EROEI (batteries now included)

As I showed in a recent post, a typical solar cell will generate at least 10 times the electricity used to produce it, and probably substantially more. This Energy Return on Energy Invested (EROEI) calculation didn’t take account of battery storage, which is needed to make solar PV comparable to dispatchable technologies like gas.

For this purpose, I’ll assume that each kilowatt of PV capacity requires 2 kilowatts of battery storage. The reasoning behind this is that we get an average 5kWh/day from the PV system, of which 3kWh is used during the day and 2kWh is stored.

According to this life-cycle assessment, a 26.6 kWh battery has a life-cycle cost of 4.6 tonnes of CO2, which comes out to around 0.4 tonnes for the 2kWh system proposed here. Assuming that the system displaces black coal, which conveniently yields about 1 tonne of CO2 per mWh, we have a cost of 400 kWh, which is only a few months worth of generation from a 1 kW system.

This seems amazingly good, so I may have made an order of magnitude mistake somewhere. If so, I’d be grateful to have it pointed out. If not, I think we can put the EROEI constraint to bed, at least as regards solar PV.

50 thoughts on “EROEI (batteries now included)

  1. @John Quiggin

    Also, distributed energy storage capacity need not be limited to batteries and it need not be limited to micro-storage.

    I would regard a bit of pumped hydro here and a bit of molten salt heat storage there and a bunch of wind generators along a coast with some flywheel energy storage in each unit (to store and smooth power) and so forth as macro-distributed energy storage.

    What people have to wrap their minds around is a complex distributed system with both macro and micro generation nodes and macro and micro storage nodes. Such a system (I suspect, not being an expert in such matters) should be very robust, contain effectively multiple redundancy or backup at reasonable cost and in a sense be self-smoothing or self-balancing across the network. Being a fully smart grid with multiple “intelligent” nodes ought to greatly assist this I think.

  2. Thanks Ikonoclast,

    Please suggest any refinements to the primary model specification. There will of course be many adaptions for specific situations, but I am attempting to put together the specification for a one installation solution that covers all of: electricity production storage backup and management; water heating and cooling for all of cleaning/bathing, space heating and space cooling; and partnered by mains natural gas for cooking and energy backup (or LPG for remote locations).

    The aim is to have a solution that suits 6 million locations across Australia, then examine the logistics of implementing that. Please feel to load a spreadsheet and examine economics of such a solution. The primary information is:

    Assumed system cost $20,000
    Australia’s total electricity demand approx: 250 billion units pa (Kwhrs pa)
    Vehicles in Australia travelled 232.4 billion kilometres in 2012
    LPG : 1 L = 24Mj = 6.9 Kwhr = $1.17 delivered
    LP engine will consume: 1.2 L/hr at 2.5 Kw output and 5kw electrical equivalent at 65 C hot water while running.
    Solar array : 4.5 Kw Thermal : 8 Kw to max 65 deg C with temp output proportional with kw output
    1 by 10 Kwhr Tesla Powerwall unit
    Cooking is by gas CNG or LPG
    I use 275 days with 6.5 hrs sun as a insolation calc model though this will be high for many areas
    The aim is to charge one or two 8.5 Kwhr batteries each day. 50 klm travel per charge.

    At the moment with my newly installed 4 Kw system, which is smaller than the model and loses about 25% sunlight to trees, I would be getting a max of 18 Kwhrs so would need to increase the size to 6.5 Kw to get the standard model in winter. I don’t have the summer figure yet so cannot verify the model rating until I do. In between time I am examining what adaptions I need to make to not waste any energy to the grid. Gas will be installed for cooking soon and from that point I can draw conclusions on energy usage requirements. For the pool I will be installing an ultrasonic anti algae system to operate with the pump so the system will be fairly representative.

    An example calculation/assumption: 6 million premises X 2 PHEV vehicles X 1 charge each = total klms 100 klms times 6 million times 365 = 219 billion klms electric travel fueled from PV.

    Does this add up as I believe it does?

  3. The bulk of the storage is going to be in pumped hydro, hot water and even hot oil (heat oil to 200 C and it has 4 times the energy than hot water systems for the same volume) and vehicle batteries. There will be a reasonable amount of gyro storage for rapid charging of vehicles.

