Small-Scale Renewable Energy Systems

Independent Electricity for Community, Business and Home

Sven Ruin, Göran Sidén

• Publisher: CRC Press
• Year: 2019
• Print ISBN: 9780367030971
• eBook ISBN: 9780429670435
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Energy

A revolution is ongoing in the field of small-scale energy solutions, which can enable lower impact on the environment, more robust supply and self-determination. Solar power and other forms of renewable energy sources, which you can implement to generate your own electricity, are growing quickly. Electromobility is transforming the car industry and transportation systems and can also play a role in your energy system. Electricity can be used much more efficiently than before, for example by using LED light, variable speed motor drives and efficient home appliances. Smart controls are available, sometimes with free open source software. All this opens up tremendous opportunities for energy independence, which is the focus of this book.

The book introduces the reader to a number of renewable energy sources, to different options for storing electricity and to smart use of electricity, particularly in the context of small isolated systems. This is important because many renewable energy sources are weather- and season-dependent and usually require storage and smart control, in order to obtain a system that is completely independent of the electricity grid.

In the book, overall system design is explained, including how to combine different sources in a hybrid system. Different system sizes and architectures are also covered. A number of real cases are described, where homes, businesses and communities have achieved a high level of energy independence or are on their way to achieving it.

This book will prove useful in university education in renewable energy at bachelor and master level, and also for companies and private individuals, who want to start or expand activities in the area of renewable energy.

Chapter 1
Introduction

The generation of electricity from renewable energy sources has undergone rapid development in recent years. Globally 14 GW solar photovoltaics were installed as of 2008. In 2018, installations reached 512 GW, according to preliminary statistics. This is an increase of 37 times in 10 years, an incredible development. Solar electricity generation was about 2.2% of the world’s electricity needs (Fig. 1.1).

Total installed wind power in the world was 121 GW in 2008. In 2018, the installed power had increased to 600 GW – a fivefold increase in 10 years. Wind power generated 6% of the global electrical power supply. In total, renewable energy provided more than 27% of the global needs for electricity.

Some other renewable energy sources, such as hydropower and bioenergy, have played a large role for a long time and are often a great complement to more fluctuating sources such as solar and wind. New developments are making it possible to have an increasing share of renewable sources in the energy mix. For example, in remote locations biofuels can be used to enable existing diesel engines to switch over to provide renewable generation. Of special interest for remote locations is also that renewable energy can be used on a very small scale (Fig. 1.2).

Figure 1.1 House with solar photovoltaic system including battery storage.
Source: Courtesy of Whidbey Sun & Wind LLC, Washington, USA.

Figure 1.2 The submerged Ampair UW100 generator can provide 100 W at 12, 24 or 48 V DC in combination with a battery (which can also be charged from other sources). It can be used, for example, for run-of-river hydropower, on towed equipment or to capture tidal currents.
Source: Seamap (UK) Ltd.

Another interesting development is the rapid growth and price drop of batteries, in particular lithium-ion, because of the mass production of electric vehicles (EVs). Electricity storage costs will probably continue to decrease, for example, because of the second-life of EV batteries. Batteries that can store electricity – for example, from renewable sources – at low prices open up interesting possibilities in both developing and developed economies. In areas without power grids, local systems for houses or villages, for example, will be more viable than ever before. However, especially in off-grid areas, many are unaware of these new opportunities. Some challenges can be lack of skilled technicians and standard solutions.

Electrification can be done in new ways, such as using EVs for vehicle-to-home, without expensive power grids. Buying, for example, a second-hand EV can often be a cost-effective way to buy electricity storage, and then you also get a car with it, which can transport more than people. EVs provide an opportunity for a “grid on wheels” that can carry significant amounts of energy. Even where large power grids exist, the possibility of building houses without connection to the grid can provide a new situation in the electricity market. The monopoly situation of grid owners is challenged. Many power utilities are aware that a paradigm shift is taking place, and some are looking into how they can be part of that future. For example, E.ON in Simris in southern Sweden is testing a microgrid.

In transportation, the ongoing small-scale energy revolution is opening up new opportunities to make fuel locally, which can be used for many types of vehicles. For example, biogas is produced by many municipalities to be sold at local dispensers, to fuel city buses or to drive generators. Small fuel cells can be used, for example, with upgraded biogas, to produce electricity more efficiently than has ever been possible with an engine. EVs can be charged from local renewable sources (Fig. 1.3), also in off-grid systems with sufficient capability Hydrogen enables fuel to be made locally from electricity and water, to be stored in large quantities at a lower cost than a huge battery bank, and to be converted back to electricity.

Renewable energy is important for global climate concerns. Renewable energy sources provide smaller emissions of greenhouse gases. So far, environmental concerns have been a major driving force in the development of renewable energy. A change now is that renewable energy sources also have become more economically competitive. Reports from Ecofys (for the EU) and the US Energy Information Administration (EIA) show that the cost of electricity from land-based wind power is comparable or lower than that from fossil sources and nuclear power. Electricity from solar photovoltaics is not far behind. In areas with good access to solar radiation, it can already provide the cheapest new power generation.

Even more competitive is usually the efficient use of energy. Smart use of energy usually goes hand in hand with renewable energy and is of vital importance for the huge challenge facing our society to achieve sustainable development. On the local level, it can, for example, make an off-grid system much more affordable, because generation does not have to be oversized.

Figure 1.3 Inauguration in 2015 of Giraffe 2.0, which is a wind and solar power station by InnoVentum. It can be used, for example, in combination with charging electric vehicles. The basic configuration is for on-grid, but could also be made for off-grid.
Source: S. Ruin.

