Put simply solar (photovoltaic) power systems convert sunlight into DC electricity which is converted by a solar inverter into AC electricity which can then be used by home appliances. Additional or excess solar energy is either fed into the electricity grid or stored in a battery system.
The Main Components in a Solar System
Solar panels and Photovoltaic cells
Most modern solar panels are made up of many solar cells or photovoltaic (PV) cells which generate direct current (DC) electricity from sunlight or energy from the sun. The individual PV cells are linked together within the panel and connected to adjacent panels using cables. Note: It is light energy or irradiance, not heat, which produces electricity in photovoltaic cells. Solar panels also known as solar modules are usually installed together in strings to create a solar array.
Solar panels can generate energy during cloudy and overcast weather but the amount of energy depends on the 'thickness' type and height of the clouds, and how much dispersed light energy can pass through. The amount of light energy is known as solar irradiation and usually averaged over the whole day using the term Peak Sun Hours (PSH) for the location.
Solar inverter
Solar panels generate DC electricity which needs to be converted to alternating current (AC) electricity for use in our homes and businesses. This is the role of the solar inverter. In a string inverter system, solar panels are linked together in series and the DC electricity is brought to a single inverter which converts the DC to AC. In a micro inverter system, each panel, or every two panels, has its own micro inverter attached to the back side of the panel. The panel still produces DC, but is converted to AC on the roof, and is fed straight to the electrical switchboard.
Distribution board (DB)
(Electricity consumption control) AC electricity is sent to the distribution board where it is directed to the various circuits and appliances in your house that require electricity. Any excess electricity generated by the solar system can be sent to either a battery storage system if you have an off-grid or hybrid system, or to the electricity grid if you have an on-grid system. Hybrid systems can both export excess electricity and store excess energy in a battery.
The three main types of Solar Power Systems are:
- Grid-tie – tied into the national grid
- Island - also known as a stand-alone power system
- Hybrid - solar plus battery storage with grid-connection
Grid-Tie Solar System
Grid-tie solar systems are by far the most common and widely used by homes and businesses. These systems are connected to the public electricity grid and do not require battery storage. Any solar power that you generate from an on-grid system (which is not used directly in your home) could be exported onto the electricity grid in the future and you would get paid a feed-in-tariff for the energy you export.
Unlike hybrid systems, grid-tie solar systems are not able to function or generate electricity during a blackout or power outage due to safety reasons; since blackouts usually occur when the electricity grid is damaged. If the solar inverter was still feeding electricity into a damaged grid it would risk the safety of the people repairing the fault/s in the network. However most hybrid solar systems with battery storage are able to automatically isolate from the grid (known as islanding) and continue to operate during a blackout. Batteries are able to be added to an on-grid solar system at a later stage if required.
In a Grid-tie system, this is what happens after electricity reaches the distribution board:
The meter. Excess solar energy runs through the meter, which calculates how much power you are either exporting or importing (purchasing).
Metering systems work differently in many countries around the world. The meter measures both production and export, and the consumer is charged (or credited) for net electricity used over a month or year period.
The electricity grid. Electricity that is sent to the grid from your solar system can then be used by other consumers on the grid (your neighbours). When your solar system is not operating, or you are using more electricity than your system is producing, you will start importing or consuming electricity from the grid.
Island Solar System
An off-grid system is not connected to the electricity grid and therefore requires battery storage. An off-grid solar system must be designed appropriately so that it will generate enough power throughout the year and have enough battery capacity to meet the home’s requirements, even in the depths of winter when there is less sunlight. The high cost of batteries and inverters means off-grid systems are much more expensive than on-grid systems and so are usually only needed in more remote areas that are far from any electricity grid. However battery costs are reducing rapidly, so there is now a growing market for off-grid solar battery systems even in cities and towns.
There are different types of island systems which we will go into more detail later, but for now I will keep it simple. This description is for an AC coupled system, in a DC coupled system power is first sent to the battery bank, then sent to your appliances. To understand more about building and setting up an efficient off-grid home see our sister site go off-grid/hybrid
The battery bank. In an off-grid system there is no public electricity grid. Once solar power is used by the appliances in your property, any excess power will be sent to your battery bank. Once the battery bank is full it will stop receiving power from the solar system. When your solar system is not working (night time or cloudy days), your appliances will draw power from the batteries.
Backup Generator. For times of the year when the batteries are low on charge and the weather is very cloudy you will generally need a backup power source, such as a backup generator or gen-set. The size of the gen-set (measured in kVA) should to be adequate to supply your house and charge the batteries at the same time.
Hybrid Solar Systems
Modern hybrid systems combine solar and battery storage in one and are now available in many different forms and configurations. Due to the decreasing cost of battery storage, systems that are already connected to the electricity grid can start taking advantage of battery storage as well. This means being able to store solar energy that is generated during the day and using it at night. When the stored energy is depleted, the grid is there as a back-up, allowing consumers to have the best of both worlds. Hybrid systems are also able to charge the batteries using cheap off-peak electricity (usually after midnight to 5am).
There are also different ways to design hybrid systems.
The battery bank. In hybrid system once solar power is used by the appliances in your property, any excess power will be sent to your battery bank. Once the battery bank is full, it will stop receiving power from the solar system.
The meter and electricity grid. Depending on how your hybrid system is set up and whether your utility grid allows it, once your batteries are fully charged excess solar power not required by your appliances can be exported to the grid via your meter. When your solar system is not in use, and if you have drained the usable power in your batteries your appliances will then start drawing power from the grid.