Smart Control of appliances with Solar PV & Bluetooth

[BruceB]

It can if I understand you correctly. Measuring the PV generation is easy; it is measuring house consumption rather than net consumption which is more tricky. You do not want to measure net as that can be plus or minus, but the sensor cannot tell which. Measuring pv generation and actual consumption are both positive values which the logic in the Wattson can deal with.
Regards
Bruce

 

[SolarCity]

I've bought one to try this out as the instructions seems to suggest that what I'm trying to do is not possible. However, the one I bought was faulty and I'm still waiting for a replacement.

 

[Scooby]

Hmm, yes, a tad more tricky than I'd first assumed!

Page 11 - as Bruce pints out - would do the trick, and should be fairly straight-forward. As a somewhat crude alternative for those reluctant to have that small mod, I wonder if the Wattson's 3 separate 'consumption' inputs (normally used for 3-phase supplies) could be used to target the 3 main circuits in your house - say a clip each on the two main socket 'rings' and the third on the kitchen circuit (assuming your electrical system is that basic!). Ok, I did say 'crude', but 3 clips should cover the bulk of your consumption, and I'm mentioning it just as a 'thinking aloud' suggestion.

Of course, the Page 11 setup is by far the most accurate, and I bet most houses already have that 'provision' - have a look; any Henley blocks near your CU betwixt meter and the CU?! (Wouldn't work that easily in my house, alas, even tho' I do have the said Henleys; the PV system is on my detached garage and this needs the protection of the MCB in the CU, so I'd also need a separate li'l CU to supply the garage.)

BiggsSolar, I did ask Kyoto about clipping the PV sensor on my garage's phase inside the house's CU and they said it should be ok (Ok course, in my case it would also record any consumption by the garage.)

j2d, where to buy? Hmm, that's a funny one... Amazon used to have them for just under £100, but no longer do... The cheapest on-line price I can find is £103 - but they are out of stock. The next cheapest is £130 (electricity-monitor.com). DIY Kyoto themselves do it for around £189, I think. I wonder why Amazon has stopped selling at the cheaper rate? Am I being cynical about Kyoto...?

 

[JohnBoyZ]

Hmm, yes, a tad more tricky than I'd first assumed!

I wonder if the Wattson's 3 separate 'consumption' inputs (normally used for 3-phase supplies) could be used to target the 3 main circuits in your house - say a clip each of the two main socket 'rings' and the third on the kitchen circuit (assuming your electrical system is that basic!). Ok, I did say 'crude', but 3 clips should cover the bulk of your consumption, and I'm mentioning it just as a 'thinking aloud' suggestion.

I would assume using multiple sensors on the major circuits would work as long as the wattson can be programmed accordingly. In fact multiple sensors monitoring individual rings is the method I am using in my concept for H/W power controller.

 

[stuart99]

That's interesting, I would certainly be interested in some more details, does your program interface directly with the inverter via bluetooth?
I've been working on various ideas for monitoring PV and utilising any excess power to heat the hot water but using a power controller rather than a simple on/off. So far my circuits are only theoretical and one of the problems I have is how best to measure the available export power. It's easy enough to measure the current in the main supply but does anybody know of a way to tell direction of current i.e. import or export. So far my circuit ideas rely on calculating excess power based on current flow from the inverter and subtracting current used in the house but there must be a simpler solution. Any Ideas?

John

Yes directly to the inverter over Bluetooth, its taken me weeks to workout and understand what the SMA protocols are (they haven't published the specification unlike older protocols), but I can get the history data, current 5 minute average and instant spot values for watts, ac frequency, ac voltage, ac current etc.

 

[JohnBoyZ]

Yes directly to the inverter over Bluetooth, its taken me weeks to workout and understand what the SMA protocols are (they haven't published the specification unlike older protocols), but I can get the history data, current 5 minute average and instant spot values for watts, ac frequency, ac voltage, ac current etc.

That's impressive, I know the older protocol was available so I guess as you are working with the later protocol you are looking at interfacing with SunnyBoy's or similar with built in bluetooth. What language and platform are you working with C on windows maybe?
You are probably aware of the SMA bluetooth connection for linux sma-bluetooth - SMA Inverter Bluetooth Connection for linux - Google Project Hosting but if not its worth a look as it has some useful C code in the SMATool.
I've done a fair bit of programming so would certainly be interested to see what you have done, what are you intending to do with alll your hard work, are you looking to develop some sort of smart control system? If so you will be faced with the problem that the data from the inverter is useful but it would be better to know what excess (i.e. export) power is available at any point which is the problem I'm up against.
Whilst I would be interested in developing a software solution at some point, I'm currently attempting a purely hardware solution for directing any excess power to the immersion using a 'phase angle' power controller. Ideally something that could be retro fitted to most PV installations regardless of inverter type and it's looking likely I'll have to use multiple clamp type sensors to achieve that.

