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Type of Generation Meter


Gone West

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I have received a quote from Wagner Renewables, thanks to @PeterW who recommended them, they were very quick. The quote includes a standard type generation meter and I was wondering if a DIN rail meter would be neater and take up less room. Has anyone used a single phase DIN rail generation meter in their CU for PV output? Are there any reasons for not using one?

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As long as the DIN rail mount meter has the right approval, then there shouldn't be a problem.  Might be more expensive, as a lot of the cheaper DIN rail mount meters don't seem to be approved to the same standard as normal ones, and normal ones are very cheap (typically less than £30), probably because they sell large numbers of them.

 

The measurement accuracy standard is EN62053-21:2003 A1:2017, Electricity metering equipment (A.C.) Static meters for active energy (classes 1 and 2).  It's a bit questionable as to whether some of the popular DIN rail meters from the far east actually comply with this, I suspect, as one or two I've bought don't comply with other aspects of EU certification (they work OK, but the CE marks are fake).

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1 hour ago, PeterStarck said:

This one is made in China, which I suppose isn't surprising, but seems to have the necessary approval. What do you think?

Rayleigh Instruments DIN Rail Meters.pdf 423.46 kB · 2 downloads

 

 

 

That looks fine, as it seems to have approval for billing, and Rayleigh have been around a long time, so I'd trust them.

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35 minutes ago, SteamyTea said:

Is there enough kVAs? shows 4kV, which is 17.39A @230V but only  16A @250V.

But I have no idea what size your system is.

Has a max wire size of 2.5mm2 on the output, so that may be a problem too.

 

 

The max wire size for the pass through current is 13mm².  The 2.5mm² terminals are for the pulse output, used to connect to other monitoring equipment if needed.

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1 hour ago, SteamyTea said:

Is there enough kVAs? shows 4kV, which is 17.39A @230V but only  16A @250V.

But I have no idea what size your system is.

Has a max wire size of 2.5mm2 on the output, so that may be a problem too.

The system is 10 panels each 305Wp so that would be 13.3A at 230V or 12.2A at 250V. The voltage around here is nearer 250V most of the time so is that ok or borderline?

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4mm² T&E clipped direct is OK for up to 37 A, or 26 A if enclosed in conduit.  This translates to about 8.5 kWp for clipped direct or just under 6 kWp if run in conduit.  Both these figures are subject to voltage drop limitations.  I opted to run 6mm² T&E for the AC run from our inverter to the meter and CU, even though it was only a short run (maybe 2m or so), just to reduce the voltage drop a little bit (our system is 6.25 kWp).  In general, it's a good idea to try and keep the voltage drop as low as possible, as this gives the inverter a bit of extra headroom to keep going when the local supply voltage rises.

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18 minutes ago, SteamyTea said:

Ah, right. It was not too clear from the data sheet.

Can I connect via that to my raspberry pi.

 

Should be able to, but I think an optosolator might be needed, as the pulse output may not be isolated from the supply.  It seems to be a 80ms pulse, that's within 5 to 27 V, with a maximum current of 27 mA.  The pulse rate is the standard one, 1000 pulses/kWh.

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1 hour ago, PeterStarck said:

What size system is that and do you have micro-inverters or a standard inverter?

 

2 x standard inverters - essentially 2 separate systems which are then combined on the AC side and then fed via the export meter and main isolator. 3.9kWp system (13 x 300w panels) but realistically its two smaller systems and never gets anywhere near that peak based on shading and orientation. Export limitation is also in place but never kicks in.

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4 hours ago, JSHarris said:

4mm² T&E clipped direct is OK for up to 37 A, or 26 A if enclosed in conduit.  This translates to about 8.5 kWp for clipped direct or just under 6 kWp if run in conduit.  Both these figures are subject to voltage drop limitations.  I opted to run 6mm² T&E for the AC run from our inverter to the meter and CU, even though it was only a short run (maybe 2m or so), just to reduce the voltage drop a little bit (our system is 6.25 kWp).  In general, it's a good idea to try and keep the voltage drop as low as possible, as this gives the inverter a bit of extra headroom to keep going when the local supply voltage rises.

