Agrivoltaics for sustainable agriculture and green energy

The sun is the ultimate source of energy in all its forms. Plants convert sunlight into chemical energy (food) through the process of photosynthesis. The fossil fuels that we use today come from dead plants and animals, which also derive their energy from the sun. Solar energy is the most abundant resource that can be transformed into heat or electricity. For instance, solar photovoltaic (PV) technology directly converts sunlight into electricity, thus avoiding fossil fuel consumption. This technology is now the most affordable and widely accessible, with prices for PV modules falling by around 90 per cent between 2009 and 2019.
Driven by falling costs, technological advancements, and growing concerns over fossil fuels, the deployment of solar PV has skyrocketed since the early 2000s. The global capacity of solar PV reached 1,185 gigawatts (GW) in 2022, representing 70 per cent of all new renewable power capacity additions.
Bangladesh began harnessing solar power in 1993 through the installation of Solar Home Systems (SHS) by the Bangladesh Rural Electrification Board. In 2003, the Infrastructure Development Company Limited (IDCOL) launched its SHS programme to provide basic electricity to rural off-grid communities, supporting the government's vision for universal electrification. This programme has been highly successful, with over four million SHSs installed by IDCOL and a total of approximately six million across the country. IDCOL also spearheaded the installation of solar mini-grids, solar irrigation, rooftop solar, solar parks, etc. Building on the success of various applications of solar energy and in line with global trends, Bangladesh's long-term energy plan - the Integrated Energy and Power Master Plan (IEPMP) 2023 - aims to generate up to 40 per cent clean energy by 2041.
To fulfil the IEPMP targets, the government has taken initiatives for large-scale deployment of solar PV plants. A significant number of ground-mounted solar power projects with an aggregated capacity exceeding one GW are now under process. A major challenge in scaling up solar PV projects in Bangladesh is the competition for land. Typically, 2-3 acres of land are required to generate one MW of solar power, depending on the geographic location and efficiency of the panels. Using large areas of land for solar farms will increase competition for land as demand for food production and energy continues to grow, competing for limited land resources. This competition is exacerbated by decreasing cultivable land and an increasing population. This calls for innovative solutions, one of which is agrivoltaics - a land-use configuration where solar power generation and sunlight-dependent agricultural activities are directly integrated. It does not have to be a choice between photovoltaics and photosynthesis; the two can complement each other effectively (Fig.1).
Adolf Goetzberger and Armin Zastrow introduced this concept in the 1980s, demonstrating significant land savings compared to separate energy and food production. Solar PV panels affect crop productivity by reducing incident irradiance levels and partially shading crops. The rate of photosynthesis increases with higher irradiance levels; however, beyond a certain point, further increases in light do not enhance the rate of photosynthesis, a phenomenon known as the "light saturation point." Japanese engineer Akira Nagashima first observed this in 2004. Based on his analysis of crop growth beneath PV modules, Nagashima later patented a specialised structure, paving the way for the development of "solar sharing" and a support scheme for agrivoltaics in Japan. Previously, solar power generation on farmland was banned in Japan, but the Japanese government eventually lifted this ban, allowing solar electricity generation alongside crop cultivation. In Bangladesh, the use of agricultural land for solar power generation is also prohibited.
In an effort to minimise competition for land, the Rural Development Academy (RDA) in Bogra piloted the first agrivoltaics project using a concept called Two-Level Agriculture, which allows solar panels to be installed above crops without significantly reducing agricultural productivity. In 2013, a Solar Irrigation Pump (SIP) was installed at RDA, successfully irrigating rice with a discharge rate of 52,000 litres of water per hour.
A conventional 24-panel solar PV setup for SIP requires 1.5 decimals of land, leaving no room for cultivation. In contrast, the Two-Level Agriculture model (Fig. 2) uses 7.5 decimals of land for 24 panels, allowing cultivation on the entire plot. However, RDA has not yet scaled up and commercialised the Two-Level Agriculture model.
Despite its potential, agrivoltaics is not without its challenges. The primary difficulty is in balancing the allocation of solar radiation between energy generation and crop production. Different crops respond differently to light limitations and shade tolerant crops are generally more suitable for agrivoltaics systems. The microclimate beneath the solar panels can affect temperature and humidity levels requiring adjustment in crop management practices. In Bangladesh, many crops have not yet been evaluated for agrivoltaics applications since it is still a nascent practice with evolving technology, designs, and standards.
Given the right conditions and configurations, agrivoltaics offers acompelling solution that could contribute to the country's growing energy needs without sacrificing agricultural productivity. The global installed capacity of agrivoltaics reached 2.8 GW in 2020, reflectingits growing popularity around the world. In Bangladesh, further research and collaboration between relevant institutions of energy and agriculture sectors such as, the Sustainable and Renewable Energy Development Authority (SREDA), Bangladesh Agricultural Research Council (BARC), Bangladesh Agricultural Research Institute (BARI) etc. are needed to explore the full potential of agrivoltaics. These organisations should work together to identify suitable crops for agrivoltaics and develop best practices for implementation offering a sustainable solution to intense competition for land, ultimately leading to a cleaner, greener future. Moreover, lifting restrictions on using agricultural land for solar power will go a long way in advancing agrivoltaics in Bangladesh.

The writer is the Rector, Bangladesh Power Management Institute
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