I have been running the turbine without ventilating the electrical side to try to reduce condensation. As a consequence, the temperature inside the compartment is higher.
In recent days, the temperature has been higher than usual because outside temperatures have been warm, and I began to notice that power output seemed to be drifting down as the temperature inside the compartment went up.
So I did an experiment. Without changing any other factor which might alter power output, I re-established ventilation. Over the next 40 minutes, the power output went up by by 6 watts.
Next day, to be sure this wasn't a fictitious observation, I reversed the experiment and blocked up the ventilation louvres again: the temperature promptly rose back to 30.4℃ and output dropped back to 616 watts.
OK, - so it's not an earth shattering observation, but nevertheless it's of interest. The same effect is noticed and commented on (see page 5) in the report written for EcoInnovation's compatibility test for a Powerspout GE 400 coupled to an SMA inverter.
22 Dec 2015 Note added later:
For the type of permanent magnet used in the SmartDrive rotor, which is ferrite ceramic, the flux density decreases linearly with increasing temperature. The obverse of this statement is that flux density increases with decreasing temperature. This would explain the above observation.
3 Feb 2017 A further note:
The resistance of copper wire increases linearly with temperature; the impedance of the stator coils will thus increase with a rise in temperature and this too will affect the power leaving the alternator.
In the course of the last ten days, as the flow from the spring has picked up, output has doubled from 225 W to 518 W .
At 518 W, more than enough power is being generated to meet the 'base load' of our house, by which I mean the total load of all those electrical gadgets which are taking power in the background most of the time. For us, 'base load' is made up of fridge and freezers, central heating pumps, lights, computers and a good number of small devices connected through mains rectified power units. The total load comes to about 350 W, but it fluctuates, particularly depending on whether fridge and freezers happen to coincide their 'on' times.
So there is a surplus of generated power much of the time, and as water flow picks up further, this surplus will get greater. What to do with it ?
Back in August this year, I had some solar PV panels put in, 3.25 kWp in total, and at the same time installed a Solar Cache, which is a device to divert surplus home generated power to useful loads 'in-house'. The greater benefit of Solar Cache comes from diverting the huge amounts of surplus power arising from a sunny day, but it works just as well in diverting the smaller amounts of surplus hydro power. By so wiring it that it registers the total of home generated power, it works seamlessly to divert power whether it is solar, hydro or a combination of both.
Here is a picture of the Solar Cache screen taken last night:
Taken as it was at 22.50, there was no solar generation and the 518 W indicated to be solar all comes from the Powerspout. House 'base load' at the time is recorded as 197 W so there was a surplus available of 321 W. The cleverness of Solar Cache is that it diverts as much of this surplus as it can to a useful load, whilst just maintaining a trickle of export to the grid. From the screen, it is trickling 95 W to grid and sending 230 W to the immersion heater in our domestic hot water tank.
Under the feed-in tariff scheme implemented in the UK, payment for 'exported' energy is not calculated from a metered export reading but from a 'deemed' amount, which for hydro is 75% of energy generated. Thus the way Solar Cache works which is to keep exported energy to a minimum (the makers claim around 50 W) does not mean that the revenue one receives for exported energy is reduced.
This, however, may be about to change. In the UK, the government are embarked on a public consultation regarding changes to the feed in tariff scheme, and one of the questions in the consultation is:
"Given our intention to move to fully metered exports for all generators, do you agree with the proposal that new and existing generators should be obliged to accept the offer of a smart meter when it is made by their supplier?"
The effect of this change, were it to be implemented, would certainly reduce the income coming from a Powerspout, and this would be the case whether one had a Solar Cache or not. A Powerspout installation, by the smallness of its output, will never generate sufficient for 75% to be exported, so any change from the present calculation method based on '75% deemed' will reduce income and prolong the 'payback time'.
But hey ! - it's not about the finances but the fun of having such an elegant source of home power.
It has been a busy few days with the Powerspout. With autumn well on the way, the weather has been warm and wet. The flow available to the turbine has been gradually increasing so I have been able to change from the reduced core stator to the 42 pole, full core one. This will now see the turbine set up for its winter period of peak output.
Whilst doing the change of stator, I also changed the bearing block. I had to deliver on a promise to Michael Lawley that once winter flows arrived, I would run another trial of ceramic bearings. The first trial was done in June and the bearings lasted just 4 weeks.
This second trial started yesterday, - and finished yesterday ! Just 8 hours ! Inspection of the failed bearings showed much the same as the first trial: pitted balls causing locking up of the race, but this time there was also abrasion of the PTFE spacer ring, leaving particles of PTFE everywhere. I think this has to be the end of the road for the ceramic bearing dream !
In the course of this repeated delving into the turbine, I have progressed the idea of trying to run the Smart Drive compartment as dry as possible. This I've done by stopping the ingress of moist outside air by blocking off the ventilation ports and de-humidifying the captive air inside with bags of silica gel.
The idea is to create a warm, dry environment for the electrical side which will inhibit corrosion and promote insulation.
It seems easily possible to obtain very low levels of relative humidity. Ten bags of silica gel, each of 100g, brings the humidity down to just 10% within an hour of closing the housing, and this is with an outside ambient humidity of 98%.
The rise in temperature is to about 6 ℃ above ambient when the power output to grid is 300 W. At the reading showing this morning, 22.4 ℃, I am happy with this, although as power output increases in coming weeks, and with it greater heat output from the alternator, the rise in temperature will have to be watched.
To touch briefly on the theory of humidity and its relationship to dew point, if the relative humidity inside the housing can be kept at this 10% level and the temperature in the housing does not rise above 36 ℃, it will completely prevent any condensation (which is dew) forming on the bulkhead, even when the temperature of the bulkhead gets down to 0 ℃. Since it is condensation forming on the bulkhead and then dribbling down over electrical components which probably causes most of the issues with insulation breakdown, this would be a significant advance.
The unknown will be how often the silica gel bags will need 're-charging', and the answer to that will be how often the compartment is opened allowing an air change with moist outside air. I'll be keeping my inspections there to a minimum.
For those interested, 25 silica gel bags of 100 g cost £18.59 and a useful dew point calculator can be found here.
