How PV Systems Work

Steve Pester

Principal Consultant

BRE

Photovoltaics (PV)

PV panels generate electricity from sunlight

PV Origins

• Principle discovered in 1839 by Edmund Becquerel in

France

• Solar panels were used for the first time in 1958 to

generate electrical power (0.1 W) for the US Vanguard

spacecraft

1.47 kg aluminum sphere

dia = 165 mm (6.4")

Common Types of PV System

Tiles

Flat roof

Retrofitted to

pitched roof

Façade

Large PV Façade

PV Shading Applications

Sun shades integrated into blinds or glazing

Car

Parks

Cells, Modules, Arrays

Cell

Module (Panel)

Array

Cell Appearance

• Monocrystalline Silicon

• Polycrystalline Silicon

• Thin film

PV Cell Layers

How PV Works

Photons deliver enough energy to liberate carriers which are then accelerated through the

field and on to the contact terminals

0 10

Amps

Most PV systems in the UK are

“Grid Connected”

• No batteries required

• Very low maintenance

• Export of surplus power

• Future-proofs property

against energy price

rises

• Earns income from

Feed-In Tariff

Typical Domestic Installation

Commercial Buildings use 3-Phase Power

Standalone PV system for a building

(i.e. not grid-connected)

Controller

Storage Battery e.g.

lead acid deep cycleDC loads

Inverter

AC loads

External

PV array

More Batteries to

suit design load and

generation

Other generators:

E.g. diesel

Wind

Hydro

Normally found on remote buildings

Batteries (normally only in off-grid systems)

• Very high short circuit currents

• Acid spills

• Heavy weights

• Possible hydrogen gas

2 Million Amp-hour battery

Safety – Why PV has Special Safety Issues:

• Beware High Voltage DC Electricity – Dangerous! few electricians are familiar with DC

• The PV modules cannot be switched off (upstream of the DC isolator)

• Fuses are not likely to blow under short circuit conditions

• Combination of hazards in fires: Falling glass, high voltages during daylight

• Micro-inverters (next presentation) may reduce some of the risks

Summary

• PV technology is simple in principle

• It is widely used in many countries with few real problems

• There are potential hazards, but these are minimised by

using good products correctly installed (MCS)

• High voltage DC electricity is a special hazard

• Batteries are a hazard on off-grid systems

• Questions?