Why are Off-Grid Inverters more than double price of Grid-Tie Inverters?

I find it interesting that MPPT Solar Grid-Tie inverters less than half the price of Off-Grid Inverters. For example, a MPPT SMA 7.0 kw cost about $1,400. While a Schneider Conext xw+ 6.8kw is over $3,000 (Off-Grid), Radian 8kw is $3,800 and even a SMA Sunny Island is $3,600.
I would think without an MPPT mechanism, you have a simple battery voltage range. I would think it would a lot more simpler to make such an inverter instead of one with MPPT plus UL 1741 (Grid Detection) features.
Any ideas that would drive up the price of Battery inverters so much?
I would think without an MPPT mechanism, you have a simple battery voltage range. I would think it would a lot more simpler to make such an inverter instead of one with MPPT plus UL 1741 (Grid Detection) features.
Any ideas that would drive up the price of Battery inverters so much?
Comments
Also as already mentioned GTI's are made by the thousands in big batches.
A serious Off Grid inverter has to give a stable HZ and a stable voltage under loads and handle power of say 15kW for short time periods.
It also has to handle very large surges.
My Ozinverter has several GTI's connected to it and these back feed through the Inverter, H Bridge design, and charge my batteries.
If you make your own 6kW OzInverter, then it can cost as little as $700, even less if you scavenge parts and totoids etc.
Everything is possible, just give me Time.
The OzInverter man. Normandy France.
3off Hugh P's 3.7m dia wind turbines, (12 years running). ... 5kW PV on 3 Trackers, (8 years) .... 14kW PV AC coupled using Used/second hand GTI's, on my OzInverter created Grid, and back charging with the AC Coupling and OzInverter to my 48v 1300ah batteries.