I have installed many Zappis and and some Eddis made by MyEnergi, but I wanted something open source to play with for my own house. I am looking for an open source solution to use spare solar and integrate battery storage system in the future.
From spare solar:
charge the car
when there is not enough spare energy for car charging, divert spare power to run immersion heater.
At night time when electricity is cheap and car battery is empty (like Octapus GO) I would like to charge the car (probably all winter). Or when there is even cheaper electricity available (like Octopus Agile) - charge the car and heat hot water (I am on Octopus Go and havent tried Agile tariff).
Few years ago I bought āOpenEVSE WiFi Emoncms EV Charging Stationā (still sitting in the box) and I was thinking to add āemonPi Energy Monitor - Solar PV Bundleā (from reading it looks like it would work to charge the car from spare solar).
But I am not sure how to deal with hot water. Can a budget option like Solic 200 be used for this? I have been reading about āMK2 routerā - would that do the job?
Robinās Mk2PVRouter is designed to be completely stand-alone. Depending on where you measure the grid current (it attempts to balance that at the place itās measured to zero when thereās surplus PV being exported), it can āmop upā surplus PV after the other devices have had priority, or probably it can have priority over the other devices, if those see it as part of the āhouse loadā.
Of course, the big advantage over a commercial unit is you can rewrite the software to suit your needs, or you can substitute a (purchased) proportional controller for the āburst modeā triac that is part of his standard kit.
Reading between the lines, it seems that you will want water heating timed on and most likely when PV is not available - the override input on Robinās diverter would give you full power when enabled, and normal operation when not.
You can email Robin at his address on his website, heās quite happy to discuss special requirements.
I know this is an old topic, but Iām just getting an EV. I already have Robinās diverter feeding excess PV into my immersion heater. I hear lots of talk about Octopus Agile, but it requires a smart meter, something I have always resisted because Iāve not found any definitive proof that my diverter will still work with a smart meter. I think that comes down to the size of the energy bucket, or if they even have one.
Iāll admit the last time I looked at this was probably well over a year ago, and things have probably changed, but can anyone say whether the PV diverter will still work with a smart meter?
As far as Iām aware, there has been no significant change in our knowledge. Iām fairly certain that nobody with one of Robinās (or MartinRās) diverters has reported how it interacts with a smart meter.
A smart meter must have some sort of āenergy bucketā, but that could be as small as one mains cycle - the minimum averaging period to get a meaningful rms value. And if that is the situation (Iām not saying I know it is, or that I think it is, but it could be), then no burst-fire diverter will āworkā ā meaning the meter reports the nett power of zero as measured over the diverterās duty cycle. You will only get maximum benefit when itās diverting for 100% of its duty cycle. The only sort that will be guaranteed to work with a meter with a āminusculeā energy bucket will be the phase controlled or PWM sort, with their attendant filtering problems.
Thatās interesting - weāre expecting our smart meters to be installed on Friday and Iād blithely assumed that the diverter I built based on MartinRās design would continue to workā¦
Surely there must be loads of diverters both commercial and home brew working with smart meters?
Define what you mean by that. I tried to say that I defined āworkingā as the meter would record neither import nor export when the diverter was operating in what it saw as a balanced condition, i.e. a nett power transfer of zero over one operating cycle. If the meter has an āenergy bucketā that is shorter than this, then it will separately record periods of import and export, and they will be billed accordingly.
The diverter will of course continue to operate as designed no matter what sort of meter is fitted. Whether that operation results in a zero billed cost is what is in question. I strongly suspect that it wonāt, and every period of consumption will result in a charge, while every period of export will be ignored (but all generation will still recorded by the generation meter, naturally).
Hi Folks,
As far as I am aware, āsmartā meters work in a similar way to ānon-smartā digital meters. Provided that the energy state of the premises remains within a pre-determined energy band, no cost or financial penalty will be imposed by the meter. The āsmartā bit appears to be the remote unit by which the user is supposed to scrutinise, adjust, and hopefully reduce their overall consumption.
There may be a display on the meter which alternates between import and export, and it may show sizeable currents flowing in either direction. However, those currents are instantaneous values and they only persist for a cycle or two before changing direction. The meter itself will correctly determine that there is no net flow of energy and hence there is no reason to charge the user for that behaviour.
Meters in France are much less tolerant regarding the energy range within which the premises must remain before penalties are applied. To work within this stringent regime, the latest version of my Mk2 PV Router code uses a modified algorithm to predict the likely energy state at the end of each mains cycle and thereby determine the optimal state of the load(s). Each predicted value is used just once and then discarded. The main energy accumulator (aka bucket) continues to be updated in the same way as it has always been.
