Sparks Electrical News

Solar distribution boards, sometimes called combiner boards, form an integral part of a solar supply system. The workings of solar distribution boards, and the differences between them and regular distribution boards are discussed below.

The basic construction of a distribution board

How do solar distribution boards differ from regular DBsA basic distribution board (DB) consists of a steel enclosure which contains circuit breakers connected to DIN rails or busbars. 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 which in turn feeds other smaller circuit breakers that control their respective load circuits.

The basic mechanisms 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, used to produce power, is arranged in a PV array. The PV array outputs a dc voltage and current corresponding to the amount of solar radiation that reaches the PV panels. This voltage depends on the arrangement of the panels, but it is usually 12 V. This dc power is then converted to ac power with the use of a dc to ac inverter to produce 220 V ac. The inverter then feeds the power to the solar DB. It is sometimes necessary to implement more than one PV array.

Fortunately, the solar DB can accept more than one inverter output. The power produced by the PV array is highly sensitive to changing weather conditions, which is why electric power systems using PV power usually rely on grid based supplies as well. The power system thus relies on a dual power supply. The 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 and the kWh meter will 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 DB upside-down?

In a solar DB, the flow of power is sometimes referred to as being ‘upsidedown’. This is because the feed of power is in the reverse direction to regular DBs. 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 DBs a collection of smaller circuit breakers feeds 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 DB, the direction should thus be reversed. Certain circuit breakers are also direction specific and should also be installed in the correct direction of current flow.

Enquiries: www.switchmanproducts.co.za

Article by Jannes Smit, 3rd year Electrical Engineering student at the University of the Witwatersrand.

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Name: Gregg Cocking
Email: sparks@crown.co.za
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