Battery based grid connect systems

This is my first posting so bear with me. My own renewable energy system is based around a veg oil powered lister type engine which charges a 24v battery bank through a 3kw inverter/charger. The battery bank is over 1100Ah capacity. I intend to add a wind turbine at a later date. I like the look of the SWEA 250w units but the voltage curves provided are really geared to direct turbine coupling. The downside to this is that a 300w turbine might average say 75w on a 24/7 bassis. I have asked if a flatter curve can be programmed so that the inverter can be used on systems that have a battery bank and Ivan has indicated that this will be possible. It could have set points of say on at 24v, output 100w, ramping up to say 300w at 27volts and shut down at 23volts. Or it could be simply on at 24v output 250w, off at 23v. Or whatever?The downside to my system is that I have to be selective about what loads I connect to my 3kw inverter. By adding a low power inverter to my system it will be like a 'dripping tap' and reducing load on my non inverter circuits. At 10p/unit 100w is costs £87.60/year, 250w would be over £200 a year potential saving. A good payback on a £300 inverter as an add on to an existing system. I am intending to order an inverter subject to it having a modified curve and being able to tie in to the grid supply which is 249v. Is there anybody else out there interested in something similar? Any observations?

If you wanted to get really clever and take it a stage further, the load on the consumer unit could be measured with a current coil with say 4-20ma output then this signal could be used to drive the inverter and subject to battery power being available then the inverter could ramp from say 25w to 250w. This would mean that you would not get into a situation where you are exporting electricity. You would be supporting the up to the first 250w of pwer drawn by your own means.