Grid-Tie Solar + Power Outage Backup!

April 9th, 2013 by Nicholas Brown

Depending on the reliability of the electricity supply in your location, you may want a backup generator. They are usually diesel or gasoline fueled, but they can very well be fueled using sunshine.

A diagram of the EnergyBridge grid-tie solar system. Image Credit: EnergyBridge Website.

The convenience of backup generators is priceless, because when there is a power outage, you will normally be bitten up by mosquitoes, sweat like a pig, and wait in silence (except for that high-pitched mosquito buzzing) without television or internet access until the power is restored.

However, I have heard of one common issue with these generators that doesn’t really change much — they sometimes can’t even start when needed. I have experienced it a few times myself.

This is because the fuel deteriorates, the starter battery dies, and mechanical parts can stiffen as well, preventing them from starting.

So, how about a grid-tie solar power system that doubles as a backup generator, minus the smoke, vibration, and noise caused by a conventional generator?

This is possible using a combination of a switch, solar panels, and batteries, and the EnergyBridge solar generator is an example of just this. The EnergyBridge is currently on Kickstarter, trying to raise money for Underwriters Laboratory (UL) safety testing to hopefully receive a UL 1741 certification.

Wait… don’t batteries fail when sitting for a long time just as do generators?

Yes, but because of the way this system is setup, the solar panels in an EnergyBridge setup keep the batteries charged, so they can avoid this issue.

The issue is caused by battery self-discharge. Batteries gradually lose their charge over a period ranging from one month to one year, depending on the type of battery, and they will deteriorate to the point where they are unrecoverable if left sitting long enough. But you don’t have to remember to “start” a solar system, so this issue completely vanishes if you choose such a setup.

From the EnergyBridge website:

Our system is less expensive to buy than traditional battery backup and is more powerful than similar sized generators. When power finally comes back on the EnergyBridge continues to work, charging its batteries and even selling the excess power back to the power company.

The EnergyBridge is a hybrid inverter for photovoltaic PV installations where AC is present (Grid-tie) or can be used to provide backup power wherever AC is needed (Off-grid). Use our inverter with solar panels, batteries, fuel-cell, wind or even hydro. Our simple installation allows any user to connect solar and solar backup to their home or business.

Sound very useful. I’m sure many Superstorm Sandy victims would have valued having one of these.

To pledge some money for this project, head on over to Kickstarter.

Follow me on Twitter: @Kompulsa.

Keep up to date with all the hottest cleantech news by subscribing to our (free) cleantech newsletter, or keep an eye on sector-specific news by getting our (also free) solar energy newsletter, electric vehicle newsletter, or wind energy newsletter.

Tags: Athena Energy, backup generators, EnergyBridge, generators, grid-tie solar, grid-tie solar with battery backup, kickstarter, Kickstarter energy projects, solar backup, solar backup generator, solar for power outages, Solar with battery backup

About the Author

Nicholas Brown writes on CleanTechnica, Gas2, Kleef&Co, and Green Building Elements. He has a keen interest in physics-intensive topics such as electricity generation, refrigeration and air conditioning technology, energy storage, and geography. His website is: Kompulsa.com.

jenny bakker

Hi Dimos,
This information may be a little out of date. Batteries for solar have evolved to expect a 15 year lifespan. A solar inverter that does this is already developed and grid compliant in most European countries including the UK. It’s called the PowerRouter.
take a look!
Linda Stu

If you have a solar electric system, now you can use an SMA inverter to draw power directly from you solar system during the day. As you mentioned in your article, before solar inverters always shut down after a power blackout in order to protect the people working on the gird. Now with 3 of the new (avail summer 2013) SMA transformerless inverters (http://webosolar.com/store/en/79-string-inverters), you can have a dedicated outlet powered directly from your grid-tie solar system during the day even when the grid is down.
Bob_Wallace

China’s BYD (who also makes EVs) is entering the home storage market in Australia.

http://reneweconomy.com.au/2013/chinas-byd-enters-australian-home-energy-storage-market-45286

NRG is introducing battery storage in the US.

http://www.renewableenergyworld.com/rea/blog/post/2013/04/nrg-introducing-solar-with-battery-storage-for-homeowners#readercomments

