With the steady decline in solar panel prices it has become an attractive option for business owners to install solar panel power systems to ensure a stable power supply. Solar distribution boards, sometimes called combiner boards, form an integral part of this solar supply system. The working of Solar distribution boards and the differences between regular distribution boards are discussed further below.
The basic construction of a distribution board
The basic distribution board (DB) consists of a steel enclosure which contains circuit breakers connected to DIN rails or bus-bars. This allows for the distribution of power within an electrical power system. In a normal distribution board the system is fed from a main circuit breaker (CB) which in turn feeds other smaller circuit breakers which control their respective load circuits. In the below image the main circuit breaker feeds the smaller line circuit breakers in a hierarchical fashion, this is a good example of a traditional distribution board.
[Diagram of a typical distribution board. Image created by Author.]
The basic working of Photovoltaic panels
Photovoltaic (PV) panels or solar panels, as they are commonly known, generate electrical power when exposed to sunlight. A group of solar panels are usually used to produce power and are arranged in a PV array. The PV array outputs a DC voltage and current corresponding to the amount of solar radiation which reaches the PV panels. This voltage depends on the arrangement of the panels, but it is usually 12V. This DC power is then converted to AC power with the use of a DC to AC inverter to produce 220VAC. The inverter then feeds this power to the solar distribution board. It is sometimes necessary to implement more than one PV array. Fortunately the solar DB can accept more than one inverter output.
As one would expect the power produced by the PV array is highly sensitive to changing weather conditions. This is why electric power systems utilizing PV power usually rely on grid based supplies as well. The power system thus relies on a dual power supply. These two power supplies need to be synchronised in order to protect the electric circuitry from damage due to mismatched voltages. This is done by synchronising the inverter output voltage to the grid voltage. The PV array can thus not completely supply an entire business without the support of grid based power, but it greatly reduces the amount of grid based power the business uses. Your kWh meter will thus have a much lower reading at the end of the month.
For an entirely off-grid solution it is wise to invest in generators and backup battery supplies to ensure that a continuous and steady supply of power is available.
Why is a Solar Distribution board upside-down?
In a solar distribution board the flow of power is sometimes referred to being ‘upside-down’. This is due to the fact that the feed of power is in the reverse direction compared to regular distribution boards. Multiple smaller lines of power feed into a bigger line of power. The smaller lines come from the PV array inverters. Thus in the solar distribution boards a collection of smaller circuit breakers feed into a large main circuit breaker, which feeds a load.
The direction of power flow is important as this determines the direction in which measurement devices such as current transformers (CT) and energy meters should be placed. In the solar distribution board the direction should thus be reversed. Certain circuit breakers are also direction specific and should thus also be installed in the correct direction of current flow.
The below image displays the flow from the small CB’s into the main CB. The solar distribution board can then feed into another DB which has feeds from a grid supply or other sources of power.
[A schematic representation of a Solar Distribution Board working in conjunction with utility power. Image created by Author.]
The solar distribution board is thus used to distribute power from separate PV arrays into a single main line which supplies a load.
For more information on Distribution Boards, visit the Switchman Website or email firstname.lastname@example.org .
Article by: Jannes Smit, 3rd year Electrical Engineering student at the University of the Witwatersrand.