When Will Battery Storage Attain Grid Parity?

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It is now generally recognised that rooftop solar has reached “socket parity” – meaning it is comparable or cheaper than grid prices – in many countries over the last few years. The big question for consumers and utilities is when will socket parity arrive for solar and battery storage?

Some suggest it is years away. Others, such as UBS and the Rocky Mountain Institute, say it could arrive in Australia and the US within four to six years. It may come even earlier.

The graph below comes from Germany Trade and Invest and outlines the metric that will govern the arrival of grid parity for battery storage. Electricity prices are rising, solar PV prices are falling, which means that if battery storage can fall to around €0.20 per kilowatt-hour, then parity will be achieved.

Australian research house Morgans, in an assessment of Brisbane-based battery storage developer Redflow, suggests that its zinc-bromine flow battery may already be commercially economic in Germany, which leads the world in terms of household adoption and government support for renewables.



Morgans notes that in Germany, the cost of household grid power is around €0.30 per kw hour ($A0.42/kWh) and the government is now subsidising residential energy storage systems that are connected to solar systems.

“Given Germany’s substantial adoption of solar PV their costs for solar power range from €0.10- €0.15 per kw hour (half the grid price) so when energy storage costs reach €0.15 -€0.20 this will mean renewable energy costs will be at parity with grid prices,” Morgans says.

The German government is currently subsidising up to €3,000 for energy storage systems. Morgans says that the €0.15 – €0.20 per kw hour range (discussed above in figure 5) for energy storage costs, combined with the German government’s €3,000 subsidy for energy storage systems means the RFX ZBM will be competitive if they can triple the cycle life.

“In our view this should be achievable,” it says.

redflexSource: RenewEconomy. Reproduced with permission.

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Giles Parkinson

is the founding editor of RenewEconomy.com.au, an Australian-based website that provides news and analysis on cleantech, carbon, and climate issues. Giles is based in Sydney and is watching the (slow, but quickening) transformation of Australia's energy grid with great interest.

Giles Parkinson has 596 posts and counting. See all posts by Giles Parkinson

82 thoughts on “When Will Battery Storage Attain Grid Parity?

  • What the heck is going on? Lead acid is already below 15c kwhr. And pv at $3 dollars installed is 8c kwhr. Voila, 23c/ kwhr! They have some strange way of calculating…or is it me? It can’t be me, because on several lead acid battery sites the life cycle costs are given from 11c -16c. And here is my simple math for pv. A 1 kw array fixed south at latitude angle will easily produce 1100(Germany) to 2000kwhr (new Mexico) year. They will function for 35 years. So minimum 38,500 kwhr lifespan. At $3000installed that is 7.7c kwhr. ( 4c in New Mexico) that cost includes inverter and estimated on 4 kw system. So…give me a reality check engineer types.

    • Is it just the cost of the battery? No inverters and voltage regulation, safety circuitry needed?

    • $3/watt, 18.75% CF (middle US), 6% financing for 20 years = 15.9 cent per kWh electricity. (No maintenance costs included.)

      Hamburg with 11.9% CF = 25 US cents per kWh.
      Frankfort with 12.4% CF = 24c.

      Assuming a 35 year lifespan will bring the lifetime cost down. But you may need to add in the cost of an inverter or two and some maintenance along the way.

      • I imagine I am reinventing the wheel here. I’m sure some finance whiz already knows at what time a $3 watt installed system pays for itself, and when it begins to generate income, against buying electricity at 30cents / kwhr. Anybody out there?

        • The payback time for someone paying 30 cents per kilowatt-hour for with net metering or a 30 cent a kilowatt-hour feed-in tariff for a system with a 15% capacity factor (Bob gave an 18.75% figure above and I’m taking 80% of that to allow for inefficiencies and sub-optimal panel placement) is 7.6 years. If you get nothing at all for electricity you feed into the grid and have a 50% self consumption rate it will be twice that long. But $3 a watt is incredibly expensive. Relatives just had it installed for $2 US a watt here in Australia before subsidy and other people are getting it done for less. I appreciate you may not be able to get it installed at that price where you are now, but it’s only a matter of time.

          • So 7 years and paid off, then profit from the investment begins at what? 15% return. That is very good since it is risk free. Where else can you get that return on investment without risk? And that is at $3 a watt. That Australians are able to get it at $2 a watt for grid tied system installed is head spinning.

          • Wow! Just wow. There are places where installed pv is $1.13 watt. Who in their right mind would not install pv if they had a suitable roof, at this price? I don’t understand how you Australians could be so much smarter than us Canadians when we share the same genes…and even the same jeans!

        • PvWatts allows you to plug in financial assumptions (cost of capital, electricity price).

