Year end results for 2023-24 water year.

The year to September 30th has seen the most generation in the eleven years my Powerspout has been running. The total energy generated was 5254 kWh.

Understanding that this figure is really quite good for a small turbine is best captured by considering what is called capacity factor.

Capacity factor is the energy generated in a year divided by the energy that could have been generated if the turbine had run everyday for 365 days at the rating specified in its technical specification.

The rating specified for my turbine is 750 watts, which means the maximum power it is meant to be able to produce is 750 W. And using this figure, the maximum energy that could be produced in a year is 6,570 kWh (calc: 0.75 x 24 x 365).

So the capacity factor for the 2023-24 water year turns out to be near enough 80% (calc: 5254 / 6570 = 0.799).

But there is a slight deception in this figure. And this is because the maximum power my Powerspout can actually produce is more than 750 W, and this is evident in the first of the plots below.

There is a reason why there is this deception: the figure of 750 W had to be specified before the turbine had even been commissioned and was a figure derived purely from theoretical calculation. This theoretical calculation had to make assumptions about a lot of things such as friction loss in the pipeline, the efficiency of the 3 phase alternator, the efficiency of the dc/ac grid-tied inverter, ...and many more factors, - all of which were little more than educated guesses.

When the turbine actually got to run, many of the guesses turned out to be on the pessimistic side and the turbine actually was found to produce nearer 800 W at full flow, and even 900 W if slightly more water than the specified maximum flow of 3 l/s was used.

So the 80% capacity factor figure is inflated, and if the true maximum power of 900 W is used to calculate it, the figure drops to 66%.  But since officially my turbine is rated at 750 W, that's the figure I'm going to continue to use for my capacity factor calculations. But I will point out that in the interests of 'honesty and transparency' you'll notice that I do say in the Scheme Details section in this blog where each year's capacity factor is given, that the figures are "taking as datum DNC 750 W" (DNC = Declared Net Capacity).

For those who like to appreciate how a small scale hydro works out in the real world, here are the figures for this past year's generation. The year 2023-24 is the black plot line, and previous years are coloured lines:

Powerspout+Solar+Battery= the perfect combination.

I've posted a video on Youtube for those who want to know the 'length and breadth' of my home's energy system.

You can find it at https://www.youtube.com/watch?v=-rmYOUQAVTk 

You'll need 20 minutes to view it all, and it comes in HD.

I'll add a link to the side bar of this blog for future access.

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Addendum: added 23 April 2024

In response to people wanting to know the cost of the battery storage scheme, below is a breakdown. The numbers are in pounds sterling (GBP).

The costs given include VAT at 20% (the installation was done before the UK Government decided to exempt retrofitted battery storage schemes from the 20% rate).

Benefitting from Battery storage

There can be no better way of communicating the benefit of having battery storage than publishing the graph below.

It records the energy my house has taken from the grid each month, starting at January 2023 and ending January 2024*; the battery storage was commissioned on 1st November 2023.

The step-down in grid consumption from November is quite remarkable, - more than I ever expected.

The data for the graph is reliable; the figures come from the meter readings sent to OVO, the electricity utility who sell grid energy to me.

I look forward now to seeing how this graph pans out over a full year; the three months in which battery storage has so far been contributing, have been months when the Powerspout has generated at its maximum and there has been little input from solar; later in the year, the mix will change, - and therein lies my interest to see how the full year looks.

* I will update the graph each month after January 2024, and do this for 1 year, to give the latest information.

Addendum added 15 April 2024

How the above graph 'pans out over a full year' will depend on how total energy generation from solar and hydro changes in the course of a year.

The pattern of how it changes is seen in the graph below.

The graph shows the total kWh generated each day from hydro and solar, between October of one year and September of the next.

The blue spiky line is the kWh generated each day.

The value of the data point for each day is the 8 year average of the energy generated on that day.

The red polynomial line is the 'best fit line' for the blue line.

It will be seen that maximum generation is from mid February to June, and in this period the graph above can be expected to show the least energy taken from the grid.

Conversely, least generation happens in September / October, and in those months grid supplied energy is likely to be needed.

Priorities ! - part 1

Having added battery storage to my home energy system, a dilemma has been created; and that dilemma is how to prioritise the different uses for where home generated electricity can go.