In the UK, I am not aware of any type of meter that the Mk2 PV Router (or Martinās equivalent) will not work alongside satisfactorily. My hands are still throbbing after washing the dishes in super hot and totally free DHW that our trusty Mk2 box has provided for us today.
Doing a bit of googling, I found that one of the types of smart meter being installed in the UK gives 4000 impulses/kWh. Which is 4 times as accurate as our current meter (which AFAIK is the standard for the UK - 1000imp/kWh).
Obviously to manage this with MartinRās sketch, Iāll have to reduce the size of the bucket by a factor of 4. His bucket is set to 3600 joules in the definitions in the sketch, so Iāll set that to 900 - assuming of course that the meter that is installed is similar to the one I read about.
If I donāt do this, then Iāll be being charged for 3/4 of the energy diverted!!
Time to dig out the trusty programmer and try to remember how to reflash the emonTXā¦
This is very interesting. @calypso_rae can you comment on the resizing of the energy accumulator? Itās so long ago that I setup my diverter, Iām not even sure I can still re-program it.
I think there might be an element of confusion here. I donāt think there is necessarily any relationship between the LED pulse rate and the size of the quantum of energy that is accumulated for billing purposes.
Looking at this from the energy supplierās point of view, they want to charge you (the consumer) the maximum theyāre allowed (by the regulator or by the market) for the energy you import, and they want to pay you the minimum they can get away with for the energy you generate. If you have a meter and diverter that together allow you to exactly balance import and export, whilst they are still paying you for your generation, youāre using their network as a battery. I can easily see that they will want the size of that quantum of energy to be as small as possible in order to maximise their income. With the old electro-magnetic Ferraris meter, that energy quantum was necessarily quite large. With an electronic meter (smart or otherwise), I can see that it could be as small as just one cycle.
The problem is, we donāt know, so Iām as keen as anyone to find out how various electronic meters actually perform with a burst-fire diverter.
Robert, Iām shocked you donāt know - you are the font of all knowledge on hereā¦
BS EN 50470-1 is the standard that meters have to be built to and there are three levels of accuracy. No mention of a minimum unit of measurement though.
Interestingly, wikipedia on electricity meters says:
The accuracy is generally laid down in statute for the location in which the meter is installed. Statutory provisions may also specify a procedure to be followed should the accuracy be disputed.
The UK gov site isnāt very helpful, talks about accuracy and testing etc but not about a minimum unit of measurement, although thereās lots of mention of watt hour meters (1000imp/kWh) although we know that some are now more accurate (4000imp/kWh) ā National regulation: gas and electricity meters - GOV.UK
Wikipedia continuesā¦
For the United Kingdom, any installed electricity meter is required to accurately record the consumed energy, but it is permitted to under-read by 3.5%, or over-read by 2.5%. Disputed meters are initially verified with a check meter operating alongside the disputed meter. The final resort is for the disputed meter to be fully tested both in the installed location and at a specialist calibration laboratory. Approximately 93% of disputed meters are found to be operating satisfactorily. A refund of electricity paid for, but not consumed (but not vice versa) will only be made if the laboratory is able to estimate how long the meter has been misregistering. This contrasts with gas meters where if a meter is found to be under reading, it is assumed that it has under read for as long as the consumer has had a gas supply through it.
I think youāve completely missed the point. No-one is talking about the accuracy of the meter, but, as you point out in your second sentence
And itās exactly that which the diverter attempts to take advantage of.
The principle of MartinRās and Robinās diverters is: the imported and exported energy is balanced within that āminimum unit of measurementā (your words), āenergy bucketā (Robinās words) or āquantum of energyā (my words). While that condition prevails, the meter does not register an import. When it no longer prevails, the meter registers and eventually, a charge appears on the bill.
I recommend you visit Robinās website to refresh your knowledge about how the diverter and meter interact. He has (or had) a video where he demonstrates a Ferraris meter experiencing successive cycles of import and export while the disc moves backwards and forwards always remaining within the same arc.
Sorry Robert, what you quoted from my reply shows I havenāt - maybe just the way things are read. I thought the information about accuracy might be of interest and might be pertinent to finding out what those units are.
And if youād been following the thread, youād have seen that I have built a diverter based on MartinRās design, so while itās useful maybe for anyone else reading the thread I think I wonāt be going through the theory again.
Anyway, to move things on, when the meter is installed, Iāll see if it is rated at 1000imp/kWh or 4000imp/kWh or something else. And if necessary Iāll adjust the sketch by the relevant factor and test things out on a sunny day to see if the meter display increments or not when the sunās out.
I shall await your measurements with interest. But one caveat, I need to know that the registers record a zero nett energy flow, as well as what the LED indicates. If those work out to be the same thing, then that too is very useful information. But my natural pessimism/cynicism says that they wonāt necessarily be the same.
