Electronics > Projects, Designs, and Technical Stuff
how to measure the direction of a.c. power flow
QuantumLogic:
You will also need to put in some sort of delay circuitry to prevent switching loads on and off with each passing cloud. Otherwise you'll burn up some stuff doing that too much (AC compressor, especially).
rstofer:
Aren't you just billed at the end of the month by the utility? Does it even matter when you export? It may matter if you are on a time-of-use schedule but, if that's the case, you would never run heavy loads during that time of day. Presumably, the utility also pays more for your exports during on-peak periods but that isn't universally true.
When I had solar, Pacific Gas and Electric would run an annual account and we 'settled up' at the end of the year. I made no monthly payment for kWh. Whatever I generated they didn't sell so the only kWh they saw as demand was what they actually delivered. I wasn't billed for time-of-use but there was a tier scheme. My 8 kW array was so large that at the end of the year we were within about $50 of paying nothing to PG&E other than the monthly meter charge.
But there's a gotcha in the scheme. Customers are not allowed to be net generators. I paid the solar company $0.15/kWh (Power Purchase Agreement) but if I over-generated when settle-up came along I would be reimbursed only $0.04/kWh by PG&E. It didn't pay to over-generate.
In any event, the new Smart Meters run in both directions and it is based on phase angle. To sell power to the grid, you have to try and lead the voltage. You are a buyer if your generator can't lead. This phase angle lead is very small.
http://www.gosolarcalifornia.ca.gov/solar_basics/net_metering.php
CodeDog:
here in Qld, I only get 8c per kWh exported, so there's not much benefit in exporting at all
cost to import is 28c, making it beneficial to use the power I generate rather than export it
early adopters still get high export rates (44c i think) and I know several people who
actually get a cheque each quarter because the value of their exports exceeds the value
of their imports
yes, there'd need to be some sort of hysteresis in the algorithm to flip the loads on or off,
so as to avoid turning things on and off as each cloud passes by
Someone:
--- Quote from: CodeDog on January 18, 2017, 03:54:44 am ---Here's the idea: unobtrusively measure the direction and intensity of power flowing along an a.c. line, and by unobtrusively I mean without a physical connection (e.g. clamp meter, Rogowski coils, ...), and the amount of power is not so important, just a relative value would be sufficient.
Why? ... Like a lot of others, I have solar panels on the roof. I also have a few high energy users such as a pool pump, and an airconditioner. Wouldn't it be great if I could immediately detect when I'm exporting power and flip on the pool pump? Or the aircon? And if it gets cloudy and I'm no longer exporting power, to turn off the pump?
--- End quote ---
Good thinking to make the best investment from your solar system, sadly the networks are making it hard to get this capability as they won't get any profit from it. If you have a smart meter you can get "in home displays" that have computer interfaces to extract the information with a usable latency, otherwise you'll probably need to add some current clamps to the meter box unless we can get some very clever solution from the crowd here.
--- Quote from: CodeDog on January 18, 2017, 03:54:44 am ---I sense a market opportunity here for a clever solution, if there isn't already something out there.
cheers,
Mark
--- End quote ---
Yes :)
reubenT:
--- Quote from: dmills on January 18, 2017, 12:18:39 pm ---Which is actually fairly easy, a clamp on current transformer with a suitable burden resistor and a voltage sampler, multiply the ac voltage and current samples together, lowpass and drive a centre zero meter. 73 Dan.
--- End quote ---
This is what I need right now. Been hunting for a practical circuit with component values designated, to make one for use in metering in/out for motor/generator experiments. The theory is all good, but I'm not an electronics engineer, just an old do it myself experimenter with all kinds of junk around to play with. Anyone have a lead on a circuit diagram?
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version