 

[stuart99]

That's impressive, I know the older protocol was available so I guess as you are working with the later protocol you are looking at interfacing with SunnyBoy's or similar with built in bluetooth. What language and platform are you working with C on windows maybe?
You are probably aware of the SMA bluetooth connection for linux sma-bluetooth - SMA Inverter Bluetooth Connection for linux - Google Project Hosting but if not its worth a look as it has some useful C code in the SMATool.
I've done a fair bit of programming so would certainly be interested to see what you have done, what are you intending to do with alll your hard work, are you looking to develop some sort of smart control system? If so you will be faced with the problem that the data from the inverter is useful but it would be better to know what excess (i.e. export) power is available at any point which is the problem I'm up against.
Whilst I would be interested in developing a software solution at some point, I'm currently attempting a purely hardware solution for directing any excess power to the immersion using a 'phase angle' power controller. Ideally something that could be retro fitted to most PV installations regardless of inverter type and it's looking likely I'll have to use multiple clamp type sensors to achieve that.

Thanks, I've initially written the code in C# in Windows, but now just ported it over to Python on Linux.

I've used/seen the sma-bluetooth code you mentioned, and it works, but doesnt really know the protocols in use so just assumes a lot which doesnt work on most of the SMA TL type inverters.

I may publish the code into the public domain, but I'm not 100% happy with it yet.

I'm going to try and see if I can use a CurrentCost meter against the house supply to give me the difference between import/export.

I know what the solar is producing, so if I subtract the CurrentCost meter, I get a +/-ve figure which should relate to import/export - fingers crossed!

I'm trying to do all this wirelessly, if possible, and the wiring of my PV won't allow me to get a clamp in without exposing or opening the fuse box and I want a solution 99% of people can use without hassle.

I like your plans to use a "phase angle" controller, I was just thinking of a simple on/off switch!

 

[JohnBoyZ]

Thanks, I've initially written the code in C# in Windows, but now just ported it over to Python on Linux.

I've used/seen the sma-bluetooth code you mentioned, and it works, but doesnt really know the protocols in use so just assumes a lot which doesnt work on most of the SMA TL type inverters.

I may publish the code into the public domain, but I'm not 100% happy with it yet.

I'm going to try and see if I can use a CurrentCost meter against the house supply to give me the difference between import/export.

I know what the solar is producing, so if I subtract the CurrentCost meter, I get a +/-ve figure which should relate to import/export - fingers crossed!

I'm trying to do all this wirelessly, if possible, and the wiring of my PV won't allow me to get a clamp in without exposing or opening the fuse box and I want a solution 99% of people can use without hassle.

I like your plans to use a "phase angle" controller, I was just thinking of a simple on/off switch!

Nice, certainly sounds like you've put in a lot of effort, I think you might have a problem using the info from a current monitor on the main supply as you wont know if its measuring import or export current. Using a single clamp sensor doesn't show direction of current flow so will show exported power as increasing usage in the house rather than negative usage.
Just as an aside, as you have some windows code up and running, have you thought of producing a stand-alone program for uploading the PV data to PVOutput.org (as in the SMA Tool) I'm currently running the script (from somewhere off the web) but that relies on SunnyExplorer & Excel, it would be nice to have something self contained.
Cheers
John

 

[stuart99]

Nice, certainly sounds like you've put in a lot of effort, I think you might have a problem using the info from a current monitor on the main supply as you wont know if its measuring import or export current. Using a single clamp sensor doesn't show direction of current flow so will show exported power as increasing usage in the house rather than negative usage.
Just as an aside, as you have some windows code up and running, have you thought of producing a stand-alone program for uploading the PV data to PVOutput.org (as in the SMA Tool) I'm currently running the script (from somewhere off the web) but that relies on SunnyExplorer & Excel, it would be nice to have something self contained.
Cheers
John

Yes, I've already got that working, but at the moment its exporting to my own site Solar Stats, no reason why it wont work to PVOutput though, the Python version does this. Heres my page Stuarts PV 3.360kW

I'm aiming to use a small always on low power device rather than a Windows PC in the long term though.

Do I actually need to measure the direction of current? I just need to find out what I'm exporting...

 

[SolarCity]

BiggsSolar, I did ask Kyoto about clipping the PV sensor on my garage's phase inside the house's CU and they said it should be ok (Ok course, in my case it would also record any consumption by the garage.)

As luck would have it, I visited a job yesterday where I missed out on a PV install (long story: I suggested 8 panels maximum due to shading - competitor suggested 11 and won the work). He had a Wattson and I set it up in this way and it worked. The instructions are misleading, I believe, and suggest that this shouldn't be possible.

The only issue is where to clamp the PV generator lead. The clamp itself cannot be run into the CU so I think a single core PVC/PVC extension of the phase cable out of the CU is needed. Pretty straightforward.

