# Category STAND-ALONE SOLAR ELECTRIC SYSTEMS

## The Flow of Electric Current

Although wires are actually very different from water pipes, electricity flowing through wire can be compared to water flowing through pipes. When electricity is flowing, there is said to be electric current.

Current (I) is the rate of flow of electrons through the wires. It is measured in amperes (called amps, A) which is a measure of the number of electrons passing through a given length of wire. This is similar to the rate of flow of water though pipes (i. e. litres per second). Current flowing in one direction is called direct current (DC), while current which changes direction of flow is called alternating current (AC). In a 12-volt DC system, a 12 watt lamp draws about 1 ampere of current.

Voltage, or potential difference, is the difference in potential energy between the ends of a c...

## Basic Extra-Low-Voltage Direct Current (DC) Electricity

This section reviews some terms used to describe basic electrical principles. If you are just beginning to learn about electricity, you should check a secondary-school text for a good introduction to the subject. Books on how to wire houses are a good introduction to the subject of 110/230V AC electricity.

Electricity is power provided by the flow of very small charged particles called electrons through metal wires. Because electrons are so small, it takes millions of them moving together in the same direction to develop a detectable electric current. Wires carrying electricity do not appear any different from wires not carrying electricity (although they may get a bit hot), so electricity is invisible to the human eye when travelling through wires.

Conductors and Insulators

Not all substa...

## Energy, Power and Efficiency

The following section is a review of the energy concepts that must be understood to install and design solar energy systems.

Energy

Energy is referred to as the ability to do work. For example, energy is required to boil tea, to move a vehicle between two points or to make a radio work. When boiling tea on a woodstove, the energy source is chemical energy stored in firewood. When driving a car, the source is chemical energy stored in petrol. When operating a radio, the energy source is chemical energy stored in dry cells.

Energy is measured in units called joules, J, or in watt-hours (see below). Because one joule is such a small amount of energy, words that name large numbers of joules are commonly used...

## Catalogues

The five companies below offer solar products through catalogues and on-line. They have interesting catalogues of products, books and specialized design services. There are many more companies like these around the world.

 Name Country of origin Products Website Real Goods USA Large line of solar and off-grid products www. realgoods. com Alternative Energy Engineering USA Large line of solar products Dealer training Downloadable catalogue www. aeesolar. com Phaesun Germany Large line of solar and off-grid products Downloadable catalogue www. phaesun. com Wind and Sun, Ltd UK Large line of solar and off-grid products, excellent printed catalogue www. windandsun. co. uk Backwoods Solar (USA) USA Specializes in independent electric power...

## Charge controllers and inverters

The list below provides a basic introduction to major inverter and charge controller suppliers in the off-grid market.

 Name Country of origin Products Website Phocos Germany Charge regulators, inverters, lights www. phocos. com Apollo Solar USA Charge controllers, inverters www. apollosolar. com Studor Switzerland Inverters, monitors www. studer-inno. com Blue Sky Energy USA Charge controllers www. blueskyenergyinc. com Morningstar USA Charge controllers, inverters www. morningstarcorp. com
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 Name Country of origin Products Website Outback Power USA Charge controllers, inverters www. outbackpower. com Xantrax USA Charge controllers, inverters www. xantrax. com Steca Germany C...

## Standards, codes of practice and policy

Codes of practices guide the installation methods, choice of materials, workmanship and system maintenance, ensuring a long and safe lifetime for PV power systems. They provide the criteria by which systems can be inspected to ensure sustainable and safe operation.

The following codes of practice and lists of pre-qualified products are available:

International Electro-technical Commission (IEC)

The IEC has developed (and continues to improve) a set of comprehensive standards for solar photovoltaic energy systems. This is done by Technical Committee 88.

www. iec. ch/zone/renergy/ren_standardization. htm

Global Approval Program for Photovoltaics (PV-GAP)

PV GAP is a not-for-profit organization that promotes the use of internationally accepted standards, quality management processes and organ...

## Lighting Africa

International finance organization dedicated to improving access to modern lighting services for low income groups in Africa. Helps in the promotion of low cost, high quality lighting products through networking, quality monitoring, policy initiatives and competitions. www. lightingafrica. org

Solar Electric Light Fund

International development organization promoting solar power and wireless communication, with many projects. www. self. org

Alliance for Rural Electrification

International development organization involved in rural electrification, with a strong emphasis on solar electrical systems. www. ruralelec. org

Green Dragon Energy

Provides training courses and is a source of books on renewable energy (mainly off-grid). Has been involved in solar energy for many years. www...