Not only that, but it’s a supremely funky addition to our power generation capacity and is also, like the water wheel, proudly made in Benfeita! (Benfeita means ‘well made’.)

The axial flux alternator on the back of João’s quad bike in its green and orange paintwork

Following our experiences, sometimes disastrous, with 3 other permanent magnet alternators/generators we were already thinking along the lines of making one since it was clear off-the-shelf solutions weren’t appropriate for the marginal nature of this site. I was consequently more than excited to hear another local friend was going to be experimenting with making Hugh Piggot design axial flux alternators.

João completed the first one before Christmas and after a coat of epoxy paint, it came here for testing today. This is a high voltage version (many configurations are possible) of the 1kW nominal power rating specification. It has very low cut-in speeds which is exactly what we’re wanting when flow rates here are low. Coupled with an MPPT charge controller which can convert excess voltage into amps, the alternator is able to produce a useful input when most others would fail.

João and his alternator

Different sprockets for gearing which Wayne created mounting plates for over the weekend … and Wayne’s breakfast roll

Siting the alternator

In position before drilling out bolt holes on the mounting framework

Mounted, braced, connected and with chain fitted ready to go

Water turned back on

Alternator running

At the moment we have it on a 3:1 gear ratio which slows the wheel down quite a lot under load. The resistance creates some splash-back which equates to power loss. There’ll be a lot more fiddling with different sprockets and the charge controller tomorrow to find the ideal ratio and settings, but what we could really do with is RAIN. The current weather forecast though is predicting temperatures in the low 20s by the end of the week and no rain before next Wednesday …

Update

January 8th

3:1 proved the optimum gear ratio of those we had available to test. We figure the splash-back is going to be pretty inevitable when we only have 1 litre per second of flow to drive the wheel. These are summer flow levels, when it was never envisaged making use of the wheel anyway since we have more than enough solar capacity for our needs once the sun reappears from behind the hill to the south.

At these flow rates, the wheel is making around 21W after the charge controller has transformed the voltage – 0.5kWH in 24 hours. Around 20% of the power we could expect from ‘normal’ winter flow levels. This may sound paltry, and it is, but to me it’s vindication of the decision to stick doggedly by the wheel against the advice of hydropower experts on various internet forums who, pretty much without exception, all advised the installation of a turbine. Why? Because having run our data through the online calculator for the output of one of the more efficient turbines available, we would be making no more electricity with a turbine. The wheel is as efficient. It just needed the right alternator.

But our present flow rates highlight a different problem to address.

This is the second year in succession the winter rains have failed to materialise, so I am now considering how best to optimise what we can produce from the water even at these low levels. We can make 1.3kWH from the 1 hour 50 minutes of sun the solar panels get at winter solstice (if the sun is shining). If I can double that from the hydro component even at 1 litre per second, then we can limit the use of our propane generator to cloudy days only, which are not that common without rain as well. To do this, the only option open to us is to increase the head, so the next project is to re-site the wheel another 6-7m lower in the barroco and lay 150mm plastic guttering into the stream bed. This will channel the entire flow at these low volumes into the wheel chute with the minimum of friction, but still leave the system open to cope easily with the torrents of water, mud, debris and rocks which fly down this channel after a heavy downpour.

Reducing friction losses and re-siting the wheel will allow us to effectively double our head. Double the head equals double the power. Plus a little bit extra for the fact that the alternator will be operating at greater efficiency once we can increase its rpm to comfortably within its operating range rather than right on the edge as it is now.

I spoke too soon.

We purchased this alternator from Presto Wind in the USA on the basis of its advertised power curves and a couple of videos showing no evidence of cogging, which was the problem with the first generator we tried. As soon as it was installed, it was running well over its claimed threshold for generating usable power, so it was just a matter of waiting for the bearings and rotors to run in and then the batteries would be getting some much-needed juice 24/7. Or so we thought …

After emails going back and forth for well over a month now, we (that’s me and my neighbours, who are installing a wheel on their part of the stream, and Wayne, the systems’ engineer) have a decidedly unpleasant taste in our mouths from our dealings with Presto Wind.

