By Bernard Preston

Grid tied residential solar power

Grid tied residential solar power is the choice way to capture the sun's energy. It's relatively inexpensive, requiring no batteries and is not technically difficult to install.

The photovoltaic panels energise the grid tied inverter which sends power to and from the mains.

The basic principle is that during the day when there's plenty of energy arriving from the sun, it is captured by photovoltaic panels, and conducted as DC to the grid tied inverter.

The inverter turns the direct current into AC which feeds into your distribution board and can be used to supply all appliances in your home.

When there's a surplus it is exported to the grid and sold to the utility.

However, at night, when the PVs are producing no power, electricity is drawn from the grid to supply your needs.

There is special protection built into the GTI; should the grid be turned off by the utility to do maintenance work the device shuts down immediately it detects no mains electricity. Otherwise your solar power could electrocute anyone working on the cables on the street.

Since this happens only very occasionally in countries with a mature and stable grid, it's not a problem.

However, in countries like South Africa, or the Dominican Republic where there's load shedding every day, it's hugely problematic.

Grid tied residential solar power

Grid tied residential solar power has serious limitations in countries with unstable utility power. With the inverter having shut down, you are simply unable to use the sun's energy even though it's a bright day with plenty of radiation arriving at the panels.

It needs an AC source to sync with, and batteries or the grid, to which it can push power.

In most countries this might happen just a few times a year at most, and one accepts the limitation. In the rare event of a hurricane like Sandy arriving where the whole infrastructure is seriously damaged, you'll be without power for a week or more, despite full sunshine; but really that's unlikely to happen more than once in a decade perhaps.

However, in South Africa where the mains fails virtually every week, either because of Eskom load shedding, or a collapse of the local infrastructure where little maintenance has been done on the aging system, this basic grid tied residential solar power is not a viable option.

Rather, you should opt for the far more expensive package of batteries and a second inverter that will provide solar energy to your home even though the GTI has shut down; it's problematic.

If you have a conventional grid tied inverter, it can only provide electricity based on what the PV panels can directly generate from the solar energy arriving on any particular day. However, new generation hybrid inverters can also use the power stored in batteries as needed.

They use a mix of renewable energy from solar panels and that from the grid to charge the batteries, and supply the load as needed.

There remains the need for batteries, and unless I'm grossly mistaken, the inverter will shut down if the grid fails, or goes into load shedding.

You'll notice that Microcare, a company involved in the advanced development of new systems, still uses two inverters if you wish to be grid tied in a country with an unstable utility.

To my mind, in South Africa, it makes little sense to be grid tied; rather accept that there will be periods that you have surplus power that goes wasted than spend a fortune on an extra inverter; and risk having your hardware damaged by a mains voltage spike.

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