          The German chart assumes that the LCOE of solar without batteries will decline very slowly, less than what’s left of the FIT. Reasonable enough for 2014-15, with the sharp recovery in global demand and manufacturers’ profits, but after that the historical trend should reassert itself.

      • Do we know anything about the relative life span of solar panels vis a vis higher vs lower sun exposure? My outside guess is that solar radiation itself is a primary aging actor therefore panels with less average exposure might last longer.

          • The report mainly list overall results but doesn’t look into why the modules failed. There are 3 main causes of degradation:

            1. Heat the constant heating and cooling can cause glues and sealants to degrade over time. Metal glass and creamic parts will not degrade but may crack.

            2. UV damage. This mainly occurs on glues and sealants used. The metals, glass, and ceramic parts are not affected

            3 corrosion. corrosion due to water on the external contacts or corrosion on internal parts due to chemicals being released by degrading glues and sealants

            Back in the 70’s there were a lot of module problems mainly caused by glues and sealants that degraded due to heat and UV Exposure. today the materials used have been proven to be very stable reducing or eliminating problems due to glues and sealants. Today most damage is due to corrosion or cracking.

    • We need to be when we discuss storage cost. There is the first cost, which is a cost for capacity. For example, a Nissan Leaf has a 24 kwhr battery pack. Then we need a term for the lifetime cost/kwhr. That has to be based on the number of cycles or years, and combined with the finance cost and payback times gives us a cost/kwhr that corresponds to an electricity rate. The operating cost/kwhr is different from the first cost. For example, if we take a PV solar installation that produces electricity at 10c/kwhr over 20 years and combine it with a storage system that has an operation cost/kwhr of 10c/kwhr, the system could be said to have a 20 year operating cost of 20c/kwhr. With lead acid, the lifetime may be less, so an initial cost does not show it operating cost/kwhr.

      • Not sure if I understood you, but I separate storage and its life cycles cost. Once you establish that, replacement and expiry etc are already included. So if pv last 35 years that is one cost. If batteries need replacing 5 times over that period that is already factored into the life cycle cost of batteries. When you add these two together all factors have been calculated and the total is 25cents.kwhr I have not factored in interest @6%. I suppose it is true if you put your money in the bank instead you would get …. Actually nothing to speak of!

        • I am just struggling with terms. cost/kwhr has the same units whether its first cost or lifetime cost.

          I think you understand. If a battery has 24kwhr capacity, it can store 24kwhr. Thats a Leaf battery. If it costs 5500, then the capacity cost per kwhr is just 5500/24 or 230/kwhr. Thats an initial purchase price for capacity.

          Likewise, if we say its good for 1000 cycles over 10 years, then we store and reuse 24kwhr x 1000 cycles. Each kwhr of usage then costs us 5500/ (24 x 1000) or 22.9c/kwhr. That is an oversimplified analysis ignoring amortization and other things.

          Here is real world. This system has a DC-DC for connection between solar and the batteries. It has Battery management system to control battery charging and preserve the LiFeSo4 batteries. It has an inverter to make AC for the home or power the grid. That is much more than battery alone.


          12,650 dollars for 36 kwhr. You can get 5000 cycles by discharging to only 80%. I recommend charging to only 80% for maximum life. So that would be

          12,650/ (0.6 x 36 x 5000) = 11.71c/kwhr

          Over 14 years with equal payments at 5% interest rate, the total cost is first cost plus interest which is exactly double the first cost. That means the cost per kwhr is double or
          23.4c/kwhr, everything but installation, operation, and maintenance. O and M should be negligible.

          • That only works if you use each and every kWh in your calculation. i.e 0.6*36 = 21.6kWh

            When you use half that to have some spare for cloudy days etc then your 23.4 suddenly becomes 46.8c/kWh, add your solar on top of that at 10c/kWh and you can see why we’re not there yet.

          • The number of charge cycles is very non linear with depth of discharge, it goes up from 100% 1000cycles, 90% 3000 cycles, 80% 5000 cycles, and 70% 8000 cycles. So no, charging it less will not ruin the economics. In fact the economics gets much better. Don’t worry about charging too little. Worry about charging and discharging too much. If you have a choice between running an EV two days in a row and discharging it completely, or charging every night, charge every night. Your battery life will be extended. And forget about running it down completely to find out how far you can go. That destroys battery life.


          • What if you use all your batteries and get no sun the next day?

