This unit is only 100w. The manual for the OK4U inverter says "The unit is designed for use in combination with a PV module consisting of 72 solar cells in series and with a peak output power of 80 to 120 W."
This tells me 2 90w panels would be too much. And as small as these units are, I wouldn't want to press one that far...
Guppy:
I saw one of these inverters on eBay & did a little research afterwards, apparently they are the cheapest grid tie inverter you can get (at least the cheapest I have seen @ $215).
FWIW, I thought I heard that they are out of production... you can check them out at
Grid Tie Inverter.com-OK4U AC DC 100 watt power inverter
-Roger