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Grid Tied Solar System during a Power Outage  RSS feed

 
Matt Stern
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Location: Williams, OR
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I have a grid tied rooftop solar system. It works great, the thing is, if the grid goes down for any reason, my system shuts down automatically. The said reason being to protect any utility workers from getting zapped by my electricity traveling back through the power grid. Makes sense to me, but is there any way to safely bypass this "feature?" IE the grid goes down but we can still use the watts we generate. I'm open to solutions that include batteries, but curious if there is a way to do it without them.

Matt
 
Peter Mckinlay
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Hello Matt,

Not being smart, its called a switch. One opens it when grid goes down and closes it when the grid is up.

Opening the switch isolates the grid so house only is on draw.

Odd that the grid gets draw before your house!
 
Peter Smith
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Location: NEPA
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I install these systems, and am always baffled why people choose grid tied as opposed to independent. Your real problem is that most of these systems ( not exactly sure what you have) have to have 110 power coming to the inverters before they will allow any power out. The reason being that the inverters have to match the phase of power going out to the grid phase. I believe you need different inverters and batteries to make it work well for you in a power outage.
 
Marcos Buenijo
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Peter Mckinlay wrote:Not being smart, its called a switch. One opens it when grid goes down and closes it when the grid is up.

Opening the switch isolates the grid so house only is on draw.


Unfortunately, this will not work. First, as Peter Smith noted, a grid tie inverter requires an external 110 VAC. However, it will not work even if this feature were somehow bypassed. Imagine you are powering your home directly off the solar panels while they're getting full sun. Well, what happens when a cloud comes by and shades the panels? The system requires a voltage buffer (grid or battery back up), which is another way of saying a means to store energy is necessary to fill in the gaps during such transients.

Matt, I recommend you investigate what is called an "AC coupled grid-tie with battery back up": http://www.wholesalesolar.com/AC-coupling.html . Basically, what this configuration does is provide an external NON-grid source for the required 110 VAC using a battery system and separate inverter. This "tricks" the grid-tie inverter into functioning. There is a little more involved, but this is the basic idea. In principle, it's possible to keep a battery system charged with a grid-tie system. Now, if the grid is lost, then an inverter on the battery can generate a 110 VAC local grid for the grid-tie inverter thereby allowing the panels to function. It seems counterintuitive, but it's possible to charge the battery with the solar array (using the grid-tie inverter to supply a battery charger) while the battery is powering an inverter that provides the 110 VAC local grid.
 
william readling
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Your system has a grid tie inverter that converts the DC from the panels, into AC. Some grid tie inverters have a stand alone mode, some don't. Read the manual, and the manufacturer's website. If you have one, you can disconnect your home's electrical service from the grid. In a modern breaker box the switch will be a big 200 ampere breaker at the top of the panel. Disconnect your home, and put the inverter in stand alone mode. You still won't have batteries, so after sunset you're out of luck.
 
Marcos Buenijo
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FROM SITE (http://www.buildinggreen.com/auth/article.cfm/2013/3/29/Islandable-Solar-PV-For-Power-Outages/)

"3. Grid-tie inverters that produce electricity when the grid is down

The micro-grid system with its multiple inverters is complicated. A simpler system would be a standard grid-tie inverter that would safely disconnect from the utility grid during a power outage, as required, but retain an ability to convert the direct-current (DC) electricity from the PV system into usable electricity for the house. The industry isn’t there yet, but there are some promising recent developments.

Several of SMA America’s newest Sunny Boy grid-tie inverters now feature an emergency power-supply feature that allows a small amount of power to be drawn from the inverter even when the grid is down. This emergency power is provided through a separate 12-amp, 120-volt outlet; the electricity cannot be delivered through the building’s wiring system. While it may not be enough power for major household loads, it can provide critical cell phone and laptop computer charging and other daytime needs. We expect that other manufacturers will follow suit."

MY COMMENTS: This configuration (grid disconnected with no battery) is very limiting. For example, there is no surge capacity, so starting motors will likely not be possible. The system output is also limited by the lowest output from the array, which can fluctuate wildly during the day. This is why all proposed configurations allow only a small amount of power that would correspond to a small fraction of the rated output of the array. For good results, a battery is required. The battery required for such systems is much smaller than what's required for an off grid system.

NEW PRODUCT: http://webosolar.com/blog/grid-tie-solar-home-system-blackout/ Provides electricity up to 1500 watts provided the solar array receives a solar flux high enough to generate the power demanded. As the article notes, this is a great system for keeping low power equipment online during a black out (might charge small batteries, laptop, cell phone, basic lighting, and possibly a freezer).
 
Matt Stern
Posts: 44
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Thank you all for the good info. I will check out the links.
 
Terry Brown
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or you buy a generator - would be cheaper if your grid tied
 
Teresa Duran
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Can i ask a question. I'm a novice more like a greenhorn but i have a battery backup system. Was part of the property when i bought it. Yesterday i list part of my power. Switched on the bypass on My inverter and all was ok. What did i did I bypass my batterries or the grid or did i switch from the top 5 batteries tp tje bottom 5 batterries thanks in advance
 
frank li
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Location: Michigan
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Most likely all you have to do is add a battery based inverter system that will ac couple to your existing inverter system. There are plenty of choices. I would read the articles on ac coupling and manufacturer specs.