These are a couple of pretty large companies getting into the business.
ronwint

This is not a “revolutionary new way” to bring solar power and backup power all together into one box as this video claims. in 1999 we sold dozens of Trace SW battery backup grid tie inverters that qualified for the California Buydown Rebate Program that did exactly what this proposed system does all in a single box and there currently exists products from several manufacturers that does the same thing in a single box. Good luck getting regulatory approval from U.L. with a grid tie inverter that uses a male AC plug as an output connection to the grid. I don’t see that happening. There’s already a bunch of cheap Chinese made illegal grid tie inverters in use that are going to get their owners in a lot of legal hot water when they get caught by the utilities that use male A.C. plugs as a source to connect to the grid. Good Luck.
- AthenaEnergy
  
  We already have one of our inverter designs (that also plugs into the wall) UL listed. We designed the system such that the male AC plug will never in any situation be “hot” or live. That would be a dangerous situation which we have taken into account. Thank you for your comments!
SecularAnimist

Related to the discussion between Bob Wallace and Jason:

I’m planning to install PV on my roof this year so I’ve been looking at proposals from both the national companies, and local independent installers. Based on what they all tell me, with a typical grid-tied PV system without battery backup, when the grid power goes down, the whole PV system is shut down and you can get NO electricity from it, even in full daylight.

So I could have a 48-panel 12 KW system on my roof, sitting up there in full sun, generating maximum rated output, and if the utility power is down for whatever reason, I get NO power from the solar panels. But with the addition of even the minimum battery backup and the associated electronics to disconnect from the grid and switch to batteries during grid outages, I would get ALL of that power from the solar panels during the day.

That’s what has me contemplating the addition of battery backup. I don’t really care so much whether there’s enough battery capacity to last through the night — what I really want is the ability to use the solar power that the panels are generating during the day. And as I understand it, with today’s standard grid-tied PV systems, the ONLY way to do that is to add battery backup.

In which case, an appliance like the “EnergyBridge”, which claims to make it easier and cheaper to add battery backup, looks very attractive.

I do have a question, though, in that the description only talks about using it with fairly small PV systems (e.g. 4 panels). Would it work with larger systems in the multi-KW range?
- Bob_Wallace
  
  I think what you want is a combination grid-tie inverter/charger. They are available up to at least 8k watts.
  
  It should be possible to use two inverters and split your system if you’re going to install more than 8k (or perhaps someone builds something larger).
  
  Here’s a page that should help you get started.
  
  http://www.sunelec.com/inverters-chargers-gridtie-inverterchargers-c-6_38.html
  
  You might want to go to the Outback and Xantrax sites and see what they have to say. Also check Home Power Magazine. They offer a ton of information on solar, etc.
  
  http://www.homepower.com/
- anderlan
  
  The typical setup right now is to have a grid-tie inverter for each panel. I believe the grid-tie function in these can be disabled. Talk to your vendor.
  
  If you can disable all the micro-inverters’ grid-tie functionality, then I can’t believe there doesn’t exist a device that you can attach to your box–on the grid side of the box–that will cut off the entire house when the grid fails. This way the array can still fill the house. However, the flaky power levels during, say, a cloud, will mess with all of your devices.
  
  So, I guess my stab at your query is: even though I know grid-tie at the customer/grid interface level is probably quite possible, some reasonable amount of storage and control hardware might be needed to smooth out the ride and have your house in either an ‘on’ or ‘off’ state depending on insolation and state of charge (and the device load).
- Jason
  
  As with any product, there are limitations. The EnergyBridge solar input has a 900W constant power handling capability. I think it would be a good idea to tap off 800W-900W of panel from your roof and use that as your solar input to EnergyBridge. That way, you will have your backup system available and achieve maximum potential from your panel investment.
  - Bob_Wallace
    
    Since most people are going to install a system larger than 0.9kW they are still going to need an inverter to handle the other 2kW+ output to the grid. And if the grid goes down they’d be able to access only 0.9kW of their array. That’s not enough to power most houses.
    
    Seems to me that you’ve designed a product that comes up short.
    
