Enecsys Monitor kWh vs. Generation Meter kWh

[jez54]

New system (commissioned on Sat 10 December):

16 x Sanyo HIT-H250E01, Enecsys Microinverters,
ELSTER A100C generation meter.

Does anyone else apart from me have the problem
that the generated kWh according to their Enecsys
Monitor is > 20% greater than the generated kWh
according to their generation meter?

I raised this with Enecsys, but they fobbed me off
with a silly reply suggesting that the difference was
because the generation meter measures KVA instead
of the KW that their Monitor system measures ......
but a 20% power loss due to Power Factor means that
Cos Phi = 0.8 which in my experience is associated
with heavy electric motor-driven machinery rather
than sophisticated electronic circuitry?

I'm still waiting for a reply from my installer, but
I thought I would see what others here have found.

[series530]

I haven't checked in the past week or so but, since my install in Nov, there is a difference of about 2% - in line with losses in the cables, etc. Aside from the fact that we have 14 panels, our system appears to be identical to yours.

[Wickham]

I check every month and the Enecsys website data is always 3.9% or 4% higher than the generation meter, due I suppose to losses in the micro-inverters and the cable.

I can't understand why your Enecsys data is 20% more than the generation meter, that seems impossible unless you have an abnormally long cable with high losses. The micro-inverters can only generate if connected to the grid through the generation meter, so the generation meter should record all the generation from the micro-inverters. It could be less if your generation started a few days before your micro-inverters were registered with Enecsys, but even then I would be surprised because in my case the micro-inverters stored data and dumped it in the first hour after registration with Enecsys, producing an impossible total for one hour.

[jez54]

Thanks, series530 & Wickham.

That confirms what I expect - just a few percent for AC cable loss.

I have a big 4-storey house, and the cable from the MCB box in the
roof to the generation meter in the basement is just shy of 50m,
which is quite long, I know.  As a result, we installed with 4 sq.mm
twin+earth cable instead of the more usual 2.5 sq.mm cable, and
maybe there will be some say we should have used 6 sq.mm cable,
or even 10, to minimise lost generation, but hey, hindsight and all
that ....

Anyway, I did the sums, and so I was expecting max 3% - 4% losses.

Please will all those professional electricians excuse me setting out
my humble calculation in detail, I'm not trying to run an egg-sucking
class, but I do need someone to tell me if / where I have got it wrong ....

Resistance of 4 sq.mm conductor = 5 ohm/km (Wikipedia)
so, total resistance of 2 conductors 50m long (there and back)
5 x 2 x 50 / 1000 = 0.5 ohm
peak generation current from 16 panels @ 250 W = 16 A
So, nominal "voltage drop" would be 16 A x 0.5 ohm = 8 V
(I do realise that the inverters latch onto the actual mains
voltage, and it is in fact current which shows the actual loss)
but in simple terms, power loss should be 8 V x 16 A = 128 W
or, as a % of peak generation 128 W / 4000 W = 3.2% loss

But, at any lower generation, such as now, when peak power
generated by the panels is less than maximum, the power
lost is proportional to the square of the power generated, so:
At 100% power = 4 kW, expected power loss = 3.2% (as above)
At   50% power = 2 kW, power loss = 25%    = 0.8%
At   25% power = 1 kW, power loss =   8%    = 0.04%

Thus, I do not expect AC cable loss to be at all significant today.

So, I get to thinking what else could explain it, as simple AC cable
resistance cannot, and I do not believe losses of > 20% can be a
KW/KVA power factor issue either.

Maybe my meter has a kW / Amp threshhold below which it cannot
register any generation?  That would explain why the day-to-day
loss of kWh at the meter gets much worse, the lower the peak
generation during the day (it has averaged 22% overall energy
lost, varying from 12% lost on our best day to a massive
67% lost on the worst day when Enecsys Monitor said we had
generated 0.6 kWh but the meter only registered 0.2 kWh.

I'm guessing I now need to get someone to take responsibility
for the cost of changing the meter.  Any suggestions of a better
brand than ELSTER A100C?  Or is that a good enough brand
anyway?

[tc847]

I only have 15 days of data so far but I have 2 observations.

There have been occasions when I have seen the Enecsys monitor showing that I have the (minimum value) of 6W per panel but the Generation Meter has a constant red light (imply no generation).  So this would imply that the Monitor is registering generation that is not reaching the Generation Meter.

