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Solar at Home

Solar at Home


The trials, tribulations and rewards of going solar
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Should you add batteries to your solar array?

The views expressed are those of the author and are not necessarily those of Scientific American.


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Editor’s Note: Scientific American‘s George Musser will be chronicling his experiences installing solar panels in Solar at Home (formerly 60-Second Solar). Read his introduction here and see all posts here.

Once upon a time, all solar arrays were off-grid. That was the whole point: solar enthusiasts wanted to, or had to, generate their own electricity rather than rely on a utility. They installed banks of batteries to store power for use when the sun went down. Today, with net-metering, we let the grid "store" the power for us. That said, batteries have not gone away entirely.

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How the grid stores power is a fascinating subject in its own right. In essence, the electricity from a home solar panel or wind turbine flows into the transmission lines and reduces the load on power plants. The line voltage changes ever so slightly and the dynamos spin up or down to compensate. If you’re familiar with the basics of electricity, you might enjoy this discussion by physicist and engineer John Denker. For a longer discussion that delves into the history of the grid and the challenges of preventing blackouts, see Massoud Amin and Phil Schewe’s article in our May 2007 issue or Schewe’s book The Grid: A Journey Through the Heart of Our Electrified World.

As more people install solar panels, their power output will eventually overwhelm the grid’s existing mechanisms and utilities will need some kind of energy storage system such as compressed air. But that is a longer-term problem and probably won’t require batteries in individual buildings.

Nonetheless, batteries can still play a role in a home solar system by providing standby power during blackouts. Our street in suburban New Jersey has an inordinate number of blackouts — and whenever we do, we lose our heat. It wouldn’t take long in midwinter for our house to become uninhabitable. You might think that at least we’d get power by day, through the solar array, but no: when the grid shuts down, so does the inverter that injects the array’s power into our household wiring. The panels dangle there uselessly.

Home Power magazine had an excellent discussion of the pros and cons of batteries, including sample cost figures. The main disadvantages are added cost and complexity. Not only do you need to buy batteries and find a place to put them, you need to install an electronic controller to charge and discharge the batteries in an optimal way depending on their chemistry. Physics Today had a great article last year on a DIY solar array which discussed how charge controllers work. I personally find them a fascinating technology, but even my enthusiasm wanes when I think about adding one more thing that could go wrong.

One person responding to my call for stories about solar installations, Ken Klatt of Mequon, Wisc., told me of his struggles with a DIY grid-tied system with battery backup. Here’s what he had to say (somewhat edited by me):

The system produces 380 watts with a planned maximum of 1,000 watts. Batteries store power during non-sun times (a challenge in Wisconsin). The entire system is off-grid (when it can be). It is monitored by a special low-power computer (Shiva Plug) that switches to grid-power when power levels drop below 40 percent available. During the months from June to September, the computer runs off-grid without major issues (there are a few planned outages where power is switched to grid power). The site data is available online.

I started out in summer 2005 with the "What can I do for $500" — and have now spent approximately $5K. The only subsidies I took advantage of were Federal tax refunds for solar power generation.

I get frustrated with websites that tout "green". You see a solar-panel mount with a clear view of the south, no neighbors complaining, no trees, etc., blocking the sun. I have had enough problems to fill volumes — neighbors, tree shading, weather, mice chewing wires, interconnections, panel locations, charge controller communications, communication protocols — the list seems endless, not to mention the expenses. I’m looking at greater than a 10-year payback period.

The issues fall into three groups, electrical, weather, and social (people):

  • I live in a suburb, and zoning laws are unclear or unstated. Positioning the panels was a major headache; there were no perfect locations available that are not shaded, etc.
  • The charge controller I bought was defective and had to be sent back to the factory.
  • The second year, the inverter failed and had to replaced.
  • I have had other hardware issues such as loose connections in the battery array, in the solar-panel terminal, and in the wire nuts (because the electrical wire supplied was not tinned).
  • The next-door neighbor complained about the look of the solar panels and made numerous requests to remove them. Last month, I relented and mounted the panels on the ground rather than the roof.
  • The entire month of October 2009 was cloudy except for two or three days and my batteries may have been damaged as a result.
  • The first winter, a storm layered the panels with ice and snow. It took three weeks to clear, during which time I had no safe access to the roof. When I was able to climb up and inspect the array, I found wind damage to the panel mounts. Similar problems have occurred in subsequent winters.
  • I created my own software drivers for the Solar Charge controller, running under Linux. I had trouble with the communications protocols and eventually had to install third-party hardware to resolve the issue.