    Like Ron says below, there are inverters which will handle the entire array and allow battery storage on a large scale if that’s what people want.
Marlon Menezes

I have some questions. I have a 6.5KW grid tied system, with no battery back up. One problem with the current set up is that if the grid goes down, my panels become useless as my inverters are powered by the grid. If the addition of this could help me keep my inverters running, it would be a tremendous value added. Typically, one needs the most power on the hottest and sunniest days – just when the panels are also producing the most. To me, whether there is sufficient storage capacity to power the home though the night is nice, but not an ultimate necessity. It is the days that matter. The big issue with powering the inverters is that they require high quality AC waveforms. That is why, one can’t power these inverters with a small generator.
- AthenaEnergy
  
  Many people that already have grid tied systems like yours face the same frustration. Once the power goes out, the PV system that you invested so much in is useless. That is why the EnergyBridge is unique. It acts as both grid-tie and backup. I would suggest partitioning your PV array and using 900 Watts of it to use with the EnergyBridge as a backup power system. That way you could actually use your investment when the power goes out.
http://www.facebook.com/rhodomel.meads Rhodomel Meads

Very important questions remain unanswered:

1. What is the roundtrip overall efficiency? That is, power output from the device divided by the power used by the device per deep cycle?

2. Being constantly connected in a bridge tie, what is the vampiric load of the device? How much energy does it use per day while staying bridge connected?

3. How many deep cycles can the battery system last?

4. What is the battery capacity after 10, 100, 500 and 1,000 deep charging cycles?
- Jason
  
  In response to questions 1, 3, and 4, I think there needs to be some clarification. The EnergyBridge does not consume AC power to export it later. It simply exports solar power to the grid when grid-tied. The energy stored in the batteries is only accessed when the grid goes down.
  
  2. it uses 2.54W continuously to stay grid connected.
  
  If you are still interested in the batteries, we planning on using the Concorde Sun Xtender PVX-490T, 12V, 49AH AGM Battery. Here is a link for the data sheet: http://www.altestore.com/mmsolar/Others/Sun_Xtender_Battery_Technical_Manual.pdf
  
  I believe the information you are looking for is on the last page (Page 40)
  - http://www.facebook.com/rhodomel.meads Rhodomel Meads
    
    Thanks!
jburt56

I like part “bitten up by mosquitoes” part!!! There’s Zen there.
- http://zacharyshahan.com/ Zachary Shahan
JustSaying

The drawback of a gas generator is:
Got to keep the gas free: Use stabill and empty it every ~6months
Got rmember to run it every couple of months so it will start when needed.
Need to keep enough gas to keep it going. If only your house lose power then drive down the street. But if big area, you have to drive a long way to get gas.
There is no free lunch, for true many day energy backup.
- JustSaying
  
  If you assume that the NG pipe to your house will have presure there are some systems to run on those that, “maintain” themselves.
- Bob_Wallace
  
  Well, that’s a bit extreme. My gen often sits six months without being started and I’ve never added Stabil.
  
  You are right that there are downsides to a generator. Noise, smell, having to fuel, having to turn on/off, oil changes, …. But the storage system at the top of the page is not a substitute.
- http://zacharyshahan.com/ Zachary Shahan
  
  I’m gonna piggy-back on this one.
  
  We’ve got someone from WV on our team who has had to go without power for many days a few times in the past year or so. His family was in a HUGE pickle. And they had to spend a fortune driving very long distances to get fuel for their generator. Not only a pain, but very expensive and nearly impossible at times.
  
  While this system may not be for everyone, it certainly has some benefits that crush those of a conventional backup generator.
  - http://zacharyshahan.com/ Zachary Shahan
    
    btw, apparently, despite being a very conservative area, there was a lot of talk from local residences in those instances about “going solar.”
Bob_Wallace

I highly doubt this makes financial sense.

Portable generators are cheap. Few people need to run them more than a few hours a year.

Yes, battery storage is easier on the climate, but it’s not financially there yet.
- Jason
  
  The reason why this system is unique is that it is grid-tied when the grid is available, selling power back to the grid and reducing your energy bill. When the power goes out, the unit will automatically go into off-grid mode and supply the critical loads plugged into it. While off-grid your panels will be keeping your batteries charged to run all of your critical loads plugged into the EnergyBridge. Your average solar panel system doesn’t have any backup capability. Wouldn’t it make sense to be able to tap into that energy when you need it the most?
  
