Grid tied systems consist of only 2 key components – solar panels and a dedicated grid tied inverter. All the electric power generated by the solar panels feeds through a mains synchronized inverter directly into your distribution board and offsets the power you would normally consume from Eskom. It will of course only do this when the sun shines!

If the panels produce more power than what is being consumed at the time, the balance will flow back into the network and it will actually reverse the electricity meter (not all types of meters can do this though). Since no batteries are used, no independent energy can be stored for later use. This means that energy required at night will still be obtained from the network.

Using actual figures will explain this better:  Let’s assume the typical daily consumption of a building is 30 kWh, over a 24 hour period. If the solar array can produce the 30 kWh during sun hours, a substantial amount of this energy will be flowing back into network and the meter will be turning backwards during this period, building up “credits”. At night, energy will be obtained from the network and the meter will turn forward again, using the “credits”.

If we get the balance right, the meter will show zero usage at the end of the 24 hour period! If our consumption were to increase to 40 units per 24 hour day, we would still get 30 units for free from the solar system and we will only buy the remaining 10 units from the network. If we only consume 20 kWh, we would have “exported” 10 kWh. Since we have now become a power producer, this electricity could theoretically be sold to the network.

The functionality of grid tied systems is such that they will only operate in the presence of an active grid network. If a power failure occurs, they will immediately shut down. This is a legally required safety feature to ensure that the electrocution of workers possibly working on the network cables cannot take place.  Since no backup energy is stored in a battery bank, no electricity will be available whilst the power is off.

Worldwide, in countries like Germany, USA and Australia, this type of system is in extensive use. The fact that no batteries are employed lowers the price substantially and there is virtually zero maintenance. For suburban areas where there are few power failures, this could be the ideal solution. Grid tied systems are easily expanded.

Legal requirements

Currently there is a lot of controversy and miscommunication regarding the legality of these systems in SA. Some municipalities have approved a net metering scenario but will not pay you for excess electricity produced. Others maintain it is illegal to feed energy back into the network. Not all electricity meters can be used with Grid tied systems. Prepaid meters can’t be reversed and grid tied solutions are not always feasible.

Main benefits of Grid Tied Solar PV Systems:

  • Energy provided by the Sun – saving money.

  • No expensive batteries required.

  • Sunlight is directly converted into electricity to use.

  • At current electricity costs, system payback is between 4 to 6 years.

  • Cost of energy yield fixed for at least 25 years.

  • The only home improvement that will save you money on a daily basis.

  • No maintenance required.

Main disadvantages of Grid Tied Solar PV Systems:

  • With no batteries, there is no independent energy storage.

  • During load shedding or a power outage, no energy is available.

  • Current legal issues in South Africa can limit the full benefits in certain applications.