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Daves CUMonitor gets an NRGDiverter

Dave’s been running with an CUMonitor for a while now and wanted to investigate driving his underfloor heating using a NRGDivert. On the 15th of May one was installed after some testing we found that the underfloor heater only consumed about 1.4 Amps when fully on.  After further investigations we found out that the under floor heating was controlled by WIFI already and the only convenient place to install the NRGDiverter was before the WIFI underfloor heating controller. This meant that the high speed switching of the supply could damage the WIFI switch. So A 100% on/off mode was added to NRGDivert.

And the WIFI Switch was controlled by a 3rd party App consequently this NRGDiverter was controlling nothing .

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CUMonitor Testing for Badger on RS485

We received and inquiry from the owner of a solar installation Nick Name “Badger” that has a wiring setup where the inverter has been wired to the consumer unit board using a 3 core cable that presents no opportunity to use a current clamp without cutting into the cable. Also there is no ready supply near the consumer unit.

So we have resolved to add Modbus functionality to read the current directly from the inverter using RS485. The functionality on the Inverter allows this.

Testing Results are here    in the badger folder.

We are also trialing Dual logging with second CUMonitor configured to record additional analog traces

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NRG Divert Algorithm

So NRG Divert needs to work as reliably as possible and what work for our use cases new use cases may not work ! So the CUMonitor will allow a record  of the results and a qualitative assessment to be made of those results.

We will publish on our website what Algorithms we are using and you should be able to see the results here


The NRG Divert relies on a CU Monitor to record the two current readings taken from the Consumer Unit feeds. It makes an assessment of the likelihood that the Grid connection is indicating that the CU is exporting to the Grid.

NRG Divert Residual (aggregate current consumption)

NRGDivert calculates the current consumption of the house simply by subtracting the Grid current from the PV generated. Obviously this is only worth doing if the CU is observed to be exporting.

This is then assumed to be a stable value and the remaining “spare” energy is calculated by subtracting the Residual from the total PV generated

The first cut of the NRGDivert software assumes the residual value does not change while it controls the load.

Spare energy and using it

So having calculated the “spare current” how to use it and only it is the next problem:

This is done be turning on a resistive load for some AC cycles every second.

Essentially every second the mains AC signal performs 50 cycles and by selectively turning the load on for these cycles you can consume this “spare energy”. Conveniently 50 cycles means that there are 100 half cycles to chose from every second.



Commanding the Load

Turning a load such as a Immersion heater on  without ensuring that zero current is flowing at the time would give rise to a very noisy electrical signal. So we can only do this as the voltage crosses the zero point to avoid this noise.

The Load is a known quantity (its Resistive load) so you know that the full current requirement will be presented when it is turn on.

This is a  power control solution known as cycle stealing. The consumed power is being monitored by CUMonitor  and we should be able to see this load appear as a change on the Grid Monitored value

Verifying the Load

The NRGDivert software  looks for the load appearing on the Grid monitored value and will only remain controlling the load if the expected value is seen and within acceptable tolerances of what it predicts.

This means if the expected Grid Value is out of the predicted range then NRGDivert will disengage the load and recalculate the residual value.


Proving that the algorithm works

On the electricity meter in Site one (ilog) there is a LED that illuminates when the the Meter is exporting to the Grid. This is recorded in the logs on the second plot as a thick yellow line

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NRGDivert Works

Testing of NRG Divert  is going well this is the latest traces produced by system.

  1. The yellow dotted (meta data) line is the confidence that the system is exporting top the grid
  2. The White dotted(meta data) line is the predicted load value that NRGDivert is expecting to see for the device diverted device after the diversion of power
  3. The Red dotted (meta data) line is t he % the device is turned on throughout most of the test it is registering less than 10% of the device is engaged the device in this case is the purely resistive load of an immersion heater which draws up to 13.5 Amps when fully engaged
  4. The Green line is the Raw solar panel generation
  5. The Orange line is the import/export amperage to the Grid
  6. The SOLID yellow line on the is the LED on the lower graph is the LED on the meter showing that the house  continues to export even though Diversion is taking place
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Energy Diverter NRGDivert

OK so the generic Energy Diverter NRGDivert needs to improve on the existing examples in a cost effective manner.

So lets examine the Pro’s and Cons of  Energy Diversion.


Pros and Cons of existing solutions


  1. Low Cost Energy
  2. Better use of Energy because of grid transmission losses


  1. Requires Wiring changes to you house.
  2.  Limited use case for energy CAR Charging /Hot Water tank
  3. Requires extra hardware

Addressing the CONs for NRGDivert

Con 1 :- By using Clip on current sensors as in the our CUMonitor Kit you don’t need to alter the wiring of you house to sense the usage.

Con 2:- If the Energy Diverter takes the form at an extension lead that may only be used to power resistive loads see NRGDivert link TBD

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Progress on Consumer Monitor and Energy Divert

The energy monitors have been running consistently and reliably on Site 1 I’m running two copies of the hardware to reduce TTF (Time to failure of the setup and gather more data). They have both been delivering data to the logging website reliably. The second remote has run intermittently but has stayed up for periods of a month and then stopped transmitting without explanation. I’m improving the software of the consumer monitors and will update them soon showing the published data on the Logging Website.