  Yes, portable generators are cheap. But they require gas and maintenance. While the price of your generator is going up over time, the EnergyBridge cost goes down over time, eventually making you money in the long run.
  - Bob_Wallace
    
    The grid won’t pay much for the solar you store during the day and sell back during off-peak hours. Off-peak wholesale is very cheap due to lower demand and a significant amount of wind.
    
    You can’t generate solar for less than 12 cents or so and it is going to cost something (probably a significant amount) to store it. The wholesale market accesses wind at 5 cents and less and NG at 5 cents.
    
    You can’t generate solar and store it cheaper than buying electricity from the grid. (In general, there may be a tiny few exemptions. Hawaii comes to mind.)
    
    The real role is to keep your lights on when the grid goes down. For most people that’s not often. And in the event of a major grid-killing event like an ice storm or hurricane there’s no way this unit will keep your lights (and refrigerator, etc.) on very long.
    - Jason
      
      The idea isn’t to store solar energy and sell it back later. Once the batteries have been maintained, they are transparent to the system. This gives you a standard grid-tie solar system and saves you money on your energy bill. When the power goes out (and it will), you will have 2400 watt-hours of energy at your disposal. With the 900W solar array, you will fully charge your batteries and keep your loads running during the day (based on 5 hours of sunlight and a 120W constant load). We used the 120W because it is the average power our full size office fridge uses. With the batteries to get you through the night and solar to charge your batteries during the day, your fridge can run for a very long time when the power is down.
      - Bob_Wallace
        
        Well, wonder why someone wrote “selling power back to the grid” if the idea isn’t to store energy and sell it back later?
        
        Confusing, isn’t it?
        
        —
        
        We don’t have a price for this puppy. We can’t determine the cost of storing electricity one might make so we can’t determine if it would be cheaper than net metering (almost certainly not) or avoiding grid purchases (probably not).
        
        —
        
        2400 watt-hours, 2.4 kWh, won’t take most households through the night. This thing is not backup for when the grid does down in a storm.
      - Jason
        
        “Selling power back to the grid” is a commonly used phrase when referring to grid-tie solar. We wanted to make a similar comparison when referring to EnergyBridge because it is a grid-tie unit as well as a backup power source. The storage component is simply for backup power. Hopefully this clarifies that for everyone reading the article.
        
        —
        
        The price is $2150 for the 2.4kWh package via Kickstarter Feel free to click on the links above for more information.
        
        —
        
        2.4kWh is enough to get your critical loads through the night. You can’t use everything, but your food won’t go bad, you can use some lighting and keep your phone, computer, modem and router on. It might not be everything, but it’s a lot when you have nothing.
      - Bob_Wallace
        
        Ah, so this is your baby?
        
        You could cut back on your electricity use when the Sun goes down. Turn off the TV and electronic games. And the AC. That might get you to the next day but then if you don’t have sunshine you’re screwed.
        
        It’s not a way to make yourself electricity self sufficient. There’s just not enough storage.
        
        There’s no way to survive a second day without sunshine.
        
        $500 for a generator. Something more for fuel. A generator can easily give one 2.4kW per hour while using about a quart of gas per hour.
        
        $2,150 for 2.4kWh. How many cycles are guaranteed? How deeply can you cycle the batteries without damage?
        
        I’m betting the numbers just don’t pencil out.
      - anderlan
        
        Bob, without some sort of buffering, panels are useless, even if you could disable the grid cutoff function in their inverters, because the intermittent power could cream your devices, however few you have connected. This is a way to get some functionality out of your panels when the sun is on and the power is off. If some people feel they need this, let them blaze the trail. Finally, there are costs to fuel that individuals can take into account even if the market and our good nation does not.
      - Bob_Wallace
        
        I agree. If you live in a place where the grid frequently goes down then you might want to add some battery backup. The major inverter companies make inverter/charger combos that will do that.
    - anderlan
      
      Well, you know what, it ought to be competitive, mandatorily, because the other stuff is storing up a world of pain for us.
      
      But anyway, there are plenty of on-peak times when the sun isn’t shining and with a battery you’ll be the only guy selling power back into the grid at full retail FiT price. Solar production peaks at midday and declines, while consumption peak lasts all the way into the early evening.
      - Bob_Wallace
        
        I’m betting that the utility is going to have access to cheaper storage than will end users.
        
