Logging micro-generation?

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skyewright
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Logging micro-generation?

Post by skyewright » Wed Aug 11, 2010 6:21 pm

Hi,

Since Germany is way ahead of the UK on micro-generation maybe this is a problem that has already been solved?

At present we log electricity usage via a CurrentCost CC128 Envi connected to Meteohub. The CC128 works by detecting power flow using a torodial clamp. The clamp is positioned between the utility meter and the consumer unit (i.e. the modern equivalent of the old "fuse box").

In a month or so we hope to have a grid-tie PV array on the roof. Generated electricity will feed into the electricity supply system via a connection to the consumer unit (UK wiring regulation apparently insist that the connection goes direct to the consumer unit).

If the PV array is producing power then it will reduce our own "import" of power from the grid, or if it is producing more than we need the excess will be "exported" to the grid.

The utility meter will tell us how much has been "imported" over time (UK meters do not run backwards during export). A separate meter right next to the inverter will tell us how much has been generated by the array. There isn't (at present) a meter that will measure the actual amount exported (This is how the UK 'FIT' scheme works. When it comes to export element of payments it will be 'assumed' that 50% of what we generated is exported. Strange, but true.).

In terms of logging to Meteohub using the CC128 the complication is that (I believe) the CC128 will no longer give a measure of "how much electricity we are using regardless of source of supply" because it is the "wrong side" of the point at which locally generated power is injected. Indeed, the CC128 figures will be to some extent meaningless because (as I understand it) it only measures power flow not direction, so a figure of 600W in the middle of the day could equally well indicate "import" or "export".

With the locally generated supply being direct to the consumer unit, there is no obvious place to move the CC128 clamp to where it could measure "how much electricity we are using regardless of source of supply".

Does anyone have any ideas on how best to log the various flows of electricity?

EmjayNet
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Re: Logging micro-generation?

Post by EmjayNet » Sat Jan 22, 2011 2:40 pm

Hi David,

I read your post some days ago, and through that someone with more experience of this sort of thing might have answered.

As no one has I'll give you my limited thoughts based on my knowledge of electrical systems from my college days (Mechanical Engineering)?

I don't know what your power ratings are, or phase your using, so I'm assuming you’re on a 100 Amp domestic, single phase.

What about putting a small consumer unit (something like http://electricsoutdoors.co.uk/product_ ... ucts_id=50) which can have up to 63 Amp MCB's, in before your existing consumer unit.
Your PV array and main electrical feed will plug into this, and then run tails out from new mini consumer unit to your existing one. If you connect your CC128 to the tails between the two units you would only measure your consumption.

I admit I don't know if this would meet current IEE Wiring Regulations, but it is the only way I can think of measuring your actual consumption, whilst getting round the fact that the PV Array has to plug into the consumer unit.

Just a thought :D

Emjay

skyewright
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Re: Logging micro-generation?

Post by skyewright » Sat Jan 22, 2011 4:59 pm

EmjayNet wrote:What about putting a small consumer unit (something like http://electricsoutdoors.co.uk/product_ ... ucts_id=50) which can have up to 63 Amp MCB's, in before your existing consumer unit.
Your PV array and main electrical feed will plug into this, and then run tails out from new mini consumer unit to your existing one. If you connect your CC128 to the tails between the two units you would only measure your consumption.
I've seen a couple of examples of that approach on older installations. Back in late August I chatted over that idea with a neighbour who is an electrician and he thought it was still okay, but wasn't keen on doing it. In the end I went with simply attaching the output from the grid-tie inverter to a spare way on the existing CU.

Now instead of the CC128 I use an RfxCom RfxMeter/RfxPulse combination to log 'import' based on counting the LED flashes (which has the advantage of being much more accurate than the CC128 - effectively 100% accurate). I also have a pulse counter on the 'generation' meter. In due course the electricity company is supposed to be fitting an export meter, and when that happens I hope to log that too (I'm realy hoping they fit a separate meter and not a combined import/export one that ony has one LED!). Until the export meter is fitted I can't directly measure our nett usage (i.e. usage = import + generation - export), but that seem to be something I just have to put up with.

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Re: Logging micro-generation?

Post by Aussie101 » Mon Mar 14, 2011 7:58 am

skyewright wrote:With the locally generated supply being direct to the consumer unit, there is no obvious place to move the CC128 clamp to where it could measure "how much electricity we are using regardless of source of supply".

Does anyone have any ideas on how best to log the various flows of electricity?
Hi David,

We are in the same boat. We have a grid-connect solar system, and we have a Current Cost Envi, and we'd like to log the generation. At this point, I have given up on trying to log the net export to the grid, but I think I almost have the rest covered.

