Tuesday, 18 October 2011

Off-grid / On-grid; what’s the difference?

By Robin Whitlock, Freelance Environmental Journalist

People install renewable energy systems for many different reasons. For some it’s a chance to save money in the face of higher conventional fuel bills, for others it is a chance to earn money from the government’s Feed-in Tariff’s scheme while for those concerned about environmental issues it is a means of reducing their carbon footprint and doing something about climate change.

One of the main advantages of using a grid-tie system, that is a renewable energy system (in most cases solar PV or solar thermal panels) that is tied in to the national grid, is that there is a back-up source of energy for those times when the sun doesn’t shine, such as at night or during bad weather during the winter. However, this leaves the householder vulnerable not only to rising energy prices but also to situations in which the national grid fails. That might seem the stuff of memory, reminders of the 70’s oil crisis, but there have been numerous power failures in more modern times too and there are some who believe such power losses will again become a regular occurrence.

The solution is to go off grid. However, this entails storing energy in a bank of batteries, ready for when the solar panels are not generating energy or the wind dies down, and this tends to be a rather expensive option, whereas a grid-tie system is relatively cheap.

Despite this, for those living in remote areas, going off-grid may be the better option, and in fact off-grid systems are becoming increasingly important to the populations of developing countries where a national grid, if it exists, cannot always be relied upon.

An off-grid system also means that you are totally energy independent. It gives you a freedom that is lacking when you are tied to the grid. It is also totally green – no power cables, no coal or fossil-fuelled energy and a lower carbon footprint. Going off-grid also means that the strain on the national grid is reduced, so in some ways it also benefits those around you who may not be in a position to go the same way. For those interested in self-sufficiency, going off-grid is the logical way to go.

For off-grid systems you will need a charge controller which manages the power generated by the panels and the  battery (usually 12, 24 or 48 volts DC). An off-grid inverter is also used to convert DC into AC for household use. You may also need a stand-by diesel generator to back-up the system for periods when the sun isn’t shining or the wind has dropped and it may also be an idea to use a propane or wood hot water heater to reduce the drain on the battery bank, which incidentally should be capable of providing energy for at least three days without a solar or wind-powered charge. Another good idea is to plan your energy use beforehand by undertaking a load analysis.



Hardy Solar


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