inverter shoot-out at high noon [RE-wrenches]

[Christopher Freitas --- OutBack Power]

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Gee - I actually find myself agreeing here with Marco...  

Although there is nothing technically wrong about the Sandia/Endecon
test proceedure - I think there is a lot more value in real world
side-by-side comparison testing of similar (or even not so similar)
inverter systems.  OutBack, together with help from SMA, has
been completing just such a test in Grass Valley with an OutBack
GVFX and a SMA Sunny Boy inverters. 

The bottom line for a grid-tie system is the number of KWH back
into the grid - how the inverters achieve that is not the point
- the end result (KWHs) is what matters.  

I think each inverter manufacturer should be allowed to optimize
the test system's configuration - including PV array configuration
and total size - although it should be done with the same brand
of PV module.  Then the total KWH produced should be divided
by the PV array's size.  

There are still some potential potholes even in this path - for
example, Henry Cutler (Solar Guppy guy / Suntie re-engineer)
found that by simply curve tracing each of his PV module individually
and then grouping the PV modules into series strings by their
amperage output levels (high with high / low with low etc.) he
was able to increase the KWH output of his suntie system by more
than 5%.  

This type of mismatch loss would not be have been noticed if
just the entire PV array was curved traced for DC wattage - you
need to curve trace each module individually - and so is not
usually seen as a loss in the performance of a high voltage series
string inverter system where the PV modules are connected in
just one or two strings and cannot be re-arranged to eliminate
these types of losses. Since we usually talk about the inverter
efficiency only (DC watts into the inverter versus the AC watts
out) and not the actual system performance, these types of losses
are not typically accounted for. A similar issue can be said
for the wire losses in a low voltage type PV system when the
PV array is curve traced at the terminals of the inverter.  
    

I also have concerns about having government agencies like Sandia
and NREL messing with what should be a competitive marketplace
- they have provided significant funding to some companies (include
a few I worked for previously) which can influence the market
in not-so-positive ways. I would rather see them provide more
support on a industry wide basis (like this type of performance
benchmarking) and not funding R&D of an individual manufacturer
which seems to me to be nothing more than them placing bets on
what they think the next big technical advance will be.

Christopher

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