a sunny day in Victoria reaches easily 2000 PPFD from mid-morning to mid-afternoon.

The shade provided by a solar panel array can shelter the crops from this excessive sunlight, reducing excess light and oxidative stress with no penalty, and potentially even benefits, for photosynthesis, crop growth and productivity.

Not every crop type has the same light saturation point. We need more research to find which crop species can benefit most from the shelter solar panels provide, considering the regional climates, water and soil conditions, in which they grow.

Figure 1: The rate of crop photosynthesis varies as a function of light. The yellow area indicates light limitation with photosynthesis increasing proportionally. The red area indicates light intensity in excess where plants absorb light at a faster rate than they can use in photosynthesis, which can result in the formation of reactive oxygen species that damage cells and impair crop growth and productivity.

2. Solar panels protect crops from water stress.

Water evaporates more slowly under shade than under full sun.

The shading effect of solar installations - limiting the direct sunlight hitting the soil and the crop canopy - can reduce canopy transpiration and the evaporative loss of soil moisture, helping to reduce irrigation requirements. This has been tested and proven in dryland areas overseas.

3. Crops keep solar panels cooler.

Solar panels can lose efficiency when they get too hot. Crops growing underneath can act as evaporative coolers, creating a cooler micro-climate below and increasing renewable energy production.

The hotter the climate, the bigger the agrivoltaic wins?

International studies have shown that many farms can significantly benefit from integrating solar installations, particularly in the hot and harsh environments typical in Australia.

A study conducted in Arizona, for example, found that the production of cherry tomatoes doubled and that of chiltepin peppers tripled under the solar panel installation. Similarly, a French study conducted by Sun’Agri, found that having vines under elevated photovoltaic systems resulted in a 20% increase in grape weight, lowered irrigation needs up to 34% and reduced alcohol content.

Other studies highlight that the relationship between shade and crop yield is neither simple nor uniform.

A recent meta-analysis of 58 studies looked at how different crops (including berries, fruits, fruity vegetables, leafy vegetables, cereals, maize, root crops, grain legumes and forages) were affected by increasing levels of shade. The analysis concluded the relationship between achieved crop yields and reduction in solar radiation is non-linear.

For example, this study found many crops tolerated a 15% reduction in solar radiation, with some (such as berries, fruits and fruity vegetables) even benefitting from a 30% reduction. Other crops (such as forages, leafy vegetables, root crops and C3 cereals) showed less than proportional crop yield losses, while maize (C4 cereal) and grain legumes experienced strong yield losses even at low shade levels.

It is worth noting, that most of the studies considered in this analysis were conducted in colder, mostly temperate climate agro-ecosystems, where sunshine may be more limited, and water use efficiencies are relatively less important than in harsher, arid, or Mediterranean climates – those more similar to the environments in Australia.

Put together, this means that more research is needed to better make conclusions on how agrivoltaics could benefit Australian farming industries.

To date, across Australia, we have only a few reported test cases, with little emphasis on understanding solar integration with crop production systems. The exception is a single pear orchard agrivoltaics experiment by Agriculture Victoria. Most other local studies, reported by the Clean Energy Council, look at solar grazing, where solar and sheep are farmed on the same area of land. All show initial promise in combining solar arrays with agricultural endeavour.

The current project, Agrivoltaics: A Win-Win for Farmers? at the University of Melbourne, is set to provide the necessary local answers, so Australian farmers can understand if photovoltaics on their land, with their crops, is the potential profit and sustainability boost they need.

For more information

• Dr Sabine Tausz-Posch, Senior Lecturer in Agricultural Food Sciences
• Chris Barnes, Senior Lecturer (Wine Technology and Viticulture)

Acknowledgements

The project ‘Agrivoltaics: A Win-Win for Farmers?’ is funded by AgriFutures. Supplementary funding for the installation of the agrivoltaics facility at the Dookie Campus was provided by the Department of Agriculture, Fisheries and Forestry as well as the University of Melbourne’s ‘Sustainable Campus’.