        The three most likely options I see right now are pump-up hydro, flow batteries, and Ambri’s liquid metal battery. All of those should store power for less money than a end-user system battery.
        
        The utility can take your surplus solar, store it for the afternoon peak, and give you back cheap wind at night. And then they can use their mass storage system to move nighttime wind to the morning peak.
- Ken Linder
  
  Portable generators also shove out pollution. Most of them are diesel, but even the gasoline ones do the same thing. Ever live right next to a major road with a lot of big trucks on it all day? I grew up next to one (about 25 feet form my front door there was bumper to bumper grid lock of diesel tuck engines). . Breathing is an issue.
  
  Image a city of 4 million people with about 500,00 to 700, 000 houses surrounding it. In the solar future you describe, all of those houses would be churning out pollution. Imagine every house in your area with a car (more often a diesel truck) running in the driveway all winter 24/7. Imagine every summer night (when you want to open your windows) that all those generators are running tto provide night time air-conditioning
  - Bob_Wallace
    
    I think you missed the point.
    
    It does not makes financial sense to add storage in order to cover the few hours a year that one might be without electricity. Financial sense.
    
    The discussion was not about running a house on a generator “all winter 24/7″.
http://www.facebook.com/rhodomel.meads Rhodomel Meads

Would be important to know what the roundtrip efficiency is. Also if it would be economically viable to sell high during peak demand to the grid and recharge at low rates, even after accounting for efficiency losses.
- Otis11
  
  My guess is that it’s economical to buy low, sell high, but it’s an energy storage system for backup power when the grid fails. It’s not meant to pay for itself doing that. (But it could reduce the overall cost of backup)
  
  But if you buy low, sell high, it may not have the power when you need it (aka a power outage), losing it’s effectiveness as a backup solution.
  - Adam Grant
    
    As the years pass batteries and other components will become cheaper. I’m hoping for a holistic control box that will:
    
    – Store a couple of days’ worth of power
    – Accept power from solar panels and small windmills
    – Sell power to the grid when that’s profitable and buy when cheap to maintain a minimum backup store
    – Exercise the batteries as required to maintain their performance and alert owner when replacement is required
    – Charge or sell the energy in a connected car’s batteries as appropriate
    – Pump energy between hot water tanks, passive solar panels, hot tub, swimming pool and a geothermal ground loop (including storing heat in the ground during the summer for use in the winter)
    – Respond to requests and price signals from a neighbourhood or central smart grid.
    – Interlink directly with neighbours’ systems, buying or selling power at prices undercutting the grid, enabling self-organizing power collectives.
    – Present a web interface for (strongly-authenticated) control and monitoring from anywhere.
    
    With such a box, even a small property could support an energy-affluent lifestyle while using the grid as a backup of last resort.
    - Bob_Wallace
      
      I expect there will be economies of scale which will place the storage at the neighborhood/community level rather than a very large number of small units in individual buildings.
      
      Small windmills are unlikely to ever play a role in energy production except at remote areas which have no grid access. In the case of wind, small is not beautiful.
      - Otis11
        
        IDK, once the price of batteries falls, I can see every house being an independent entity that is only tied to the grid for periods of excessive demand/abnormally low supply or abnormally low demand/high supply.
        
        And about the windmills – in most cases I would say you are correct, but there are a substantial number of cases where small scale wind might work. For one, I know my brother’s house has a great roof for solar, but if they were to drive 2 EVs for their normal commute, solar would not be enough unless maybe they covered the barn. But for those who don’t have a barn to cover, such as their neighbors, they could easily put a small scale turbine in the back yard. And neither of these houses are anywhere near remote… they’re walking distance from the city limit of a top 10 largest US city.
      - Bob_Wallace
        
        Obviously we’re all guessing about the future.
        
        What I’m seeing is that the least expensive battery storage is likely to be something like flow batteries or Ambri’s liquid metal batteries. Those aren’t likely to work small scale, but you should be able to stack up ‘shipping containers’ full of them on cheap real estate.
        
        I can’t see a ‘household’ battery that would be cheaper than a large scale utility battery.
        
        —
        
        A hundred dollars invested in a small wind turbine will produce far less electricity than a hundred dollars invested in a 80 meter high 5MW monster with enormous blades. Sitting up high where the wind blows hard and steady.
        
