Category Electricity from Sunlight:. An Introduction to. Photovoltaics

PV water pumping

Infectious diseases caused by tainted drinking water and primitive sewage disposal are largely unknown to those of us who live in the developed world. We tend to take the benefits of pure water for granted. But whom should we thank for this blessing? It has been said that the civil engineers of the nineteenth century did more to improve public health than all the doctors and surgeons put together, by designing and building the infrastruc­ture for modern water supplies.

The situation can be very different elsewhere. In rural areas of some of the poorest countries in the world millions of people, especially women, spend

Figure 5.25 Clean and accessible: PV-pumped water (EPIA/Schott Solar).

Подпись: Figure 5.25 Clean and accessible: PV-pumped water (EPIA/Schott Solar).
hours each day fetching and carrying water, sometimes from polluted streams or pools...

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Island electricity

Providing a small island community with an economic, convenient, and reliable electricity supply can be a major challenge. Traditionally, islanders in the developed world have installed diesel generators and depended on fuel deliveries from a mainland depot. But diesel engine maintenance is expensive, fuel costs always seem to be rising – and there is a noise and pollution problem that people who cherish their natural environment would rather avoid. Most islands have a valuable wind resource, many have lots of sunshine and free-running rivers or streams...

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PV in Space

For more than half a century spacecraft have relied on solar cells for their power supplies. In the early years of the modern PV age solar electricity was so expensive that space exploration provided its only significant market. The costs of designing, manufacturing, and launching vehicles into Space are so large that the price of cells to power them is relatively

Figure 5.18 PV encircles the Earth (NASA).

Подпись: Figure 5.18 PV encircles the Earth (NASA).
unimportant, the main criteria being technical performance and reliability in the harsh space environment...

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Applications

Подпись: Applications
The variety of applications for stand-alone PV systems is extraordinary. Almost any need for electricity in isolated, remote, or independent locations can, in principle, be met by solar cells. We have already mentioned a number of examples in this book, from solar-powered watches and calcula­tors to space vehicles, but our main focus has been on electricity supply for remote buildings far from an electricity grid. This has provided a chance to describe typical units that make up medium-power systems, including PV arrays, battery banks, charge controllers, and inverters, in a setting that most of us can easily imagine. It is now time to move out into the wider world – and beyond – to discuss a number of key application areas where PV has made, and continues to make, major contributions...

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PV arrays and battery banks

In the previous section we estimated 2.2 kWh as the average daily electric­ity requirement for a holiday home in southern Germany, and it is now time to decide on the amount of PV and battery storage needed to meet the specification. In this section we shall often refer to arrays and battery banks, terms appropriate for medium-size and larger systems, but our approach is also valid in principle for small systems containing a single PV module and battery.

The first task is to work out the size of the PV array: how much peak power should it have to satisfy the electricity demand? As it stands, the 2.2 kWh/ day applies throughout the year whereas the amount of sunlight falling on the array is bound to be seasonal...

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System sizing

Подпись: System sizing
Assessing the problem

In the popular imagination science provides firm answers to firm questions, leaving little to chance when it comes to technical decision-making. But things are not as simple as that. For example, while almost all experts agree that global warming due to greenhouse gas emissions poses a major threat to life on Earth, there are wide-ranging views on its exact severity and timescale because the supporting evidence is essentially statistical. Scientists and engineers are trained to understand technical uncertainty, but it often confuses the public, and offers scope for vested interests to declare the whole idea erroneous or exaggerated.

In this book most of our discussion is based on ‘hard science’ and we have been able to describe the performance of individual system ...

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Hybrid systems

Подпись: Figure 5.13 (a) Efficiency curves for two types of inverter; (b) a daily load profile for a solar home.
Подпись: Hybrid systems

Stand-alone systems that rely on natural energy flows in the environment must inevitably cope with intermittency. Their main defence against unreli­ability and loss of service is a battery bank to store incoming energy when­ever it is generated and feed it out to the electrical loads on demand. But in many cases system reliability may be enhanced, and the size of the battery bank reduced, by a hybrid system based on two or more energy sources. PV and wind power are often attractively complementary, espe­cially in climatic regions such as Western Europe where low levels of winter sunshine tend to coincide with the windiest season of the year (and, of course, wind does not refuse to blow at night!)...

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Inverters

We described a stand-alone PV system for a remote farmhouse at the start of this chapter (see Figure 5.1). It includes an inverter, connected to the battery bank, for supplying AC to the various household electrical appli­ances. Of course, inverters are not required in systems having only DC loads; but when they are used, it is important to understand the special features required in independent, stand-alone, units. As the stand-alone PV market develops customers are increasingly opting for AC systems because they like the flexibility offered by a wide range of consumer electronics, household appliances, electric tools, and even washing machines. AC systems are also used by hospitals and remote telecommunications sites, and for running machinery in small factories...

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