          • You have to size the battery capacity to need. And if you are wasteful, it will cost you. It will pay you to store refrigeration and heating. Then I ask, what did you do to use 36 kwhr in one day? Admittedly, its not enough for a week, but a day? Heres the deal. Nobody who has been off grid has illusions about going off grid in the suburbs. Until electricity is seriously expensive, its just not in the cards. Now micro grids, and municipal utilities, that might be different. Single users are just too isolated and too independent. There is strength in numbers. And geographic dispersal. The costs of electricity could get so high, that the utilities drop the hammer and just charge as much or higher for providing very little or no electricity. We are heading that way, but not there yet. Utilities screwed up. They want us to pay for idled central power plants instead of investors. Good luck to them with that. Conservation is eating a hole in their pocket. I could see municipalities getting together to generate their own solar, wind, maybe even gas generation. Lots of business are doing that. That seems more likely than rogue off grid individuals. Even in Hawaii, its more likely that villages micro grid.
            Where does residential and commercial self generation make the most sense? CHP. If furnace gas was also used to make electricity, there would be a lot of savings. Direct at the point of use cogeneration is the best way for the heat to be efficient. Between that and solar, the electricity use would almost cease. And heating use would be lower, too, if electricity was produced. Its this model that attracts the Germans to the Power to gas approach. There may be merit in it. I don’t know, its early.

          • You’re absolutely right, but if i size my batteries for your 21.6kWh on the basis that it’s two days storage, then i can only use half of it per day, then my batteries aren’t costing 23.4c/kWh, it’s 46.8c/kWh. Similarly if the solar panels are costing 10c/kWh for every kWh, and i only use half of them because my battery is full, then they’re really costing me 20c/kWh.

            I fully agree on thermal energy banking and there needs to be a smart battery management system that turns on the hot water heater and HVAC to preprogrammed settings to bank excess generation.

          • Hmmmm. I have to think about that. I don’t think you would use that capacity for two days storage, if that is your aim. Also, that seems high for off grid, kind of luxurious usage. Biggest drain of grid (and on) is the fridge. Provided you don’t live somewhere really hot with air conditioning. You would go for the larger unit. You would still get more than two days supply at 60% or less! but since it’s two days! you would get much more calendar life! provided you never or rarely charge to max. That lifetime equates to 20 years or more, but we are in uncharted territory for LiFeSO4 calendar life. I think you are better off restricting your usage somewhat and going with the 36 kwhr system. I don’t think the math is correct. The number of kwhr and first cost is the same. It’s the interest rate that really has the most effect, because the payback is extended. Without interest rate it’s the same. Let’s take your case. Two days, 5000 cycles, 60% of capacity used per cycle. That’s 10,000 days.. 3 years is about 1000 days, so you are pushing 30 years. That’s way high, and you would probably experience battery aging sooner than that. I wonder how often you double day. Given the nature if solar, you would be in a really cloudy climate if that happened frequently. Then you would benefit from wind or a wind solar combo. I have seen places where run of water or even tidal could generate off grid juice. Most places can generate enough electricity.

          • I did some numbers below in AUD, including importing and taxes on the Balqon (scaled where necessary) using average Aussie prices for solar on 25 year LCOE with replacement inverter at year 15 and 165/year maintenance. You’ll see that in the 5kW solar example i’m using about half of the storage of the balqon, but some of this is concurrent with production so storage is 70% of that which is about the numbers we’re using above.

            Scarily the less you use, the higher your cost of power. My power cost is 27c/kWh plus grid access of 50c per day, which puts the 18kWh usage at just over break even. However i use only 3-5kWh/day.

            On the battery management, i want a system that lets me only charge to 80% in summer because i have no doubt at all that i’ll be able to recharge the next day even if i use it all. In winter a few cloudy days in a row and i’d be starting to get short of power, so i’d happily charge to 100% knowing that i’d only be there for a few hours anyway.

            Here’s an example of outputs by day where i live:


          • Hi Vensonata. I checked out the annual solar you posted. Most months there is at most a day dropout, but then you get rainy months with 4 low days. This makes it appealing to look at a spreadsheet and see what is most economic, wind, solar, storage, etc. You also have to consider thermal storage and the exact nature of your demand. (demand management). Having a few occasions of long storage increases your storage costs, because you have to increase storage capacity just for them. Not shown, but I assume there is a daily day/night charge/discharge pattern.

            This looks interesting. Its in Australia. Check it out.


            Silicon solar is affected by temperature, so that cooling can improve efficiency. The heated water can be used as solar hot water, but not so obvious is the benefit of night sky radiative cooling, which can be stored for daytime use.

            Unfortunately, systems are at an early stage, so its difficult to find off the shelf solutions. Since air conditioning is so important in Australia, its worth a mention.

            This is kind of dry.

            I probably don’t need to mention that insulation and double pane windows are really good for off grid or anyone considering efficient energy use. Same with passive solar. The best way is to not create the need in the first place.

