The ElectricLoadCenter:Storage:Simple
models the characteristic of a (very) simple electric battery object in an ElectricLoadCenter:Distribution
(ELCD). How that Storage object is controlled is actually defined in the ELCD itself, see the I/O ref guide for Storage Operation Scheme in particular (depending on what you pick here, you'll have to use some others field in that object in conjunction). You also need to pay attention to the electrical buss type as you need to pick one that allows for a storage object, and may require a ELCD:Storage:Converter
too.
OpenStudio has a set of regression tests hosted publicly on GitHub at NREL/OpenStudio-resources that are also great resources to demonstrate use of API for objects.
I wrote two tests in there (each has a ruby (API) version and the resulting .osm file, so you'll find 4 files): pv_and_storage_demandleveling
and pv_and_storage_facilityexcess
.
For peak shaving, see pv_and_storage_facilityexcess.rb where I basically try to limit the demand to 250 kW via the storage object, that could be a good starting point for you.