Author Topic: Solar power switching.  (Read 1591 times)

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george65

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Solar power switching.
« on: July 03, 2017, 08:44:34 AM »

I'm an electronics dilettante so this may not be even possible or maybe it's one for the boffins.....

I have bought a new house with 3 phase power. 1 meter is a smart meter, the other 2 are regular spinny meters.  The smart meter is on the circuit for the hot water heater  ( single phase) and the 3 phase Ducted air. 

I want to put up panels and back feed the 2 analogue metered circuits and move everything off the circuit with the smart meter so as to have my power bill as low as possible. Obviously I'll need to still use the leg the smart meter is on for the AC.
As the area we are going is cold as hell in winter and hot as the same in summer, the AC is going to get a workout.  It appears I have no chance of having the smart meter replaced with another analogue meter and back feeding it will cause the thing to register as power useage.

What I am wondering about is wether it is possible to somehow monitor that phase to detect when an appliance is running on it  ( AC) and when such detection is made, power from  a group of panels is given to that phase so the consumption through the mains is reduced. 
When the load is not present, the power from the panels is cut off. The power supplied to that phase would be less than the AC drew so as not to further register a consumption.

Second thing is -IF- this is possible to set something simple up like an arduino a newb can do or use a pre made board chinese board, would the panels and inverter feeding that phase need to be dedicated or when they are not being used, could they be switched to back feed on one of the other phases with the analogue meters so the power they are making is not wasted?

I figured the switching to the AC unit could be as easy as tapping into the compressor line so when it is active, it switches a relay that is connected to the solar inverter output and feeds the phase with the smart meter.
It would be more efficient and useful to monitor the phase so any 3 phase machinery I may add later could also be solar offset.

Also, what is the cheapest and easiest way to take the hot water heater off the off peak meter and put it on a basic timer that would kick it in through the day?
If I move it off the smart metered phase and on to one of the analogue phases it may not matter and I can have it kick in whenever it likes as I do where I am now, but I am still curious as to the method and economical hardware that might be out there to do this?

I have seen the over priced units that monitor and switch the solar input but I'm looking for something cheaper and more basic even if it does not take into account cloudy days etc.

Thanks for any suggestions.


dnix71

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Re: Solar power switching.
« Reply #1 on: July 03, 2017, 09:36:24 AM »
Backfeeding the analog meters may not work, either. Some are still set to throw a flag if they are run backwards, or worse yet to keep running forward.

Direct thermal for heating water is cheaper than electric heating in the long run. Unless you live on the north or east side that gets hit by cyclones, direct thermal heating is easy to maintain.

Moving the hot water heater off the peak meter may get you in trouble. Here in the US you can get a discount by allowing the power company to add a box that permits them to disconnect the hot water heater remotely so they can shave peak loads. Mess with that box and you will be fined.

Also, are you sure that the two analog meters are not sub-meters behind the smart one. That would be common practice here. Rent out a room or two and add sub-meters so you can keep track of use in those rooms.

DamonHD

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Re: Solar power switching.
« Reply #2 on: July 03, 2017, 10:50:19 AM »
Have you looked at something like the GridZero mode for Outback?

http://www.outbackpower.com/outback-products/make-the-power/item/flexpower-three-fxr-series

Explicitly designed to avoid backfeeding, and zeroes out all but your last amp of consumption when possible...

Rgds

Damon

PS. Just happened to run across this... https://www.treehugger.com/renewable-energy/solar-powered-air-conditioning-finally-here-and-its-totally-boring.html
« Last Edit: July 03, 2017, 11:37:18 AM by DamonHD »

george65

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Re: Solar power switching.
« Reply #3 on: July 04, 2017, 01:12:03 AM »
Have you looked at something like the GridZero mode for Outback?

Seemed ideal!..... Right up to the bit about the price.... $12,000!!
I wouldn't live long enough ( nor would it!) to make it Viable.  Spose if you could use the thing to capacity of 9 or 10 KW it may work out ok but for me....

Thank you for the suggestion but that's a lot out of my reach for such a thing.  Wonder if there are any Chinese Cheapy knockoffs of such a devise?

Quote
PS. Just happened to run across this... https://www.treehugger.com/renewable-energy/solar-powered-air-conditioning-finally-here-and-its-totally-boring.html

I really don't get that.  It's a low output split with a panel.  Why the hell would you not just run your AC as normal from the backfeeding from your panels as they do anyway? I'll bet this thing is priced way more than a regular split of the same size and you could put the extra to more panels that would be giving you benifit and running other appliances when the AC was not going.

It seems now that a lot of Ducted systems are single phase.  Given the system is lilely 15+ years old, Might have a look at it and think about updating.  Would be more efficient, easy to put in as I would only need to change the condenser and evaporator units and the control's as the ducting would all be in place and wire it into one phase. Place can do 100A per phase so shouldn't be a problem as there will only be the AC, water heater and stove as the main loads and they can be split across the remaining 2 phases.

Still be interested to know if there is anything like the outback unit at a better price.

DamonHD

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Re: Solar power switching.
« Reply #4 on: July 04, 2017, 04:58:33 AM »
Other inverter brands have similar modes, though that 'GridZero' was best for a vaguely similar application that I had in mind.  Sadly I don't seem to have made notes that I can find to share with you.

Yes, the price, the price: it burns.  And the standby power IIRC.

Another scheme/mode that is close, and may be a better price point, is to use one of the ship-to-shore power limiters that understand downstream power from solar.

Or, at a pinch, you may be able to adapt one of the PV-to-hot-water power diverters, but change any PWM output to a nice slow signal that your AC can cope with, either on/off or a power level control.