        Solar panels are different. A hundred dollars worth of panels on a house produces the same amount of electricity as a hundred dollars worth of panels installed in a very large solar farm (assuming equal insolation).
        
        Your brother isn’t likely to charge his EVs off his own solar panels. Most folks charge at night when their cars are parked for a long time. The best solution for him is probably to cover his barn with panels, ship the surplus power to the grid and take back (cheap wind) power at night. Storing in a separate battery bank for nighttime charging adds a lot more expense and inefficiencies.
        
        (Have you calculated the area needed for that many solar panels? When I have for a single EV it didn’t take a lot of my roof space.)
      - Otis11
        
        On the batteries – agreed, it really depends on what technology the future brings.
        
        On the wind – Yes, but it is fairly easy to throw $100 into a small turbine to put in the back yard one afternoon, it’s exponentially more work to get a share of a large wind turbine. When you factor in the cost of your time, I don’t know that they’re significantly different… But yes – solar will likely always be cheaper on small scale.
        
        As for charging EVs – Yeah, didn’t think about the time of charging. But for the EVs, assuming 4,000 Wh/day/m^2 in his area at 10% efficiency and the 18KWH battery of, say, a focus electric, that’s
        
        18/(4*0.1) = 45 m^2 per car or 90 m^2 total or 1,000 sq feet of roof top just for the cars. That quite a fair chunk IMO…
      - Bob_Wallace
        
        10% efficiency is kind of low.
      - Otis11
        
        Record setting efficiency is 21%… Looking it up now 15% is average, so 60 m^2 or ~670 sq feet. Better, but still not trivial.
        
        If it were my house though, I’d forget about the math and just cover the whole thing with panels and sell the rest back to the grid, but that’s just me.
      - Ken Linder
        
        You can;t do that becasue your local piece of the grid can only carry so much power, or it will fail. To go really far into independent on-grid generation we are going to need computerized cooperative power feed-ins where each persons feed in can be controled based on teh maximum grid capacity.
      - Nesster
        
        Verticle axis turbines are the exception here and can definitely play a role in certain locations
      - Bob_Wallace
        
        Sure. If one isn’t concerned about getting the most electricity for their dollar.
      - Nesster
        
        Yes you are right. Currently that technology is still very immature and expensive compared to traditional turbines. I totally agree with you around storage for renewables being the most economical at a community level most likely with one of the multiple new battery technologies you have mentioned. I also have to agree with the many analysts out there that see the continued drop in both battery and solar prices quickly making feasible the ability to take yourself off-grid for cheaper than buying power from utility. This reality is going to quickly (5-10 years) force utilities to implement alternative solutions like community level grid storage and generation,etc in order to build in the resilience in the grid people are looking for in order to keep people on the grid. This is also what we all should want in order to build a resilient and adaptable power generation infrastructure in the most cost effective and resource effective manner.
      - Bob_Wallace
        
        Look, engineers have been working with verticals for over 30 years. Over 200 very large verticals were installed over the years and none produced enough electricity to keep them in use.
        
        China launched a big VAWT program a few years back and abandoned it.
        
        Numerous people have shown up with “new, exciting” VAWT designs and, as of today, none have produced performance data that shows that they work well enough to be usable.
        
        Now, seems to me that we should curb our enthusiasm about VAWTs until one is evaluated by a reliable independent lab and found worthy.
        
        Batteries, solar panels, inverters, etc. There’s data on them that show them to be sorth the investment.
    - Otis11
      
      That’s actually not nearly as difficult as you may think. Sketching out the hardware needed, the actual electronics of that box could be made for about $150-200 by my estimates. The reason it doesn’t exist is that the engineering costs would be substantial. Lower than most projects, but with the high cost of batteries necessary for this device the market would be incredibly small, meaning less units to divide the engineering costs over.
      
      Also, licencing and certification for this would be prohibitive. I wouldn’t even know where to start from that perspective.
      
      Overall, it comes down to a battery cost problem. We don’t have it because it’s not economical to buy batteries solely for the purpose of grid smoothing in all but the most extreme circumstances, even for large utility companies. Once it is, expect something to do all of this on the market rather quickly.