25 August 2014
By Kevin Norris, Executive Director, Jasco Power and Energy
Energy costs
continue to increase year-on-year, and while the National Energy Regulator has
limited electricity price hikes to just 8% over the past few years, this will
likely increase in 2015. As a result, electricity is fast becoming a major cost
centre for homes and small businesses, leading users to seek alternative energy
solutions. 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.
The benefits
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.
Ensuring supply reliability
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.
Energy optimisation is key
One additional factor
to bear in mind is that solar installations require approximately 10 square
metres of solar panels per kilowatt 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.
In conclusion
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.