Inverter meter reliability [RE-wrenches]

[John Raynes]

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Ian,

Actually the randomness I was talking about is in the manufacturing 
process.  Any measuring instrument built in quantities will exhibit 
unit-by-unit variances in accuracy, due to component tolerances.  As one 
might expect the manus see to it that this variance has a bias in their 
favor.  Usually once a given unit is manufactured, its particular degree of 
inaccuracy will likely stay fairly stable and repeatable over time.  There 
may be some temperature-dependent inaccuracies remaining, though.

What I don't understand is, that it's a fairly straightforward matter 
adding almost nothing to the design and manufacturing cost of any modern 
inverter, to correct or at least improve on this in firmware using 
calibration coefficients.  Measurement errors are readily determined during 
final production test, and correction factors permanently stored in 
non-volatile memory, inaccessible to anyone in the field.  In fact, I'd bet 
that most or all of them are already doing this, they just aren't doing it 
to a very tight spec, apparently.

I would be curious to hear the various manus explain the current situation 
as observed by others here.  I do mostly off-grid and don't have a lot 
observations of my own about grid tie metering inaccuracies, but I'm not 
the least bit surprised by what I'm hearing.

John Raynes
RE Solar



At 09:53 AM 5/28/2008 -0700, you wrote:


>Hi John,
>
>I'm waiting to see this one become random. The two meters have been 
>tracking very closely from the start. Dumb luck? ;-)
>
>Best,
>
>Ian
>
>>Ian,
>>
>>Agreeing with what other have said here (i.e., inverter meters tend to be 
>>somewhat inaccurate, and also biased in the manu's favor):
>>
>>It's kind of like shooting inaccurately at a target, being off to the 
>>left but with a lot of random scatter.  Occasionally, random scatter 
>>shots are going to fall very close to target.
>>
>>John Raynes
>>RE Solar
>>
>>
>>At 08:02 AM 5/28/2008 -0700, you wrote:
>>
>>>I'm surprised to see that a Sunny Boy 4000 that we installed this spring 
>>>is tracking the utility's digital production meter very closely. 
>>>Yesterday's cumulative reading was 629 on the utility meter (resolution 
>>>is whole numbers) and 628.7 on the inverter.
>>>
>>>Ian
>>
>>
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>
>
>--
>Ian Woofenden <ian.woofenden at homepower.com>, Senior Editor, Home Power 
>magazine
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