Clean Power

Published on June 15th, 2012 | by Zachary Shahan


Home Solar Power Storage — Another Option

June 15th, 2012 by  

In addition to the home storage option recently announced by Panasonic, below is another story about a some storage option that could greatly benefit those with cheap solar power on their rooftops in Germany (and some other locations). This is a full repost from the awesome site Renewables International:

At the ZSW's solar test field in Widderstall, researchers conducted long-term tests on the Sol-Ion storage system. Photo: ZSW

Researchers in a Franco-German project have come up with a power storage system that considerably increases direct consumption from roof arrays. Such applications are becoming increasingly important in countries like Germany, which has implemented a kind of real-time net-metering called “own consumption.”

As a part of the Franco-German Sol-Ion research project, scientists at Baden-Württemberg’s Center for Solar Energy and Hydrogen Research (ZSW) in Stuttgart have come up with a new storage system for solar power. In a test building, they were able to increase “own consumption” – solar power used directly within the household without being exported to the grid – by 26%. The ZSW says the amount of energy stored in the new system covers the average power demand in a single-family home of four people in the evening. In other words, the system turns fluctuating, intermittent solar power into a source of energy that can be consumed as need be.

The Sol-Ion storage system is about the size of a normal household freezer. It contains the power inverters needed for the solar array as well as a battery charge rectifier, both of which have a nominal output of five kilowatts. The system also contains electronics for device controls, which the researchers optimized. They then collected data during various long-term tests over six months. Lithium-ion batteries with a useful storage capacity of 6 kilowatt-hours are the centerpiece of the system.

In the long-term tests, the researchers demonstrated that the battery’s capacity was utilized to a great extent. Power came from a 5.1 kilowatt array on a carport. “Even from February to mid April 2012, the battery was charged with four kilowatt-hours of solar energy on the average, and it was often even full,” says Michael Powalla, head of photovoltaics at ZSW. “We look forward to seeing the results in the summer. When the sun shines for a long time, the energy stored can suffice from the late evening until sunrise,” Powalla says.

Such technology has moved into focus particularly since the current governing coalition announced that it will only be offering feed-in tariffs for 80% of the solar power produced. The remainder is to be consumed directly. Rough calculations show that investments in PV rooftop arrays pay for themselves for homeowners under this policy regardless of the returns from feed-in tariffs. After all, the feed-in tariff of 19.5 cents for a kilowatt-hour of solar power is much lower than the retail rate in Germany, which ranges between 23 and 25 cents. And the lower feed-in tariffs drop, the more “own consumption” pays for itself. At the same time, the cost to society would be lower if only feed-in tariffs were offered; essentially, the “own consumption” policy pays homeowners a bonus to invest in storage systems and tailor their consumption to their own power production.

But up to now, power storage systems have been the main obstacle because they remain expensive. The bonus paid for “own consumption” does not currently suffice to pay for battery systems. If this problem is not solved in the next few years, the policy of “own consumption” might not allow Germans to install more photovoltaics then without the policy. “At present, the average household can only consume around 30% of its solar power directly without some kind of storage system,” estimates Powalla – and that level is considerably greater than the 20% currently required by law. But the law could change and require more direct consumption.

The only way that consumers can respond without storage is to have some appliances – such as washing machines and refrigerators – run mainly when the sun is shining, but there are no such appliances on the market at the moment. For the time being, the only way to increase direct consumption is to store as much solar power as possible in the afternoon for consumption in the evening and at night. Unfortunately, the policy of “own consumption” is still limited to solar power; no such bonuses or incentives are offered for wind power (not even for small generators in backyards) or to people without solar roofs who nonetheless wish to adjust their consumption so that more photovoltaics can be installed. (Sven Ullrich / Craig Morris)

Check out our new 93-page EV report, based on over 2,000 surveys collected from EV drivers in 49 of 50 US states, 26 European countries, and 9 Canadian provinces.

Tags: , , , , , ,

About the Author

is tryin' to help society help itself (and other species) with the power of the typed word. He spends most of his time here on CleanTechnica as its director and chief editor, but he's also the president of Important Media and the director/founder of EV Obsession, Solar Love, and Bikocity. Zach is recognized globally as a solar energy, electric car, and energy storage expert. Zach has long-term investments in TSLA, FSLR, SPWR, SEDG, & ABB — after years of covering solar and EVs, he simply has a lot of faith in these particular companies and feels like they are good cleantech companies to invest in.

