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How Solar Power Systems Work

What is solar power?

Solar power is electricity generated from solar radiation. This process of converting energy from the sun into electricity is known as photovoltaics (PV).

About photovoltaics

PV technology utilises layers of micro-fine crystalline silicon to convert sunlight into small electrical charges.

A single PV cell consists of two or more thin layers of crystalline silicon semi-conducting material. When the silicon is exposed to light, small electrical charges are generated and conducted away by metal contacts as direct current (DC). More simply, photons from sunlight knock electrons into a higher state of energy, creating electricity.

Single solar cells are connected together and housed in a module (panel). These modules are the building blocks of PV systems and are, in turn, connected together to generate usable volumes of electricity.

SILICON WAFERS   –>   SOLAR CELLS   ->   SOLAR MODULES

Types of PV technologies

There are essentially two types of PV technology – crystalline and thin-film, and crystalline can be further broken down into two types – monocrystalline and polycrystalline.

Monocrystalline Cells

These are made using cells cut from a single cylindrical crystal of silicon. While monocrystalline cells offer the highest efficiency (approximately 18% conversion of incident sunlight), their complex manufacturing process makes them slightly more expensive.

Polycrystalline Cells

These are made by cutting micro-fine wafers from ingots of molten and recrystallized silicon. Polycrystalline cells are cheaper to produce, but there is a slight compromise on efficiency (approximately 14% conversion of incident sunlight).

Thin Film PV

Thin film PV is made by depositing an ultra thin layer of photovoltaic material onto a substrate. The most common type of thin-film PV is made from the material a-Si (amorphous silicon).

A photovoltaic module is composed of individual PV cells with an aluminium frame and glass on the front.

Monocrystalline Module                                         Polycrystalline Module

Renesola-Monocrystalline-Module                                                    Renesola-Polycrystalline-Module

 

Types of PV systems

PV systems operate in two basic forms – grid connected PV systems and off grid PV systems.

Grid Connected PV Systems

A grid-connected PV system is an electrical generation system which links to the electricity mains to feed any excess capacity back to the mains electrical grid. When insufficient electricity is generated to cover usage, electricity is drawn from the mains grid to make up the short fall.

PV-Diagram

 

Off Grid PV Systems

As the name suggests, off grid PV systems are used in isolation of electricity grids. They are also known as Stand-Alone systems.

What are the benefits of solar power?

Solar energy is a clean, efficient, and sustainable form of renewable energy.

A solar power system is a sound financial decision. With solar panels powering your home, you’ll see this every time your electricity bill arrives.

How will I use the electricity from a PV system?

For grid-connected solar systems, the electricity will work just like the electricity supplied through the electricity grid providing you with 240V AC electricity. During the day, your PV system will generate electricity from the sunlight available. Any excess electricity not immediately used in the home will be automatically fed back into the electricity grid. When the sun isn’t shining, or when your electricity demand is greater than the solar system’s generation, you will draw electricity from the grid.

For standalone systems, the electricity generated will be fed into batteries for storage. As you use power in your home, the system’s inverter will automatically supply energy from the batteries. Your inverter and/or regulator will indicate how much energy you have left in your batteries. If your system has been designed to suit your energy needs, you should not run out of electricity, and standalone systems are often designed to include a generator for back-up in periods of high demand or extended periods of cloudy weather.

How is the solar electricity metered?

Net metering:  excess electricity generated (generation exceeding consumption) by your solar power system is exported to the mains electricity grid.

Gross metering:  all the electricity generated by your solar power system is exported to the mains electricity grid.

What happens at night?

Solar photovoltaic (PV) technology requires sunlight to produce electricity, therefore will not produce electricity during the dark hours of the night. If your solar power system is grid-connected, your local utility will continue to supply your electricity at night. If you have a standalone system, your batteries or back-up generator will provide you with electricity at night.

What happens in electrical blackouts?

A grid-connected solar electricity system will shut down until utility power returns in order to assure a safe working environment for utility line workers. The system will automatically start again when the blackout is over.

What affects the performance of solar power systems?

Weather naturally affects the performance of solar panels but not entirely as you might expect. The amount of sunlight is most important in determining the output of a solar electricity system, but temperature is also important.

Contrary to most people’s intuition, solar electricity panels actually generate more power at lower temperatures with other factors being equal. This is because solar cells are electronic devices and generate electricity from light, not heat. Like most electronic devices, solar cells operate more efficiently at cooler temperatures. In temperate climates, solar modules will generate less energy in the winter than in the summer but this is due to the shorter days, lower sun angles and greater cloud cover, not the cooler temperatures.

Solar panels are naturally inefficient in low sun and cloudy conditions. Output is directly proportionate to the amount of sunlight available at any given moment, so although systems can generate 50 – 70% of their typical output under bright overcast conditions, production will continue to diminish as less light reaches the surface of the solar modules.

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