          • Glad you mentioned insulation and windows etc. Serious energy squandering occurs in the thoughtless construction of houses…clean energy production is much easier if you seriously address efficiency. The huge house we have is used for many purposes and has up to twenty five people using it at times, but we have systematically reduced its energy needs to 37 kw per year per sq meter. That is total energy use, heat, hot water electrical etc. It is cold here in Canada! For those who are new to these numbers, the German passivhaus, highest world standard allows 110 kw per year per sq meter. So we have squeezed it down by 70%, and there is still fat left.

          • Where i live, we don’t need double glazing, ceiling insulation is a must though. For us, keeping the heat out in summer is a function of shading windows and ceiling insulation, staying warm in winter is a function of solar insolation through the windows. If we can do both those things, we have a comfortable house 98% of the year by taking advantage of the aforementioned and the diurnal temperature swings. Heating and cooling is a result of lazy design. That’s the bottom line.

          • Our magic comes by using insulated closing window panels at night and in certain rooms through the winter (bathrooms) They are R 25 at least…better than most peoples walls and better than some roofs. They outperform the best windows for a fraction of the cost. That is how we allow heat in without allowing it out at night.

          • What did you use for your window panels?

          • The panels are two varieties: interior and exterior. We started with a daunting 1350 sq ft. of double glaze argon E. Can you imagine the heat gain and loss? So we began with fixed exterior panels R 30 fiberglass 2×10 frame and douglas fir plywood. It worked so well and we realized we didn’t need to open them even seasonally…the light was fine so 500sq ft of windows disappeared. Next. interior closing panels…I had to invent them because I could find no examples. Birch cabinet grade plywood, fir frames, green water based glue and R25 Polyisocyanurate foam board. Hinged like doors they close onto foam gaskets, so little condensation if any. Leave open 7 months of the year, then on a regular schedule of open during day to let in solar, closed at night to keep it in. We weren’t sure it would work, but by gosh it does! We went from 40 cords to 6. Of course other stuff too…like R 80 in the roof. several walls to r 50, air lock porch. This month we just finished a “low mass solar porch” 140 sq ft south facing glass into a super insulated porch. Leave the interior door open during winter days, capture heat, close it at night. Estimate a further 1 cord reduction through that alone. That idea I got from “Build it solar” a DIY site..check it out, great backyard inventors.

          • The R25 Polyisocyanurate foam board was the part I was after.

            I used dual pane, Argon filled windows which also have a low-e film. That’s helping keep out summer heat as well as winter heat in.

            I’ve got a lot of windows (a lot) and really don’t want to cover them. No curtains, nothing. Acres of trees provide the privacy. I am thinking of making a few removable covers for the very coldest of nights, but that’s probably overkill.

            We burn about a cord of wood a year. Have far more ‘storm down’ wood than we can use so cut up only the stuff closest to where we can drive the truck.

            What I did to cut winter heating needs is to separate the “day room” from the rest of the house and place it where the winds hit least. On the east side there’s the dining room which gets closed off in the winter with French doors. On the north side my workshop. The main room (living, eating for two, and kitchen) has its ceiling insulated from the upstairs bedrooms/baths. That way I’m only heating about 600 square feet and it’s a protected 600 sq.ft.

            The main room never goes below 50F over night, even with the doors open to the upstairs to let them heat up some. It’s usually about 55F when I get up and doesn’t take a lot of wood to keep in the 65 to 70F range during the day. (Love that radiant heat from a wood stove.)

          • Ya, woodstoves… amazing pieces of low tech wisdom. We also are the Saudi Arabia of firewood. Thank you, pine beetle infestation for devastating 80% of the largest pine forest in the world! And thank you carbon users for global warming which caused the pine beetles to explode. But really, I’d be happier with the original green forest that was here 15 years ago. Call me nostalgic! By the way if the dead pine is not burned it creates methane as it rots a over twenty years release about 10 times the amount of heat trapping gas into the atmosphere…so those who hesitate to burn dead trees take warning, it is worse if you don’t.

          • you guys talking LFP batteries? 🙂

            count me in.

          • If you’re using “half the battery” today then you’ve saved the “other half” for use tomorrow.

            That may be a bit too simplified if calendar life comes into play.

            And it ignores the value in getting a return early rather than lately. (Small effect.)