Energy Diverting

So the excess power generated by Solar panels at each site is exported to the Grid. Power companies pay micro generators a very small bounty of a few pence per Kilowatt hour generated and an energy diverter would allow the micro generator to make use of that energy themselves.  If you have a use for this energy there are very few ways that you can get at it. But I can see ways that that this energy can be harvested and deployed beyond current available technology


Existing Energy divert solutions

The following are the existent energy divert solutions.

  1. House Battery Storage : Many solutions
  2. Dump excess energy into your hot water tank Eddi
  3. Charge your Electric vehicle e.g.  Zappi Charger

New Energy Diverter Solution

I’m proposing another energy divert solution that will use our CUMonitor Box and Divert energy to any Resistive  load such as a Hot water immersion heater.

Here is a log recorded from last summer you can clearly see that the chosen points for attaching the current clamps show the record of the PV generated(Green Trace) and the power flow to the Grid (Orange Trace). The Astute will also notice the strong correlation between these two traces.

Also we can see the difference between the two traces  must be the Residual power consumed by the house.

The Solid yellow line on the bottom plot reflects the state of an LED on the electricity meter which indicates power flow to the grid up until the sun goes in at about 3.5 minutes into the trace.

So from the values provided by the CUMonitor we may calculate the spare energy.

Another interesting point on this plot it the switching off of a load in the house at just after 9 minutes it.

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What size House Battery

So I need an idea of the size of House Battery to get.  To Store the excess solar energy from our solar panels.


Well the CUMonitor plus the tel-tec web calculator lets you model the problem so you can try out different house battery capacities at the different times of the year. see example logging data here.

If you are interested in joining the CUMonitor user group fill out the form here. Note you will have to purchase a CUMonitor box to log your house it you want to take part as a member

The Battery size is entered at the top of the page and the first (light green) bar chart is of the Power remaining in the Battery and the second is the Power from the solar panels. The Assumption is made that the 24 hr period starts with the Battery full.

Some CU Meters have an LED that illuminates when the Meter is exporting the to Grid CUMonitor can optionally monitor this or use an internally calculated flow,

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Actions to take before getting an EPC

Before getting an EPC there are a number of measures we can take to improve the outcome of the EPC

  • Fit energy saving lighting
    • We already have energy efficient lighting
  • Double glaze all windows
    • We already have double glazed windows
  • Improve loft insulation
    • We currently have 10cm of loft insulation this should be increased to 27cm
  • Cavity Wall insulation
    • We have cavity wall insulation. But this was done to the property before we bought it and we have lived here for nearly than years. I will see if we have any documentation for this.
  • Upgrade to an efficient boiler
    • Our gas central heating boiler is a condensing boiler and less than 10 years old. Nominally considered efficient so our energy rating from this should be OK

The main deficiency our house has is the loft insulation. So we will increase this to 27cm.

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To apply to join the RHI you must have a current (within two years) energy performance certificate EPC. The EPC needs to be generated by an accredited energy assessor. Which essentially means you have to pay someone to assess your home. The sort of questions you have to answer are:

  • When was the property built? When were any extensions and conversions made?
  • If you converted the loft into a room, when was the work carried out?
  • Has the property been inspected for, or does it have any cavity wall insulation?
  • Have you very recently added any double glazed windows or doors?
  • Does the property have any under-floor insulation? Can this be seen, or do you have the receipts for this work?
  • Are you on a single or double electricity meter?
  • Have you installed any heat recovery technology

The rating of your home will depend on many factors. But typical recommendations are :

  • Insulation for your floor, roof, loft or walls. Better insulation reduces the need for heating, thereby lowering your energy bill.
  • Double glazing: windows keep in significantly more heat when they’re double-glazed, again reducing the need for heating. Solar panels: these produce cheaper, greener energy.
  •  Low-energy lighting: a smaller change that involves no structural alteration, using low-energy light bulbs is a cheap, easy way to lower energy bills.

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The most cost effective way forward appears to be applying for the RHI (Renewable Heating Incentive): The Domestic RHI is A government scheme to pay incentives for using renewable heat.

Options include:

  • biomass boilers (Our house is old enough to have chimneys but is in a smokeless area)
  • solar water heating (Our house has solar panels fitted on the south facing roofs)
  • certain heat pumps (The plot our house is on has space for either a air based heat pump or a ground based heat pump)

We will consider each in turn.

Biomass boilers:

  • Burn wood or pellets which require storage :
    • We have room to store fuel for a biomass boiler.
    • Fuel will need to be bought in.
  • Require manual feeding (CON)
  • Can function on demand(PRO)
  • Require tending ash disposal and cleaning (CON)

Solar water heating : Our southern facing Roofs are in use so this option is not suitable. We have out buildings that may be used but the piping and insulating of water to these locations make this problematic.

Heat Pumps :

  • Air source heat pump
    • Electrical power required to run pump.
    • Requires suitable space away from property boundaries
    • Lower Operating temperature requires resizing of radiators (CON)
    • Potential for icing in cold weather (CON)
  • Ground source heat pump
    • Electrical power required to run pump
    • Requires more space close to the house (CON)
    • Lower Operating temperature requires resizing of radiators (CON)
  • Heat pumps have a COP (Coefficient of performance) a good COP is anything over 3 with 4.5 being the max possible. The heating for our house for the last year required 26834.5 KWH. Assuming a COP of 3 we would need 8945 KWh of electricity to do this. About 50KWH per day in winter.