    In the system profile that I am suggest there will be up to 228 gigawatt hours stored each day in power walls, water cylinders and PHEV batteries.

  4. @BilB

    My household uses electricity for all household needs except that the hot water comes from an evacuated tube solar hot water system (which still has an electric back-up). We have a 5.5 kW nameplate rating on our solar PV / inverter system. We have no back-up power, feed excess to the grid and in turn use power from the grid at need so it is our “giant battery”.

    We have 4 people, heaps of electrical and electronic devices like most homes and a biocycle double-tank sewerage system which uses electric pumps. But we have no swimming pool. We cook all electric. We use aircon sparingly in one large room and hardly ever use heaters. This is Brisbane after all.

    According to my bill, an average 2 person household in my area used 1,260 kWh of electric power last quarter and an average 4 person household used 1,944 kWh of electric power a quarter. We used 1,263 kWh in the last quarter. We are a 4 adult household and we make absolutely no effort to economise or stint in any way on using electric power. So heaven knows how these other households use so much power.

    Basically our system provides enough power for 1.75 households like ours so over the year we feed another .75 of our use into the grid. This tells me that in Brisbane a 5.5 kW PV system plus solar hot water produces 75% more electric power than any sensible but still non-economising household of 4 adults needs.

    With this 75% extra power, I suspect (without doing the numbers) that I could power an electric vehicle and pay the energy inefficiency costs of back-up battery storage. All I have to do is be prepared to pay the financial capital costs of a Powerwall (or more likely two) if I go off-grid.

    So I would have to pay maybe $10,000 for a 10kWh Powerwall or $20,000 for two of them. Big deal! Nobody in the Aussie middle-class blinks twice at $20,000 for a second family car (new or second-hand) so why blink about Powerwall costs? When the time comes to replace my private power pole to get power on to my acreage, I will look at that cost and grid connection costs. I might decide to go off-grid and have no grid connection, 2 x 10 kWh Powerwalls and one electric car instead of two IC cars. I believe I would be much better off but I will do the numbers in due course to make sure. If anyone in the family is really stuck to get somewhere they can use public transport or a taxi. Much cheaper that way.

    I don’t even believe any other back-up power would be necessary for the Brisbane climate. In round numbers we use 14 or 15kWh per day. Despite all the drivel that anti-renewable advocates go on with there is simply NEVER a day when my solar does not make some power in Brisbane.

    For example, on a winter’s day that is light grey overcast and even some drizzle most of the day it will still make at least 1.5 kW per hour for I would say at least 5 hours. That is 7.5 kW.

    A really dark gloomy day might see an average of 0.5 kW for 5 hours for 2.5 kW. But Brisbane often sees a few gloomy hours with a big storm and then the sun is out again (in summer).

    The worst possibility would be a week of cyclonic weather in summer when one might average only 1.0 kW per hour for 5 hours (being very conservative here) per day for a whole week.

    Okay, start week with 20 kWh storage. Use brains. Figure out “gloomy week ahead”. Cut daily use to half; that is 7.5 kWh per day or just a smidge under so its just 50 kW for the week. Seven days’ gloomy generation still tips in another 1.0 kW per hour x 5 hrs x 7 days = 35 kW. 35 kW plus 20 kW stored gets you through a 1 in 10 or 1 in 20 year cyclone-gloom event: the gloomiest 7 days you are ever likely to see in Brisbane. I really don’t know what the anti-renewables people are on about. They must have shares in coal mines. It’s the only logical explanation.

  5. Because many people aren’t aware of this, I will point out that Australia needs no additional energy storage to meet Labor’s suggested 50% Renewable Energy Target. This is not to say that new energy storage would not be useful, or could not pay for itself, but just that it is not required.

    With 50% renewable electricity and no new energy storage, a small portion of renewable electricity generated would be curtailed, but this is currently a cheaper option than building enough new utility scale on-grid storage to prevent it. Even with today’s cost of renewables, as fossil fuel generators age and need to be replaced, curtailing some renewable production will be cheaper than relying on coal for electricity generation and it will definitely cheaper if the cost of coal’s externalities are included.