Rgds

Damon


Mary B

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Re: Solar power switching.
« Reply #5 on: July 04, 2017, 11:16:12 AM »
I use transfer switches with a 30 second delay for switching. When I have power the morningstar relay control module turns the inverter on and that load goes to solar from grid. I use a small UPS after the transfer switch so the transfer has no power drop on my computer. For compressor loads like my chest fridge(chest freezer used as a fridge) it has a 3 minute compressor delay after a power bump so no worries about being out of phase on the motor.

dnix71

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Re: Solar power switching.
« Reply #6 on: July 04, 2017, 01:18:52 PM »
The Enphase micro inverter M250 has off-grid/micro grid capability. That might be cheap enough to experiment with. Create a micro grid around an inverter that allows the Enphase to sync with. This arrangement requires batteries, but only enough to last a day or so. Run your a/c and or hot water from a microgrid and use an automatic transfer switch to isolate your microgrid from the power company. There is a church in Fort Lauderdale that installed a 40kw genset that only runs the a/c because it is cheaper to run a generator than to pay the peak charges for the a/c on Sunday morning. They can switch to grid if needed, but using the grid even once in the monthly billing cycle costs them big money.

https://www.solarpaneltalk.com/forum/off-grid-solar/off-grid-solar-panel-systems/22274-enphase-m250-specs-for-off-grid-tips-and-tricks-and-results

george65

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Re: Solar power switching.
« Reply #7 on: July 05, 2017, 12:22:32 AM »
Thank you all for the replies.

I'm thinking the way to go might just be to look up updating the system to single phase.

The micro inverters being around 250W would not be worth while on a system that as pulling 3-4Kw off that leg. You were right though, they are cheap enough to play around with.  That said, being a tight arse I was trying to work out the ROI on these things.
They would be about $200 at the best price here and I was trying to work out pay back time. Initial calcs of hours and power cost came out to about 3 months which I instantly thought could not be correct. And I was right.  They might only be producing an extra 50W over what the panel would do itself, not the full 25w Rating.  I imagine it would be an infinate variable so very difficult to calculate.  That said, may be possible to recoup cost in a year or 3.

Again though I come back to what I am seeing as the immutable law of solar, with used panels anyway..... Cheaper to get more panels than make the ones you have more efficent.  For what I am paying for a used 250W panel being $40-50, one inverter would buy another 1.5Kw.  No way a single inverter is going to make a panel that much more efficient and again the difference in ROI would differ greatly with the inverter taking years if ever to catch up. The thing I have learned from my solar experimentation and test setup is it's not so much the output you want to look at on a sunny day ( even though no shortage of them here) it's more about the not so sunny days you want to think about.
Even though the inverter bump the usable output of a panel on a cloudy day, they don't produce extra power like more panels would.

I know this wasn't the reason a micro was suggested but looking at them for the purpose of which they were intended..... Even new 280W panels are going for under $200 here now. 

I'll look up more about these transfer switches as they sound like a much useful thing.  Not real clear in the head today but the ability to use a micro to run a normal  grid tie inverter is a very useful thing.  I'll look more into that when I am thinking better.

OperaHouse

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Re: Solar power switching.
« Reply #8 on: July 05, 2017, 05:58:02 AM »
This video has some good graphic explanation of concepts of diverting power.

 https://www.youtube.com/watch?v=7WpN022E2MI

Be sure to watch Part 2.  This has multiple examples of equipment you can build economically.

The trouble with all of these current commercial diverter systems, besides the expense, is that they will likely be outdated in a few years as smart appliances become available.  These would be water heaters, dish and clothes washers/dryers and likely some other things.  These would tell the controller what devices are available to use power and what priority they have.

Certainly the water heater diverters are effective, but just how much can you divert to tank storage?  There have to be a few other devices to absorb the power during peak production. Probably 75% of the benefits can be done with just simple timers that at least schedule power use at typically peak times.  So. that 25% is what the cost savings is what is left over to pay for more fancy controllers.  The advent of the smart electric meters means that the utility company will be able to change pricing minute by minute.  At current pricing there isn't much incentive to  control usage. Even reduced utility payback isn't enough presently to stimulate a market for these products.  When they change pricing by the minute and actually charge you to dump power, these will become common place. It will be all wifi. Running new wires all over the house isn't practical.

Monitoring power in vs power out and scheduling isn't that hard for a micro.  Rather simple programs can be quite effective.  It is interesting to see how my water heater can go from 500W to 20W in less than a minute. It just hums along grabbing every watt it can.  PV is linear, the eye is log. You never notice these dramatic changes in light. A momentary wisp of a cloud can greatly reduce panel production.  Time for everyone to learn a little programming.
« Last Edit: July 05, 2017, 06:21:33 AM by OperaHouse »

george65

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Re: Solar power switching.
« Reply #9 on: July 06, 2017, 06:48:39 AM »
This video has some good graphic explanation of concepts of diverting power.

That was VERY interesting!
I have watched that channel before with his DIY power wall.

I would like to try and have a crack at making what he did, looks very worthwhile if I can follow it and pull it off.  One of those units I take it could be fitted to the one leg the Air Con is on and supply the power for that without putting power back into the circuit when it was off which would register as a draw? When it was not being used it would divert which could be on another phase.

 As it stands, the hot water is also on that circuit so would be ideal if it could do the 2. The devise seems to mimic the demands of the circuit so should be OK.   If not, wouldn't really matter, I could move the hot water to another of the analogue meter circuits and have it connected all the time and just average the use out with the panels.

Just saw an ad for 8Kw of used panels at a good price so messaged the seller about getting them.  that and the 2Kw of panels I already have should be more than enough ( I think?) to cover all my power needs.