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Energy generation

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Electricity

I haven't been planning to connect to the grid for our power supply or space and water heating, so we aim 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 total of 30m potential head, 15m of that at an angle steeper than 45%, but the flow is less than 1 litre per second 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.


Hydro-electricity

The hydro part of the equation seemed reasonably straightforward and the barroco 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 water wheel. 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 an over-shot 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 civil works are necessary to deliver the stream flow to the wheel with no damming of the flow necessary, unlike turbines which require a feed pipe or 'penstock' and generally a small dam, or collecting pool fed from the main stream, to fill it. And as for debris, it's just thrown straight off the wheel, so no necessity for grates, screens or filtration devices and their associated maintenance, or problems with clogged nozzles and blocked penstocks. Gearing can be changed to suit different flow rates if they are hugely variable.

After a long-running saga trying out a number of different alternators to generate power from the wheel, we finally opted for a Hugh Piggott-designed 48V axial flux alternator, built locally by a friend. This was eventually installed in early 2014. Over the next few months it kept the batteries of both systems on the quinta fully-charged, generating anything between 40-200W continuously, depending on stream volumes.

You can follow more detailed progress of our installation with facts and figures through the blog, but here is the wheel generating winter power for us.



Solar power

The solar part has been more problematic conceptually (though quite the opposite practically - they're very simple to install). There's something about the inefficiency of photovoltaic panels, particularly in view of their cost, which bothers me enough to want to explore possible alternative solutions. I'm not convinced I'll necessarily find anything that works any better at this point in time, though there are some promising developments, like holographic planar concentrator (HPC) film, on the way.

Barroco

Early January: the barroco and the amount of sun available at 1.30pm.


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.

With our water wheel-based hydro system, we were hoping it would be possible to relegate the solar component to a more secondary role in our plans. We initially installed a 24V system with only half the generating capacity originally envisaged, but with the lack of rain through winter 2010-11 and the trials and tribulations sourcing an appropriate generator for the wheel to match our water availability, we upped our solar generation to the original planned capacity in early 2011, and added a separate 12V system for the smaller building in 2013.


Household heating and cooking

The more I read about rocket stoves, the more I liked them ... until I put an experimental one together and realised an essential weakness in the design. Nevertheless, the idea of being able to construct a stove ourselves with minimal capital outlay to burn small timber with great efficiency still appeals. Consequently, rather than expensive cast-iron cooking ranges and stoves (with or without back boilers), I'm looking at constructing low-tech, but far more efficient masonry cooking, bread oven and heating stoves.






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