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The PV Router is based on UK practice, which pays a tariff based on the energy generated (not just the energy exported), and the rate paid for exported energy is lower than is paid for imported. So, until the rules change, it's clearly advantageous to divert.

In your case, if you read and interpreted the rules correctly, it looks as if it won't pay you - as you say until you export above 150 kWh/month and need a top-up during the day.

I understand in some places, exporting energy is penalised, then it's essential to divert all possible energy that would otherwise be exported.

I think I would be looking at how much you divert each month and then if you are going over the 150kWh doing a modification to one of Robins sketches so it will automatically divert to your immersion once you've reached the magic 150kWh.

Of course you could just manually turn the diverter on with a changeover switch.  

As long as the system isn't ever turned off, a Mk2 Router should indeed be able to stand idly by as the first 150 kWh is exported, and then spring into action thereafter. 

Making this kind of change to the control mechanism would not be particularly difficult, the tricky part is deciding exactly how the logic should operate.  It all depends on the particular circumstances in which it will be operating.  The 'month' as known to the meter would presumably need to be made known to the Router in some way.  Getting everything synchronised could be tricky ...

For a NZ customer, I've already supplied a variant which automatically tops up the diverted total to a pre-set amount each night.  This means that free surplus power is used by day, but there should always be hot water for the morning shower. 

Thanks guys - appreciate the feedback. My current thinking is to modify your script Robin and do the following;

1. Add an ethernet shield to the PV router Arduino and add MQTT support. I would prefer to use ethernet IO rather than RF wherever possible.

2. Add handling to the router sketch to support enabling/disabling via MQTT publishes. Already have a few Arduinos around the house with this sort of setup controlling various systems (i.e. central heating, monitoring security systems)

3. Send reports (via MQTT) of import/export and PV generation totals

4. Move all the logic for keeping track of monthly generation and making decisions as to when to enable diversion and/or manual dump load switching, into openHAB.

So I will need two CT clamps, one for measuring PV generation, and one for measuring import/export - as I have a Type 2 system. With these I can begin sending usage reports to openHAB via MQTT. openHAB has its own persistence bindings so I can store timeseries data.

The router will then have 3 modes;

a) Off - no diversion and dump load OFF

b) Diverting - diversion enabled, dump load only ON if excess power being generated

c) ON - no diversion, but dump load ON

openHAB will make decisions as to which mode it should be running and update via MQTT messages. So at the start of each billing month the router will be switched to mode (a). Then once I hit that magic 150kW of exported power it will be switched to mode (b).

I will also add temperature monitoring to my HWC, via another Arduino since the HWC is in a different location to the distribution board. This will allow me to boost the HWC (via mode (c)) if the water temp is below 55 at 4am. I.e. to ensure there is hot water for the morning shower.

This should hopefully reduce the complexity of the logic in the PV Router - it just has to handle the 3 modes. 

Is there anything in there you think I am missing or not considering?

There is the added complexity of the solar evacuated tubes controller - I could either replace this with another Arduino which controls the circulating pump and uses the same set of temperature readings I am using above to make decisions about when to pump etc. But I quite like the idea of that controller remaining stand alone - since it works well and means if I have any issues with my Arduinos my solar hot water will continue to function.

Perhaps I just disconnect it and make it easy to reconnect if there are any issues, i.e. as a backup system?

Getting quite excited about all this!

OK Ben, if you need any Mk2-type hardware, I'd be happy to supply same.  There seems to be no shortage of possibilities as to how you could use it!

There's quite an active 'Mk2' community now in NZ, so there should be several like-minded thinkers that you can exchange ideas with.  

Send me a PM if you need any introductions :)

Hi Ben, I'm in Rotorua and have 4.5kw PV. I'm with Meridian Energy and have similar tariffs to you. I try to export as much as possible. Meridian read my meter every 2 months so the 150kwh per month at 25c kwh is averaged over 2 months. I'm curious where you are and what plan you're on to have "from 9pm till 7am I only pay 13.5c/kWh for anything I import. My day rates are about 33c/kWh"

I have an emontxv3 and are waiting for a raspberry pi to arrive from RS. Only monitoring I have at present is a Uno with RFM12b controlling and RGB LED to show import/export status.

