La photovoltaïque flottante [English]

Brief Introduction to Solar PV

Although solar energy has been, is, and will be the most abundant source of energy on Earth, it was not until 1839 that Alexandre Edmond Becquerel observed that the sunlight striking certain materials generated electric current. That is, he discovered the photovoltaic effect. Forty-four more years were needed to develop the first solar cell, which had an efficiency lower than 1%. Thanks to the great interest raised by these first developments and the use of this technology during the space-race years, the less than 1% efficiency devices invented in 1883 became 10% efficiency commercial solar cells by 1959. However, the proliferation of these devices was not fast, and by 1999, the total worldwide installed photovoltaic power was only of 1.000 MW, the equivalent to one single nuclear power plant.

2009 estimate of finite and renewable planetary energy reserves (in Terawatt-years). Total recoverable reserves are shown for the finite resources. Yearly potential is shown for the renewables. Note that with a small fraction of the total solar energy that reaches the Earth we could supply the consumption of the whole planet. Source: A Fundamental Look at Energy Reserves for the Planet, Perez et al.

In the 21st century, the story changes though. A drastic decrease on PV panels’ production costs and a slow but steady increase in their efficiency has greatly promoted the installation of solar PV systems, both in the form of big utility-scale power plants and small residential installations. These improvements made solar PV jump from the 1.000 MW installed worldwide by 1999 to 480.000 MW by the end of 2018 (IRENA).

Evolution of solar PV modules price from 2010 to 2018 for different technologies. Note how the price for the most common solar PV technology (crystalline) has decreased from 3.4 USD/W in 2010 to less than 0.5 USD/W in 2018 (this is more than an 80%!). Source: IRENA.

Evolution of solar cells efficiency from 1975 to 2015. Note that these solar cells are not commercial. Therefore, the efficiency shown can only be reached in the laboratory. Current commercial solar PV panels achieve efficiencies close to the 20%. Source: NREL.

However, solar PV is still far from reaching the generation level of conventional energy sources, such as fossil fuels, and other more abundant renewable sources, such as hydro or wind. Currently, solar PV generation represents less than the 1,5% of the total electricity generated worldwide (IEA).

Electricity generation by fuel. Worldwide data from 1990 to 2016. Note how Solar PV is the small dark green line appearing from 2005 onwards. Source: IEA.

Leaving the political and economic interests of the fossil fuel oligopolies that rule the energy sector aside (hi Exxon, Shell, BP, Total…), and having reached the point where building and operating a solar PV power plant is cheaper than doing so in a fossil fuel equivalent plant, the main problem that the photovoltaic technology encounters is its low energy density. As an example, if a solar PV facility and a nuclear power plant producing the same amount of electricity were to be built, one would need a PV panel area 60 times bigger than the land occupied by the nuclear power plant (Nuclear Energy Institute, NEI).

However, the construction of pharaonic solar PV power plants is not the solution. Although just by covering the 1.2% of the Sahara’s desert with solar PV panels we could generate all the electricity consumed in the whole world (Forbes), a centralized system, were electricity has to travel thousands of kilometres from its production to its consumption, does not seem the most efficient one (and not only in terms of electricity losses during this transport). If produced locally, each country or region is responsible for its energy and does not depend on third parties, which may use the power they have on energy supply as a political tool to threaten and influence its counterparties. In addition to this increase in energy security, the local generation of energy promotes the regional energy sector and all the other interrelated sectors.

Therefore, in order to make solar PV reach the levels of other mature renewable energy sources there are two main conditions that must be satisfied. First, a steady increase in the efficiency of solar panels, so every time less solar PV area is needed for generating the same amount of electricity. Secondly, the use of non-conventional surfaces, such as residential and industrial rooftops or water bodies…  yes, water!

Floating Solar PV

The idea of installing solar PV panels on water bodies’ surfaces, known as floating solar PV, was conceived in 2009 by two German engineers while visiting the Maldives. Back then, they had the belief that the island could get rid of the expensive and pollutant diesel generators that supplied electricity by substituting them by renewable energy. However, their initial thoughts stumbled upon the island’s lack of available land. Six years later, in an attempt to solve the aforementioned issue, the company Swimsol, created by one of these German engineers, launched the world’s first floating solar power plant, named SolarSea.

One of the floating PV platforms used in the power plant SolarSea. Source: Swimsol

The Maldivian project was a great success, since the electricity produced by the floating PV plant was cheaper than the one obtained from the diesel generators. Thanks to this milestone, dozens of studies regarding the viability of this technology have been carried out, suggesting alternative locations to the sea surface, such as natural lakes, human made basins or hydroelectric power plants.

As an example, a recently released study from NREL (National Renewable Energy Laboratory, USA) estimates that installing floating solar photovoltaics on the more than 24.000 man-made U.S. reservoirs could generate about 10 percent of the nation’s annual electricity production. However, floating PV sites are being deployed more overseas, with more than 100 sites as of the end of last year. Japan, for example, is home to 56 of the 70 largest floating PV installations, and in Singapore, the municipal water utility company is planning the construction of a 50 MW power plant, a size equivalent to 45 football fields.

Largest floating PV power plant (150 MW), located in the Three Gorges Dam basin (China). Source: Ciel & Terre International.

The use of floating solar PV entails additional benefits others than reducing the land dependence, such as a reduced water evaporation from lakes and basins and the growth of natural ecosystems, such as algae. Additionally, if floating solar PV is operated alongside hydroelectric facilities, the existing electricity transmission infrastructure can be used, reducing the capital expenses of the solar project.

Nonetheless, PV panels also take advantage of the presence of water. A study from the Solar Energy Application Centre (SEAC) had revealed that floating panels can, in some cases, remain up to six degrees cooler than on-land peers could. Since the efficiency of a solar PV panel decreases the higher the temperature is, the fact of achieving cooler temperatures increases the electricity production of these panels if compared to the ones installed on-land.

Floating PV being installed in Walden, Colorado. Credit: Dennnis Schroeder/NREL

Finally yet importantly, the cost of acquiring and developing land is becoming a larger part of the cost of a solar project. In some places where the price of land is quite high, such as islands or small countries, a rapid adoption of the floating solar PV technology is already underway. Several projects in the Netherlands, Belgium, Seychelles, China, India, Japan, Singapore… are going to be commissioned on the following years.

Links of Interest

  • IRENA’s interactive charts on renewable energy: IRENA
  • IEA interactive database on worldwide energy statistics: IEA
  • NEI, Nuclear power plant vs Solar PV in terms of size: NEI
  • NREL article about floating solar PV: NREL
  • Where Sun Meets Water : Floating Solar Market Report: World Bank

Author: Eloi Delgado Ferrer

Specialization: Residential Solar PV and Energy Auditing.

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