Our M-24 units are not producing anything approaching their advertised power curve. To begin with, when we had more water volume (it hasn’t rained in well over a month), they were producing about 50% of what they should be. Now it’s not even 30%. They’re not even producing enough power to contribute to the batteries and because of the particular way the company have responded and dealt with this, I’m taking the step of writing about our experience in some detail so others can read and judge for themselves.

At first we thought we must have got something wrong, but checking and rechecking the wiring found no errors and all connections were tight. I reported the low output to Presto Wind. The company asked was I sure the tachometer I was using to measure the rpm was accurate, but if we weren’t getting the expected output then something may be wrong. So far so good. I then, over the course of many emails, supplied full details of my system (and relevant details of my neighbours’) with photographs of all wiring plus regular updates on the rpm of the units and the power they were generating, making clear on every occasion that this was being measured open circuit with no load, which is the same conditions under which they produce their power curves. And we weren’t using a tachometer. We were counting wheel revolutions over a timed minute and multiplying that by the gear ratio, so we knew the rpm of the M-24s (+/-5% depending on whether you calculated the ratio by gear wheel diameter or number of teeth).

I frequently had to hassle them into responding after supplying them with information and getting no reply, whereupon I would be asked questions I’d already answered. After repeating myself several times and resending photographs, I was beginning to wonder if they’d paid attention to anything I’d sent, but still didn’t think more of it than that.

Eventually the company responded by saying there was nothing more they could do to help, claiming the underperformance could all be explained by water flow, wheel size, and other system components which, together with 35% efficiency, would easily explain our results. It wasn’t their PMA. It was physics. The units were installed and we couldn’t return them. I pointed out, as I had several times already, that not only was the water flow data irrelevant since we knew the rpm of the PMA (which they were obviously aware of, having asked about our means of measuring it), the rest of the system was completely irrelevant too. We were measuring the power open circuit straight off the rectifiers. And while 35% efficiency might be relevant to wind power, it was not appropriate for hydro. 60% is more the norm.

To prove beyond doubt that it was nothing to do with the rest of the system, we disconnected it all from the rectifiers, measured the power at the rectifiers in exactly the same manner as their demonstration videos (and of course got the same readings we’d been getting all along), took photos of it all, and sent that off with a request that they respond within a week. No response.

I emailed again, saying we wanted to return the units under warranty for a full refund because they were not performing as advertised. This time their explanation for the units’ underperformance was that we must have ‘damaged’ them, despite the units being installed by a qualified engineer in exact accordance with their instructions and with them having seen photographs of the installation and being able to identify no error.

During the course of the exchange, I asked them at least 3 times to confirm the basis of the relationship between rpm and power output in their permanent magnet alternators, because to do this would focus the discussion on the precise nature of the problem and clarify whether there was a fault in the units or whether they were making false claims for their performance. They ducked the question every time. When I sent an email asking just this question, they answered a different question.

We are still trying to get our money back, but it looks very much as if we’ve been had.

Since this has happened, we’ve heard reports of other people using these units in wind applications and finding the same underperformance, including units that have been re-badged for another company. And there’s posts on forums (here and here) suggesting that the company’s advertised power curves are intentionally deceptive.

So we’re back to looking for the right generator again. Intensely frustrating, particularly since Wayne hasn’t had to use a generator all winter with his wheel. Even though it’s now producing only 100W with the river being so low, his batteries are still full every morning. Unfortunately the PMG on his installation is no longer in production. Wayne is beginning to think about building one himself …

(The bottle of Portuguese cava was very good though. That I can recommend.)

Today the sprockets arrived for the water wheel’s gearing. They have been waiting for the last couple of weeks to have US threads machined into them to fit on the spindle of the new permanent magnet alternator from Presto Wind in the USA. So it was just a matter of fitting the M-24 plus framework to the existing framework housing the water wheel’s gear wheel, chain and chain tensioner, adjusting the chain to the correct length, connecting up the M-24 to the junction box and switching on the generator and its charge controller. It only took about half an hour.

