Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)


Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!

powered by Surfing Waves

Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.

    I have a 3.7 kWp solar system which has been installed for nearly four years now. I'm able to monitor generation form both the Solar Edge inverter which is connected to the internet and at the generation meter. I've noticed that the inverter reads consistently 5% higher then the meter.

    The meter is one of these (I'm pretty sure):

    Has anyone else noticed anything similar on their systems? Any ideas what I might be able to do about it?

    I don't earn a lot in FIT tariffs so there is no point me spending a lot of money to resolve the issue, but I was curious to know if anyone else has had a problem. The company who installed the system is no longer trading so I won't be able to get them back to take a look at it unfortunately.

    • CommentAuthorowlman
    • CommentTimeDec 18th 2019 edited
    From my experience none of them are perfectly synchronised. I have two arrays and two gen. meters and neither read the same as the inverters; Just submit the gen meter reading.
    Thanks. It is good to know I'm not the only one who experiences this. I do submit the generation meter reading and EDF (who pay me the FIT tariff) have been out to check the meter once.

    Posted By: owlmanFrom my experience none of them are perfectly synchronised. I have two arrays and two gen. meters and neither read the same as the inverters; Just submit the gen meter reading.
    • CommentAuthorbhommels
    • CommentTimeDec 18th 2019
    Only the consumption and generation meters are properly calibrated, so those are the ones that are "right" by definition.
    I usually apply a blanket correction factor, determined from the data. This is not entirely accurate as the difference gets relatively larger at lower power levels. The more accurate your data is, the more you can play around with trying to deconvolute all kinds of subtle effects. Not really worth it in my opinion..
    Yep - I have the same issue. Not quite as big as 5%, but it's there nonetheless. However, it does not surprise me, if you have to meters (whatever - temp, level, flow) they WILL measure differently. Unless they are calibrated to death to an enrealistic level of accuracy.
    It is a bit of modern thing - we "expect" our meters to be "accurate" - and when they aren't it upsets us.
    • CommentAuthorLF
    • CommentTimeDec 18th 2019
    Could losses in the inverter not be part of the story ?
    In industry I always expect an inverter to use about 3% power (minimum)
    • CommentAuthorMikel
    • CommentTimeDec 18th 2019
    Many years ago I did an estimate for the output of our system using PV-GIS Classic. The estimate was prefaced by:

    "Nominal power of the PV system: 3.8 kW (crystalline silicon)
    Estimated losses due to temperature: 7.7% (using local ambient temperature)
    Estimated loss due to angular reflectance effects: 3.2%
    Other losses (cables, inverter etc.): 14.0%
    Combined PV system losses: 23.1%"

    The average difference between my datalogger on the inverter and the generation meter is 3.6-3.8% lower on the generation meter.

    Today, when the weather has been appalling the generation meter read 0.1 kWh and the datalogger 0.360 kWh.

    So, similar to the others here!
    • CommentAuthorCWatters
    • CommentTimeDec 19th 2019

    Selected quotes:

    National Measurement& Regulation Office
    Electricity Meters - Disputed Meter Accuracy Report June 2015

    3.1 The limits of meter accuracy for meters approved under GB national legislation are prescribed in The Meters (Certification) Regulations (SI 1998/1566)4. Unlike most other countries, there is no additional tolerance for electricity meters operating in-service and they are required to maintain the same limits of accuracy as when new.

    3.2 Electricity meters are considered “accurate” if the permitted margins of error do not exceed +2.5% to -3.5% throughout the entire load range at which the meter is designed to operate.

    3.3 For MID meters the limits of accuracy at reference conditions are derived from the harmonised standard BS EN 50470-3:2006. The accuracy tests take into account the additional errors due to variation of influence conditions. However there are relatively few MID electricity meters installed in GB and, to date, only a handful have been submitted for determination.

    MID Accuracy Class Maximum Permissible Error Limits

    Electricity Meters (Class A)
    ±2.5% at minimum current flow;
    ±2.0% at one fifth of maximum current flow; and
    ±2.0% at the maximum current flow.

    Electricity Meters (Class B)
    ±1.5% at minimum current flow;
    ±1.0% at one fifth of maximum current flow; and
    ±1.0% at the maximum current flow.

    Electricity Meters (Class C)
    ±1.0% at both minimum current flow;
    ±0.5% at one fifth of maximum current flow; and
    ±0.5% at the maximum current flow.

    end quotes.

    So a meter approved to the EU/EN standard might be more accurate then the GB standard meter.
    • CommentAuthorbxman
    • CommentTimeDec 19th 2019
    Richard .

    If you do a search for " performance curves of Grid tied inverters" you will find that at this time of year most of the day most of the solar input is simply powering the inverter itself .

    Your GEO Solo Monitor will be nowhere as accurate as the Feed-in Generation Meter
    that will not be your generation meter .

    There will be an approved meter fitted somewhere what do you take the readings from when you submit them to EDF.
    • CommentAuthorJeff B
    • CommentTimeDec 19th 2019
    I have never really taken much notice of the difference between the PV generation according to the Enecsys monitoring system and the generation meter as I only use the former to check that all the microinverters are working. As I am paid only on what the meter indicates, then that is what I record.

    Like Mikel's observation above, the weather is so gloomy here at the moment (west Wales), we have had three days in a row with zero PV output. This has never happened before in the 8 years we have had our PV system!
    • CommentAuthorJeff B
    • CommentTimeDec 20th 2019
    A magnificent 1.2 kWh today!
Add your comments

    Username Password
  • Format comments as
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   

© Green Building Press