Energy security is another driver. Renewable energy reduces reliance on imported energy. If done in a smart way, distributed renewable energy can also contribute to grid reliability and to the better handling of emergency situations. One example of the latter is a study and field tests done by Spirae and Energynautics for eneginet.dk in Denmark regarding coordinated control of local assets. They found that in the event of a transmission system emergency, local distribution networks (60 kV and below) could be rapidly isolated from the transmission network (150 kV and above) and operated autonomously using local resources. This “safe island” operation would reduce the impact on electricity consumers and contribute to a more rapid recovery from the emergency.

An individual home or business owner can provide for their own energy security in a more economical way than before, for example with a grid interactive renewable energy system that normally sells surplus generation, perhaps also participates in grid frequency regulation and, in case of a grid failure, provides grid backup at least to the most important local loads. Such systems can reduce the burden on the grid during a shortage, thereby reducing the risk of grid collapse. Should the grid fail, being able to generate your own electricity can be very important, for example to drive a water pump.

There are many reasons why people want independent power systems. Tiny systems with solar photovoltaics or small wind turbines, batteries, charge controller and perhaps inverter for AC are used in many holiday homes, caravans and pleasure boats. They often provide the most fundamental needs for lighting, refrigerators and supply to electronics such as computers, mobile phones, radio and TV. With the ongoing development of for example batteries, they can meet even more needs in a fully acceptable manner, also in mobile applications.

For many holiday homes it is actually economical not to connect to a power grid. For users who need only a small amount of electricity, the high fixed costs of the grid can be especially prohibitive. If the distance is long to the existing grid, the case for grid connection becomes even weaker.

In remote villages or areas that are difficult to reach with electricity grids, for example on islands, it is often a necessity to rely on small independent systems instead of national electricity grids. Where they have small isolated electricity grids, they have so far often been supplied with diesel-powered power plants. Such power supply is often both insecure and expensive per kWh. With local plants that produce renewable energy, they can get a better and cheaper supply.

In developing countries, for example in sub-Saharan Africa and in South Asia, many people still lack access to an electricity supply. It is estimated that more than one billion people are in this situation. In many such areas, small local, renewable energy solutions are being developed as a more viable way to increase access to electricity compared with national electricity grids. For example, the World Bank [1] has reported on investments in countries such as Bangladesh, Ethiopia, Kenya, Haiti and Bolivia. A total of US$ 1.8 billion has been invested over the past eight years. Also in large economies like Brazil where most people have access to electricity, there is a disadvantaged minority who don’t. One approach to changing this is through training of local actors [2].

Electricity access is not a binary question. An additional one billion people are estimated to live with unreliable or insufficient electricity service. Electrical safety is also an issue in many places.

Our society is becoming increasingly dependent on a functioning electricity supply for household, business and many other needs. For example, water supply, fuel dispensers, internet communication and modern payments will normally not work without electricity. This dependence is actually a danger. Therefore, many people want the opportunity to be independent and have control over the electricity supply. Smart-grid solutions can also provide new opportunities for managing the electricity supply, also locally, but if designed in an unsuitable way, they can contribute to the danger (perhaps they can also be hacked).

An important development is also improved understanding of the renewable energy resources. In many cases, such knowledge is becoming more accessible to anyone. For example, the International Renewable Energy Agency, IRENA, has on the Internet published global resource maps of average solar irradiation and wind climatology [3], which are free to access. Knowledge is also shared directly between interested stakeholders on online platforms such as Energypedia (energypedia.info).

To summarize: While environmental concerns have been driving much of the development of renewable energy, we are now in a situation where the economic aspects are emerging as drivers. With the new, cheaper renewable energy, the improved storage possibilities, smart controls and energy-efficient technology, the costs can be lower in the long run – both for those who already have electrical power and those who don’t. However, we also should not underestimate the force inherent in the idea of being completely self-sufficient. Off-the-grid (OTG) has become the symbol of a system and lifestyle designed to meet needs without the support of remote infrastructure, such as a power grid. Off-the-grid homes aim to achieve autonomy; they do not rely on community services for water supply, sewage, gas, electricity or similar services. This brings opportunities to provide energy for all and empower local people.

References

[1] Riccardo Puliti, “Off-grid bringing power to millions”, World Bank blogs, 2018-02-26. [Online]. Available from: http://blogs.worldbank.org/energy/grid-bringing-power-millions [Accessed 2019-05-27].

[2] Instituto Peabiru, “Light for a Better Life”. [Online]. Available from: https://peabiru.org.br/lightfor-a-better-life/ [Accessed 2019-05-27].

[3] IRENA – International Renewable Energy Agency, “Global Atlas for Renewable Energy”. [Online]. Available from: https://www.irena.org/globalatlas/ [Accessed 2019-05-27].

Chapter 2
Electricity generation

2.1. Solar power

The most common technology for solar electricity generation is photovoltaic (PV) cells, which convert the photons, the energy carriers in sunlight, directly into electric power. The building blocks of PV technology are truly small scale, but can be combined to make large systems. The solar cell that supplies a watch generates power equal to only a few milliwatts, while the largest modules generate some hundred watts. Big solar power plants are composed of thousands of modules. But technically speaking, a solar module on a street ...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Dedication
• Contents
• 1 Introduction
• 2 Electricity generation
• 3 Electricity storage
• 4 Use of energy and electricity
• 5 System design
• 6 Case studies
• Index