The Presto Wind M-24 plus framework ready to be bolted into position

Adjusting the chain to fit

Bolting the framework together

Then all we had to do was direct the water back down the chute onto the wheel. I’ve become so accustomed to seeing the freewheeling wheel flying round at anything between 65-85rpm over the last couple of weeks that memories of its sluggish performance with the Miniwind permanent magnet generator we originally installed had been temporarily obliterated and the penny didn’t drop for at least a full minute.

The wheel was still flying round.

We didn’t count the rpm before diverting the water, but having done so so frequently over the last month, I’ve got pretty good at estimating the rpm from just looking at the water volume coming down the barroco. About 3 litres per second. So about 70rpm. After connecting it up with a 4:1 gear ratio, it was doing 56rpm equating to 14rpm of resistance against a loss of 35-40rpm for the Miniwind PMG. 56rpm for the wheel means 224rpm for the alternator which would, according to Presto Wind’s power curves, translate into around 80W for the M-24: with the 2 stators in the M-24 wired in parallel, that would be 20V at 4A, not far off the 24V it needs to be to start putting power into the batteries. We still have to wire in an ammeter and play around with different gear ratios.

Generating hydro power

Meaningless gibberish? It was to me to start with but I think I understand it a bit better now. With independent (ie. off-grid) renewable energy systems, any input over the system voltage – 24V in our case – charges the batteries, and it’s not really of benefit to have too high a voltage. Over a certain level, the batteries don’t absorb the majority of it so a lot of the power is wasted. This is what happens when you use a portable generator to charge solar batteries. It keeps them going but doesn’t really do much for the state of charge. Simply put, when you want to store electricity, you don’t want speed (= voltage) because speed can’t be stored. You want volume (= amperage). So out of the total wattage (volts x amps) you want to maximise the current (ie. the amps) rather than the voltage. 4A is a nice steady healthy input to have 24/7 – about the same amperage that a portable generator running at 240V and blasting in 1.0-1.4kW is producing – and is what we’re aiming to achieve once we get the system running optimally with the right gearing. At the moment it’s running just under the threshold to contribute.

After running-in the M-24′s bearings and rotors, it will take about 2 weeks of constant charging to get our 770Ah batteries up from their very low state of charge to anywhere approaching full, so the LPG generator hasn’t completed its tour of duty quite yet, but the long wait is finally over.

Big thanks to Wayne Sutton of Pico Hydro Portugal for his genius design and impeccable engineering, and to the guys at Presto Wind for what appears to be an excellent product.

Now we celebrate! Premature? Possibly, but it’s a good excuse for some champagne anyway …

Update, December 16th:

We’ve now upped the gearing on the wheel to a 5:1 ratio, and in the process discovered that part of the resistance was down to an overly tight gear chain. Slackening this off increased the wheel’s speed at 5:1 from 35 to 48rpm under about 2.5 litres per second flow (at 4:1 it had been doing 52rpm). This equates to 240rpm for the M-24 and around 100W open circuit once the M-24 is fully run-in at water levels more usual in June than December. At the moment it’s producing 11V from one stator and 16V from the other (open circuit) after 6 days’ operation. Ammeter still to be connected.

Interestingly, extrapolating the rpm increase resulting from loosening the chain from a 5:1 to a 4:1 ratio would give almost 70rpm. This is pretty much what would be expected from a free-wheeling wheel at these water volumes, suggesting that the M-24 has next to no resistance. With only another week or so to go before it’s run-in, we’re like a bunch of kids waiting for a big treat and can’t wait to see how it’s going to perform.

With rainy days becoming more frequent now – so that finally, after a long dry summer, there’s more than 1 litre per second coming down the barroco – we’ve had the chance to finally commission our water wheel installation and see how much power it’s capable of generating.

So far, next to nothing.

With the stream in full spate, it was generating power, until a particularly heavy downpour sent a massive surge of mud and rocks down the barroco and washed away the temporary dam we’d built to direct water down the wheel chute.

