[RE-wrenches] AC Coupling Standard?

Windy Dankoff windydankoff at mac.com
Fri Dec 2 07:08:22 PST 2022

Dear Mike,

As co-author of upcoming book "The Handbook of Solar Water Pumping", we have expanded its definition to include micro and national grid-tied systems in which pumping is synchronized with power availability from PV. I had known about frequency-based load control for microgrids (from an SMA-based microgrid I toured in Israel). I had no idea it was a happening system on public grids until I read your response here. I love how it requires no communication lines or digital signals. It's a "natural" and logical concept from the old days of spinning generators under varying load.

I see your PG&E reference, but is there also a reference text you can recommend that I can use in the book as a universal explanation of how this works?  It can be SMA documentation, or other ref.  You can reply here if it's useful to the list, and/or contact me off-line.

Thanks!  – Windy

> On Dec 1, 2022, at 5:47 PM, re-wrenches-request at lists.re-wrenches.org wrote:
> From: Harry Mahon <Michael.Mahon at sma-america.com <mailto:Michael.Mahon at sma-america.com>>
> Subject: Re: [RE-wrenches] AC Coupling Standard?
> Date: December 1, 2022 at 5:47:18 PM MST
> To: RE-wrenches <re-wrenches at lists.re-wrenches.org <mailto:re-wrenches at lists.re-wrenches.org>>
> Definitely it is possible for newer grid-interactive inverters.  However, for grid-tied operation, the utility that runs the grid sets the rules (and sets the setpoints as it were), and it can be confusing....
> Looking at PG&E’s Rule 21 tarriff (submitted Aug 12, 2022, effective Nov 4, 2022) Freq-Watt reuirements are:
> “When system frequency exceeds 60.036 Hz, the active power output produced by the Smart Inverter shall be reduced by 50% of real power nameplate rating per hertz (5% of real power nameplate rating reduction per 0.1 hertz)”
> Bottom of Sheet 207 of : https://www.pge.com/tariffs/assets/pdf/tariffbook/ELEC_RULES_21.pdf
> So a 5kW inverter needs to ramp at 2.5kW/Hz.  But if it is only producing 2.5kW, it has to be at 0W at 61.036Hz.....
> Mike

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