Our power project

It will cost many thousands to get grid power to our land, so we're instead going to use the money to set ourselves up with our own independent power sources. We don't need much power as our main requirements are just for lighting, internet and laptops which is around 100W of power when all in use. I estimate that we'll be able to get by on about want about 600W hours of power per day initially.

We'll be using solar for water heating, gas or fire for cooking, a water-wheel for pumping water to four or five meters height for some pressure, and we won't be using a fridge because we have no dairy products and all our vegetables stay fresh by only picking them as we need them. For things that require high power such as power tools, we'll be using a petrol generator.

Which ever sources of power are used (solar, hydro, wind etc) storage batteries are required to cater for the varying voltage and current supplies from these different sources and their variable power availability. And this means that a charge controller is required to match the voltage and current of the varying input sources with the varying requirements of the battery depending on its state of charge. Unfortunately it's very expensive to get the kind of hardware that can accept multiple varieties of input sources, so we'll need to have separate sets of batteries and charge controllers for each kind of power source we use. The load outputs of these charge controllers can then be joined with some power diodes prior to the input of the inverter.

For our small initial requirements, one or two 100Ah batteries and a cheap car inverter will be fine since we're only running LED lights and some computer equipment which all have their own power regulation. I've ordered this cheap 200W model for US$20 which should do the trick.

Solar

If we consider a worst-case of about four hours of sun per day (which is about right for winter in Rio Grande do Sul) and we want at least 600W hours of power per day then we need at least 150W of panels initially. I'd like to double this reasonably soon and eventually have 1KW of panels so that we can afford to be less frugal with our power, for example by beaing able to keep the computers running when we're not using them so that we can receive incoming calls etc.

We're going to start with a basic 150W kit like this. Building our own panels from the a kit of individual cells gets the price down to around R$2.40 per Watt which is about half of the best prices available in Brazil for ready-made solar panels.

Another requirement is the charge controller which is best to be a good one using MPPT technology so that we get the most out of our energy sources and batteries. Unfortunately MPPT systems are too expensive here in Brazil, so we'll need to settle for a cheaper PWM system such as the SML-25 or SML-60 from MovTec here in Curitiba (Rua Carmem Maito Stinglin, 80, ph. 30145114).

SML-60	SML-30

• Charge controller basics
• MPPT controller details

Wind

We'll eventually get a small wind turbine set up, but we'll start with the solar and work on this later.

See also

• Our rural net connection
• Energy