Things to log.
1) Gross PV Production (and other solar stats)
2) Gross household consumption.
3) Net Export
4) (just an idea) Should be able to get a solar w/metre2 measurement.

Responding in Order:

1) PV production should be available at your inverter. Most brands seem to have this capability. In our case, ours is a SMA inverter with inbuilt bluetooth. This can be read by a computer with BT or a suitable device. We have a SMA Webbox on the way that will do this automatically and upload the data to a webpage. Check your inverter manual.

2) During the solar install, I asked the electrician to separate the solar feed from the home consumption, with the clamps just recording the consumption (we have 3-phase, so three clamps). The clamps only measure flow, not direction. This was just after the PV went live, and I had already seen that the Envi was confused and the figures from it would be meaningless during the day whilst the solar was producing. So that is problem number 2 out of the way for us. Perhaps you could do likewise.

3) Net Export is a problem for us. The only real figure is the number on the power company's meter, and as yet there is no method available to us to read it electronically. I am considering making a calculation by subtracting production from consumption, but will see.

4) Our AWS does not have a Solar watts/sqm capability. I'm wondering is it would be worthwhile to calculate this from the figures available on the inverter data - we know the watts (instantaneous and cumulative) we know the area of panels, and we know the panel efficiency.

I did look at the CurrentCost solar solution, and it is not pretty - involves another Envi or Trek and more clamps. Just seems to be getting more complicated, and as you know, these devices do not correct for PF so they may not be that accurate. We do have the CC Bridge which uploads our consumption to their website and links into Google Powermeter. That's pretty good.

HTH

Michael

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Re: Logging micro-generation?

Post by skyewright » Sun Mar 20, 2011 6:00 pm

Aussie101 wrote:4) Our AWS does not have a Solar watts/sqm capability. I'm wondering is it would be worthwhile to calculate this from the figures available on the inverter data - we know the watts (instantaneous and cumulative) we know the area of panels, and we know the panel efficiency.
Are you trying to record the w/m2 on the panels or are you trying to simulate a standard weather station solar sensor?
If the latter then you'd need to compensate for the slope & direction of your array too.

PS. Our utility company has now fitted an export meter. However instead of adding a second meter, they replaced the only import meter with a dual purpose import/export one. The new meter only had one flashing LED and that flashes regardless of direction, so now the RfxMeter/RfxPulse based logging has no more sense of direction than the CC128! :(
On the bright side I can at least monitor usage again now (usage = import + generation - export), provided I make regular manual checks of the meter readings. :)

I know someone (not a meteohub user) who has just imported a Brultech. That's a CT (i.e. clamp) based solution that can handle both direction and power factor. I'll be interested to hear how he gets on...

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Re: Logging micro-generation?

Post by Aussie101 » Sun Mar 20, 2011 11:49 pm

Trying to simulate a standard weather station solar sensor. I'll have a crack at it when I get the chance.

Your Export meter sounds just like what they install here. I think it has half hour registers and is a variation on what gets installed in commercial premises here by default. Various people here in Aus have been trying to get access to the data in these devices for logging, but the power companies are not keen.

I still think the best bet is to capture the usage at the main switchboard by separating the usage from the solar feed so the CC only 'sees' usage.

:)

Michael

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Re: Logging micro-generation?

Post by skyewright » Mon Mar 21, 2011 11:46 am

Aussie101 wrote:Your Export meter sounds just like what they install here. I think it has half hour registers and is a variation on what gets installed in commercial premises here by default.
I know what you mean, but I don't think this is the same. The new meter is simply a normal domestic multi-rate meter (i.e. the sort that might be used if you have a different tariff at night), but wired up slightly differently so that one channel measures import and the other export. It's make and model is Landis+Gyr 5254E.

An odd thing is that there are 3 LEDs on the face of the meter, but only one of them seems to be used!

The only documentation I've been able to find on the web is a "Technical Specification", which doesn't have much useful to say.
http://www.landisgyr.com/uk/apps/produc ... ation1.pdf
I still think the best bet is to capture the usage at the main switchboard by separating the usage from the solar feed so the CC only 'sees' usage.
Yes. That should be good for solar (the feed from the invertor ought to have a consistent power factor, so that should not be a significant problem).

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Re: Logging micro-generation?

Post by marc10k » Thu Mar 24, 2011 9:52 pm

I do have an Landiy+Gyr ZAMD120APEC 3 phase meter. There is one LED that says 10000pulses/kWh. The LED seems also not in use. But I have read in the manual or somewhere else that it is an infrared LED. Probably it is the same with yours.

Marcus

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