          • Bob, breaking news on cost per kwhr of lithium pack from Balqon. The 36 kw pack. After several discussions and recalculations and carefully re examining the specs at their web site… This is closest to accurate. At the sweet spot of 50% degree of discharge, the batteries have 5000 cycles(I looke very, very, closely) that makes for a kwhr price of 13.8cents! That is superb when you think it includes a complete battery management system, metal housing meters and built in cell balancing. As well the pv input is 20% more efficient than lead acid even during bulk charging let alone that last 15% taper charge, where efficiency of absorption drops to 2% in lead acid if the pv is producing full power. This is really a game changer for off grid. Now I’d love to hear from anyone who is actually using the system for any weak points in what appears to be almost, too good to be true.

          • They want us to pay for idled central power plants instead of investors.

            I keep thinking back to the age of US coal plants. Seems like utilities have probably already written off the cost of most of their plants and must have calculated in the cost of new capacity. They were going to spend for coal, now they can spend for wind and solar.

            Perhaps they are just angling for additional profits. Money they would not have received had the transition to renewables appeared.

          • Are you saying that the Balqon lithium batteries get 8000cycles to 70% depth of discharge? Or 30% depth of discharge? Sometimes it’s confusing what is meant. In the first case 70% of 36kw = 25.2kw x 8000 = 201,600kwhr lifetime. In the second case 30%=86,000kwhr lifetime. In either case that is a fantastic price per kwhr. At $12,500 for 201,600kwh = 6.2cents kwhr. And in the second case 14.4 cents kwhr. I’ll buy either but of course would prefer 6.2cents kwhr!

          • Its from the Winston battery site, 40 Ahr prismatic cells. Balqon is much more conservative even tho the cells come from Winston. If you add in interest cost over the payback period, those costs/kwhr go up. The farther in the future they are (the longer it lasts) the less they contribute to the bottom line. If that seems odd and unnatural to you, join the club.

          • Update: Winston battery test by Czech technical university at Prague . Are you sitting down? 13,000cycles no degradation at 1.5c, 90% d.o.d.!!! These are the batteries Balqon is using. This detective mystery keeps unfolding. The Winston site is almost arbitrary with their claims, sometimes 2000 sometimes 3000, maybe it just doesn’t matter to customers after 3000, in various retail literature cycle life is all over the map. However I feel the Prague test seem actually scientific. I f so these batteries can be cycles for 35 years without degradation!

          • I’m skeptical. Unless this battery is brand new and the Czech study has just been released then you think someone would be putting these guys on the grid somewhere.

            Even if Winston doesn’t have the ability to market it would seem that some other company would have reached out and taken over.

            And why got to a Czech university. Why not go with a well recognized independent lab for verification? Perhaps the U study was a cheap/freeby for establishing a selling point for more funding and higher reputation testing.

            A battery with 13,000 cycles, priced at lead-acid levels or a bit below should shake up the grid.

            Hope you’re right, but I’m still in wait and see mode.

          • Oh, link to the study?

          • By the way Winston is the new name of thunder sky battery which have been around some years making the first ev lithium batteries for DIY people. I think they are Chinese, so maybe Czech study is as sensible for them as American. Funny they don’t display the study…but as I mentioned above Coleman decided to reduce the actual 500,000cycle life of the ultracapacitor screwdriver to 50,000 on the package…I noted that as an interesting marketing approach…not that I understand it!

          • Sorry I am inept in how to create a link. But here is how to see the study: Wikipedia lithium iron phosphate battery article. Footnote 15, zaps you right to the PDF . Winston battery test. 6 pages easy to read with photos and method. They themselves said they were surprised and very impressed…they did two tests. One to 10,000 cycles,no degradation, the second to 13,000 cycles no degradation. I don’t know what to make of it, it is hair raising if true! And it does look legit. But I really appreciate a hard look, especially by any electrical engineers out there.

          • Short report and seems legit, at least to my amateur eye….

            “Conclusion of the charge characteristics after 13 000 cycles:

            There is no degradation in the performance of the cell. The cell performs the same way and no significant change of in the charge characteristics has been measured.”

            From the Wiki page –

            “LiFePO cells experience a slower rate of capacity loss (aka greater calendar-life) than lithium-ion battery chemistries such as LiCoO2 cobalt or LiMn2O4 manganese spinellithium-ion polymer batteries or lithium-ion batteries.”

            And LiFePO cells hold pretty close to full voltage until the are close to fully discharged.


            They sound very good. Where’s a battery expert when you need one?

          • After reading the Wiki page over a few times I see only two potential downsides. Slightly less energy per volume. But only 14% which is irrelevant for offgrid/grid storage.

            And a lower discharge rate than lead-acid or LiCoO2 which might be an issue if one had a big draw item on their system. (My air compressor can really pull a lot.)

          • Bob, this seems quite important if true. Our little dialogue is lost in a 4 day old thread. Can anybody with some real expertise do a well researched article on this topic? I mean in my half baked opinion it seems to be a game changer, yes?