    Because of the decreasing cost of home energy storage, high retail electricity prices, and the declining cost of rooftop solar, Australia is likely to end up with a large amount of home and business energy storage. But we don’t need to wait for energy storage to develop before expanding renewable generation and reducing our fossil fuel use. We can remove barriers to installing rooftop solar (I’m looking at you, Queensland) and expand our Renewable Energy Target without being concerned about energy storage. In a few years time things on the energy storage front will be much clearer. But being unable to perfectly predict the future of energy storage is no reason to delay the building of new renewable capacity and reduce fossil fuel use, no more than you’d wait to see if a drowning child learns to swim by themself before rescuing them.

  6. @Ronald Brak

    I agree. The anti-renewables lobby simply repeat ad nauseum a whole set of irrelevant and out of date objections. I don’t think it matters however. The real physics and real economics of it will simply roll right over their position. “Words are wind” – George R.R. Martin.

  7. BilB and Ikonoclast, for home energy storage one would want the 7 kilowatt-hour Tesla Powerwall which is made for daily cycling and not the 10 kilowatt-hour Powerwall which is designed for weekly cycling and is mainly for business that want to reduce their demand charges and/or a backup system. The price for the 7 kilowatt-hour Powerwall is set at $3,000 US which at current exchange rates comes to $4,050 Australian. Unfortunately, it is not yet available.

  8. Perhaps a bit not exactly on topic, but if you were getting nationally serious about clean energy, would it make sense in future to mandate in building codes that all new stand alone houses had to have a minimum amount of solar and storage? Given that we could easily be talking about (perhaps well under) $10,000 or so, it would represent a modest percentage increase on an average build, no? I have my doubts it would put any permanent dampener on the building sector.

  9. @Ronald Brak

    Excellent thank you. I would buy three of them if I was going off-grid. 21 kWh would be fine for me to go off-grid. At $10,000 (I could probably get a deal for three units) this would be eminently do-able if not actually sensible financially. If my private power pole was going to cost $5,000 to replace anyway, then my net cost to go off grid would be down to $5,000. Looking better and better.

    I pretty much demonstrated in post no. 29 that with that much backup, 21 kWh, in Brisbane I would expect to need to ration power at my place about one week in every 10 to 20 years.

    It would be vanishingly rare for my 5.5 kW (nameplate capacity) PV system to generate less power in a week than 35 kWh. That plus 21 kWh backup is 56 kWh. We use about 14 to 15 kWh per day for a family of 4 adults with no attempt to save power. If a whole very gloomy week portended we could survive on 7.5 kWh a day no trouble.

    There are such things as sunshine forecasts. A little smart program could work in sunshine forecasts, known household useage and patterns and give the home user (very rare) rationing alerts based on probability assessments. I think it would almost fun to live like that. Make all your own power and take responsibility to self-ration on those rare occasions when rationing was necessary. What’s the big deal? A tepid shower and a cold dinner never killed anyone.

  10. @steve from brisbane

    Absolutely, great idea. Why not make First Home Owner Grants (which often amount to $15,000 or more depending on state or territory) dependent on building in mandated solar hot water, solar PV and a Powerwall or equivalent. Too easy, makes sense, therefore our stupid pollies will never do it… or WILL they? I guess we just have to await the day, not too far away now, when jobs for the boys comes from solar not coal. Then they will do it.

  11. In Christchurch we had one spell where it rained every day for 10 weeks. That happened once in 17 years, so it can happen, but rarely. I haven’t yet got any numbers for how much my system produces on cloudy days of various sorts.

  12. Ikonoclast, you might want to consider getting two Powerwalls and using the money you save (sorry, you won’t get a special deal for bulk orders) to expand the number of solar panels on your roof. There’s no need to get a large inverter to match them, although you will need an islanding off-grid inverter that is compatible with Powerwalls. Provided you can get extra panels at a low enough cost you may be better off with the extra electricity they will generate for you on cloudy days than with a third Powerwall. After all, you can expect typical solar panels to last for decades while a Powerwall only has a warranty for a decade, so you can expect lower running costs doing it this way.

  13. @Ronald Brak

    That’s a good point. And our whole discussion certainly illustrates that in a place like Brisbane the average household could run on solar PV panels (extras if necessary as you say) and a couple of Powerwalls. The times when one ran out of all power would simply be very rare to non-existent. And if it happens, pull out the gas barbie and try a family conversation rather than TV or internet!