My "month" figures from Enecsys Monitor are 27.5kWh.  The generation meter only shows whole numbers of kWh and read 0 the first time I looked at it but 0.7 according to the MCS certificate.  At most that would indicate 27.5+0.7=28.2 (but showing as 28) would be my current generation meter reading.  But in fact it said 30 last night which is actually *higher* than the monitor would imply.

I shall continue to monitor the monitor!

Happy Solstice everyone!
Looking forward to more hours of daylight starting tomorrow.

[jez54]

Nice one, tc847...

"... which is actually *higher* than the monitor would imply"

Now that IS a trick well worth studying ........ !!

[ovonrein]

Does the Enecsys system claim to monitor the DC or the AC side?  Assuming it measures the AC side, how are all the inverters connected together?  It might be worth taking a reading, somehow, at the roof end of your 50m run.  You worry about your losses in the 50m run - there's some chance the losses you are seeing are in the connectors in the roof.

[ovonrein]

Nice one, tc847...

"... which is actually *higher* than the monitor would imply"

Now that IS a trick well worth studying ........ !!

The answer lies in your original post, jez, I am guessing.  Enecsys record "kW".  Actually, they measure current, like any other cheapo energy monitor does, then multiply by some assumed V and, hey preto, we have W.  In tc's case, the actual voltage is higher - typical in the UK - than the assumed voltage, and hence the accurate export meter actually records a greater W.  Perhaps the assumed translation voltage is configurable, and yours is set too high?

[jez54]

Thanks ovonrein,

Good suggestion about the "nominal" voltage used by Enecsys, I will ask them, and
also whether their Monitor is measuring at the DC side or the AC side of the inverters.

To answer your first question, here is the connection diagram (defo worthy of Picasso!)
(except no doubt all the spacings will go awry when I post it, so it will be unreadable!)
And, yes, there are lots of accessible places where I could hook on a CT device to check
the current at the roof, and that's another good idea.

P=M_O_M=P         P=M_O_M=P          Key:  P=M :  Panel to Microinverter by 2 x 1m long (panel) cables
         |                          |                            M_O :  Microinverter to 4-Way Connector Block by 0.9m long (microinverter) cables
P=M_O_M=P         P=M_O_M=P                   O_O :  4-way Connector Blocks joined by (pre-fab) 2m long 3-core 1.5 sq.mm "Solar" flex
         |                          |                          O__X :  Last Connector to Isolator Switch by 4m long 3-core 1.5 sq.mm "Solar" flex
P=M_O_M=P         P=M_O_M=P             X__MCB : Isolator Switch to MCB (2 x 10A) by 2m long 3-core 1.5 sq.mm "Solar" flex
         |                          |                      MCB__X : Roof MCB to Main Isolator Switch by 50m long 4 sq.mm T+E cable
P=M_O_M=P         P=M_O_M=P                 X__G : Main Isolator to Generation Meter by 0.2m long 4 sq.mm T+E cable
         |__X__ MCB__X__|                      G__CCU : Generation Meter to 16A MCB on Main CCU by 0.3m long 4 sq.mm T+E cable
                       |
                       X__G__CCU

I've also spoken to Elster whose generation meter it is ... they claim there is no way their meter could be that faulty and still work ... (ha!)
           

                 

[Wickham]

Does the Enecsys system claim to monitor the DC or the AC side?  Assuming it measures the AC side, how are all the inverters connected together?

I'm guessing, but I'm fairly sure that they monitor the DC output. Each micro-inverter then sends the data by wireless via internet before converting to AC and outputting to the cable. So the conversion to AC would probably account for most of the loss.

http://www.enecsys.com/downloads/Enecsys_SMI-S200W-S240W-60-UK_30.05.2011.pdf says typically 92% efficiency, night power consumption  <30mW.

The units are connected by looping cables one to the other, all AC, then only one cable goes into the house (mine was a 13A or 15A black reinforced underground cable like is used for drainage pumps).

[ovonrein]

I'm guessing, but I'm fairly sure that they monitor the DC output.

I don't know either, and there is some argument for taking the DC side, but reading tc ("in fact [the e-meter] said 30 last night which is actually *higher* than the monitor would imply.") seems to suggest to me that it is reporting AC.  Taking into account 8% inverter losses, his numbers would otherwise be even harder to explain.

[ovonrein]

The units are connected by looping cables one to the other, all AC, then only one cable goes into the house.

I assume that, although this description sounds a little like a series connection, that these things are actually all connected in parallel?  And that the grid dictates the voltage (and frequency) to which these things transform?  So ... if there is an unexplained large loss relative to what each inverter is reporting, then it is *unlikely* to be an individual roof connections.  My favourite in jez's "Picasso" is the MCB in the loft.