After rebuilding a more robust and permanent dam and playing around with gear ratios for a bit, we finally had to recognise that the Miniwind 2200W-24V permanent magnet generator is not suitable for this site. It had looked perfect on paper, but in practice, it has too much resistance – cogging torque or ‘magnetic reluctance’ – to allow the wheel to reach effective generating speeds with our average water volumes. With the stream in full spate, the water wheel was maxing out at 52rpm (though had been capable of 65rpm at only 2 litres per second before the PMG was hooked up and a maximum velocity of around 85rpm freewheeling). For a 24V system such as ours and with a 4:1 gear ratio, the water wheel needs to be turning at 50rpm (ie. 200rpm for this particular PMG) to start producing 24V power. Consequently, this generator needs to be in a situation where the water wheel is continually running at its maximum capacity, ie. where water volumes are very much greater. And unfortunately this particular model is wired internally in delta mode so can’t be switched over to star by altering the wiring configuration on the rectifiers (which would enable it to contribute at less than 24V).

After a lot of internet research, Wayne (the wheel’s engineer) has managed to source a permanent magnet alternator designed specifically for low wind (and consequently low water) situations. The Presto Wind M-24 is capable of generating 24V power at only 80-100rpm. The genius of this particular generator is that it’s a dual output system: effectively 2 generators in one with 2 rotors and 2 stators, meaning that the magnetic reluctance is half that of a single generator. Since the water wheel in its present configuration is capable of 20rpm at flow rates of 2 litres per second, this PMA would generate power. And with half the resistance, at 2 litres per second, we should theoretically be getting somewhere nearer 40rpm out of the wheel.

It’s on order. Watch this space! (And the Miniwind PMG already has a new home lined up in a situation with much greater water volumes.)

Solar panels on their temporary framework. They’ll move to their final position when renovation work on the main building is complete.

This post comes to you powered exclusively by the sun. Not only is this site hosted on 100% solar-powered webservers, but the computers and router servicing it are now 100% solar powered too.

We at last have power in the yurt! Lovely though the candlelight has been for the last 7 months (though not without its costs at around €6 a week to maintain), it’s a real pleasure to finally see every detail of what I’m cooking in the evening and read a book after dark without a candle balanced precariously on my knees. The best part is that the daily trek up and down from the village 2-3 times to charge the computer batteries and the daily fight over who’s turn it is to use the internet USB modem are now a thing of the past. (The SIM card from the dongle is now installed in a completely wireless modem/router so we can all be online simultaneously.)

At the moment, there is only around 1 litre per second of water flowing down the barroco, which is not enough to power our water wheel with its present gear ratio. This was always anticipated in high summer, and is why we have the solar panels as well as the wheel, but Wayne being Wayne, new sprockets are now being machined so we can change the gear ratio and see if we can’t get the wheel generating power even at such paltry levels of flow.

Present water volumes in the barroco. Not huge. About 2 litres per second.

After debating the relative merits of plastic piping versus wood, we settled on wood. Wayne measured up, I ordered from the woodyard. The wood should have been delivered to us a fortnight ago, but hey, this is Portugal. After two visits to the yard from me and a fair bit of hassling to no avail, Wayne and I turned up at the yard on Wednesday, helped mill the timber on the spot, and took it away with us on the roof of the van. British Health & Safety would have been apoplectic at the mere thought! And this being Portugal, getting out my purse prompted the woodyard owner to suggest he should wait as long for my payment as I had to for the wood … I love this country!

Today Wayne put the chute together on a temporary framework and we measured the rpm. 65-66. Better than expected, and developed with a very small volume of water. My original research on Pelton-wheeled impulse type turbines indicated I could generate 150-200W with a flow of 2 litres per second, using all 15m of potential head available down the steepest section of the barroco, but this wheel will likely generate as much sited only a third of the way down that section. Add to this the absence of any problem with debris coming down the barroco (it’s simply thrown straight off the top of the wheel), or any need for civil works in the form of dam construction to feed a penstock, and a system like this becomes a complete no-brainer. I love it!

