Off the grid for 5 years

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Off the grid for 5 years

By Dr Garth Cambray

The solar powered house seen nestling in its green, grid electricity free valley. Note the main solar panel on the house and the smaller solar powered telephone provided by Telkom on the left.

With rolling power cuts across many parts of South Africa and many parts of the world, people all over are saying 'I want to go off the grid'. To live off the electrical power grids that we are all so used to, is a big challenge. In this article we will look at a little house close to ScienceinAfrica's heart, which has been off the grid for its whole life of five years.

In designing this house, the builders divided the normal power requirements of a house which is on the grid into the following categories:

Lighting - small amounts of power needed for long periods of time
Heating - water heating for showers, cooking, climate control
Cooling - fridge
Consumer electronics - laptop, sound system
Cleaning equipment - vacuum cleaners, washing machines

Power for the lighting and consumer electronics is provided by a solar panel and battery system coupled to an inverter to provide 220 volt alternating current. Heating and cooling systems are powered by gas canisters. The house is designed in such a way that a vacuum cleaner is not needed. It is situated in a valley with high unemployment, hence rather than employing an electrically thirsty washing machine, a person is employed to wash clothes, thus creating employment and stability.

The solar power manager. It provides an indication of the level of charge in batteries and the presence or absence of solar electricity coming from the panel.

The solar panel, purchased 5 years ago, and operational for this entire time, had an original cost of R2800 (current R2000 - R4500). The solar system works as follows. A solar panel, oriented on the roof to catch sunlight the whole day provides about 120 watts at peak insolation. This output is taken through a solar power manager and used to charge two Willard 105ah Solar model batteries. (original cost R350 ea, current R900). These batteries are different to normal car batteries which are designed to provide very short bursts of high current. The Willard Solar batteries provide a lower current output over a longer period of time and are designed in such a way that the repeated charging and draining cycles of the battery does not cause the type of damage it would to a car battery.

The two batteries provide 12 volt direct current output. This is used to power 12 volt fluorescent electric lights. If all 4 lights in the house are left on for 6 hours this drains the batteries from providing 13 volts to 11.8 volts - with no effect on the amount of light produced. On a rainy cloudy day, the solar panel is able to recharge the batteries to full power (13 v) in 4 to 5 hours.

The inverter - this really is a 5 year old, ugly inverter. New inverters look far better, but this one works!

For consumer electronics, an electrical inverter is needed. This inverter will convert 12 volt direct current to 220 volt 50 Hz alternating current. The output of the inverter at this house is 200 watts. This is just sufficient to power an advanced lap top. It is probably recommendable that a more powerful inverter should be installed (as an example, a 400w inverter will cost about R250 (US$41), a 1800w system R650 (US$109) and for the superadventurous 4000w system R1730 (US$289)). If one were to run a hairdryer for a few minutes, the 4000w system would be needed. Invertors can be purchased from car part suppliers such as Middas and Autozone.

It is important to realise that the more powerful the inverter, the more it will draw from the batteries, and the more it will draw from batteries, the more batteries you will need, and the more batteries you need, the more solar panels you need. Currently, more solar panels equals more money - normally making this option financially unviable to those with access to the grid - however, new South African inventions are changing all this (see article on the new South African solar panel invention).

Two Willard 105ah Solar batteries nestling discretely under the kitchen shelves.

Many people who have houses that are off the grid use wind powered alternators to provide additional electricity to charge batteries. Where these are insufficient, a small generator can be set up to provide additional power. However, a far more exciting alternative exists, fuel cell systems.

To summarise the solar house. Assuming an average daily use of electricity equivalent to that of 7 100w light bulbs (the house uses more efficient bulbs but if it were on the grid it would not) operated for 6 hours a day on a grid powered house, the solar house has self generated electricity worth about R3500. Given that the system cost R3900 to set up, and will run for many more years with little maintenance, it means that from this year onwards, the energy is for free. And is that not a lovely dream - free energy?

More information:

Garth Cambray garth@scienceinafrica.co.za