how_to_integrate:faq:from_pv_inverter_to_energy_storage_inverter [Sinexcel ESS knowledge base]

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====== From PV inverter to energy storage inverter======
This short article is prepared for these clients whose main business was PV installation and seeking for change to capture the tide wave of distribution generation tech.

===== Why energy storage =====
Nobody will deny that solar PV is one of the most acceptable clean energy until now. Unlike wind turbines, in a solar PV system, everything is static, bringing high robustness. 

Once upon a time the high price of PV panels is an obstacle but thanks to the Chinese PV panel manufacturers' competitions, the price is much cheaper now.

The only problem is the sun. Once the electric companies accepts users to feed back the extra power that generated by PV system but not consumed at site. but in the noon, there are too much more power generated than consumption, on the other hand, there are zero power generated by PV since there is no sun.

So modern PV plans are mostly considered as non-export plan.

===== Difference between PV + ESS and PV =====
A grid-tied PV system is a passive system, before CA rule 21 and HECO rule 14H, the PV inverters always generate as much power as they can output. even after CA rule 21 and HECO rule 14H, the smart PV inverters has to support reactive power when the grid needs support, the PV system is still not scheduling power.

But in a grid-tied PV+ESS system, there must be a controller, aka EMS, to intelligently dispatch the power flow at the sites.

The EMS must know how much power is being generated, how much power is being consumed behind the meter, to calculate how much power can, and should be stored in battery. and the EMS shall always have their algorithm to calculate when to discharge, how much to discharge, focused on optimizing the energy usage.