Solar panels are used in solar electric systems to generate electricity from sunlight.
Different types of solar panels have different performance due to different conversion efficiency of their solar cells.
There are two main types of solar electric (photovoltaic) systems – connected to the grid (‘grid-tied’) and disconnected from the grid (‘off-grid’).
Grid-tied systems allow you to offset a part of or all of your electricity demand to photovoltaics thus reducing your electricity bills. Most of the existing photovoltaic systems are connected to the local utility grid or are ‘grid-tied’.
A typical grid-tied photovoltaic system generally does not provide electricity storage. Such a solar system generates electricity to provide part of the energy needs of a building in daytime.
Grid-tied systems can be with or without power backup option.
Grid-tied systems without battery backup are built in regions where power outages happen rarely and for short periods. In case of an outage a grid-tied PV system shuts down until the utility is up again.
By shutting the PV system down technicians that might be doing certain repair works on the utility grid at a certain moment are prevented from getting an electric shock.
Here is a simplified view of a grid-tied solar system without power backup:
Here are the main components of a grid-tied system which does not provide any power backup:
- Photovoltaic array – generates DC electricity from sunlight
- DC disconnect – disconnects the solar array from the rest of the system
- Inverter – converts DC electricity into AC electricity
- Main distribution panel – the connection point between home electrical network and utility grid
- AC loads – the devices operating on AC electricity
- Net meter – measures the electricity imported from and exported to the utility grid.
If you have a grid-tied system, you use the electricity generated from the system during the day while the sun is shining. After the sun goes down, your home network automatically switches to using electricity from the grid. Thus you need to pay the utility for the electricity provided during night periods only.
Certainly you use electricity from the grid when electricity generated by your PV system does not fully cover your household electrical consumption. Moreover if your photovoltaic generator produces more electricity than you consume, the ‘excess’ of electrical energy is exported to the grid, for which you get paid.
An obvious disadvantage is that grid-tied systems shut down in case of power outage. This can be avoided by buying a grid-tied system with a battery backup option.
Grid-tied systems with battery backup are preferred in areas where power outages happen more often and by users for whom electricity outage is not an option even for short periods. A grid-tied system with battery backup comprises the following components:
Here is a simplified view of a grid-tied solar system with power backup:
The components of a grid-tied system with power backup are:
- Photovoltaic array – generates DC electricity from sunlight
- Charge controller – regulates battery charging, thus increasing battery lifespan
- Battery bank – stores the electricity generated by the PV array
- Inverter – converts DC electricity into AC electricity
- Main distribution panel – the connection point between home electrical network and utility grid
- Backuped loads – all the AC and DC devices provided with power backup
- Non-backuped loads – those electrical devices which are not provided with power backup
- Net meter – measures the electricity imported from and exported to the utility grid.
Grid-tied systems with power backup are recommended to:
- Remote grid-tied home-owners living in areas where utility grid needs a long time to recover from frequent power outages as a consequence of adverse weather conditions (e.g. damaged by heavy snowfall utility network infrastructure during winter), and
- Businesses for which 24/7 availability of power is crucial for their production or storage process.
Another main type solar systems are off-grid ones. They can be stand-alone (purely photovoltaic) and hybrid ones.
Off-grid solar electric systems are not connected to the grid.
They are preferred in remote areas where buildings are far from any utility infrastructure. In such a situation it is cheaper and easier to install a PV system to meet your daily electricity needs rather than pay for utility interconnection.
Here are the main applications of off-grid solar systems:
- Small solar systems for household use in developing countries
- Schools and hospitals in developing countries
- Cooling for medical or veterinary use
- Solar systems for remote homes or summer villas in well-developed countries
- Power supply for telecommunication equipment
- Water pumps
- Street infrastructure equipment – street lamps, bus station dashboards, parking meters, etc.
- Recreational vehicles
- Remote meteorological stations and airports
Here is a picture showing the application of various off-grid solar system types:
Stand-alone systems are typically provided with battery storage. Battery storage however is not always present, as is the case in directly couples stand-alone systems:
Below is an example of a typical stand-alone solar panel system designed to replace utility grid for remote buildings:
Here is a list of components of a stand-alone system:
- Photovoltaic array – generates DC electricity from sunlight
- DC disconnect – disconnects the solar array from the rest of the system
- Main DC breaker – connects the inverter to the battery and charge controller
- DC loads – all devices operating on DC power
- Charge controller – regulates battery charging, thus increasing battery lifespan
- Battery bank – stores the electricity generated by the PV array
- Inverter – converts DC into AC electricity
- Main distribution panel – the connection point between home electrical network and utility grid
- AC loads – all devices consuming AC power.
Stand-alone systems are ‘photovoltaic-only’ systems. They contain no additional power generator apart from the solar array.
The second subtype off-grid systems are hybrid systems:
A hybrid system is actually a stand-alone solar electric system with an alternative power source added – wind generator or fuel generator.
Hybrid systems are preferred in cases where too high energy consumption and/or long periods of cloudy days require a too bulky battery bank which is expensive both to buy and to maintain.
Click here to find out what kind of solar system is recommended for your specific case
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