I was going to use 4mm2 cable run in conduit in insulation, which as you say, in Appendix 4 of BS7671 would be ok for 26A. I'm thinking my system would be around 13A and the voltage drop would be small at 0.48%. So it seems I should be able to use the Rayleigh DIN rail meter which is only £4 more than the standard Rayleigh meter so would be a good solution for me.

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One thing to bear in mind is that the inverter will shut off when the supply voltage reaches 253 VAC, so if the local supply is around 250 VAC you only have a little bit of headroom.  We're in the same position, in that our local supply voltage is often up around 250 VAC, and we do end up with the inverter limiting from time to time, even though I used 6mm² to reduce the voltage drop.  Losing a volt through a 4mm² cable might not seem worth bothering about, but if that extra volt causes the inverter to reduce power or shut off due to hitting the 253 VAC limit, it may be a bit of a nuisance, especially for us, where we get paid for electricity generated and exported. Depending on how the inverter limits this may or may not cause a problem for a new system, as if it soft limits (ours does) then it will probably continue to offset consumption in the house. 

 

There are, I believe, some inverters that just shut down when the voltage at their output reaches 253 VAC, so it may be worth asking the supplier how the inverter they intend to fit will behave.  Also worth monitoring the supply voltage to see if it gets close to 253 VAC and then trying to get the DNO to reduce the supply by dropping a tap on the transformer, although I've been trying in vain to get our DNO to do this for a long time now.  The lowest supply voltage I've recorded is 244 VAC, the highest 253 VAC, for a supply that is supposed to be 230 VAC, +10%, -6% (so 216.2 VAC to 253 VAC).

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9 minutes ago, JSHarris said:

One thing to bear in mind is that the inverter will shut off when the supply voltage reaches 253 VAC, so if the local supply is around 250 VAC you only have a little bit of headroom.  We're in the same position, in that our local supply voltage is often up around 250 VAC, and we do end up with the inverter limiting from time to time, even though I used 6mm² to reduce the voltage drop.  Losing a volt through a 4mm² cable might not seem worth bothering about, but if that extra volt causes the inverter to reduce power or shut off due to hitting the 253 VAC limit, it may be a bit of a nuisance, especially for us, where we get paid for electricity generated and exported. Depending on how the inverter limits this may or may not cause a problem for a new system, as if it soft limits (ours does) then it will probably continue to offset consumption in the house. 

 

There are, I believe, some inverters that just shut down when the voltage at their output reaches 253 VAC, so it may be worth asking the supplier how the inverter they intend to fit will behave.  Also worth monitoring the supply voltage to see if it gets close to 253 VAC and then trying to get the DNO to reduce the supply by dropping a tap on the transformer, although I've been trying in vain to get our DNO to do this for a long time now.  The lowest supply voltage I've recorded is 244 VAC, the highest 253 VAC, for a supply that is supposed to be 230 VAC, +10%, -6% (so 216.2 VAC to 253 VAC).

Thanks for that. I'm going to be using Enphase IQ7 microinverters so I'll look into how the inverters deal with that limit.

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We should just measure all energy in the derived SI unit of joules (or kJ, MJ, GJ, EJ).

Would make life so easy to compare then.

Seems barmy to me that we sell bottled gas by the kg, liquid fuels by the litre, coal by the sack, timber by whatever someone want so to quite (bag, tonne, cubic foot, lorry load).

No wonder people are confused.

We can label food with kJ, why not the rest of the energy market.

And don't get me started on BOE, Therms and what Americans use.

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At the moment it’s got 3 CT clamps - one for each array and then one on the main tails so I can get the ‘live’ generation, house consumption and import export values. Currently capturing them every 60 seconds. 

 

With the pulses I guess you have to guesstimate the power draw based on pulse frequency and time lapsed? I know the export meter also has the IR interface as well but not played with that. 

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4 minutes ago, SteamyTea said:

Why is the RPi not counting the pules off the meter?

It is generally recognised that using burst firing of an immersion heater, you need to keep the flow of energy back and forth to under 1Wh so it does not get metered.  I suspect just counting 1Wh pulses would be too coarse for that to work.

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