Submerged and Floating Photovoltaic Systems

Modelling, Design and Case Studies

Marco Rosa-Clot,Giuseppe Marco Tina

• Publisher: Academic Press
• Year: 2017
• ISBN:
  9780128123232
• Topic: Technology & Engineering
• Subtopic: Renewable Power Resources
• Index: Technology & Engineering

Submerged and Floating Photovoltaic Systems: Modelling, Design and Case Studies investigates how the use of photovoltaic systems in and on the water can create a positive synergy by increasing the cost effectiveness of PV systems, satisfying the local energy demand and creating positive effects on water. Tina and Rosa-Clot combine their wealth of experience to present a theoretical, numerical, experimental and design-focused analysis of water-integrated PV systems. Thebook isdedicated to providing a very accessible and understandable analysis of the theoretical and modeling aspects of these PV systems.

The authors explore and analyze many existing projects and case studies which provide the reader with an understanding of common design and installation problems, as well as a thorough economic study to help the reader justify the adoption of this very clean method of creating renewable energy.

• Investigates the installation of photovoltaic systems and storage systems over and under the water's surface
• Offers theoretical and practical explanations of how to study, analyze and design photovoltaic energy systems which are complemented by MATLAB simulations for an enhanced learning experience
• Considers how the use of submerged and floating photovoltaic systems can work to fulfill domestic energy demand

Chapter 1

Introduction

Abstract

The electric energy sector throughout the world is briefly analyzed with particular attention to renewable energy systems (RES) and to photovoltaic (PV) sources. The importance of floating PV solutions is discussed both on freshwater basins and on the sea. The availability of large water surfaces near urban areas is the trump card of this new technology, together with its lesser environmental impact. Other advantages of the floating solution are discussed and trends in costs and scale economies are suggested.

Keywords

Renewable energy systems; PV floating and submerged; Cost and futures trends

1 Renewable Energy Penetration

Energy demand is continuously increasing worldwide and the electric sector is becoming progressively important. The electric sector represented 42% of energy demands in 2015 and this percentage will rise to 47% in the next 20 years [1]. At the same time, there is a dramatic parallel environmental crisis due to the burning of fossil fuels and, in particular, due to the electric energy production.

This crisis must be tackled and the most promising prospect is constituted by the expansion of renewable energy sources (RES). This is why, in the last few years, investments in RES (excluding the large and more stable hydroelectric sector) have registered a 12% yearly increase in the installed power in the last 20 years. This trend is likely to continue in the next 20 years at a level of 7.1% [1].

Two main competing technologies have emerged in the course of the last two decades: wind farms and solar plants. Photovoltaic (PV) fields and large wind turbines have a great visible impact, and today have become very popular, flanking the more important, if less showy, hydroelectric sector. The penetration of these two technologies in most industrialized countries and the dumping of their costs are processes which suggest that, within the next few years, the scenario of the energy world will undergo a structural change.

But how long will this process last? Can RES completely replace fossil (and nuclear) energy plants? What will the time scale be?

The answers to these questions must face a two-pronged problem:

• Power density. While traditional thermal energy plants, powered with fossil or nuclear fuels, are highly concentrated structures with a typical size of 1 GW or more, both solar plants and wind farms need very large areas for energy harvesting, and therefore entail a problem of land occupancy.

• Energy availability. The energy produced with thermal plants is produced continuously and has, therefore, two fundamental advantages: it is constantly available and can be modulated according to the needs of the end user. Biomass and geothermal energy are also constantly available whereas solar energy, wind, and even hydroelectric sources have intrinsic limitations due to the intermittency of their energy yield.

Because of the structural need for large surfaces and because of the intermittency of the energy output, solar energy still represents only a small percentage of energy production, as shown in Fig. 1, which captures electric energy production at the end of 2015 [2].

Fig. 1 RES in the electric sector (worldwide data, end 2015) [2].

If we wish to tilt the balance in favor of RES and fully develop solar potentialities so that they are competitive with fossil fuels, two distinct problems need to be solved: the availability of large surfaces and the issue of energy storage.

The wind energy sector has partially solved the problem of land occupancy. The production of huge wind turbines triggered a great expansion in this sector, which reached 3.7% of the total worldwide production in 2015. The availability of off-shore technology contributed to this trend, and 24% of wind power installed in Europe in 2015 was constituted by off-shore wind turbines [3].

The PV sector could adopt a strategy similar to that used in the wind sector by finding large areas for huge PV installations. However, this is more complex. Large surfaces with intense solar radiation can be found but, if used for PV, they would be not available for other purposes, and land in industrialized zones is very expensive. Notwithstanding these problems, a great effort has been made in this direction, with plants of up to 500 MW having been installed so far, and further efforts will be made in the future [4].

In this perspective, the floating photovoltaic (FPV) solution is a perfectly viable and feasible strategy. Its extension to submerged PV plants will be also discussed. The two technologies are different but the basic principle is the same: exploit large existing water surfaces and profit from the water as a useful medium for managing a large plant of PV modules. We show two examples of floating plants in Figs. 2 and 3: one fixed and one with a tracking system. In Fig. 4 the rendering of a large submerged plant is shown.

Fig. 2 Floating PV plant: fixed plant, 100 kWp Singapore.

Fig. 3 Floating PV plant: plant with tracking, 200 kWp Suvereto (Italy).

Fig. 4 Rendering of submerged PV plant.

2 Floating and Submerged PV Plants: Where?

As mentioned above, the large-scale deployment of PV energy entails the use of a significant amount of land. According to the data reported in Ref. [5] for the United States, the capacity-weighted average land use for large PV plants ranges from 0.42 (fixed) to 0.27 (1-axis) MWp/ha, while more recent research on land use and the so-called geographic PV potential suggests that the power installable for a fixed plant is 0.5–0.7 MWp/ha [6]. The concept of geographic potential can be extended to water surfaces. In this case, however, we would be working with technical problems which are very different from land-based PV plants and we would be able to arrange the modules more compactly. In floating plants values increase to more than 1 MWp/ha (see Chapter 8).

It should be noted that land hunger, land cost, and land management heavily affect the PV sector. Large areas of free land are not normally available in developed countries, and the growth of human settlements in industrialized countries generates the demand for strong power units concentrated in a limited space, which pollute very large areas and trigger issues of air quality and CO₂ emissions.

However, it must be observed that wherever human settlements are built, water is also present. It can be found in a variety of forms such as lakes, sea, large artificial basins built for various purposes (water storage, irrigation, or civil use), wastewater treatment, hydroelectric basins, abandoned mines, etc. These very large existing surfaces suggest a very simple solution to the problem of power/surface limitations: they could be used to install FPV plants.

Furthermore, in most cases, around or next to basins or lakes, there are human settlements which are already equipped with an electricity grid, if not with electric power plants. In the United States, 78% of the electricity is used in states bordering an ocean or a Great Lake [7].

But how large are these surfaces? Can they account for a substantial expansion of the PV sector and increase its contribution to RES? A simple analysis of the available water surfaces shows ...