  • Using lossy and expensive batteries seems a bad idea.

    Better to convert excess solar to hydrogen which can also be used as a fuel for vehicles.

    • Bob_Wallace

      Batteries are lossy.  About 15% lossy.

      Hydrogen is at least 50% lossy.  That’s big time lossy.

      We don’t know how the cost things will play out.  Right now batteries are pricey but hydrogen generation and fuel cells are just plain expensive.

      Perhaps hydrogen gen and fuel cells will get cheaper than batteries, but they’ll have to get significantly cheaper in order to make up for the overall system inefficiency.  When you  throw away half the incoming energy your operating costs soar.

      • I’m talking about when sitting there.

        Hydrogen keeps its energy 100%.

        Batteries especially the lithium-ion type lose charge rapidly.

        And batteries are expensive because you need to add them as you need storage.

        Whereas hydrogen can be stored very cheaply in a simple tank.

        The fuel cell is not a storage device but a converter…it doesn’t have to scale with the storage, only with the peak demand from it.

        And also hydrogen is very portable.

        • Bob_Wallace

          First, newer lithium-ion batteries have low self discharge rates.

          Second, you can’t look at one element in a system in isolation and declare it a winner.  Hydrogen tanks might be cheap to manufacture but the cracking and burning gear is not.  And there are significant operating expenses due to the energy wasted in the overall system.

          I suspect there may be a use for hydrogen for deep grid storage – those few strings of days each year when both wind and solar input are low.  

          You could store a lot of hydrogen cheaply and you could generate it with a moderate amount of equipment because you could generate gradually over time.  But you’d be looking at installing a large amount of hydrogen->electricity equipment.  

          Fuel cells are quite expensive.

          • 1. “Will have” means they have high discharge rates now.  Everyone knows that to get a full charge with a Li battery you have to keep it charged in until you use it.  Works ok for a cell phone, but bad for storing renewables like wind when you don’t know when you’re going to need it.

            2. Tanks have advantages…they are completely passive, they are cheap to make, and most of all, as I said, the costs and weight don’t scale linearly with size — like with batteries!

            3. You can “suspect” things, or you can look them up on the web.  Germany and England have already benchmarked and are implementing grid scale hydrolysis systems for hydrogen storage of renewable energy.

          • Bob_Wallace

            I have no idea what “will have” means.  Current tech lithium-ion batteries have low self discharge levels.

            If Germany and England are giving hydrogen a test, great.  That means that we’ll eventually have some data to tell us the most cost efficient way to store power.

            It might, in fact, be neither hydrogen nor batteries.  Isentopic’s heat in gravel is making progress and promises to be very cheap if it works.

        • Bob_Wallace

          Let’s look at one grid storage battery now in site testing…

          EOS Energy Storage 

          EOS Energy Storage is manufacturing a zinc-air battery that uses a saline-ion electrolyte.

          Safe, won’t burn. Cheap, commonly available materials. The US has lots of zinc.
          Designed to last 10,000 cycles

          Cost $160/kWh.

          At $160/kwh and 10,000  cycles it would cost morning hours, daytime solar -> evening hours) storage.  That battery charging and DC -> AC conversion equipment will be in place in order to deal with daily cycles.

          If we increase the amount of storage in each system then we can supply for days at a time rather than hours at a time using equipment already in place.  Those few ‘deep storage’ hours of power would cost us 6 cents for the wind and 2 cents for storage.  

          •  You can slice it all different ways, but either a tank, or a solid state material that absorbs hydrogen is going to be lighter, cheaper and more expandable than any current chemical battery technology.

          • Bob_Wallace

            John, there is more to a hydrogen storage system than just a tank.

            You’ve got to crack water into hydrogen and you’ve got to ‘burn’  hydrogen to create electricity.

          •  So, in your bubble of the multiverse, the fuel cell was never invented.  Interesting.

          • Bob_Wallace

            Check my 7:47 AM comment.

  • Mooseinthebarn

     another thing that could help the situaiton of storage is to develop more home appliances that use nmematics (air) as the means to drive power.  Air tools are less expensive as they have no electric motor (no electromagnetic radiation), last longer, and easier to fix.  They could run a compresor in the fridge or turn a waher, and be stored in a efficient tank.  The house could be plumbed for air tools similar to a dentist office where blenders and vacuumes could all use air. 

