Inverter Power Ratings [RE-wrenches]

[William Miller]

John:

I'm convinced.  This was a rather idle thought, now it's dead.

WM


At 09:43 AM 4/30/02 -0700, you wrote:
>William:
>
>I think the whole idea of trying to maximizing the inverter output does
>not make sense (economically).
>What we really are trying to do in a PV system is to maximize the energy
>we capture and convert from the PV array.
>
>The cost of the inverter is typically 20 to 30% of the module cost and
>maybe 10% of total installed system cost.
>Even if you ran the inverter at 75% of it's rating you are only
>"wasting" 25% of 10% of the total system cost.
>At 75% of rated power (very conservative) the inverter is more efficient
>so we are really talking about less than 2.5% of total system cost.
>This must me weighed against the economic impact of trying to run the
>inverter al full power all the time.
>IMHO, trying to get a few more Watt Hours out of the inverter by adding
>expensive modules does not add up.
>For the price of the 20% more modules you could almost pay for a second
>inverter. 
>Then  both inverters would operate at lower power, higher efficiency,
>and cooler temperatures.
>Lower temperatures = longer life = happier customers.
>
>While there are lots of variables, most of the power in a "typical" grid
>tied system is generated during the middle of the day during in Summer.
>If you add modules that you can't use during this mid day peak period
>most of the output of the additional modules is wasted.
>Yes, you will get a little more on the slopes of the bell curve but at
>what cost ?
>The inverter will probably flat top the curve and limit power during the
>peak part of the day.
>When you add up the Watt hours gained and lost I think the net result
>will be very small.
>In addition, you have added complexity to the system which will reduce
>the long term reliability.
>
>UL imposes limitations, and rightly so, on inverter input, output, and
>temperature.
>If you run into one of these UL limits and the inverter reduces it's
>output power then you are going backwards (economically speaking).
>We (SMA) consider some derating to be normal in Spring and Fall but too
>much or too often is costing you money.
>Array sizing is always a trade off between Winter/Summer performance
>when array output is lower and Spring/Fall when it is highest.
>
>If you have any questions, or if I can be of any further assistance,
>please do not hesitate to contact me.
>
>Best Regards,
>
>John Berdner
>
>SMA America, Inc.
>20830 Red Dog Road
>Grass Valley, CA  95945
>530.273.4895 (voice)
>530.274.7271 (fax) 
>
>

__________________________________________________________________
William Miller
Miller Power and Communications
PO Box 50, Santa Margarita, CA 93453
Voice :805-438-5600		Fax: 805-438-4607	VMail: 805-546-4875
email: wrmiller at slonet.org
http://millerpowerandcomm.com
License No. C-10-773985
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