AC kWH Production Metering Effects (Was: ratcheting cyclometers) [RE-wre

[Antony Tersol]

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Matt Lafferty said

>I further contend that claiming this "artificial production" falsely
>inflates what is ultimately claimed as "efficiency" by Inverter
>Manufacturers.  These same numbers are pointed to by Module
>Manufacturers whenever confronted with the issue of "estimating or
>projecting".  When we as Integrators rely on these Manufacturer provided
>efficiencies without calculating in the losses, we end up looking bad
>when the Customer's monthly bill isn't as positively affected as we
>"estimated".  Not just by the Customer, either!  Bad news travels fast!
>(This is not just isolated to battery-based applications!)  

All of us are using some kind of model to estimate production figures.  We can only refine our models with real world data.  Each of us tend to rely for that data (if we are trying to improve our estimates) on the systems we install and monitor.  We can't rely on the manufacturers for data for at least three reasons: 1. they have limited numbers of systems in real world conditions that they are monitoring 2. they want to make their product look as good as possible 3.  the benefits to them are somewhat diffuse and long-term - their internal incentives are typically toward end-of-quarter sales figures.

Our own small data sets are subject to the uncertainties inherent in small data sets.

It would be extremely helpful to create a database of our collective data.  Isn't SMUD monitoring a large number of systems?  

Why not collect the following pieces of info as a start?  (grid-tied only as a start)

Location (zip code?)
System Size (name plate - # of modules X manufacturers rating)
CEC Size (for california wrenches: # of mods X CEC PTC rating X inverter CEC efficiency)
Module Qty
Module Manuf & Model (use California eligible module table for consistency and since its available to everyone via the web)
Inverter Manuf & Model
Batterys (Yes or No only)
String Size (# of modules)
Module Azimuth
Module Tilt
Predicted Annual Production (kwh)
Actual Annual Production (kwh)
Estimation method (this could be a description or a name if you use a product such as Maui software or Clean Power Estimator)

I would be willing to collect this data and make it available to the list.  Don't send it yet!  I will create a format and/or web page so it can be emailed and automatically processed.  

What do you think?  Helpful? 

Any other data fields that would be helpful?  Perhaps nearest TMY station (weather data site).  Altitude?  Pathfinder estimate of annual production as % of unshaded?

If it's a multiple inverter installation, submit the data for each inverter seperately?
We could allow for installations with strings at different orientation by expanding the fields to 

String 1 azimuth
String 1 tilt
String 1 Qty

String 2 azimuth... etc.

Any systems that are more complex then that I don't want to know about.  Just collect data on the most prevalent type of install.  

This would allow us to refine our estimation methods, and also to evaluate the estimation methods.

Should we do this?

Regards,

Antony

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