  • Pingback: Home Solar Power Storage — Another Option – CleanTechnica | Solar Energy()

  • Sirsparks Electrical

    I am 100% PV powered, I solve the mentioned fridge (well freezer actually) problem by running it on a time clock without an in circuit thermos stat.  It runs continuously from 8am till 2pm and then 13 minutes per hour for the remaining time until 8am the next morning.  Temperatures are quite stable at -18C to -14.5C. I avoid a considerable amount of battery drain this way.

    I have also converted the same type of freezer to a fridge by installing a different thermostat and it now consumes only 200 watt hours per day which is about  25% of a normal fridge.

  • wattleberry

    I remember a survey a short time ago showing Germany as the favourite place to live in the world. It came as a surprise at the time but this sort of progress explains it. Imagine policies being implemented based on scientific objectivity, Saxon but not Anglo Saxon.
    A more and more prominent storage facility will be the recharging of EVs.

  • jonesey jonesey

    An option that is being explored by some utilities is sending a signal to electric water heaters to absorb excess generation in the grid (e.g. from wind power at night). A modern water heater can store 20+ kWh of electricity.
    In a similar vein, and relevant to this post, I would think that some control circuitry that tells a water heater to turn on in order to store energy from solar PV would be less expensive, take up less space, and have much less environmental impact than a battery bank.

  • anderlan

    All these places with 23-25c/KWh retail electricity, I don’t see why they need a feed-in tariff.  Not that I think that’s a bad thing, but my state has net metering, and 14c/KWh. If I bought panels and inverters and did the install myself, I could make my money back in 12 years.  At 24c/KWh, that would be 3-5 years!  In other words, with only net metering (never even allowed to go below $0) and no FiT,, at 24c/KWh, residential solar is a no-brainer.

    DIY is not that complicated. The hardest part is mounting. I’d use my shed. Take the opportunity to buy a nicer shed, and position it for maximum insolation. The next hardest part is connecting to your wiring box. Find a friend with experience in house wiring. The rest is just connecting wires like any other electronics. (Your utility must inspect everything before you go live.)

    The meager expense of my fossil electricity, and most of the world’s, keeps us subservient. In my state and country, we are being given a product that doesn’t include externalities in the price. We are in a co-dependent relationship with the fossil fuel sellers that can only be ruinous in the long term.

    Back to the content of the article…I am wondering what is different algorithmically than a normal battery storage system. This type of thing is a software problem now, just like the blending of gas and electric power in a plugin hybrid is very much about software.

    As a programmer, one who really enjoys the minute details of kernel (OS) *resource* optimization (discussed so especially openly by Linux developers), I relish and look forward to discussion of all the algorithmic resource optimization that is happening within vehicles, household power, micro grids, and the macro grid.

    • Bob_Wallace

      The cost of solar is rapidly dropping.  Thanks to subsidies like feed-in tariffs which have grown the solar market large enough to create competition and innovation.

      The price has dropped so rapidly that sometimes those FiTs seem to be unreasonably high, and they likely are based on current solar prices.  They are being adjusted downward.

      In the US we’ve taken a different approach via a subsidy based on 30% of the installation price.  That means that the subsidy has automatically tracked downward with solar costs.

      I think what we are seeing in Germany is a great decentralization of the grid.  Solar has worked very well for many people. They’ve got their installed price down to roughly half of what we pay in the US.  The next step is to install some storage at the house level so that even less power flows back and forth on the German grid.

      Since storage is being installed at the retail, rather than the wholesale, level the numbers work better.  Purchasers of storage are avoiding retail prices and using those savings to pay for storage.  Storage at the utility level means that the storage has to be paid for with the spread between wholesale and retail prices, a smaller number.

    •  Why is a feed in tariff needed in places with high retail electricity costs?  Because otherwise coal plants will be paid for supplying electricity to the grid and PV won’t, resulting in less solar electricity capacity being built and less CO2 emissions avoided. Not to mention the fact that their is nothing fair about electricity distributers taking electricity provided to the grid by point of use solar for free and then selling it for a profit.  You are right that in a place with high retail electricity prices like Australia point of use solar systems can pay for themselves, but fewer will be built and they will be smaller in size than otherwise if people aren’t compensated for electricity they provide to the grid, especially as easy energy storage isn’t yet available (although that should change over the next 2 years).  Electricity provided by point of use solar doesn’t have to be compensated for with a feed in tarriff, but I definitely think it should be paid for. 

Back to Top ↑