[jez54]

ovonrein, I'm sure you are right that all the panels and microinverters are in parallel.  My understanding of the Enecsys connector blocks (shown as "O" on my pretty diagram, and which each have 3 input + 1 output sockets, for: 1 upstream cable, 2 incoming microinverters, and 1 downstream cable) are configured such that all 4 live pins are connected, all 4 neutral pins ditto, all 4 earth pins ditto, which would effect a parallel system automatically.

I still have not managed to find out whether the Enecsys Monitor is doing its thing at the DC side or the AC side of each inverter.  In any case the loss due to microinverter efficiency is (said to be) within 5% - 8%.  Plus a few percent for AC cable losses in these low kW generation days, is still less than half the losses I am seeing at the generation meter.

That's an interesting suggestion that the roof MCB might be responsible for losses?  I had thought of such beasts as more or less passive in terms of their energy consumption?

[Nick57]

I have the opposite :-)

I think their monitoring system is still in development, lets put it this way I HOPE SO!!!

But your 20% seems quite a lot! Not sure if your 50mtr cable is down to that or the MCB?

Think of this, the Zigbee in each Inverter sends the information to the gateway, from the gateway to the Enecsys server on the Internet,  all raw data is processed and sent back to your monitor as useful information [on-line account] That's why I think that the monitor should show always a bit more then your generation meter.

The information in your account is having a huge delay, why? for the simple reason, Enecsys has only 1 point to send ALL DATA from ALL SYSTEMS too. Digging in their infrastructure all our DATA goes to the United States to a cloud server, not sure how much CPU cycle power they have but I noticed a delay of at least 3 minutes!!

I also noticed that you have to look the next day to find out how much KwH you generated the previous day.
Seems to me they have a cronjob running to do this adjustment, but err, who am I to think this, I just hope they will improve it!
Just try to imagine what will happen if they add another 10.000 users...

PING gateway.enecsys.net (206.80.44.117) 56(84) bytes of data.
64 bytes from 206-80-44-117-compute-ag1-ash01.opsourcecloud.net (206.80.44.117): icmp_seq=1 ttl=53 time=78.9 ms
64 bytes from 206-80-44-117-compute-ag1-ash01.opsourcecloud.net (206.80.44.117): icmp_seq=2 ttl=53 time=78.1 ms
64 bytes from 206-80-44-117-compute-ag1-ash01.opsourcecloud.net (206.80.44.117): icmp_seq=3 ttl=53 time=78.2 ms
64 bytes from 206-80-44-117-compute-ag1-ash01.opsourcecloud.net (206.80.44.117): icmp_seq=4 ttl=53 time=78.4 ms
64 bytes from 206-80-44-117-compute-ag1-ash01.opsourcecloud.net (206.80.44.117): icmp_seq=5 ttl=53 time=78.1 ms
64 bytes from 206-80-44-117-compute-ag1-ash01.opsourcecloud.net (206.80.44.117): icmp_seq=6 ttl=53 time=78.2 ms
64 bytes from 206-80-44-117-compute-ag1-ash01.opsourcecloud.net (206.80.44.117): icmp_seq=7 ttl=53 time=78.2 ms

--- gateway.enecsys.net ping statistics ---
7 packets transmitted, 7 received, 0% packet loss, time 6002ms
rtt min/avg/max/mdev = 78.149/78.371/78.980/0.429 ms

ISP:    NTT America
Host Name:    206-80-44-117-compute-ag1-ash01.opsourcecloud.net
Organization:    OPSOURCE
City:    Englewood
Country:    United States United States
Country code:    US
Latitude:    39.569
Longitude:    -104.8582
Region/State:    CO

http://www.opsource.net/Services/Cloud-Hosting

Note: I hope that Enecsys has taken legal action to have our data stored in the United States [CO]  Google is your friend "safe harbour"

[series530]

Back home now and did a comparison:

Enecsys says : 133.6 KWh generated since installation.  AC100 meter says 131.0. I seem to recall the AC100 saying 0.6KWh when first installed so let's say that the real generation is 130.4. That's a loss of 2.4%.

Our system has 14 inverters which share two buses of 7 each. Each bus feeds into a common AC isolator. The longest run of either bus, at a guess is about 8 metres. The down link to the garage is spec'd with 6mm T+E cable and has an approx run of about 15m.

I'm trying to find out the delay between the system and the website. No data as yet.