          • I don’t know where to look for “expert” analysis.

            I try to follow the “if it sounds too good to be true then it probably is” guideline. And this sounds pretty much too good.

            When one doesn’t see the storage industry all over it another flag is raised.

            Large numbers of lithium-ion batteries are being installed on the grid. Air-zinc is getting a trial. What not these batteries?

            Here’s an idea. We could put together a few paragraphs on these batteries. Use the Wiki info, Czech U study, and retail price comparisons to lead-acid and lithium-ion and get Zack to stick it up as an article. That would get some fresh eyes looking.

            Title the article something like “Why are these batteries not the holy grail?”

          • See that’s why I asked you how to get some fishing expedition going, you’re the man with the ideas. I will be waiting for the article.

          • Nope, team effort. I’m emailing you.

            Anyone else wanting to get on the effort let me know here.

          • Vensonata – be careful here. One other factor in lifetime is the C rate of charge and discharge, at least in part because of self heating. External temperature matters also. Thats why Balqon is so conservative. I have an insiders perspective of the complexity of these batteries. To get the best performance, you have to carefully control and monitor the batteries. A good BMS can do this, measuring every cell temperature and voltage. Balqon can control the charge/discharge rate, but I don’t know if you can set it lower. You have to factor this into account when you consider system design. Balqon shows both charge/discharge near 1C. Balqon is probably assuming it cannot control all these factors. For example, look a the ambient temperature rating. -45 to +65C. Thats pretty hot. I have installed Winston (Thundersky) batteries in two EVs and several Prius plug in conversions.

          • Good to have you on board here. There are kinds of factors that need checking…here is my first mistake. “13,000 cycles to 10% d.o.d.! Not 90%”.. But we are still talking a whole different ball game than lead acid. The best lead acid can get (theoretically) 5000 cycles at 10% and then it is finished. These Winston batteries have not begun to degrade at 13,000 cycles. I can’t emphasize enough that that is 35 years at 1 cycle per day. It would be entirely possible to hit 20,000 cycles with a gentle decline….but Prague technical university did not test beyond 13,000. The implications are enormous for off grid storage and yachts. If your battery is sized for 3 days storage eg. 10 kw/day = 36 kwh pack. then your normal night time use about 250 days a year will be about 10% (3.6kwhr) perhaps 10 times a year 90% discharge in cloudy winter, 50 times to 50% and 50 times to 30%. These are all gentle charge and discharge rates, optimal. Remember charging an Ev or even on grid with storage are different scenarios. Ev is rapid both ways. Off grid is gentle both ways. So we are talking about a battery pack with a theoretical lifespan easily 35 years! That fully matches pv panel lifespan! So, I am just getting started sorting out the full implications. Please contribute any informed perspectives from EV world…but remember the parameters for off grid solar storage are a different kettle of fish.

          • Vensonata-Hi. The cycle life must consider that batteries degrade over time without use. Its just normal chemical decomposition over time. So 35 years is probably not possible. The key metric in aging is charged voltage. It has to be kept below max. Thats why I recommended only charging to 80%. Temperature is another life reducer. Thats why Balqon is so conservative. This territory is relatively uncharted because LiFe has only been around in numbers for about a decade.

          • eveee –

            Would you critique the Balqon battery system for off-grid storage? In your opinion how well would it work compared to the best lead-acid batteries? (I’m thinking the Trojan RE series rather than more exotic brands.)

            And what, in your opinion, is the likely cycle life of the batteries under normal off-grid use? Let’s say 75% of the time they are 25% discharged and 25% they are taken down below 50%. Or some mix of sunny days in a row and cloudy days in a row before backup is cranked up.

            I’d assume most people would install where is would not reach 0C and not exceed 40C.

          • Correction: looking closely at balqon site for 36kw battery bank. 5000 cycles to 50%. We need to be careful about these numbers. That still gives storage at 13.8cents kwhr, which is fabulous considering the many other advantages over lead acid, that lithium ferrous has.

          • I’m assuming that lithium batteries will pass lead acid sometime soon. Perhaps they already have.

            Personally, I’m not an early adopter. I’d want to see some real world experience before I’d jump. YMMV.

          • I am looking at Winston battery that source the cells, 40Ahr prismatic battery, Balqon shows more conservative numbers.


            The Balqon website gives 3000 cycles at 80% DoD. The graph contradicts it with 2200 cycles at 80% DoD.


            Its a LiFeSO4 battery. The graph shows that cycles go up non linearly as DoD is reduced. but does not match the Winston curves. The reason for derating may be temperature or other effects. They also only warrant 5 year life. I have experience with these cells. Balgons curves show the same non linear increase in cycle life as DoD is reduced, but with lower numbers than Winston. Winston is a major stakeholder in Balqon and supplies the batteries.