It makes the power calculations almost impossible though. Generally, ‘head’ is taken to be the vertical height that the water falls in its descent from a collecting point (often a small dam) to the generator, whether that be a turbine or a wheel. This makes for a relatively closed system, so you measure the vertical height between point A and point B, make adjustments for the length of the pipe run and the number and angle of bends in it (since there will be losses due to friction and the braking effect of bends), measure your volume, do your calculations and you end up with a pretty good indication of the power you can extract from the water.

But mountain streams are open systems. There is no clearly definable point A because the wheel is installed in the middle of a running stream with the chute’s main purpose being to deliver the entire flow of the stream to the top of the wheel before it carries on its way down the valley. So what is my head? The height difference between the wheel site and the stream source (190m)? Clearly not. The course of the stream is straight enough over the half kilometre or so it takes to drop from that height, but it’s not comparable to a closed pipe run. There’s much more friction from the stream bed, many changes of gradient, falls and pools, trapped debris, overhanging vegetation, etc, on the way down, all of which affect the power of the water. The volume top to bottom is not consistent either. But yet the impact on the water’s power of its 174m drop before it reaches our quinta boundary and gets channeled into the barroco can’t be wholly ignored either.

At the other end, the vertical height of the chute is only 2-3m, but there’s a steep fall down smooth rock of another 3m immediately above its entry point. The water doesn’t slow down much in the transition. And while the gradient above that fall is much less, the water is still travelling at some speed as it’s being channeled down a straight barroco. You see my difficulty? It’s almost a case of pick a number, any number, between 5 and … well … Let’s say 5 and 25. That equates to potential power of between 100 and 500W with a flow of 2 litres per second (the lower end of our winter flow range) before subtracting efficiency losses. 100W is marginal, 500W comfortable.

At the end of the day, we’re having to go as much by noses and seats of pants as physics. Seat of the pants says around 200-300W ought to be achievable with winter volumes, but we could be talking out of our arses. Only time will tell.

The chute.

Water wheel!

The gear wheel and chain can now be ordered. Should be roughly 2 weeks.

Battery house is almost complete. The 3 tonnes of schist stone facing the building have a layer of insulation between them and the concrete blocks inside. The roof is also insulated and has a massive slab of concrete on top (it will eventually form part of a schist-paved area in front of the building). As a result, the interior of the building keeps a nice steady cool temperature, meaning the batteries will neither overheat in summer or become too cool in winter.

Having seen local engineer Wayne Sutton’s water-wheel installation on his own property, it was immediately obvious to me that this was exactly what we needed for the hydro component of our planned renewable energy generation system.

Wayne’s water wheel, appropriately geared, drives a 1100W-24V permanent magnet generator from a wind turbine. On his site (the old water-powered olive mill on the valley floor) it was the perfect solution to both the lack of head and the prodigious amount of debris washing down the main river which had made his run-of-river turbine next to useless.

Even though we have a reasonable head (15 up to 30m, depending on whether we use all of it or just the steepest section) on our site, it’s also a perfect solution for our variable flow rates and the debris washing down the barroco. No dams, no penstocks, no fiddling about with turbine jets, and no clogged nozzles. Any debris just gets thrown straight off the wheel. It should be capable of being driven by lower flow than required for an enclosed hydro turbine (they can cavitate if volumes drop below ideal operating parameters) and can potentially develop more power for a given volume of water. Also, we can site the wheel and batteries much closer to the point of use, cutting down on cabling (and power loss) as it won’t be necessary to use the full height of the barroco to develop sufficient head to drive it.

Since installing his wheel, Wayne’s had more power than he knows what to do with, even with 4 loads of laundry a day and computer and DVD player on all evening. His batteries are now being maintained in a state of full charge and the charge controller is cutting in to shut off the solar panel, as well as diverting excess power to the dump load.

Our system will be based on the Miniwind 2200-24 permanent magnet generator.

Wayne will have his own website shortly (once I’ve designed and built it!) and will be offering his design more widely.

The site

The beginnings of the battery shed

Constructing the PMG base

The PMG base

Shuttering in for the wheel base the other side of the barroco