Not sure of your house/inverter supply voltage. If you are in north america, and have a residential size system, the common form will be 240vac split phase power.

 
frank li
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Teresa Duran wrote:Can i ask a question. I'm a novice more like a greenhorn but i have a battery backup system. Was part of the property when i bought it. Yesterday i list part of my power. Switched on the bypass on My inverter and all was ok. What did i did I bypass my batterries or the grid or did i switch from the top 5 batteries tp tje bottom 5 batterries thanks in advance


Very likely you bypassed ac power aroound the inverter, like its not there anymore. The label should indicate this so there are no mis understandings. If you leave it in bypass, when the utility grid power goes out,  so will yours, instead of going into backup. Your inverter may indicate backup mode, but the output has been opened and the grid line is now the only line to your distribution system.
 
Teresa Duran
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Frank - thanks for that info - so here is what happened. There was power coming from the Grid none of my non-solar neighbors lost power. I only lost part of my power. My friend who is an electrician checked everything out and we were getting power from the grid through PG&E. I have a large residential home all on solar about 3,000 sq ft, I have large panels and about 8 batteries in the battery back up. When he checked the power there was no power coming from the inverter to the panel that manages the kitchen lights, the well and the other areas that were impacted by the outage. We found nothing shorted out, disconnected etc. So finally we put the two bypass switches that were on the inverter to the on position and switched the two that were on to the off position. Do I have a battery problem, an inverter problem or a panel problem. Excuse my ignorance but I am not even sure where to start digging for information -I can read about it and I am pretty good at following instructions. If you would be so kind to suggest where I might begin that would be great.
Teresa
 
frank li
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It sounds like a dead power inverter.  If it is a good one and under warranty, you may be able to repair it in place or onsite with tech support.
 
Teresa Duran
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Frank thanks for the info I will check that out ! I appreciate the guidance. Also, another question - I know that this solar was put in during 2003. The battery back up system was installed then as well. Is there a way that I can check the batteries effectively myself as I was told they are only good for about 10-12 years.
Thanks again in advance
Teresa
 
frank li
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You could conduct a load test. Turn off your house main breaker and pv input breakes(s) and apply a load of a known size, then time how long it takes for the inverter to disconnect. This will be easier if your system has a monitor that displays amps or watt hours out of the battery.

Load testing with an load test instrument is probably best, but if you get good backup time, use it for a season or until it limps.
 
Justin Dorr
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Matt Stern wrote:I have a grid tied rooftop solar system.  It works great, the thing is, if the grid goes down for any reason, my system shuts down automatically.  The said reason being to protect any utility workers from getting zapped by my electricity traveling back through the power grid.  Makes sense to me, but is there any way to safely bypass this "feature?"  IE the grid goes down but we can still use the watts we generate.  I'm open to solutions that include batteries, but curious if there is a way to do it without them.

Matt


Without reading all the replies. Yes it's possible to safely have a grid tied system and switch that system to batteries at your convenience.

All compliant grid tied inverters connect to the panels via plug and socket, typical MC4 connectors. Unplug these and connect to a separate circuit that isn't connected to the grid, problem solved. Typical, keep a spare battery bank and charge via panels when your grid is down. NB. Must physically disconnect the panels, no fancy switch gear.
 
Justin Dorr
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frank li wrote:You could conduct a load test. Turn off your house main breaker and pv input breakes(s) and apply a load of a known size, then time how long it takes for the inverter to disconnect. This will be easier if your system has a monitor that displays amps or watt hours out of the battery.

Load testing with an load test instrument is probably best, but if you get good backup time, use it for a season or until it limps.


Some inverters shut down when they don't like the power from the grid. Over voltages, etc, also shut down an inverter, depends on the model. Really require more data.
 
frank li
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You are right to suspect the battery, it is a possible cause for an inverter that will not power on. The system should have a display or interface for the inverter and possibly the charge control.

You can check voltage at the inverter dc terminals or at the battery main terminals that lead to the inverter or system distribution center.

The battery may have labels that can be used to deduce the battery voltage by wiring arrangement, but the inverter has a required battery voltage.

The inverter will likely not power on if battery voltage is above or below a certain point, so battery voltage nedds to be reasonably close to inverter indication.
 
Teresa Duran
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Thanks - I checked there is voltage coming from the batteries but it seems that there is not voltage from the inverter going to the panel that manages my kitchen lights, well, frig etc. With the bypass turned off, I am getting some power in the home, it looks like minimal power but the normal power I get when the grid goes down and my neighbors have no power and I usually have power due to the battery back up. However, normally on the battery back up I have my Water Well and this time I did not. When I turn on the bypass that was off I do get power to that panel that sends power to the well.  When the bypass that was off is turned on and the other switches are moved from on to off on the inverter I get power. I am thinking 1 of 2 things, either it is the inverter (the system was installed in 2003 and I bought the property with the system) or the batteries are pushing some power but not enough to power it all. I am a true greenhorn/novice so I guess I need to get to doing some more learning about this. I leave out in the country so I might need to call a tech but I am always worried about who I will get cause I am so far out in the backwoods.

