AC kWH Production Metering Effects [RE-wrenches]

[Joel Davidson]

Antony,

Thank you for offering to collect the data. I hope other wrenches
participate.

Here is the data for my system:
Location 90230
System Size 2,240 W DC STC
CEC Size 1,771 W AC PTC
Module Qty 32
Module Manuf & Model Siemens SP70
Inverter Manuf & Model Trace SW4048
Batterys Yes
String Size 4 modules in series
Module Azimuth 160 degrees
Module Tilt 12 degrees
Predicted Annual Production 2,544 kWh
Actual Annual Production 2,640 kWh for 2003
Estimation method PVWATTS Los Angeles input 1.45 kW AC (STC x 0.65)

Joel Davidson

----- Original Message ----- 
From: "Antony Tersol" <tony at appliedsolarenergy.com>
To: <RE-wrenches at topica.com>
Sent: Saturday, January 17, 2004 9:46 AM
Subject: RE: AC kWH Production Metering Effects (Was: ratcheting
cyclometers) [RE-wre


> 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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