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10 Solar Power

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10

Solar Power

Solar generators can be divided into two broad types, photovoltaic (PV) solar cells and concentrating solar power (CSP) plants. The scale of PV generation varies greatly from single panel systems to recharge a battery via individual house rooftop PV arrays (Fig. 10.1) to large utility-scale PV and CSP projects. The ecological impacts of solar generation have been reviewed by Tsoutsos et al. (2005).1 As the installed capacity increases and operational experience expands, it is likely that ecological impacts and concerns will also increase.

Photovoltaic Generation

We are all becoming familiar with solar panels fitted on our houses, farm outbuildings, commercial buildings and boats. There is also a steadily growing number of larger-scale facilities. Photovoltaic cells use light to generate electricity. A variety of panel designs are available, including polycrystalline, monocrystalline and thin-film. The technology is rapidly developing and new designs are continually being tested. It is now possible to install PV roof tiles.

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5 Steam Turbines and Their Cooling Systems

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5

Steam Turbines and Their

Cooling Systems

This chapter reviews ecological issues common to all power-generating systems that use steam turbines, irrespective of their power source. About

86% of total electrical output is generated using steam turbines. Nuclear, coal, oil, gas, solar boilers and biofuel power sources generate using steam turbines and share common environmental impacts relating to the need for cooling to condense steam.

When possible, power stations are placed close to water sources able to supply condenser cooling water. The water requirement per unit of electricity generated varies with the cooling system design and power source.

It is common, even in the scientific literature, to read that large cooling water flows are needed to cool the reactor or generators; this is a misleading statement and so it is useful to first summarize why power stations equipped with steam turbines need large cooling systems.

Steam from the boiler is passed through a series of steam turbines to generate the turning motion that generates the electricity. At the exhaust end of this turbine set, the steam is condensed to form liquid water, which is then passed back into the boiler to become steam again. Water reduces greatly in the volume occupied as it condenses, forming almost vacuum conditions in the condenser. It is the formation of this very low pressure that continually draws the steam through the turbine. The cooling system is used to condense the exhaust steam and carry away the heat. This waste heat is an inevitable thermodynamic cost inherent in the use of a heat engine. It is true that large power stations also have other pieces of machinery that need to be cooled, but the cooling of electrical components, gear boxes and bearings is small when compared with the need to remove heat from the condensers.

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12 Batteries

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12

Batteries

A battery is a device that converts chemical energy to electrical ­energy as required. Grid-connected large-scale batteries have long been desired by utility companies because they could aid the balancing of electrical supply and demand. In the last few years technological advances have made this possible. Batteries are not the only approach used for the storage of energy; another approach is pumped storage (see Chapter 2, this volume). A further approach is energy storage using compressed air; this is not considered further in this book because there are presently only two compressed air storage facilities, one in Germany and the other in

Alabama, USA.

There are a number of battery technologies that have been used for utility-scale storage. The main types are:

• Lead–acid. The standard car battery we are familiar with is lead–acid.

They are of declining interest in terms of large-scale electrical power storage, although large banks of lead–acid batteries are still used for emergency back-up on power plants.

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3 Tidal Generation

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Tidal Generation

There are many designs for the conversion of tidal energy into electricity.

These can be divided into two groups: (i) tidal stream generators that use tidal kinetic energy and (ii) tidal range generators that use the potential energy in the raised head of impounded waters. Suitable resources for tidal stream and tidal range generators are not necessarily found in the same localities.

While estimates of global potential may vary, it is widely agreed that tidal stream energy capacity could exceed 120 GW globally. The UK has one of the largest marine energy resources in the world, estimated to be more than 10 GW and representing about 50% of Europe’s tidal energy capacity.

Tidal power is far from evenly distributed, and only selected coastal localities can ever offer viable locations for tidal generation. The distribution of spring tide tidal energy around the British coast is shown in

Fig.  3.2. In Great Britain, the majority of tidal stream resource is in the north of Scotland and around the Pentland Firth, also around Alderney,

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6 Nuclear Generation

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6

Nuclear Generation

Nuclear power stations use nuclear power to generate the heat used to make the steam that powers the turbines that generate electricity. Therefore, they potentially have all the environmental issues discussed for steam turbine plants in Chapter 5 (this volume). When possible, direct, oncethrough cooling is preferred, possibly because there is a risk that radioactive material released from the reactor might concentrate in the cooling towers. The ecological impacts of direct-cooling, in particular impingement and entrainment of aquatic organisms, is discussed in Chapter  5

(this volume).

The world’s first commercial nuclear power station was opened in

England at Calder Hall, Cumbria, in 1956. Bradwell Nuclear Power Station in Essex opened several years later.

There are many designs of nuclear reactor and the most common is the pressurized water reactor. Figure 6.2 shows the basic design and Fig. 6.3 shows a typical example. Heat is taken from the reactor by the primary coolant, which is then transferred via a heat exchanger in the steam generator to the secondary circuit, which drives the turbines. Most nuclear reactors use uranium as fuel.

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