Re: [pvusers] PV inverter reliability

["Robert Warren" <robertwarren@mail.com>]

I would like to add a fourth rule to the good advise Joel has given: get an amp hour meter and watch your batteries. If you own and live with an inverter, you get to know what it will and won’t do. In terms of your loads, you probably need it to run your water pump, washing machine, refrigerator and a host of unexpected loads when the family gets together for Christmas.  But the weakest link in most any PV system is the batteries: do you have them sized properly for your system and needs, and do you monitor capacity with an amp/hr meter? You want to try to always keep your batteries on the full side of 50% capacity, not only because this will prolong the life of your batteries, but also your inverter. Heat is the main enemy of inverters, and if battery voltage goes low, then current goes high, and then the FETs need more heat dissipation. Most inverters now have overload protection circuits, so they don’t overheat, but if the inverter frequently gets to this trip-out level, it is more likely to fail. So probably the best thing you can do for your inverter is to buy and use a battery monitor which is capable of measuring amps in vs. amps out, figuring out the actual battery efficiency, and showing you the percentage of capacity. I have seen lots of inverters run well for over ten years, but I have also seen failures in just a few weeks. The inverter industry has matured greatly along with the rest of the electronics industry, and it will continue to do so. You may find your inverter still works well in five years, but that you want to change it because of new improvements we haven't even thought about yet. 
Robert Warren
Senior Engineer,
Solar Century, London

----- Original Message -----
From: Joel Davidson <joeldavidson@earthlink.net>
Date: Sat, 04 May 2002 09:41:45 -0700
To: pvusers@crest.org
Subject: [pvusers] PV inverter reliability 


> Inverter failures has been blown way out of proportion. Sure, inverters
> fail as do any electronic device. I have sold thousands of inverters,
> have about 1.5 megawatts of on- and off-grid PV in the field with
> inverters and have personally used inverters since 1963. Many of my
> customers read these posts. Perhaps they can write in and attest to
> inverter reliability.
> I predict an inverter failure rate decline analogous to the decline in failures of another complex electronic device, the television. Four
> decades ago, TV power supplies and tuners failed fairly regularly. Today billions of TV are in use and 100s of millions of TVs are sold yearly and the failure rate is very low.
> 
> If you are concerned about buying a good inverter, ask your supplier for a recommendation.
> 
> If you install inverters, follow these 3 simple rules:
> 1) Size the inverter properly. Running an inverter at full rating all
> the time is poor system design. An inverter "running on red line" in a poorly ventilated equipment room suffers heat stress which shortens
> component life.
> 2) Size your inverter cables properly. Undersized cables stress
> inverters. Wire is cheap compared to the price of an inverter. If "the book" says 2/0, then use 2/0. Or better yet, use 4/0. You are only talking about a few feet of cable.
> 3) Tighten all battery and inverter cable connections properly. If you don't know how to use a torque wrench, then you are not qualified to tighten cables.
> 
> This email was written in a net-metered PV powered office. See system
> wiring diagram at http://www.solarsolar.com/sysdwg.html Our SW4048
> inverter was installed June 1998 and has functioned perfectly through 2 SCE scheduled blackouts (remember the California energy crisis?), 2 utility power outages (1 was 16 hours long when a pole mounted transformer when out on the next block) and my regular system tinkering.
> An added benefit is that I have not had to replace a computer mother
> board or hard drive since going solar because power quality from the
> inverter is better than grid power.
> 
> Editorial - I think Xantrex's ST-series and SW-series troubles could
> have been avoided or quickly corrected if the talented engineers that
> use to work at Xantrex and the talented people still there had been
> given the freedom to make better inverters. Trace had a tradition for
> making great inverters. It is time for Xantrex to pick up the Trace
> banner or lose the race. Employers either help their eagles fly or herd turkeys.
> 
> 
-- 


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by Robert Warren 
robertwarren@mail.com

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