Generating in a drought

The drought of 2026 in the UK is going to be remembered for a long time and in spite of no rain for 2 months my Powerspout is continuing to generate.

The flow available has dropped to half a litre per second (0.53 l/s) but that small amount at a head of 53 metres and an overall efficiency of 40% is enough to make 111 Watts (2.66 kWh per day).

0.53 l/s pictured today being strained of trash before dropping into the header tank.

The onset of the drought can be seen graphically from daily energy output declining from March onwards:

Rainfall had been unusually heavy during the five months October to February, totalling 944 mm which is not far short of the total rainfall expected for 12 months. Yet in spite of this generous topping up of groundwater in the hillside, the water issuing from the spring fell off steeply from mid-March onwards.

In many years, the month of June sees a good amount of rainfall, what I call the 'June Monsoon', but in 2026 it didn't happen and the decline in yield from the spring continued inexorably.

Happily though, the rate of fall in spring water yield seems to have flattened off after May and from experience I know it will be quite likely that even with no rain falling, the 0.53 l/s issuing at the moment will continue to be available for several weeks to come. 

The reason for this ongoing yield of water, with no rainfall to support it, is that the geology of the hillside above is a type of rock called Old Red Sandstone. It is a rock which can take up and hold prodigious volumes of water with the result that the yield of its springs is largely unaffected by droughts of just a year's duration.

The nozzle I am using to deliver a flow of 0.53 l/s is Roman numeral II in my numbering of nozzles. I have been curious to observe how good the efficiency is with this smallest of nozzles because efficiency always drops off at low flows. 

It turns out Nozzle II is giving a respectable efficiency of 40.1% and that is not bad. For reference, the best efficiency I get is 56.4% which happens when flow is between 2.30 and 2.74 l/s.

To know efficiency for your hydro scheme, you need to know accurately two parameters: output power and flow.

The new monitoring system I installed in January of this year (see previous post) allows me to know power very accurately indeed.  The meter measuring it is one accredited by the UK's Measuring Instruments Directive (MID), which means it is in a class of meters accurate enough to be used for billing purposes.

The power output trace from this meter for nozzle II today, over one hour, is shown in the picture below:

The meter is so accurate that it records the 'hunting' of the Powerspout's inverter as the inverter seeks its 'set point'. 

This is seen as the saw-tooth pattern in the power output trace. 

The 'set point' it is seeking is determined by the inverter measuring incoming dc voltage from the Powerspout's Smart drive alternator and then trying to deliver the output, in watts ac current, that its 'table', - stored in memory in the inverter, - tells it is the appropriate power output for the incoming dc voltage.

But like all control systems which change what they're controlling, it continuously overshoots and undershoots its set point and fails to give a straight line.

You can see that the time in takes to complete one full cycle of this unwanted oscillation, - what is called the 'period', - is between 5 and 10 minutes.

Before I installed this MID accredited meter, because of this oscillation I had difficulty measuring power output accurately, but now calculating efficiency correctly is easy using the MEAN power output, which can be read in the red oval. 

It is 111.8 W.

Another thing I've learned from this spell of using Nozzle II is that my previous obsession with keeping rpm (revs per minute) close to the optimum rpm for my pelton (1000 rpm) has been wrong.

I used to keep rpm high by packing off the alternator rotor. 

In fact I packed it off so much that rather little of the shaft's splines engaged in the plastic splines of the rotor, - and this led to rotors being damaged.

What I've learned now is that whatever gain in efficiency might result from having the pelton operate near its optimum speed, is counteracted at least as much by a loss of efficiency in the alternator because of impaired flux linkage between permanent magnets and stator cores.

So the efficiency I'm seeing now with Nozzle II, the respectable 40.1%, is actually obtained with little packing off and with a resulting rather slow rpm, - just 742 rpm .

This slow rpm can be seen in the concluding pic below, where the splash pattern of water exiting the pelton cups is way off to the right. At the optimum rpm of 1000 it is at 6 o'clock. Note that only the bottom jet is in use.

