Category Electricity from Sunlight:. An Introduction to. Photovoltaics

Charge controllers

A charge controller is used to regulate the flow of current from the PV array into the battery bank, and from the battery bank to the various electrical loads. It must prevent overcharging when the solar electricity supply
exceeds demand, and over-discharging when demand exceeds supply. Various subsidiary control and display functions, depending on the price and sophistication of the unit, are included to protect the batteries from damage and to ensure an operating regime that maximises their perform­ance and length of life. Batteries are an expensive part of most stand-alone systems, especially those required to provide a highly reliable electricity supply day and night, so the relatively modest cost of a good charge con­troller is money well spent.

In the previous section we saw how the...

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System components

Подпись: System components

Batteries

Reliable energy storage is crucial to most stand-alone PV systems. Without it operation of the system is confined to daylight hours when the sunlight is sufficiently strong; with it the user becomes independent of the vagaries of sunlight and can expect electricity by night and day. Many new types of storage battery have come on the market in recent years, including nickel – cadmium, nickel-metal-hydride and lithium-ion, but since the great major­ity of present stand-alone PV systems use the more traditional lead-acid type we shall concentrate on it in this section.

You are probably familiar with 12 V vehicle batteries, and at first sight they might seem suitable for storing the output of a PV array...

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Stand-alone PV systems

5.1 Remote and independent

Imagine living in a remote farmhouse, supplied with electricity by an elderly diesel generator and a long way from the nearest electrical grid. The generator needs replacing – but you dislike polluting fumes, the cost of diesel fuel always seems to be rising, and the local electricity utility has just quoted a large sum to connect you to the grid network. How about PV as an alternative? What are the possibilities and pitfalls if you decide on a completely independent stand-alone system?

Figure 5.1 shows a possible scheme. The farmhouse roof faces east-west making it unsuitable for mounting a PV array, so the modules (1) are placed on an adjacent field, south-facing and tilted at an optimum angle...

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PV outside

The PV on these buildings and installations is highly visible from the outside.

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Figure 4.11 This building in Tubingen, Germany, proudly proclaims its solar identity (EPIA/BP Solar).

 

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Figure 4.12 Traditional stone and PV in harmony: a building at the Technical University of Catalunya, Spain (EPIA/BP Solar).

 

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Figure 4.13 Architects in countries with a tradition of social housing can spread their influence widely. This example is in Amersfoort, The Netherlands (IEA-PVPS).

 

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Figure 4.14 A Swedish supermarket embraces PV technology (EPIA/NAPS).

 

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Figure 4.15 A huge solar pergola at the World Forum of Culture in Barcelona, Spain, supports a 4000 m2 PV array (EPIA/Isofoton).

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Figure 4...

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PV outside, PV inside

The aesthetics of successful BIPV may be hard to define and judgements are inevitably subjective – yet most of us know instinctively when a solar building feels right for its setting and context. In this section we consider a number of examples to illustrate the wide range of recent international BIPV. Since a picture ‘ is worth a thousand words ’ in the field of visual impressions our focus is on photographs accompanied by short explanatory captions.

All PV installations are ‘outside’ in the sense that they must receive sun­light. Building facades and sloping roofs are often highly visible to the public; flat roofs are more likely to be hidden. Any PV array on public display should appeal to passers – by and bystanders as well as users and owners of a building...

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Building-integrated photovoltaics (BIPV)

Подпись: Building-integrated photovoltaics (BIPV)

Engineering and architecture

We have seen how a grid-connected system is built up using PV modules, inverters, and BOS components. In previous chapters we included several photographs showing PV roofs and vertical facades. So what exactly is

implied by the term building-integrated photovoltaics {BIPV), and what more is there to be said about giving buildings a ‘face to the Sun’?

Photovoltaic technology is unique among the renewable energies in its interaction with the built environment. Future generations will find it entirely natural to see PV arrays on roofs and facades, in gardens and parks, on bus shelters and car ports, and as electricity-generating windows and screens inside homes, schools, offices, and public buildings. Most will be grid-connected...

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Completing the system

Подпись: Completing the system

Various items are required to complete a grid-connected PV system. They may be less glamorous than solar cells and PV modules, but they are essen­tial to a properly engineered installation. Costs, long-term reliability, ease of maintenance, and sometimes appearance, are important considerations. They are generally referred to as balance of system (BOS) components.

As the prices of solar cells and modules continue to fall and PV manufac­turers achieve the cherished long-term objective of ‘one US dollar per watt’, the cost of BOS components can, unless carefully controlled, seriously inflate total system costs. In the past a figure of about 50% has often been quoted, including inverters...

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From DC to AC

Подпись: From DC to AC

The inverter is the key item of equipment for converting DC electricity produced by a PV array into AC suitable for feeding into a power grid. Inverters use advanced electronics to produce AC power at the right fre­quency and voltage to match the grid supply. While a single inverter may well be sufficient for a domestic installation such as that illustrated in Figure 4.1, multiple units become the norm as we advance up the power scale and their efficiency, reliability, and safety are major concerns of the system designer.

Inverters must obviously be able to handle the power output of a PV array over a wide range of sunlight conditions. Normally they do this using maximum power point tracking (MPPT) to optimise the energy yield...

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