We own two of the older Trace-branded SW4024 (no "MC2") version of this inverter/charger and have been using them in a grid-tied, 4KW PV solar rig for several years now with 0 problems. We have our PV panels connected in parallel to a small bank of batteries and the two inverters. The inverters individually output 120vac, but can be connected together and synced up to produce 240v output. We do this with ours so that we can connect them to the public utility grid on the AC side and do the net-metering thing.The inverters completely manage the grid-interactivity, battery SOC maintenance, and solar array management, including keeping the batteries charged, but also keeping the arrays from overcharging the batteries. Normally the inverters draw off enough power to keep the batteries from overcharging by delivering it to the house loads and/or pushing it back onto the utility grid. Since our arrays are more or less directly connected to the batteries, there is a possibility that if the grid goes out on a sunny day that the batteries could be overcharged.
To avoid this, we split our PV panels into 4 arrays, each one going through a cutoff switch before reaching the batteries. The inverters each have 3 general-purpose relays, and we use two on each inverter to control the cutoff switches. If the battery voltage rises above a certain threshold, the relay(s) disconnect the arrays from the battery. If the voltage falls below another threshold they're reconnected.
The point at which the relays trip on is configurable in 0.1v increments, and each one has a hysteresis setting that you can use as well to keep the relays from "chattering" if the voltage fluctuates around the trip setting. Very handy.
The inverters also manage the grid-interactivity seamlessly. Obviously they take the DC and convert it to AC for the house loads, but they also take any excess and push it back out onto the utility grid. (Yes, we have seen our meter spin backwards!) If the utility goes out, the switch to battery power is instantaneous and uneventful. As it should be. When the grid comes back up, the inverters will automatically detect this, sync back up, and reconnect. They'll even automatically recharge the batteries for you if you want using a 3-stage recharging cycle to quickly but safely bring them back up to fully charged.
It does this so well in fact that we had to rig up a buzzer (again using one of the remaining two relays on the inverters) to let us know when the grid goes out, otherwise we wouldn't know until the batteries run dry. This gives us a chance to cut back our usage, turn off computers, etc. if we need to. Our battery bank is small enough that if the outage is going to last more than a few hours running out of power is a real possibility. (We did this to cut maintenance and cost, since the batteries are really the only consumable in our system, and the only component that requires any real maintenance. Unless you count dusting off the panels occasionally.)
The only nit I can pick after several years of using these inverters is that the firmware seems a little picky about the quality of the grid it is connected to. If there is a brownout or the frequency drifts out of spec then the inverters will disconnect from the grid. This is to prevent islanding and is a Good Thing.
However, the inverters do this a lot, and each time they do they stay disconnected for 5 minutes after the grid goes back into spec. Even if the glitch was only a fraction of a second, the inverters still stay disconnected for a full 5 minutes.
Normally this isn't a problem since even our small bank of batteries can easily cover such a small outage. Still, it seems like a "grace period" of a few seconds at least would be in order before disconnecting entirely.
These inverters also have a lot of features we're not using in our particular system. You can have it connect to the grid or charge the batteries only during certain times of the day so you can charge the batteries at night when it is cheap and sell power back onto the grid during the day when it is expensive, provided your utility allows it of course. There's another AC terminal besides that for the utility grid connection that can be used for a wind/hydro/gas/diesel generator. It can automatically start most any generator with 2or 3-wire starting circuits.
I would heartily recommend this inverter to anyone trying to build themselves an alternative energy system, especially one that is tied to the grid. It does what it is supposed to, and does it reliably and efficiently. You can't ask for more than that. The sine-wave output means that you can run anything on it, even in inverter mode, and tons of configurable options makes it appropriate for a wide range of applications. I have no reservations giving this inverter/charger 5 stars.
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