  With rolling power cuts across many parts of South Africa the phrase “I want to go off the grid” is being heard more often. 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.
Power Requirements & Solutions
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
Consumer electronics - laptop, sound system
Power for the lighting and consumer electronics is provided by a solar panel and battery system coupled to an inverter to provide 22 volt alternating current.
Heating - water heating for showers, cooking, climate control
Cooling - fridge
Heating and cooling systems are powered by gas canisters.
Cleaning equipment - vacuum cleaners, washing machines
The house is designed in such a way that a vacuum cleaner is not needed, it is also 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.
How Does It Work? How Much?
The solar panel, purchased 5 years ago (and operational for this entire time) had an original cost of R2,800 (current R3,500 - R5,800). This is oriented on the roof to catch sunlight the whole day providing about 120Watts at peak insolation. This output is taken through a solar power manager and used to charge two Willard 105ah Solar model batteries (original cost R350ea, current R1,300 - R1,800).
These batteries are different to normal car batteries, which are designed to provide very short bursts of high current. Instead they 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 and are used to power four 12volt fluorescent electric lights. If all four lights in the house are left on for 6 hours this drains the batteries from providing 13volts to 11.8volts - 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 (13volts) in 4 to 5 hours.
For consumer electronics, an electrical inverter is needed. This inverter will convert 12volt direct current to 220volt 50 Hz alternating current. The output of the inverter at this house is 200W which is just sufficient to power an advanced laptop. It is probably recommendable that a more powerful inverter should be installed, if you were to run a hairdryer for a few minutes for example, a 4000W system would be needed. Smaller invertors can be purchased from car part suppliers such as Middas and Autozone (400W for R500), and the larger ones from a dedicated solar power company such as KG Electric (1000W for R3,700 - 3000W for R10,000).
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.
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.
Cost vs Saving
Assuming an average daily use of electricity equivalent to that of seven 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 R3,500 to date (in 5 years of operation). Given that the system cost R3,900 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?
For more information and articles by Dr Garth Cambray visit www.scienceinafrica.co.za, South Africa’s first online science magazine.
Disclaimer: Harmonious Living is written for and read by a community of individuals with strong and independent opinions. While the publishers of Harmonious Living are dedicated to providing a forum in which views can be openly expressed, those views do not necessarily reflect those of the publishers.
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