Yes like murry said. But if you are using the 14v model you wont need a diode. After the battery reaches full voltage and gets to 14v then the grid tie will pull the rest. If you have a 10.8 or 11v then you will need the diode or it will pull the battery bank down to that voltage. That low will be about the cut off point for your power inverter. You also ask how you can rate it to half the rated watts. well the only way really is with solar. 250w solar panel on a 500w grid tie. with wind its a little harder but you could have 2 500w for 1 500w turbine. if you use a battery bank there is no way to regulate it. it will just suck as much as it can till it cant no more.