Going off the grid with a grid-tied system

Xringer · 03-14-09, 10:27 AM

I've been looking at the idea of using a grid-tied PV system, and it seems one of the draw-backs is,
the system is useless in a power failure..
It's designed to drop off-line and play dead, while the main grid is down.

Assuming the power fail occurs during a nice sunny day. At night, it would
make no difference.

http://i46.photobucket.com/albums/f1...roInverter.jpg

If you go to your main breaker box and flip the main supply breakers open,
you are still out of luck.

BUT, if you opened the breakers and then applied 230V to your in-house circuit using your own battery backed-up inverter,
that should re-start your PV system and allow you to turn on some low powered items you might want to use during a power failure.

I'm sure that doing this would be in violation of regulations..

I guess a more legal way to doing this would be to disconnect your PV system from everything, and plug it into a big Back-Up box.
The Box would supply 230VAC voltage to the PV system, allowing it to turn on.
The Box would have eight 120VAC outlets on it, that you could use
during the power failure.
You would unplug your radio etc from the grid, and plug it into the Box..

If the battery back-up inverter in your Box was large enough, it might be able to handle the load while clouds were passing..

I'm just thinking back to the days after the recent ice storms and the Blizzard of 78 when the power was off for many days, sunny days.

knowbodies · 03-14-09, 12:08 PM

I found this linked through a thread over at ecomodder.com - linky, linky. It's an uninteruptible solar power supply that switches to mains power when solar is insufficient. Calling it a solar UPS is a bit of misdirection though, it's really an offline UPS where primary power is provided by a solar array and backup power is provided by the grid. Depending on the size of your array and batteries, it should be ok for a small electrical load.

Xringer · 03-14-09, 01:14 PM

That's a very interesting approach to the problem. It's almost the exact method that I've been considering.
Bypassing the legal requirements is a plus. But, it's for very small PV systems with low output.

The two small PV packages that I've been eyeballing can make 700W & 1400W.
Enphase Grid-Tie Packages
I'm not sure what my 'standby' load is, but my guess is under 700W.
So, I would want a fully legal grid-tied system, so as not to be wasting
any extra power made during the day when my use is low and the sun is high.

I have received the info pack with the required forms from the power company, and it doesn't look really complicated.
If my town inspector(s) cooperate, I should be able to DIY and get the net-metering installed without a hitch.

If the inspectors don't cooperate, a low powered Stand-by load mini-system
using the Enphase inverters with some panels in the backyard is my plan-B.
Since there is no way that I'll pay $15,000 for someone to install a $4600 system.
When the tax breaks etc get wiped out by labor cost, the break-even moves out past my life span.

Cheers,
Rich

Ryland · 03-15-09, 08:11 PM

What you want is called a Grid tied system with battery back up, they tend to cost about 30-40% more then then a standard grid tied system due to the slightly more complex inverter and the battery bank, but you can buy everything off the shelf, there are inverters out there that are designed for exactly what you want to do already and are safe for everyone and are covered under your home owners insurance, as well as qualifying for public funding.

Xringer · 03-15-09, 11:07 PM

One of the main reasons for going to a grid-tied system is to use the grid as your battery.

A Grid tied system with battery back up might be required for places where they have a lot of power failures. But, they are rare around here. Too rare to justify the added cost.

It might be possible to activate an EnPhase system with an inexpensive inverter unit..

03-14-09, 10:27 AM	#1
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Going off the grid with a grid-tied system I've been looking at the idea of using a grid-tied PV system, and it seems one of the draw-backs is, the system is useless in a power failure.. It's designed to drop off-line and play dead, while the main grid is down. Assuming the power fail occurs during a nice sunny day. At night, it would make no difference. http://i46.photobucket.com/albums/f1...roInverter.jpg If you go to your main breaker box and flip the main supply breakers open, you are still out of luck. BUT, if you opened the breakers and then applied 230V to your in-house circuit using your own battery backed-up inverter, that should re-start your PV system and allow you to turn on some low powered items you might want to use during a power failure. I'm sure that doing this would be in violation of regulations.. I guess a more legal way to doing this would be to disconnect your PV system from everything, and plug it into a big Back-Up box. The Box would supply 230VAC voltage to the PV system, allowing it to turn on. The Box would have eight 120VAC outlets on it, that you could use during the power failure. You would unplug your radio etc from the grid, and plug it into the Box.. If the battery back-up inverter in your Box was large enough, it might be able to handle the load while clouds were passing.. I'm just thinking back to the days after the recent ice storms and the Blizzard of 78 when the power was off for many days, sunny days.

03-14-09, 01:14 PM	#3
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Thanks for the input That's a very interesting approach to the problem. It's almost the exact method that I've been considering. Bypassing the legal requirements is a plus. But, it's for very small PV systems with low output. The two small PV packages that I've been eyeballing can make 700W & 1400W. Enphase Grid-Tie Packages I'm not sure what my 'standby' load is, but my guess is under 700W. So, I would want a fully legal grid-tied system, so as not to be wasting any extra power made during the day when my use is low and the sun is high. I have received the info pack with the required forms from the power company, and it doesn't look really complicated. If my town inspector(s) cooperate, I should be able to DIY and get the net-metering installed without a hitch. If the inspectors don't cooperate, a low powered Stand-by load mini-system using the Enphase inverters with some panels in the backyard is my plan-B. Since there is no way that I'll pay $15,000 for someone to install a $4600 system. When the tax breaks etc get wiped out by labor cost, the break-even moves out past my life span. Cheers, Rich

03-14-09, 12:08 PM	#2
knowbodies Home Improvement Goon Join Date: Oct 2008 Location: Moose Jaw, SK, CA Posts: 96 Thanks: 0 Thanked 2 Times in 2 Posts	I found this linked through a thread over at ecomodder.com - linky, linky. It's an uninteruptible solar power supply that switches to mains power when solar is insufficient. Calling it a solar UPS is a bit of misdirection though, it's really an offline UPS where primary power is provided by a solar array and backup power is provided by the grid. Depending on the size of your array and batteries, it should be ok for a small electrical load.

03-15-09, 08:11 PM	#4
Ryland Master EcoRenovator Join Date: Mar 2009 Location: Western Wisconsin. Posts: 913 Thanks: 127 Thanked 82 Times in 71 Posts	What you want is called a Grid tied system with battery back up, they tend to cost about 30-40% more then then a standard grid tied system due to the slightly more complex inverter and the battery bank, but you can buy everything off the shelf, there are inverters out there that are designed for exactly what you want to do already and are safe for everyone and are covered under your home owners insurance, as well as qualifying for public funding.

03-15-09, 11:07 PM	#5
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	One of the main reasons for going to a grid-tied system is to use the grid as your battery. A Grid tied system with battery back up might be required for places where they have a lot of power failures. But, they are rare around here. Too rare to justify the added cost. It might be possible to activate an EnPhase system with an inexpensive inverter unit..