6.48 mm diameter nozzle delivering 0.91 l/s to the runner which is rotating at 1084 rpm and generating 225 watts into the grid at an overall efficiency of 47%.

Sunday 4 February 2024

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 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.

* I will update the graph each month after January 2024 to give the latest information.





Wednesday 24 January 2024

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 where I want home generated electricity to go to.

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 determines which, if any, of its 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.

Monday 11 December 2023

Battery storage completed.

In previous blog posts on battery storage, I waded through the deliberations that burdened me as I struggled to reach a decision about proceeding with it; in this post, I just want to show what actually came of it all.

In a future post, I’ll look at the system's pros and cons, but I'll write that when more time has passed with it being operational. At present, it has only been operational for 6 weeks. In that time our energy consumption from the national grid has been less than 5 kWh (before it was 200 kWh for the same 6 week period in previous years), - so early impressions are favourable.

Location for 'battery bunker' BEFORE construction

Battery bunker AFTER completion

Inside the bunker

Meters for ac frequency and volts, and battery dc volts; the switch is the 'black start switch' for manual operation of battery back-up

BYD HVS battery tower, 4 battery modules totalling 10.24 kWh, with Battery management Unit on top

SMA Sunny Boy Storage 3.7-10 inverter with ac ON/OFF switch

Connection compartment at bottom of SMA inverter; additional devices on the right are a DIN rail mounted, 5 way, Ethernet switch and its 12vdc power supply

Cable entries to underneath of Enwitec Battery Back up box; the Enwitec box accomplishes all the switching arrangements for transfer from grid supply to battery supply when there is a grid outage, and back again to grid when the grid is restored; this it does either automatically or manually; manual control is by means of the "black start switch".

The inside of the Enwitec box; The key component monitoring power flow at the grid connection point is the SMA Home Manager 2; it is the device to which the green Cat 6 (shielded) ethernet cable is plugged into. The contactor Q1 on the left side is the device which isolates the property from the grid when battery backup is in operation. Relay Q3 is the device which ensures grounding of the neutral conductor when in battery backup mode. F1 and F2 are mccb's protecting the power supply to the Enwitec box, one for grid supply and one for battery backup supply; F201:1 and F201:2 are respectively an mcb and a rcd on the ac line connecting to the SMA SBS inverter.

The incoming National grid supply, and its meter, were moved into the bunker from their previous place in an outside receptacle on the wall of the house; this was to make more simple the cabling arrangements for battery back up; the earthing arrangement when on grid supply is TT, and on battery back-up operation it changes to TNCS. 

In the house, two new consumer units were installed, one for house loads and one for in-coming power from the two renewables available:- these are the Powerspout and 3.2 kWp of solar; the total generation from these two renewable sources is measured by an SMA Energy meter; this is the device with a red ethernet cable connected to it; the data from the Energy meter is made available by Ethernet cable connection, via a LAN network, to the SMA Home manager (in the Enwitec box housed in the bunker); also, the data from all devices in the system is made available, via a www connected router, to SMA's web interface; this they call Sunny Portal; next year 2024, for systems which have a Home Manager, SMA will be replacing the classic version of Sunny Portal, with their new web interface called Sunny Portal powered by ennexOS; when that comes, the User interface will have, so they say, a new fresher look.

The user interface provides all the expected features of instantaneous and historical energy flows that one expects from such technology; the parameters and configuration of the SMA SBS inverter can also be accessed directly via the LAN network, and this is essential in setting up the system and for investigating faults when they arise; following SMA's advice, which they strongly encourage, I went for cabled communication throughout, rather than using WiFi.

This is our meter measuring in-coming energy from the national grid; the pencilled readings top and bottom were the readings on the day when the battery storage first started operation, and that was 41 days ago; you can see that in those 41 days only 0.6 kWh of low rate energy has been used, and 3.1 kWh of normal rate; in that time we have cooked, heated our domestic hot water, charged our Nissan Leaf umpteen times, and met all the 'base load' requirements of a normal modern house; as I mentioned at the start, normally this would have taken around 200 kWh, - so the battery has, thus far, been 'transformative' !

For the really technically minded enthusiast, here are the schematics for the scheme as it was finally constructed: