How does a grid-tied solar system work?
A grid-tied solar system is also referred to as a:
- Grid-tied photovoltaic system;
- Grid-tied PV system;
- Grid-connected solar system;
- Grid-connected photovoltaic system; or
- Grid-connected PV system
Grid-tied systems are connected to, and dependent on, a utility grid to function. Electricity is generated from solar panels.
Grid-tied system components
Grid-tied systems consist of three main components:
- solar panels;
- one or more inverters; and
- an energy meter.
Batteries are not connected to a grid-tied system.
How it works
Rooftop solar panels convert sunlight into DC (direct current) electricity. The solar panels are connected to a grid-tied inverter, which converts the DC electricity into AC (alternating current) electricity. The inverter is then connected to the main DB (distribution board).
AC electricity has a specific frequency (normally around 50 Hz Herz). The inverter synchronises with this grid frequency. Electricity produced by the solar panels supplements electricity supplied by the grid.
Grid-tied solar system diagram
Normally, electricity only flows from the grid to the building. But when a grid-tied solar system is installed, electricity can also flow back to the grid i.e. electricity can flow in both directions (as shown by the arrows in the diagram above).
The electricity produced by the solar panels will always follow the shortest route. This means electricity is first used within the building. If the solar system produces more electricity than the building requires, the excess is exported to the grid. From there it is used by your closest neighbour.
On the other hand, if the building is using more electricity than the solar system is producing, the grid supplies the shortfall.
Measuring the energy produced, used and exported
The inverter and energy meter measure all electricity produced, used, imported and exported. This data is uploaded to an internet server which can be accessed later, either on a website or via an app on your phone.
Advantages of grid-tied solar systems
- Cost-effective system: there are no expensive batteries.
- Quick return on investment: the typical payback period for a system is 4 to 6 years.
- High reliability: as there are fewer components and system requirements compared to hybrid or off-grid systems.
- Little to no maintenance required.
Disadvantages of grid-tied solar systems
- No backup power: there are no batteries and the system is dependent on the grid to work. When there is a grid power failure, the system also shuts down.
- Dependent on a stable grid: if the grid frequency or voltage is outside an acceptable range, the system shuts down.
- Energy production does not match energy usage: solar energy is produced in a typical solar production bell curve, mainly between 9 am and 4 pm. If the energy is not used immediately it is exported. Typically, the tariff earned for exported electricity is lower than the tariff paid for imported / self-consumed electricity.
Using actual figures will explain this better. If the typical daily consumption of a building is 30 kWh and the solar system can produce 30 kWh during daylight, then a substantial amount of the electricity generated flows back into the grid. During the day, the meter turns backwards and builds up “credits”. At night, electricity is drawn from the grid and the meter turns forward again, using the “credits”. If the balance right, the meter will show zero usage over 24 hours!
If consumption increases to 40 kWh in 24 hours, the solar system still supplies 30 kWh for free. The remaining 10 kWh are purchased from the grid. If the building only consumes 20 kWh, the solar system “exports” 10 kWh. The solar system is now a power producer and the electricity can theoretically be sold to the grid.
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