Permaculturing in Portugal

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Energy generation

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I haven't been planning to connect to the grid for our power supply or space and water heating, so the challenge is to be self-sufficient in energy from what we can reasonably generate on site. Reasonably being the operative word. This is quite a challenge in view of the capital outlay required for some components of small scale renewable energy generation systems.

The quinta's aspect varies from west through north right round to south east, though being situated one third of the way up the eastern slopes of a mountain ridge with a ridge also to the south, most of the site is effectively north-facing in winter and only really open to the east. This makes solar power less than optimal in the winter months.

We have year-round water in the stream and a good 12-15m of head, but the flow is not much more than a steady trickle by the end of the summer, so neither solar nor hydro generation alone are likely to provide sufficient power for our needs. It will need to be a combination of the two.

At least we'll tend to have more water during the months when we have less sun, and vice versa, but we'll likely achieve the optimum balance by cutting back substantially on our use of energy as well as using it more mindfully. This seems a satisfactory solution in many ways: having kilowatts of power at our disposal would do nothing to encourage us to use power efficiently, and that's as much the point of the exercise as being independent of the grid.

Though this in itself is an interesting dilemma.

The hydro part of the equation seemed reasonably straightforward and the levada almost purpose-built for the installation. I looked at Navitron's high-head turbine range and the Canadian Stream Engine, and even considered the intriguing possibility that we might be able to use some 18th century technology to increase our generating capacity, but finally opted for a locally-designed turbine. Very local. From 250m down the hill in our nearest village, Benfeita.

Having tried various run-of-river solutions for his valley floor site at the old lagar (olive mill) and experienced endless problems with debris in the river, engineer Wayne Sutton hit on the idea of using a water-wheel to drive a permanent magnet generator from a wind turbine, appropriately geared. To me, this system is pure genius. It's every bit as suitable for my low flow, high head situation as it is for his with minimal head and higher flow rates. Wind turbines are designed with the flexibility to generate power over a wide range of wind speeds, so the same flexibility in relation to variable flow is inherent in this system with none of the problems of suction and cavitation that enclosed turbines experience when flow rates drop below a critical level. Minimal friction also means that once the wheel is turning, it requires far less water to keep it turning for a given head than an equivalent Pelton or turgo-wheel turbine. And as for debris, it's just thrown straight off the wheel, so no problems with clogged nozzles and blocked penstocks either. There is even the potential to change the gearing if flow rates are hugely variable.

Pico Hydro Portugal will shortly be offering Wayne's water wheel-based generation systems throughout Portugal. You can follow the progress of our installation through the blog.

The solar part has been more problematic, at least conceptually. There's something about the inefficiency of photovoltaic panels (particularly in view of their cost) which bothers me enough to explore possible alternative solutions, though I'm not convinced I'll necessarily find anything that works any better at this point in time.

I've become very interested in Stirling engines, another piece of industrial revolution technology, which are being used in combination with parabolic solar reflectors to produce electricity at the utility scale, and feel sure that something domestically useful and efficient will emerge from development in this direction, but it doesn't seem to be there yet. One thing that particularly appeals is that Stirling engines have cogeneration potential, ie. they can provide domestic hot water as well as electricity, with a theoretical efficiency approaching 100%. For more on the subject, check out the American Stirling Company's forum.

However, with our water wheel-based hydro system from Pico Hydro Portugal and its capability of generating power from much lower flow rates than would drive a Pelton turbine, the solar component has now been relegated to a secondary role in our plans. We will be installing only half the capacity originally envisaged, and seeing how we get on with that before reviewing the situation. No doubt there will be a substantial amount of trial and error involved ...

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