I appreciate the guidance from you all.


Thanks
 
frank li
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Teresa Duran wrote:Thanks - I checked there is voltage coming from the batteries / or the batteries are pushing some power but not enough to power it all. I am a true greenhorn/novice so I guess I need to get to doing some more learning about this. I leave out in the country so I might need to call a tech but I am always worried about who I will get cause I am so far out in the backwoods


Thanks


If you call a reputable solar installation company, you will likely be in good hands. Someone who has been around a while is generally doing good business in solar.

I think you will want to have someone look at the inverter and battery for you. Sounds like a good system to have, hope you bring it back online.
 
Teresa Duran
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so here is an update - I was able to get the system back on line and all was fine - after cycling it and restarting everything - however, it runs for sometime and then the inverter shuts down and gives an overload red light.
Suggestions?
 
frank li
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Teresa Duran wrote:so here is an update - I was able to get the system back on line and all was fine - after cycling it and restarting everything - however, it runs for sometime and then the inverter shuts down and gives an overload red light.
Suggestions?


Is there a display of the reason for shutdown?


If not, what is the battery voltage at shutdown?

Sounds most like low voltage disconnect, knowing your prior details in brief.

There should be a system status display or at least a light indication scheme. This is like the dash instrument cluster in a car. It tells you what mode and what condition or loads are pertinent, depending on what you have.

What system make and model is in place there?

What is the battery?

Photos of the display at shutdown would be cool!

Also, your inverter should only come on backup mode during grid outage or disconnect, as main breaker in your service panel or breaker feeding your back-up/grid tie inverters ac input.

1- Note the battery voltage and ac load on the critical loads panel or inverter load center. If the load is not displayed, apply a known load either an appliance, group of appliances or lights that add up to a moderate load for your battery/inverter sizing.

2- Switch the breaker feeding the inverter to Off.

3- Note the load, if indicated and the duration that the system operates and the battery voltage at shutdown.

If there are no local solar service persons, a forklift or floor scrubber machine repair service may be able to load test and inspect your battery system, maybe golf car repairmen?

Assuming the system functioned properly and the power equipment is ok. This is no good though, and the entire system should be inspected by someone familliar with the type.

A good electrician will be able to review the manual and make sure it is wired correctly and operates as intended.
Many are daunted...it can be expensive. If i remember right, you had an electrician inspect it to a degree. A pv tech who is familliar with the type, will be able to make a quick check and determine the issue, battery health and all.

You can learn how to do the same inspection and have operational knowledge by reading the manuals and calmly looking at what you have going on, if you are fearless!

Again, if the wiring is good and the load, moderate, it sounds like lvd short cycling. Either a shallow setting or under capacity battery due to size, maintenance or wear.

Be sure the battery is charging and charging to full and in absorb for long enough. If the battery goes from full to empty to full too quickly, its likely the battery is needing maintenance or is damaged.

Check settings charger(s) settings and amp-hours charged during the cycle if indicated.

Check all the cables, battery and inverter side for bright and tight and or continuity, if this in not known to have been done recently, especially if the problem is new and condition unknown. While checking cables, check individual battery voltages. The system needs to be at rest for a time for this.





 
danielr long
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Thanks for having an interesting forum and this topic! I have a related question. I am looking at installing up to 24 panels of PV and going grid-tied. I was very disappointed to learn that they shut down during outages! I want to be able to run at least a 2hp pump and some low draw controls for irrigation when power is down. I have a generator that can do this short term. What happens if it's a loooong time before power comes back? (OK, let's talk in terms of never for the sake of argument) What would it take to convert a grid-tied system to an off-grid at least strong enough to start and run the pump and a few more amps? Are there things i can do now while building the grid-tied system that will make the switch to off-grid easier? In this doomsday scenario, i don't need power at night. Just a few hours per day running the well would work for me. A different controller and a small battery for intermittent clouds? More? Design considerations up front? Cost of a different controller?
 
David Baillie
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Location: North central Ontario
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Hi Daniel, if you are looking into it now the biggest thing would be to incorporate an inverter that supports grid tied, off grid, generator, and grid supported.  I am very fond of the Outback Radian system myself. http://www.outbackpower.com/outback-products/make-the-power/radian-series-inverter-chargers/item/radian-series-gs8048?category_id=529 Other companies have different flavours of the same thing. Traditional grid tie inverters feed the grid and shut down power during outages.  The Radian will charge batteries and feed the balance into the grid.  Should the batteries not be enough it will supplement with grid power if available or start up a generator.  Building new that's what you would plan for.  The grid is there, not there, there sometimes, you are covered.
Best regards, David Baillie
 
danielr long
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Thank you for that thorough and well constructed answer!
 
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