Rooftop solar

Planning for PV – the ins and outs of photovoltaic (PV) power generation for residential and commercial use

One of the key ways in which residential, commercial and industrial energy users are looking to ease their electricity costs and better secure their energy supply is through photovoltaic (PV) electricity generation.

What is rooftop PV?

A rooftop photovoltaic power station (rooftop (PV) system), is a system that has electricity-generating solar panels mounted on the rooftop of a residential or commercial building or structure. Solar panels, which are made up of solar cells, are exposed to direct solar radiation and generate electricity which is called a photovoltaic effect.

The solar power flows via a cable to a device called an inverter which converts the direct current (produced from the panels) to alternating current (AC) and that power is then synchronised with the national grid and allows it to be fed back into the network to supply electricity to the building or residential household.

With the inverters synchronising the solar power and the national grid, the power can be fed directly into the internal electrical network and save electricity. Every KWh generated by the solar system is a kWh less required from the utility.

Planning for a PV system should include analysing the current electricity usage, implementing energy efficiency measures, studying local council codes and feed-in requirements (if any), and deciding whether to operate the system entirely off grid or use a hybrid or grid-connected solution.

Why PV?

Many people like the appeal of a grid-tie PV system which allows the use of PV during daylight hours and then to switch to utility power at night.  Considering that most businesses have their peak demand during the day when they operate, and many residential areas run a pool pump, then utilising the sun as a day energy resource is a wise economic decision.

A grid-tie system allows you to perform all your daytime activities powered by the sun, and save on the more costly battery back-up needed to store PV electricity to use at night time.  Many businesses also use PV in conjunction with back-up power sources like diesel generators to provide a continuous source of power.

Why implement energy efficiency measures beforehand?

Implementing energy efficiency measures before investing in a PV system will reduce the electricity usage and allow for the purchase of a smaller and less expensive system.  For example, converting geysers to solar or heat pump, installing LED low energy lighting, using gas for cooking, putting movement and day/night sensors on office lighting.

New building developments should incorporate renewable energy solutions into the design from the outset.  In fact, some measures are already legislated in South Africa with energy efficiency in buildings no longer being the preserve of just those wanting to do the right thing.

What was a voluntary standard has been written into law in the SANS 10400-XA: Energy Usage in Buildings, and SANS 204: Energy Efficiency in buildings. This requires a focused solution for areas such as water heating, whereby 50% of all hot water in new houses needs to be produced by methods other than electrical element heating.

Codes and Regulations

Each region handles the connection of PV systems to the grid differently. The words net-metering and feed-in-tariff are commonly used in conjunction with PV systems but consideration of the municipal office is required.

Each region has its own set of codes and regulations that will need to be adhered to in order to add a PV system to your home or business.  It will determine whether to connect the system to the electricity grid or use it in place of grid-supplied electricity.  The system can also take advantage of future expected changes to feed-in tariffs which are very likely given the need for grid relief.

Types of PV Connections

  • Solar PV system 1 – No batteries, grid connected system
  • Solar PV system 2 – Some batteries, grid connected system
  • Solar PV system 3 – Only batteries, no grid connection

System 1 is used to supplement the energy usage. In the event of a blackout or power outage, the solar system is forced to shut down. Therefore, even if the outage occurs in the middle of the day during full sunlight hours – no power will be produced. If net-metering is allowed, this type of system provides a one for one credit on the monthly electricity statement.

System 2 is commonly referred to as a hybrid system and with the correct installation will act as a UPS (uninterrupted power supply) in the event of a power outage. The PV system will charge up the batteries first and the excess production will supplement the property’s energy needs.

System 3 is useful for areas where no grid exists. The energy produced will charge up the batteries which should allow for three days’ worth of energy needs. These batteries will then feed the power requirements of the property.

It is important to note that adding batteries adds to the cost and therefore the systems above are ranked from the least expensive to the most expensive.

Opinion piece by Christo Kok, Director, One Energy                 

(Pic Credits: slunchevdom)

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