Anyone who has undertaken any sort of DIY project will empathize. Hang in there, Ken. Most people have it easier, since they hire installers — though, of course, contractors have their own issues. Solar is still an emerging technology and we can expect hiccups. Over time, the early adopters will pave the way for the rest of us.

Ken Klatt’s solar panels in the challenging winter months, courtesy of Ken Klatt

 





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  1. 1. candide 3:36 pm 12/11/2009

    Batteries, aka electrical storage devices, are one area of technology that has not had the huge leaps of other areas.

    Once newer storage technologies are developed it will make ALL other forms of renewable energy even better than they would be by themselves.

    Link to this
  2. 2. d5fox1 5:29 pm 12/11/2009

    We are currently at a preschool level when it comes to harnassing and storing solar energy. Nasa with an open checkbook has developed cutting edge technology that is a fantasy to obtain or use at a single home application level. Going green is everones concern with the added joy of being expensive and in its infancy on tecniques.

    Link to this
  3. 3. Sentient Meat 12:40 pm 12/12/2009

    Terrific, informative article. Shame on Ken Klatt’s neighbors for criticizing his rooftop solar panels.

    Link to this
  4. 4. DonPaul 1:31 pm 12/12/2009

    I wonder how massive the transmission lines would have to be to power the dark side of the earth from the illuminated side? The sun is always shining somewhere…

    Link to this
  5. 5. lakota2012 1:40 pm 12/12/2009

    "Solar is still an emerging technology and we can expect hiccups. Over time, the early adopters will pave the way for the rest of us."
    ————–

    Yep, but the forward progress over the past 5 years has been amazing, and only confirms through hindsight, where we could actually have been if the first solar revolution of the 70′s had continued unabated instead of offshoring the technology to Europe and Japan.

    I live off-grid with a wind/solar hybrid system, so I must deal with the archaic technology of deep-cycle batteries, the only part of my system still stuck in the "middle-ages." Solar controllers and inverters are state-of-the-art today, but I’m still waiting for Robin at MidNite Solar to release his Classic MPPT Charge Controller, promised to "stand the renewable energy industry on it’s ear." http://www.midnitesolar.com/

    I just don’t understand why so many fossil fuel syccophants bash clean and green RENEWABLE ENERGY every chance they get, and prove they have NO VISION for the future!

    Link to this
  6. 6. Michael Hanlon 7:28 pm 12/12/2009

    There is an energy storage type that has gone out of favor in the last 3/4 century since the introduction of the dry cell. Prior to that invention, high power was stored mechanically via a flywheel. They were massive but they worked well enough that the generators were run off them and the engines(coal/steam) were just used to boost flywheel rpm’s as necessary. Maybe with today’s better bearings, better lubricants and more efficient electric motors, the flywheel can make a comeback!

    Link to this
  7. 7. fbcooper 9:38 pm 12/12/2009

    I believe if you need 1-2 day backup for an on-grid solar electric, consider getting a gas powered generator. There are numerous types of generators available. They can be installed by most professional electricians. The idea is that, in an emergency, you can run some of your household needs (freezer, frig, fans for house heating). You need regular gas (which should be available locally), and some switch to cutoff the utility power completely from your house. Then you can run the generator and your home may still get power from the solar inverters as they ‘sync’ with the generated power ..

    Link to this
  8. 8. Michael Hanlon 2:03 am 12/13/2009

    Yes, let’s not limit ourselves to only storing the energy as electrons. There are many other ways of power storage Potential Energy by its very name is stored power. Can we use our electrons from the PVs to lift water to heights efficiently? Are there other weights which can store the power and retreive it later by simply turning on the ‘gravity’? I’ve already mentioned the mechanical method of employing a flywheel. Are there other more modern ways of mechanical storage? Another avenue of investigation of energy storage is through temperature difference. Make some cold, make some hot and when you want the juice, stir them together. Pneumatically we can store energies through pressure of gases stored in strong vessels.When the pressure is released you get an added benefit of temperature drop.
    Well, maybe batteries will turn out to be a curiocity of the 20th Century!

