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#211937 - 11/23/13 08:30 PM Grid tie inverter question
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
If I had a grid tie inverter and the power was out, could I isolate the line side with the appropriate transfer equipment and switch in a small battery operated inverter to tickle the array back into operation and then run offline (using appropriate load management)?

Once it was going, the load on the battery inverter should be nil because the grid tie would be putting out a slightly higher voltage. You could then use some of the developed power to trickle charge the battery.

For that matter the "battery" could just be a 12v solar charger.

I know this sounds like a perpetual motion machine but the power is coming from the sun. The only question is how you handle sundown.

The solar charger would deal with that.

With a battery you would need some kind of diode isolation and a push to start button.
You could certainly make the controller smarter but I was just wondering if the idea would work.
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#211938 - 11/23/13 11:38 PM Re: Grid tie inverter question [Re: gfretwell]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
In my jurisdiction such a set-up would disqualify you from all California and Federal tax subsidies.

The regulations, as interpreted, INSIST on PV systems going absolutely dead during system power interruptions.

Attaining power during outages is limited to stand-by generators.

I suppose that some NEMA company could devise a scheme that would met the utility's safety concerns -- but it's not any kind of priority.

The current PV schemes are boondoggles. They entail trivial, retail, installations that can't approach the economy efficiencies of large power systems.

PV arrays should be sited where natural conditions are absolutely prime: the high deserts of New Mexico. These have low rainfall and consequently no farming nor much grazing. It's sterile land -- typically over 7,000 feet up. Such land is absolutely ideal for massive PV arrays.

In contrast, the solar boiler schemes are now understood to kill / fry migrating birds. They are that powerful.

The other idea that stinks is wind turbines. They're killing off everything from eagles to migratory birds. They're uneconomic: wind energy is so variable that to make the mechanism last it has to be wildly over engineered. That ruins the economics.

All over California there are broken wind turbines. The engineers simply never imagined that peak wind energy would be so hard to shed. So the gearboxes burn up.

PV is the only solar powered scheme that looks like it can hold up: it's solid state. It scales well.

There are schemes afoot to have next generation cells able to split water at efficiencies of 40%. With that, finally PV would come into its own. Right now the technology is just too primitive, expensive.

It's only looking good because the government is massively cross-subsidizing it. That comes at the expense of all the other electrical goods that we, as professionals, love to install.

For every dollar going into solar, multiple dollars that would've gone into plain old electrical wiring don't get sold -- or installed.

Spain took this to the limit -- and broke their national budget. They so over subsidized PV systems that a national mania took hold. At the end of the day, the factories and contractors imploded. The two biggest German producers shut down entirely -- writing off billions!

And Spain is left with power bills that are crippling every consumer of electric power... large and small. Staggering rates like $0.40/ kWHr are just too much -- when French power sells for $ 0.13/ kWHr -- right over the border.

PV is elegant... but can't be so exaulted that rates are taken to wholely uneconomic levels.
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#211939 - 11/24/13 04:17 AM Re: Grid tie inverter question [Re: Tesla]
shortcircuit Offline
Member

Registered: 06/27/04
Posts: 608
Loc: massachusetts
Originally Posted By: Tesla
In my jurisdiction such a set-up would disqualify you from all California and Federal tax subsidies.

The regulations, as interpreted, INSIST on PV systems going absolutely dead during system power interruptions.

Attaining power during outages is limited to stand-by generators.


Do they not allow battery back-up systems like the ones available from Outback Power Technologies?

Outback offers systems for Grid-Tie Solar Voltaic with battery back-up.

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#211940 - 11/24/13 04:33 AM Re: Grid tie inverter question [Re: shortcircuit]
shortcircuit Offline
Member

Registered: 06/27/04
Posts: 608
Loc: massachusetts
I'm much in favor of Solar Energy versus Wind Energy.

The answer to managing power from the Sun will come in the form of storage...battery storage. One of the top companies in the country working on development of such a battery is Ambri in Massachusetts, started by MIT professor Donald Sadoway. He is working on a Liquid Metal Battery for Grid Storage and it nears production.

Although this battery may not prove to be the answer to storing the Suns power...eventually someone will come up with one that will.

IMO, harnessing the Suns power is the answer to our energy needs here on Earth...and for our Planets sake the sooner the better.

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#211943 - 11/24/13 09:27 AM Re: Grid tie inverter question [Re: gfretwell]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
A transfer switch would solve the safety problem and if this was done after you cashed the rebate check it would solve the California problem.

My real question is whether it would work.
How much power does it take to tickle the inverter into turning on? The way I understand it they only use the line to clock the inverter if solar output is greater than load.
I would be very frustrated if the power was out, I had $50,000 worth of solar PV on my roof and I was still running a dollar a KWH generator. That was be the real deal breaker for me when I was looking at it ... before the end of the Florida rebates.
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#211944 - 11/24/13 10:39 AM Re: Grid tie inverter question [Re: gfretwell]
sparkyinak Offline
Member

Registered: 07/08/07
Posts: 1297
Loc: Alaska
It will depend on your system, it's configuration, local ordinances, and local utility rules regarding grid tie systems. Most inverters I worked with can be either a grid tie or off grid, not both. It maybe just more then a transfer switch. Plus start tinkering with a grid tie system will make the loco poco nervous. In a sense you are tinkering with their grid. An off grid configuration would do what you want but you won't be selling power to the grid.
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#211945 - 11/24/13 10:50 AM Re: Grid tie inverter question [Re: gfretwell]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
Once you flip the transfer switch, it is not on the grid, any more than a generator would be. The PoCo is out of it.
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Greg Fretwell

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#211948 - 11/24/13 12:10 PM Re: Grid tie inverter question [Re: gfretwell]
shortcircuit Offline
Member

Registered: 06/27/04
Posts: 608
Loc: massachusetts
Greg...if your asking if you can use a generator for the power source to activate the Grid Tied Inverter...that's a bad idea because where will the excess power go if the loads are less than Solar production? Right back into the generator and that's not OK. A grid tied inverter is not designed to work with a gen-set and will also be a problem and both would void warranty's.

That's why they have systems like the Outback with battery storage.

I think SMA just came out with a grid tied inverter with a single circuit 120volt receptacle that's still works when the grid is down...but it only works when the sun is up.

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#211953 - 11/24/13 02:32 PM Re: Grid tie inverter question [Re: gfretwell]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
No I was talking about using a small inverter to feed the big inverter a clock signal and jump start it.
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#211955 - 11/24/13 08:43 PM Re: Grid tie inverter question [Re: gfretwell]
LarryC Offline
Member

Registered: 07/05/04
Posts: 776
Loc: Winchester, NH, US
I believe APS now offers UPS that will start up off the internal battery without being connected to the wall outlet (or grid). That might get the inverter started. The Outback inverter that I used in a mobile application would take the shore power input and charged the batteries with whatever current was left over from driving the connected load.

How about utilizing a transfer switch in a different way?
Connect the output of the grid tie inverter to the LOAD terminals.
Connect the Grid terminals to the grid.
Connect the house loads to the Generator terminals.

When the grid is present, the GTI feeds into the grid. When the grid goes away, manually transfer the GTI to power up house loads. The transfer switch only has to be sized to match the inverter output or the house loads whichever is larger.

There has to be a second contactor or transfer switch to isolate the powered up house loads from the grid.

Or just use a large central battery bank to feed a bunch of local battery less UPS's and let each UPS take care of its local load. The UPS's do not have to synched to each other. Use a central charge controller to keep the batteries in shape.

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