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Energy Diversion to a Battery

What is needed to Divert usable energy to a Battery ?

Assuming that the Voltage of the Battery is 48V. We need at least this voltage to Charge it.

If we are going to use make domestic use of this Battery power we will need an inverter.

Scope of this Development

The scope of diverting energy from an existing Solar PV setup to a Battery and making use of that energy is daunting ! Being at the scale of a full PV System just without the actual Panels. So we are left with the practical problem of how much of a Home Generation system we need to duplicate !

 

Possible approaches

  1. Use NRGDivert to create a 48v Compatible Charger for the Battery
  2. Find Component subsystems to Interface CUMon to and then program them.
  3. ??

Arguments and Reasoning

Regarding 1 above the simplest approach is to transform the diverted power,rectify  and stabilise it.This works to fill the Battery however  does not then provide a solution to make use of this power. The problem of providing the energy back into a domestic environment is that this is constrained by a plethora of regulations any Niche-tec system  would have to comply with.

In the case of 2 above we would need standalone systems to work as our subsystems.

So we are looking to energy divert using a Hybrid inverter. This will ensure the existing PV system remains inviolate and allow the add on system to be stand alone.  This perhaps marginalises the usabilitiy of the system for other developers.

Development Description

The aim of the development therefore is to emulate a CT (Current Transformer sensor) to interface back to a hybrid inverter and that way control the charge and discharge of the battery on the new inverter. This emulation to be completely digital by emulation of the RS485 Modbus Protocol.

This limits the scope of the development to a manageable and achievable goal. Removes the Legal/regulation conformity and produces a system that diverts Excess Solar into a Battery. Furthermore a WIFI CT RS485 Device could find other applications.

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NRGDivert Non Intrusive energy diversion

 

 

Home solar installations generate power allowing your home to use what power you can and any excess is exported back to the grid.  if you don’t have any way to store this electricity and can’t make use of it, then it is exported back to the grid at a low nominal rate.

Making use of that energy yourself is usually the most cost benefit to you.

There are many reasons you may not want to change your electrical setup to upgrade your system to make better use of the energy.

There is a way to determine how much spare electricity you are generating CUMon does that function and logs your consumption over time allowing you to identify when you are exporting and how much energy you could be using. CUMon requires no actual wiring changes to your house. Providing you can identify the wire that connects you to the Grid and the one returning to your Consumer unit from your inverter  you can wrap a current sensor around it. So CUMon requires no electrical rewiring. Just Clamping the sensors around wires  is truly non Intrusive. This can be performed by anyone !

CUMon connects to your home WIFI and broadcasts this information within your  home network.

What is non intrusive energy diverting.

Non intrusive Energy Diverting energy diverting is when the signal from CUMon is detected and acted upon by a device.

 

Current developments

We have NRGDivert  Boards that can turn on driving power to devices within your home. They are experimental but they work we trying to identify the final form of these.

They currently they fit behind an existing 3 pin socket and proportionally turn on or off.

Example testbed is an 13A  Immersion heater that heats hot water allowing the energy to be stored in the hotwater tank these could be used with any resistive load that can handle being Switched On and Off.

Or take the form of an ESP-01S Board that works in a switch on when spare current exceeds a preset value and switch off when it drops below

 

ESP-01S Board

Future Development Aims

We wish to expand on the functionality of the NRGDivert to send that energy to a House Battery.

 

How can I get involed

We are looking for test beds to add to the CUMon logging and welcome fellow developers to put your CUMon logs online and will make available  the broadcast message format for home users that wish to participate and control their own energy usage. 

We  have spare prototype boards for CUMon users wishing to build their own NRGDiverter we offer these free while they last and will charge remake costs for future ones when we have to reorder so get in early if you want a free NRGDivert PCB

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Why you should Zero Export

There are many reasons to Zero export some are conditional on your electricity tariffs some are contractual obligations and some are ethical.

 

Ethical Reasons to zero Export

We should all be moving to net zero and this can be assisted by micro generation. So I will assume you are micro generating power from renewable sources as you are reading this article.

  • Exporting power is costly in infrastructure in building everything from pylons to substations.
  • If you are micro generating you have the option of storing,using or exporting your power. Exporting power to other users is fine if the sub grid you are connected to needs it but has an efficiency  cost for transmission. (you are heating the world thru the cables you are exporting with)
  •  

Legal or Contractual reasons

These will depend on your situation and the local laws. But Include

  • Duty of Care : Keep the Grid  safe for line engineers working on the Nation Grid
  • Constrained to export within limits specified by your authorities.
  • Feed-In-Tariff  restrictions for the contracted period. (If you fall under this you are contracted not to change your PV installation for 20 years)

Financial Reasons to zero Export

Exporting can be lucrative if you are on the correct Tariff. But as the prices for electricity are set by the supplier differential Tariffs dictate if you can use that electricity you should

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CUMonitor as Canbus Controller

CanBus Control with CUMonitor

So the aim is to create a  zero export controller using CUMonitor.

To interface with the Invertor a device is required to connect to the CAN bus.

From a previous investigation for Badger we established that using a daughter board with the CUMonitor is a viable way to interact with the CAN Bus.

So establishing control of the inverter should be possible using similar hardware.

The good part is that no existing wiring will need to be changed and adding the control will only require low voltage CAN bus connections.

One problem is that the inverter is mounted in the roof space and that the Can bus controller will need direct access to the inverter

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CUMonitor as a Zero Export technique

What does a Zero export Controller do and can we replace it with a CUMon ?

A zero export controller balances the energy from the Inverter and Battery with that consumed within the house. By ensuring that non of that energy is sent to the Grid. It proves that it has achieved this by measuring the current to the grid and finding it zero.

 

CUMon already uses the two current sensors to read PV current generated and the Exported Current. It then makes a prediction of whether the system is exporting to the Grid. To get it to function as a Zero export controller it needs to exert control over the inverter.

This should be possible using control on the RS485 or CAN bus. Most modern inverters have the export monitoring and control as an option built in. 

CUMon  offers the advantage that there is no rewiring of Mains Power and it is attached purely by using current clamps of existing cables

To get control of the inverter would require connecting to the CAN bus inputs and acting as  a grid export current sensor.

This is definitely worth considering as there is no mains voltage involved it should prove a safe option for energy divertion

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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

CUMonitor

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

PROs:

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

CONs:

  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