Turbine on 19 August 2026, on 0.53 l/s of water, at 742 rpm, generating 111.8 W to grid.

To round off this blog post, I have to admit that with such a memorable drought happening, it amuses me that I can still be using water to generate a bit of electricity. 

Long may it continue !

A new on-line monitoring system.

Home energy systems need to be monitored; they need to be monitored not least because it is satisfying to know how much energy you are producing and how it is being used, but also because monitoring can be critical in picking up small problems before they become big problems.

In operating my Powerspout, since it was commissioned I have relied on the on-line visibility of the power being produced to know when to change nozzles. As the header tank begins to empty so the power generated begins to drop, - not by much, only by about 5 Watts. But it is enough for the downward trend in the data seen on my iPad to tell me I need to change to a smaller nozzle.

With this being a key observation for me to run my scheme efficiently, imagine my consternation when, at the start of 2026, the company which had been hosting the output of my turbine, decided it was time to close down the service they had been giving. Suddenly I was in the market for a new system to replace what was no longer available.

This blog is about the new system I found. I am enthusiastic about it and want to make known the company marketing it in case others might be interested in following the same path. If you click where it is written "Live Power and Energy" on this blog page, you'll see the new 'Dashboard' provided by the company. It displays the power and energy being produced by my Powerspout in real time and is updated every 10 s.

The hardware capturing my Powerspout's output.

The system is provided by OpenEnergyMonitor.org. The company provides all kinds of monitoring, from simple systems like mine where there are only two data feeds, power and energy, to whole house systems where feeds can come from solar generation, individual house loads, room temperature sensors, EV chargers, heat pumps and more.

The company is based in Wales, UK and when you buy products from them the deal is that 20% of the value of what you've bought is credited to you against the charge for them hosting your data on the web. Each feed you sign up to costs GBP 1 per year (excluding VAT, 1.20 with VAT). The cost of the kit I purchased was GBP 345 excluding VAT, and has therefore given me credit of GBP 69. I have two feeds at a VAT inclusive cost of GBP 2.40 per year, so that gives me 29 years worth of web hosting included in the cost of buying the hardware (calc 69/2.4). 

The guys behind the company are super helpful. I received much help, willingly given, to get my system up and running. Being an 'open source' data handling enterprise, if you have the computer skills to set things up yourself, then so much the better. I don't have those skills but with their support, all went smoothly.

The 'dashboard' accessed via this blog page is the way of publishing your data for anybody to view it, but it is not the only way of accessing your data. From the account you open with OpenEnergy when you purchase from their on-line shop, you have secure access to the raw data of your system, and you can make graphs, choose time frames and make downloads. It is a very versatile platform and much better than what I had before. The picture below is an example of how detailed the view can be of the power coming from my turbine.

A detailed, more granular view of the power output in Watts from my turbine.

Here in Wales, the rain is incessant. Last month I recorded 271 mm. That makes January 2026 amongst the top 5 wettest months in the 12 years I've been keeping records.

Of course, it's good news for electricity generation. It has been the month where we have used the least energy from the grid ever, just 12.6 kWh.

And the revenue earned in Feed in Tariff (GBP 267) has contributed most of the cost of my new monitoring.

Happy days !

Year end results for 2024-25 water year.

 For those few people around the world who search the internet for good data on how productive domestic scale micro-hydro is, here are my figures for the past year.

As years go, it has been a dry year in terms of rainfall, and the turbine's output has consequently been not as good as some years. The year end figures were saved from being too bad by the year starting off very wet and this meant that a good deal of the year's total energy was generated by the end of February. After that, rain became scarce and generation steadily declined for the remainder of the year.

Nevertheless, with 4534 kWh generated, I can't grumble.

In each graph, the bold black line represents data from the 2024-25 water year (Oct 2024 to Sep 2025).

1. Daily output (mean power W = total daily energy kWh / 24)

2. Cumulative energy output (kWh)

3. Power duration curve (number of days generating at measured levels of power output)

4. Whole year rainfall vs whole year energy generated.