 

[Scooby]

Thanks, Biggs - good to have it confirmed! Can you describe exactly how you set it up - will it record both generated and consummed energy accurately?

(I should probably clarify that Kyoto didn't actually suggest to me I could fit the clip inside the CU, only that my garage-mounted PV's clip could be fitted at the house end of the cable - that was just my simplistic way of describing it... )

(Interesting that the customer asked you to install the Wattson even tho' you didn't fit the panels! Is there a story there...?!)

 

[stuart99]

If so you will be faced with the problem that the data from the inverter is useful but it would be better to know what excess (i.e. export) power is available at any point which is the problem I'm up against.

Have you seen this? AC current direction & level sensing suggestions - DiscoverCircuits Forum

You will not know the direction of AC current by measuring the current alone. You could by using the voltage and current phase relationship. It might make an interesting project to come up with a circuit which used a clip-on AC current probe and some kind of capacitance linked AC voltage probe to monitor the phase. It would require several AC current probes to figure things out and come up with a total of the power feed into the grid Vs the power being used by the house.

Its an interesting problem. You have actually three currents to consider, :- 1 current flowing from your PV inverter, 2. the current taken from the grid, 3 the current flowing to your local load. I think the sum is :- I2 = I3 - I1. The only thing that is certain is that if you are supplying power to the grid your locally generated voltage must be greater then the incoming mains voltage, if only by a few millivolts. Just thinking of numbers, domestic supply, 230V @100 A at 2% regulation (probabley worse then this!). so when 100A is drawn, the voltage drops by 2% or 4.6V. This means that the mains has an "impedance" of 46m ohms. Like wise if you want to "push" 100A into the mains you need an extra 4.6V over the nominal mains voltage. What I would do is to get two mains to 12V AC transformers, label each one, I/C and PV. Feed two bridge rectifiers each with its own resevoir capacitor and identical load resistors. Now you can measure the difference between the two voltages (~18V), with no PV it will be say +18V and with no mains and full PV it will be -18V. The range you will be interested in will be 0 -> -.36V. So feed this voltage via current limiting resistors and limiting diodes into an OP amp and you should get a nice big voltage swing indicating when you are supplying the grid.

I have been considering this problem a bit more, no real change in philosophy. One point is that the mains voltage must be monitored as close to the incoming mains as possible, not on your switchboard. I think that your PV generated voltage must be monitored as close to the inverter as possible. The reason is that you must rely on the voltage drop down the cables to separate the I/C and PV voltages. the corollary to this is measuring two points on the mains fuse box and consider them to be some how different (other then the voltage drop across your fuses and/or MCBs).
Did you ever do Kirchoffs law at College?, this is a typical problem. Take a "T" network of resistors, feed two different voltages into the upper arms, work out the voltages/currents through the various resistors. Depending on the voltage differences and the size of the resistors, the results can be very different. You will have to work out the various resistor values from your local configuration.

Has anybody tried this? I know what the inverter is reporting as voltage (to 2 decimal places) so if I can get the mains incoming voltage (and none intrusively) then I can determine if its import or export.

 

[SolarCity]

Thanks, Biggs - good to have it confirmed! Can you describe exactly how you set it up - will it record both generated and consummed energy accurately?

(I should probably clarify that Kyoto didn't actually suggest to me I could fit the clip inside the CU, only that my garage-mounted PV's clip could be fitted at the house end of the cable - that was just my simplistic way of describing it... )

(Interesting that the customer asked you to install the Wattson even tho' you didn't fit the panels! Is there a story there...?!)

Very straightforward setup although I wasn't there long enough to make sure it was doing what I wanted. I simply clamped to the incoming tails and clamped the other lead onto the cable to the inverter. Exactly how the device determines if the tails are exporting or importing - I'm not sure but I'll take another look at the instructions when I get a chance.

To be fair, the customer didn't ask me to install the device - I offered. It was mutually beneficial.

The reason I went back to the install is that the customer was unsure if the installation team had done a good job - they hadn't. Manufacturers guidelines had been widely ignored and shading had been all but ignored.

 

[JohnBoyZ]

Have you seen this? AC current direction & level sensing suggestions - DiscoverCircuits Forum
Has anybody tried this? I know what the inverter is reporting as voltage (to 2 decimal places) so if I can get the mains incoming voltage (and none intrusively) then I can determine if its import or export.

Hmm interesting. Ive just had a quick read through and the power factor Idea might have possibilities but I'm not certain about the measuring voltage (two transformer method). Bearing in mind that both transformers are effectively connected together via the PV AC cable, the comment (+18V and with no mains and full PV it will be -18V) won't be the case because if the PV is not generating, the transformer at the PV will still be supplied by the mains. It appears to be simply looking at the volt drop over the length of the PV AC cable so all that would achieve is a measure of the generated power regardless of whether it is being used in the house or exported.

 

[stuart99]

I can also tell when the inverter is generating or not, if that helps!