          • It’s a lithium iron phosphate, not sulphate battery. Interestingly they use yttrium, i assumed doped into the phosphate ala appatite.

          • So…who do we believe, the battery maker or the pack assembler? Is Winston just boasting or is Balqon just being modest so no one is disappointed? One thing I have encountered with ultra capacitor ratings is this: coleman made an electric screwdriver with an ultracapacitor which could recharge in 90 seconds, amazing and inexpensive, but they advertised it as having 50,000 cycles. It actually had 500,000 cycles! They knew that but it seemed unbelievable to the general public so they used a more believable number. Maybe that’s what Balqon is doing. Second theory: the price is remarkably similar per kwhr to best lead acid…could they have made it even cheaper?

          • I don’t know. I have experience with that battery manufacturer, but who has 10 year info on a battery that barely existed 10 years ago? I would go with Balqons more conservative numbers, but I would also operate the system with less full charge and full discharge whenever possible to extend system life. All the curves agree on that. I suspect Balqon is more conservative because it is integrating a whole system. If you are wrong and too conservative, there is little downside.
            Yes, its lithium iron phosphate. My bad. It should be LiFePO4. Balqon says its energy storage is also. Winston started using yttrium on some batteries.
            IMO, this system is a real steal with the inverter, DC-DC, and BMS all in one, fully constructed. If you ever assembled BMS in a battery pack, and I have, you would not consider it trivial. The DC-DC, storage cabinet (and cooling?), and inverter alone are worth thousands, probably about 3000, not to mention assembly. The battery only cost is probably about 8k.

          • Yes, I am teetering on the edge…it is really good to get some knowledgeable discussion on this break through…I still don’t understand why there isn’t more excitement around this…hello anybody out there? Lithium batteries are finally affordable!

    • For new builds, you ‘should’ be able to subtract the cost of running an A/C line into the house & the expense of unnecessary electrical infrastructure.

    • My 4D Political Analysis applies even here.
      No graph will show this issue properly.
      You need little flashlight bulbs on your data points over time….
      To be understood by the most people…..

    • lead-acid has a very limited cycle life.

      • I just bought a set with 4,000 80% DoD cycles.

        That ain’t chopped liver….

          • Oh man, I did it again.

            20% DoD. 80% SoC.


      • There are some terrible fibs that battery makers tell about each others batteries. Lead acid, good deep cycle lead acid can get 5000 cycles…see surrette 5000. Forklift batteries can get even more. We are just seeing lithium coming close now. The thing about lithium is its lighter, smaller and maintenance free, and most importantly it does not need full charging like l.a. Does. That lst issue is the clincher for me.

        • 5000 cycles at what DOD and price per kWh nameplate?

    • I disagree with your calculations on one point: not everything produced by the PV system needs to go into a battery: some can be
      – used immediately on-site
      – fed back to the grid, with some form of compensation.

      Your case was: PV + batteries covering 100% of needs => 23c/kW⋅h.

      Alternative: same PV, grid, no battery.

      #1, worst scenario: no feed-in tariff, zero compensation for overproduction.
      Say PV now only covers 1/4 the total consumption at 8c/kW⋅h, the rest must be purchased from the grid at a hefty 30c/kW⋅h.
      Average: 24c/kW⋅h. Well… about the same!

      #2: ditto, but load is now arranged such that PV manages to cover half of it. One example: a significant fraction was air conditioning, so it is now set to coincide with PV (over)production.
      Average: 19c/kW⋅h, already cheaper than any battery.

      #3: slightly better: measly 6c/kW⋅h feed-in tariff, otherwise same as #1.
      3/4 of the PV production is sold, only to be purchased later for 5x the price (ouch).
      Average: 20c/kW⋅h.

      #4: best case: net metering.
      Here, regardless of usage, as long as PV covers it all eventually, only its cost remain: 8c/kW⋅h.

      In short, what batteries need to beat isn’t the retail cost of electricity, but the difference between that and the compensation for energy fed back to the grid.
      In areas with net metering, this difference is zero, meaning batteries won’t ever reach parity.

      • Good thinking. The whole grid tied pv thing is usually a much, much better economic scenario than off grid battery pv. But consider that in summer if 25% of houses feed in to the grid and they have a reasonable size array (say 6 kw) then they can saturate the residential grid. Kind of like filling your battery up by 11 am. then the rest is excess and needs storage or is wasted. So with commercial pv wind and residential pv all feeding in, summer may have many days of 200% -300% production. Should we celebrate or store it. So it seems the government is aware that storage is necessary to some degree otherwise outlandish overproduction (nice problem), just like I have off- grid in summer.