    Link to this
  9. 9. jack.123 5:45 pm 12/14/2009

    I agree,compressed air is the cheapest,cleanest,and easiest way to go,and will be untill small superconducting batterys are developed.

    Link to this
  10. 10. jerryd 8:23 pm 12/14/2009

    While batteries can be charged by RE, better is charging them at night from the grid cheaply then selling the power back in the day at higher prices.

    Lead batteries cost about $100/kwhr and last 8-10 yrs so about $10-12/kwhr/yr. Generally you buy power at the 50% rate and sell at 2-300% rate they easily pay for themselves and still have back up power.

    Since you already have the inverter there is no cost there.

    Next most in the future will be in EV’s, PHEV’s charged at night and used by the utility in the day to supply peak power. This is worth so much they could charge the EV’s for free and still save money.

    Link to this
  11. 11. Jokunen 11:15 pm 12/14/2009

    Why don’t people install solar thermal systems and store their energy as heat in the warm water tank? Those panels are cheaper than EVs and have better efficiency. And you spare the energy used to make hot water and heating. Heat can also be used to generate cold, as in adsorbtion fridge, but with lesser efficiency. The circulating pump can be used with small PV panel energy and/or from battery, even during black outs.

    Link to this
  12. 12. Gary Wayne Cook 1:26 am 02/7/2010

    Lead acid batteries for storing RE are dinosaurs that should be extinct. The industry has made great advances in technology for PV efficiency and true sine wave solid state inverters. Yet the failure to improve storage is irresponsible. I am researching storing energy in capacitors. Capacitors can be charged instantly during non peak or full sun periods, and last much longer than any of the other RE components. The issue is that they may take up to 25 times the space as lead acid batteries. So if space is not an issue, then they may be viable. I installed a battery less grid tied 3 KW PV system with Enphase micro inverters to become net zero (annually my home produces all of the energy that it uses). The grid is my storage. However, I want to add storage such that I dont use grid power during peak load periods. I already have designed the battery bank and bimodal inverter to do just that. I installed my critical loads sub panel when the PV system was installed. My heat and hot water heater are on timers or programmable thermostats such that they dont come on during peak load periods. So the sub panel carries only those loads necessary for lighting, bath fans, refrigerator, smoke detectors, and cooking during peak load periods.

    There are ultra capacitors and super capacitors out there used for utility or military purposes. Getting them the right size is the issue. I can wire those I have found on the market in a combination of series and parallel connections to get exactly what I need. However, my handy work would leave me with a storage device that isnt UL listed as required by code, even though the individual components are UL listed. So I would like to see the industry start producing PV sized capacitors for storage. Transformers can step up or down the power as needed, and can be switched off when the storage is not in use.

    Link to this
  13. 13. Gary Wayne Cook 1:32 am 02/7/2010

    Lead acid batteries for storing RE are dinosaurs that should be extinct. The industry has made great advances in technology for PV efficiency and true sine wave solid state inverters. Yet the failure to improve storage is irresponsible. I am researching storing energy in capacitors. Capacitors can be charged instantly during non peak or full sun periods, and last much longer than any of the other RE components. The issue is that they may take up to 25 times the space as lead acid batteries. So if space is not an issue, then they may be viable. I installed a battery less grid tied 3 KW PV system with Enphase micro inverters to become net zero (annually my home produces all of the energy that it uses). The grid is my storage. However, I want to add storage such that I don’t use grid power during peak load periods. I already have designed the battery bank and bimodal inverter to do just that. I installed my critical loads sub panel when the PV system was installed. My heat and hot water heater are on timers or programmable thermostats such that they don’t come on during peak load periods. So the sub panel carries only those loads necessary for lighting, bath fans, refrigerator, smoke detectors, and cooking during peak load periods.

    There are ultra capacitors and super capacitors out there used for utility or military purposes. Getting them the right size is the issue. I can wire those I have found on the market in a combination of series and parallel connections to get exactly what I need. However, my handy work would leave me with a storage device that isn’t UL listed as required by code, even though the individual components are UL listed. So I would like to see the industry start producing PV sized capacitors for storage. Transformers can step up or down the power as needed, and can be switched off when the storage is not in use.

    Link to this

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