Hi Segei
The VSD reduces stress by taking around 30 seconds to start and or stop a compressor, fan or pump instead of upto around 6 seconds for a large motor. Yes at full load the VSD driven motor defiantly uses more power. Yes load shifting will save on power costs from cheaper tariffs also loading and unloading of product at lower tariff rate times. I saw a documentary where in the USA they are starting to use solar PV panels for super markets saving around 15% over a 10 year period.
They are working on prototypes for electromagnetic bearing compressors for the lo temp range - so in the near future we will see COPs of 18. Yes we at the end of the day need to look at the plant on a wholeistic approach over the life cycle of machinery to get the biggest savings on energy.