        Another issue of conscience is, isn’t this whole site called “clean Technica”? If you save a few bucks on a coal fired or gas fired grid, what’s that got to do with “clean”. So if your grid is filthy then in good conscience one might bite the bullet and go off as a non-participant. Happens all the time where goods are cheap but immoral.

  • The moment the residential battery energy storage will produce a roundtrip electricity at less than the retail rate, it is good bye for the utilities’ profits.

  • During the winter months, my PV production (in Texas) simply does not keep up with my overall usage as compared to the summer. More cloudy days, the sun is not directly overhead, and shorter days are the factors. For me to go off the grid, I would have to beef up my system to absorb the few periods in which I use more than I produce. Even though I produce 20% more (overall energy) than I use during the summer, I would have to increase my solar production by more than 20% during the winter months.

    Looking back historically, I found a two week period in which just about every day was overcast and the days were at their shortest length. It would have taken a pretty large battery to get me through that two week period. Even adding additional panels would have had minimal effect, since solar production simply was not that great for the month.

    Going off grid is simply not as easy as placing in a battery and disconnecting your system in locations where usage and production fluctuate significantly. A 75 kwh battery with my 8.33 kw PV system might address 97% of my electricity needs, but I possibly might need to double that battery size in addition to adding more panels to get by during the couple of solar lulls.

    I do see sense in adding a battery if the power company should at any point decide not to reimburse me for energy I send back to the grid. At that point, using it for evenings would be a preferred option.

  • This is a very, very good discussion. Excellent points. I think that realizations emerge out of free thinking discussions at the foggy dawn of a new age. One thing that off-grid has taught me ( by the way, I have 25 people staying with me for the weekend and at the end of it I announce the total electrical use per person…usually about .65kwhr per person per day, and the total propane for on demand at 95% efficient water use, we have our own meter for that.) – is that there is an unbelievable amount of fat in the ordinary household system and wasteful habits. That is, negawatt mining is fun and profitable.

    • Another aspect of going offgrid that hasn’t been brought into the costs by you and everyone else is the reliability.
      As of October of this year I have been offgrid with no power outages for 8 years using a combination of solar and wind, and managing my own storage. My next door neighbors that have been relying on the local cooperative electric utility during that time have had anywhere from 3-5/year black outs lasting from 30 minutes to 3 days in that same time period.
      While maybe for many homeowners the extra costs of storage may not seem worthwhile to accommodate those outages. It would seem that small businesses will see it as cost effective to be able to carry on production and sales during these times of grid failure.

      • I’ve been offgrid for over 20 years and experienced no power outages. I did have one a bit over 20 years ago due to my under sizing a component in my system.

        But the other side of that statement is that I find myself out in the snow at 11PM, 12PM filling the generator tank and then sitting up for a couple of hours in order to put enough power into my batteries to keep them above 80% for the night.

        (A better memory might get me out earlier in the late afternoon, but I haven’t found anywhere to download one….)

        • I am as lacking as you in finding a place to download a personal memory upgrade.
          However I have found that carrying around a smartphone over the past few years with Google keep and its checkoff to do and shopping lists with time and place reminders and the timely alarm clock with day and time reminders with labels to be a fair substitute.
          Just something to consider. 🙂

          • So how do you remember where you left your smartphone?

          • You ring it from your land line, or you iMessage it from your iPad or computer, or Skype it if you bought the wrong brand.

            If all that fails, remember that you were just about to make a cup of tea.

          • It doesn’t respond when you call for it? That’s not very smart. Obviously a robot you can call for which goes and finds your smart phone when you lose it is required.

        • That generator thing is the only truly iffy part of my system everything else behaves itself, that is why I’m willing to overkill the the pv…to cease from the big diesel.

  • I’m anticipating a large increase in panels next summer. My do list is pretty loaded up this year.

    Need to get the fence upgraded so the foxes don’t make off with all the apples. They’ve already had their way with the peaches and plums.

    And there’s finishing the garage concreting.

    And converting the storage room into a sewing room.


    • Understood, have already done my share of griping to you about the projects I want to get done before it gets to cold to do anything but keep up on the firewood plus keeping up with the rugrats.
      Just meant that one as a humorous/sarcastic reply because I remember hearing about the plans for more panels.

  • After 132 years it is time for our fast moving and nimble utilities to meet us here in the 21st century so that the question becomes; When will the grid be seen as in parity with battery energy storage? It’s getting so bad that it’s hard to get through a day without someone’s conjecture that at some point Solarcity will take over a utility company 🙂 It is going to be an interesting period in time isn’t it?

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