Norm

Hey Norm,

I am down in ChCh. Meridian have a day/night tariff down here which I am on, and then the same export tariff you are probably on - I get billed monthly and the 5kWh per day is averaged over the whole month - so I can export 1kWh on day 1, and 9kWh on day two, and still get a full credit for 10kWh for those two days - sounds the same as you.

I have just received my Arduino EmonTX shield - I would have preferred the EmonTx v3 but I want to publish my data over MQTT/Ethernet and eliminate RF so needed to build my own Arduino sketch using the EmonTx shield. Still in the process of installing everything but so far it is working ok.

My goal is to export as much as I can each month, until I hit 150kWh, and then try to use as much as I can. Still not sure the best way to achieve this, but I am thinking probably one of Robins remote load modules directly wired to my custom Ardunio EmonTx.

Are you using EmonCMS yet? I guess not, until you receive your Pi?

Seems like there are quite a few Kiwis floating around on this forum...

Hi Ben,

I'll have to check out the Meridian day/night tariff again. Last time I looked it was not attractive. I'm aware tariffs are not the same nationwide. Might be more attractive now that I have a heatpump.

When I first installed solar, Meridian removed my smart meter and installed a dumb import/export meter. I wasn't happy at the time to loose the smart meters monitoring. I manually recorded the import/export meters registers daily for a while until I had enough! Hence the attraction to OEM. In hind site Meridian did me a favor because my import/export is now averaged over 2 months.

Ultimately I would like to host emoncms on a Pi locally, post to emoncms.org and add consumption data to PVOutput http://pvoutput.org/list.jsp?userid=24408 I've had PVOutput posting since the day I got my solar up and running and find it very useful. Use of excess PV power in summer would also be interesting. I exported around double what I imported last summer.

The microSD arrived today for my Pi, I've transferred the emoncms image. Can't wait to actually get the Pi! I actually received a ENC28J60 Ethernet module (from China) yesterday because I was going to go the Arduino base route. Have since decided I go with the Pi instead.

I've had and Arduino Uno with Ethernet shield posting temp and barometric pressure data to emoncms.org. Worked really well. Was going to add the RFM12B to this until I discovered the issues with the RFM12B and W5100 Ethernet shield. This is why I ordered the ENC28J60 Ethernet module. Then I thought for the price I'll order a Model B+ Pi and connect the Uno RFM12B combo to it. Hope to get this up and running any day now.

Great to meet another kiwi!

I've been lurking around OEM for a while but only signed up when I purchased the emontxv3 a couple of weeks ago.

One question for anyone that knows: are the features of emoncms.org the same as a local install?

Norm

Hey Norm,

Never came across PVOutput before - what does that give you that EmonCMS doesn't? 

I think my import/export meter is still 'smart', since I get the day/night tariffs, but I am pretty sure they only count up the export kWh for the whole month and pay 25c for the first 150kWh, 10c after. I have only had my PV array installed for a month so I guess I will find out when I get my first bill.

I am hosting EmonCMS locally on my home server (Ubuntu) and it seems to have all the features available on the hosted site. But someone more educated can probably give you a more definitive answer.

Good luck with your project!

Ben

Hi Ben,

Just compared power pricing in Rotorua vs Christchurch. So much cheaper down south!

If your meter is smart, you should be able to view your import/export data on the Meridian website. I could view consumption until Meridian replaced my meter with a dumb one.

PVOutput is an Australian site and is great for comparing PV systems locally or worldwide. Just down loaded their API for  my Enasolar inverter and away it went.  Hope to recreate the PVOutput posting in Python on the Raspberry Pi I plan to run EmonCMS on. 

I had a go getting EmonCMS running on Ubuntu. Failed. Plan was to use an old netbook running EmonCMS with an Arduino providing the data. I'll have another go with the pre built Raspberry Pi image.

All a great learning experience!

Norm

Indeed - so how does the Enasolar (that is the inverter I am using too) interface with the PVOutput API - is there a process you run which queries the Enasolar HTTP server and then transforms/uploads to the PVOutput server?

Hi Ben,

I have the PVOutput API running on Windows. From memory all you do is configure the PVOutput .ini  file with Inverter IP, PVOutput account write key and you're away. The API must query the inverter's log file using HTTP. There is info on the Enasolar website about extracting the logs. PVOutput has a nice Android app and widget.

The Rasberry Pi arrived today, daughter was very disappointed! She thought the box was cool though! I'll get to work connecting the arduino and forwarder to EmonCMS.

Norm