I’m setting up a 2,600-watt grid-tied, battery-based solar-electric system (using SunPower 320-watt modules). The guy I talked to at the electric company said he was not familiar with the inverter that I’m using—an old Trace SW4024. Is there a way of getting a list or some kind of information on electric companies that have approved Trace inverters?
Martin Mladenka • via email
Electric utilities take the safety of grid-tied power systems very seriously. Any such inverter must meet UL 1741 and IEEE 1547 standards, which are intended to protect utility workers from electric shock as they repair power lines during a blackout, and also protect a homeowner’s equipment and appliances from damage due to power quality fluctuations. To meet the standard, inverters must:
In your case, it’s likely that your utility simply isn’t familiar with your inverter because the Trace SW series was discontinued a few years ago. The SW4024 inverter was first introduced in 1994, and thousands of them are still in use for both off-grid and grid-tied applications. The SW series has gone through many different hardware and firmware versions since then, and most of them meet UL 1741 standards.
Some utilities think UL 1741 isn’t stringent enough. They may require that all grid-interactive equipment be chosen only from their list of approved models, which may also specify only certain model years or firmware updates. In other cases, it is the state utility commissions that determine allowable equipment. Unfortunately, I don’t know of any master database of inverters approved by different utilities, though many provide that information on their websites or will mail it to you upon request.
Utilities and electrical inspectors like to see new installations that are tidy; contain modern, new equipment; have ample documentation and schematic drawings; and were designed and installed in a professional manner. That puts the do-it-yourself homeowner with old equipment at a disadvantage. Your vintage Trace SW inverter is an old workhorse that will likely continue to perform for years to come—but is best placed into service in an off-grid situation.
Dan Fink • Buckville Energy Consulting