Solar energy is the largest energy resource on earth that offers abundant renewable energy resource to mankind relatively well-spread over the globe. It can be captured and transformed into heat or electricity. There are several technologies commercially available for converting solar energy into electrical energy. These are broadly classified into two groups: solar photovoltaics (PV) and solar thermal or concentrating solar power (CSP).
In Bangladesh, only solar PV has gained acceptance because of ease of application and affordability. The main limitation of solar PV is that it requires a huge land for useful power generation from ground-mounted solar PV ranging from 3 to 4 acres of land per megawatt depending on solar irradiance and efficiency of the solar PV system. Thus, in a densely populated country like Bangladesh the space for generating utility-scale solar power is very limited because of competing demand of land for agricultural or other uses.
The technological innovation that has minimised the burden of land requirement is Floating Solar PV. The general layout of a floating solar PV system is similar to that of a ground-mounted solar PV system. The only difference is that in floating solar PV system, the PV arrays and often the inverters are mounted on a floating platform. The floating platform is held in place by an anchoring and mooring system (figure 1). The direct current (DC) electricity generated by PV modules is gathered by combiner boxes and converted to alternating current (AC) by inverters. For small-scale floating solar PV plants near the shore, it is possible to place the inverters on land. Otherwise, both central or string inverters on especially designed floats are typically used. The platform, together with its anchoring and mooring system, is an integral part of any floating PV installation.
A floating solar PV system can conveniently be installed on still water bodies such as ponds, lakes, dams and reservoirs. Floating solar PV technology has a number of advantages over land-based equivalent. The foremost benefit is that it takes the advantage of idle water surfaces, and hence there is no direct competition with agriculture or other uses of land. Secondly, floating solar PV panels have higher power generation efficiency compared to the ones installed on land, thanks to the cooling effect of water underneath the panels. The cooler environment also reduces stress on the system, extending the system’s lifespan. Thirdly, floating solar panels can shade the water they float on and reduce evaporation which is crucial for water conservation in dry season. Fourthly, floating solar PV is potentially less prone to shading and typically performs in a low-dust environment. Finally, operation and maintenance costs are also often reduced because the water needed for cleaning is available at source and components are less likely to overheat.
Exploiting its advantages, Japan built the first floating solar PV plant with an installed capacity of 20 kilowatt-peak (kWp) in 2007 in Aichi. Following Japan, many countries including France, Italy, the Republic of Korea, Spain, and the United States tested small-scale floating solar PV systems for research and demonstration purposes. Consequently, the first commercial floating solar PV plant of 175 kWp installed capacity was built in the US state of California in 2008, which was floated atop a water reservoir. Afterwards, medium-to-large floating solar PV plants, larger than 1 MWp, began to emerge in 2013. Recently, plants with capacity of tens and even hundreds of megawatts have been installed in China; more are planned in India and Southeast Asia. China is also credited with the installation of world’s largest floating solar PV plant of 150 MWp capacity on a lake that formed following the collapse of a coal mine in the Anhui province. Floating solar PV plants now exist in nearly every region of the world surpassing total installed capacity 1 gigawatt-peak (GWp) in 2018. The rise of floating solar PV is also opening up opportunities for combining floating solar PV plants with hydropower stations. Establishment of the first-ever hydropower-connected floating solar PV plant with an installed capacity of 220kWp in Portugal is a case in point. Installation of floating solar PV plants in diverse countries at different scales clearly manifests the maturity of the technology to be replicated elsewhere with similar conditions.
Realising the benefits of floating solar PV technology, Mongla Port Municipality, for the first time in Bangladesh, installed a 10kWp floating solar PV system on the water surface of the reservoir of its water treatment plant in 2019 (figure 2). The Successful operation of this 10kWp floating solar system with net-metered connection paved the way for installing many more similar systems and even developing megawatt-scale floating solar PV plants.
Bangladesh, located on the delta of three major rivers, possesses an enormous quantity of water bodies including rivers and streams, lakes and marshes, haors, baors, beels, reservoirs, ponds, and estuarine systems with extensive mangrove swamps. These water bodies dispersed throughout the country offer ample scope for expansion of floating solar PV plants of different capacities, provided the authorities concerned might find them out.
Bangladesh, with high population density and competing uses for available land, simply cannot afford to keep her water bodies underutilised when there exists a potential to use them for solar electricity generation. Following Mongla Port Municipality, unexploited and non-revenue-generating water surfaces may be turned into commercial solar power plants taking advantage of the floating solar PV technology. The authorities in charge of the management of water bodies are required to take initiatives to find out the ones suitable for installation of floating solar PV plants. They may either take steps to set up floating solar PV plants themselves, or let private-sector sponsors set up the same. Wider deployment of floating solar PV plants will contribute to scaling up renewable power generation while ensuring better management of water bodies otherwise left unutilised.