Hybrid and more

[Yianie123.]

Hello everyone.  I am interested in Solar, but want to keep all access energy and I don’t want to involve the utility company.  Here in Phoenix, it’s like they have more control then you do over your Solar.  I was thinking hybrid inverter.  From Solar panel to house, then excess to battery, then just use the grid for backup, without feeding the grid back.  Feeding the grid is where the problems start.  I know how to do it for my air conditioning unit, but what do I do in the winter time?  How do I feed the rest of the house?  Everything is electric and the system would be too large and expensive.  Would still like to use the power in the winter time.  Any ideas are valued. Thank you

[Mary B]

Could move some loads to a generator transfer switch, solar input in place of generator, when solar is there it switches over, when not it falls back to grid... BUT this doesn't work for large loads.

Or size it so that you produce about 20% less than you use, go thru the grid tie crap but since you never export...

[Yianie123.]

Thank you for your reply.  What I need is a method to measure house load and turn on microinverters on and off as required to match the load.  Have you ever heard of this devise?

[DamonHD]

I think that new Enphase microinverters are able to balance solar PV generation with load and without storage (are grid forming), and may well be able simply to avoid ever exporting to grid if that is necessary logistically.  Other systems can avoid exporting to grid while remaining connected to it.  I am not permitted to export to grid from my storage for example.

I auto-switch a small load to off-grid when the off-grid system has enough energy.

Rgds

Damon

[Yianie123.]

Thank you for your response.  I could not locate emphase inverter that will measure load and turn on inverter to compensate.  The goal is to not export to the grid.  Model number or any more information will be appreciated.

[DamonHD]

Here is a press release for the IQ8:

https://newsroom.enphase.com/news-releases/news-release-details/enphase-energy-launches-iq8-industrys-first-microgrid-forming

Other brands (eg Outback I think) do inverters that restrict the amount that is exported to grid, to 0 if necessary.

Rgds

Damon

[SparWeb]

That's true.  Outback, Schneider, and SolarEdge (and some others) have inverters that allow "self-consumption" modes that do not export to the grid, and prefer your generation system over the grid to minimize your consumption of electricity you must pay for.  This works, but it comes with specific installation conditions to make this technically possible.  For instance, if a temperature sensor switches on a large heating load in your house, then that's a drastic shift in the supply/demand balance within a fraction of a second.  The system needs to know exactly what's going on with your loads at all times.  It is absolutely not possible to do this with "I'll keep an eye on things then flip the switch here and push that button there".

You also need an extremely large generation system (lots of PV or wind) to keep up with winter demand (assuming you live in the Northern Hemisphere above (approx) latitude 40 degrees).

[Yianie123.]

Thank you everyone for your input.  I have found the perfect hybrid inverter at a non-perfect price.  The Aims hybrid does everything I want, but the price is  way to high.  It seems that the only difference is a circuit and current transformers that measure the household load, then compensates with solar, battery or grid, without back feeding the grid. Any access will charge batteries.  But the price is $2700+.  That is a hard pill to swallow as compared to big screen tv, washer/dryer, or living room furniture.  Any any additional options are appreciated.

[joestue]

https://www.amazon.com/dp/B0CFNPWXGD

https://www.amazon.com/dp/B0CGMWL9ZM

Looks like the term to search for is solar inverter charger to find the cheaper solutions.

Now as for your ac system, is it a hard starting compressor or an inverter?

You have to have a direct grid connection to handle the 140 amps locked rotor current.

https://www.renvu.com/Solis-10kW-S6-HV-Single-Phase-Hybrid-Inverter-with-Tigo-Transmitter

If your heat pump is an inverter, an isolated 400 volt dc power supply to supply the  dc bus directly, offsetting the utility load. You can use 60hz transformers to generate 265 to 280vac and a diode block to do this. The dc bus runs at 380v in many of them, i would only be concerned about trying to push to much power in through a small inefficient tx because under no load you may over volt ans it will trip an error code.

If you are willing, a single phase scroll compressor can be driven from a vfd. You need a 4 to 6 amp rated 120vac to 240vac transformer, and you may need an additional 208:32v transformer to push current through the capacitor aka start winding.

You can then augment the vfd with a 340v power source.

Lowest i would run a scroll compressor is 45hz due to the lubrication problems.

[Yianie123.]

Thank you again, but the inverter must have current transformers that clamp to L1 and L2 to measure load from grid to panel.  Then supply the right amount of Solar or battery power and backup from grid if need be with feeding into the grid.

[dnix71]

Still risky. If anything fails and you backfeed the grid, the power company will know, and you may cause damage or personal injury to others. That is part of the high price for an inverter capable of doing that. Two completely unconnected systems is fool-proof and much less expensive to operate.

The hard part of that arrangement is deciding which appliance is connected to which system. That one is your best call.

[joestue]

Still risky. If anything fails and you backfeed the grid, the power company will know, and you may cause damage or personal injury to others. That is part of the high price for an inverter capable of doing that. Two completely unconnected systems is fool-proof and much less expensive to operate.

The hard part of that arrangement is deciding which appliance is connected to which system. That one is your best call.

The issue isnt backfeeding the grid when it goes down, unless its just your local, single pole transformer fuse that blows. Your system will not be able to power the neighbors house and their 4500 watt water heater when it turns on.

I've only found one account online of a backfeed situation, a whole neighborhood and a dozen generators, and im not sure i believe it. Likely the power company lineman thought the circuit was off when it wasn't.

I trust the ul1741 standard that just about everything complies with will work in a grid down environment, as you will need a minimum of 20kw system to supply even a couple houses.

My concern is the power company finding out the meter is turning backwards. Some say it will record it as if power is being consumed. I called my utility and they wouldn't tell me. A friend is on the same utility and his milling machine spindle sends 25kw back up the power grid for 100 to 200 milliseconds during spindle stop. They dont care about that. But, that 2000 joules is not enough for the meter to spin 1/4 turn backwards, each turn of the meter is 7.2 watt hours or 25,920 joules.

Also the utility has no incentive for you to use their grid as a battery due to the duck curve. They may let you if you sign up for 8 cents off peak and 30 cents on peak kwh.

So either use a non grid tie system that can't backfeed, or trust that a dual redundant non backfeeding grid tie system was installed without the utility permission and take the chances that if it does backfeed, they will disconnect your service.

As long as you dont backfeed more than 6000 joules, the meter wont flag the regen power on many smart meters because they use a mechanical 2 flag quadrature encoder to count the turns.

The problem would be more like 50 watts backfeed for an hour, 6000 watts for a tenth of a second wont matter

[dnix71]

I have been told the new meters here will set a flag if you backfeed. They are also network capable and if you disable or try to disable remote disconnect features like time of day or loading shedding arrangements they pay you to accept (disconnect a/c or hot water during peak loads) they will know and fine you big time. You can get an free app for your phone that will show realtime use. It makes no sense to risk your account just to save a few dollars backfeeding sometimes without permission. If you just don't plug it in to their system, they cannot and will not know.

[MattM]

Tyrants.  Especially if the danger from backfeeds are minimized with controllers.