To be clear what these uses are, and to place them in a descending order of rank, they are:

1. the moment by moment electricity needs of our house 
2. domestic hot water heating (DHW), - or more precisely, topping up the temperature thereof from the temperature reached by a log burning stove whose back-boiler also supplies central heating warmth to radiators, and never gets to be > 40° C
3. charging the battery of our BYD home energy storage system (10.2 kWh of storage, max. input / output capacity of battery inverter is 3.7 kW)
4. charging the battery of our old model, Nissan Leaf EV (which has the smaller 3.3 kW on-board charger)

Apart from the dilemma of ordering the prioritisation of these loads, there is the matter of devising a way of ensuring that home generated electricity goes where I want it to; and in order for it to be possible to make it go where I want it to, for that I have to have some means of 'seeing' where power is going at any given moment.

Another fundamental matter to be clear about is the philosophy I follow for how I want my home micro-grid to operate; although I am grateful for any savings I make on needing to buy-in grid energy, I am not in the business of 'doing home generation' for the sake of making money; my hydro and solar installations are both accredited for Feed in Tariff payments, and there is thus a nice revenue stream coming from those; beyond that source of income, fancy schemes such as are offered by Octopus Energy, - a company offering attractive reduced tariffs for bought-in energy at certain times of the day, and generous Smart Export Guarantee (SEG) tariffs for exported energy, - these I view as 'baits' simply to get me to sign up, and for me they hold no appeal whatsoever.

Rather, the philosophy that guides me is one of simple self-sufficiency, - the contented feeling of being able to cook, light the house, bath in hot water, and travel the limited distances we need for shopping, - and know that all the energy for these things has come from one's own 'power station', using 100% renewable energy.

At the time of writing, in January 2024, my home battery storage has been up and running for just 3 months, and those three months have been exceptionally wet; as a result the Powerspout has been producing at maximum output (900W) almost continuously and its 24 hour total output of 21.6 kWh has been more than enough energy to supply all our needs; in fact much of the time there has been so much energy that there has been some to spare which, rather than let it go out to the grid, I divert to one or both of two subsidiary loads; one of these is a DHW load and the other a space heater load, and both are in a part of the house which is presently not occupied; though unoccupied, sending power there helps to keep away the winter chill in that part of the house.

Visualising and controlling how electricity is being used around my home is crucial. 

The 'visualising' is made easy with an iPad because each bit of kit in the system can be called up in the local area network (LAN) or via SMA's Sunny Portal interface; thus the battery state of charge (SOC), the power flow at the grid connection point, the total of home generation from combined hydro and solar, whether the inverter is charging or discharging the battery, and which load the DHW diverter is feeding to, - all these are accessible from the comfort of an armchair.

Controlling is achieved with no less a degree of ease; it involves a certain amount of 'automaticity' and a certain amount of 'manual tinkering'.

Careful scrutiny of the single line diagram below indicates that the design of my system ensures that diversion to heating DHW is the first priority for where surplus home generation goes; the diversion device controlling this is a Solarcache, and by way of it, two priorities of load are controlled; when the first priority load, which is the main house DHW supply, is up to temperature and its thermostat is OFF, the second priority load is switched ON; as a result of the way I have set it up, the second priority load is comprised of the two loads previously mentioned, one being the subsidiary DHW load and the other the space heater load, both located in the chilly part of the house.

Each of these 3 Solarcache loads (one on first priority and two on second priority) is wired from the main consumer unit via its own dedicated RCBO (residual current breaker with overload), and whether a load is capable of receiving power is easily controlled by manual operation of the RCBO switch; thus 'automaticity' is achieved by the way Solarcache switches between its two priority options, and 'manual tinkering' by the RCBO switches, which determine which, if any, of Solarcache's connected loads is actually available to receive power. 

Happily the RCBO switches are very close to the armchair previously mentioned, and that makes 'visualising' and 'control' not only a convenient task, but a fun one too.

So much for the basic layout of how electricity is used around my home for meeting the first two priorities on my list, - the moment by moment power needs of the house and using any surplus primarily to heat DHW.

In Part 2, I'll explain how the BYD storage battery is kept charged, how the Nissan Leaf is charged from stored energy in the BYD battery, and why the technology of a MyEnergi Zappi doesn't seem to have a place in my set up.