Grid-Connected PV Provides the Ideal Solution for Home and SME Solar Installations
By Kevin Norris, Executive Director, Jasco Power and Energy
Electricity is fast becoming a major cost centre for homes and small businesses, leading users to seek alternative energy solutions.
Energy costs continue to increase year-on-year, and while the National Energy Regulator has limited electricity price hikes to just eight percent over the past few years, this will likely increase in 2015.
Grid-connected Photo-Voltaic (PV) installations offer the ideal solution for the home or Small to Medium Enterprise (SME) consumer, providing a cost-effective solar power generation system that can be used to offset the cost of electricity from the utility provider and reduce the burden on the national grid.
PV installations, more commonly referred to as solar panels, are an increasingly viable option for sustainable alternative energy supply in South Africa.
Off-grid solutions are connected to a battery, which stores solar energy by charging the battery. These solutions are not connected to utility grids at all, forming completely separate or ‘island’ solutions, ideal for areas where there is no utility power supply.
However, in most residential or business installations, this is not an ideal solution, as the battery is often an unnecessary cost, and the purpose of solar energy in these scenarios is to complement utility power during daylight hours, rather than replacing it entirely.
Grid-connected PV installations, on the other hand, work together with utility power, providing solar energy when this is available and reverting to grid-supplied power when it is not. These installations also provide the capability to feed back into the grid, but this is not currently an option in South Africa.
The principle of grid-connected PV
A grid-connected PV installation consists of three components: energy generation, power conversion and energy utilisation.
Solar cells or solar panels generate electrical energy directly from the light that falls on them. This is direct current (DC), which cannot be used as is in a utility environment. Power conversion therefore must take place whereby DC is converted to alternating current (AC).
This task is performed by a Grid Tie Inverter, which includes monitoring and protective devices, and which also regulates the optimal operating mode according to the current solar conditions. Finally, energy utilisation can take place.
Grid-connected systems can be used for self-consumption, meaning that they will supply power to the home or office they are connected to in place of utility power. The excess energy generated can then be fed to the utility grid in two ways. Can be supplied on a nett metering basis (i.e. no money changes hand.
You either have a debit or a credit account with the utility) or in the form of a feed in tariff, where you get paid for every kWh of energy supplied back into the national grid. South Africa is currently not set up for two-way metering, on a large scale as a result of complexities with municipal legislation, however this should become available in the near future.
Grid-connected PV systems are less expensive than standalone off-grid installations with battery storage, since the energy storage component is not required.
This also improves the efficiency of the solution, and decreases its environmental impact, since batteries are not a required component.
In addition, the size of grid-connected PV systems is more flexible than off grid systems, as any desired size from 250 watts up to several megawatts can be implemented.
In the event of a power failure, grid-connected PV systems must be isolated from the utility for safety reasons in order to prevent uncontrolled stand-alone operations – in other words, when the power fails, the grid-connected PV system will also go offline.
This is a safety requirement to prevent the possible electrocution of any utility personal working on the grid during the power failure. However, without compromising the safety requirements required by the utility, a grid-connected system can also be configured to work in conjunction with either a diesel generator or UPS.
This will allow the solar powered system to continue to operate and provide power supply to the load. If the power is being generated by the solar panels, the Grid Tie invertor will prioritise the use of this energy and the generator or UPS will only supply a minimal load and will thus be highly efficient.
Grid-connected PV systems can thus enable homes to provide continuity of supply in the event of a power failure.
One additional factor to bear in mind is that solar installations require approximately 10 square metres of solar panels per kilowatt (kW) required to be generated.
A typical South African home system, suitable for a family of four people, would require a design capacity of between 3.5kW and 4kW.
This in turn requires a surface area of 35 to 40 square meters to accommodate the necessary solar panels. While many homes have a roof footprint of more than this area, in order to maximise the efficiency of a solar solution, the panels need to be north facing.
The majority of homes simply do not have enough north-facing roof real estate to accomplish this. Consequently, it is recommended that prior to embarking on a solar installation, users should upgrade conventional home geysers, lighting and appliances to the latest energy efficient products.
In this way it is possible to reduce the required capacity to as little as 2kW, which would require a PV installation of around 20 square metres - the average roof size of a double garage. This also dramatically reduces the cost of the solar installation, as the number of panels required is effectively halved.
Solar pays for itself
Alternative and sustainable energy solutions are fast becoming a must for home and SME users, as the rising costs of electricity are placing ever-increasing burdens on the monthly budget.
In addition, offloading the requirements of homes from the national grid will take the pressure off the utility providers, enabling them to focus on equalising supply and demand more efficiently.
Grid-connected PV solutions offer a cost effective option for users to leverage the advantages of solar power, and will pay for themselves within just a few years of operation, given the inevitable continued energy price increases that will be put into place in the coming years.
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