We installed a couple of 100kW grid tied rooftop solar PV plants in factories which worked without flaw for quite sometime thereby contributing to electricity consumption and reducing the overall utility bills. Noted power factor was always in the range of .95 to .98 lagging, energy meters are bi-directional.
For reasons beyond their control, some of these factories had to shut down for a good part of the month. At this time solar plants were fully operational so majority of kWh was exported and only about 10-15% of total load (lighting, air-conditioning, fans, etc.) was catered to during this period.
To the horror of factory owners, electricity bill for this period carried around 70% penalty for low overall pf, around 0.25 lagging. No change in method of pf calculation, which is, accumulated kWh divided by accumulated kVAh for the duration. Capacitor banks were intact and operational.
Analysis showed that if the solar plants were shut down, all other conditions remaining same, the power factor improved to .91 lagging. Why? To the best of my knowledge, solar power is supplied at unity power factor and GT inverters are not power factor controllers. So it boiled down to 'some' issue with the bi-dir energy meter. But this happened at 3-4 factories so not all meters were defective.
Utility answered that this problem will get resolved on installation of Netmeter. What's the difference - bi-dir vs. Netmeter? How will it resolve the pf issue? Answers are welcome.