    Perhaps people from other places and other climes just don’t appreciate how much sun a place like Brisbane gets. Examples;

    (1) Under total light grey cloud cover with drizzle in winter my panels can still push out about 1 kW for hours on end. So wet days simply do not mean no power generation.

    (2) A big storm knocks power gen down to 500 w for an hour then the sun comes out with tufty clouds all over the place and hey presto the lensing effect and power gen shoots up to about 5.2 kW for hours on end (on a nominal 5.5 kW system)

    (3) Winter days are clear and cool. Cool solar panels are more electrically efficient. Even mid-winter in Brisbane a 5.5 kW nominal system can push out 3.5kW to 4 kW for hours on end, no problem.

    I had no idea how good solar PV and solar evacuated tube hot water would be in Brisbane. The performance of my system has knocked my socks off. And given that EROEI for solar is getting up to at least 10:1 it’s a no-brainer now.

    Yes, I used to doubt renewables’ EROEI and dependability. Now that my knowledge has caught up with the facts I have changed my mind.

  14. @BilB

    Christchurch may well be different, but solar panels still make some power in Brisbane even on rainy days. The assumption that the panels produce zero power on rainy days is not correct, at least not for Brisbane.

    Anyway, Christchurch, Sth Island! Heavens man you have massive hydro, real and potential. 🙂

    Why would you even care about solar power?! See that’s the thing. Just about every place in the world has some sort of renewable power that is very good for it regionally.

  15. I’ve been back in Sydney for twenty years, Ikonoclast. Good point though. NZ has committed to shutting down its last 2 coal fired power units replacing their energy with geothermal. Thanks for doing some evaluation above. I have been been through it completely yet but will do tomorrow.

    I firmly believe that the backup generator will be an important part of the solution for the distributed system. It will generate DC which will feed directly into the power wall at a constant rate topping up its charge during extended low solar periods.

    A complete solution has to accommodate high rise apartment buildings and city commercial high rise. Lifts must be kept running reliably. Wind power is part of that sector along with hybrid CSP and gas turbine power. there will be a very significant amount of surplus capacity with the combination of distributed rooftop solar, wind CSP, Gas and hydro. The future is looking very appealing from an energy point of view.

  16. Aukland is sunnier than Melbourne and the average price paid for electricity in NZ is higher than in Melbourne. Also it is possible to get massive feed-in tariffs there that are higher than 6 Australian cents! So New Zealand is a fine spot for rooftop solar, provided they can install at around Australian costs. New Zealand certainly could build more wind turbines and with its large geothermal and hydroelectric capacity quickly remove fossil fuels from electricity generation, but their government is a bit lame when it comes to climate change. But as far as I am aware their Prime Minister isn’t actually an alien infiltrator actively seeking to terraform earth into a more venus like environment.

  17. It’s worth noting that Tesla’s Powerwall was announced with an option to upgrade the warranty to 20 years. I’m not sure if that is due to confidence that most will indeed last that long or that sales without the extra warranty will subsidise those that don’t. I’d like to think they will last that long, but my understanding is that Tesla’s batteries are built out of ‘standard’ LiIon types, and if there is anything new it’s being able to manufacture at lower cost. Other entrants worth paying attention to are Alevo – that are into megawatt hour scale LiIon batteries that are not an established type, that they are promoting as having very long service life. 24M is a startup that looks likely to produce LiIon that is cheaper to manufacture and overcomes some of the problems of ‘standard’ types by having a semi-liquid electrode. Vanadium redox flow batteries and variants, with electrolytes that can be endlessly reused, just keep getting better and cheaper. Organic quinone based flow batteries, based on cheap and non-toxic chemistry went from lab curiosity to startup in under two years – short life/few cycle curiosity became tens of thousands/long life in short order – worth keeping an eye on.

    A lot of positioning of establish battery giants for the new low emissions era is going on – even if costs are not quite low enough to kickstart major investment at utility scale yet. At domestic scale, if prices Tesla has been claiming were available here and now I’d be looking at one or two powerwalls – with a big expansion of PV capacity to go with it. I suspect that I would not be alone.

    It will be interesting to see if Ergon Energy’s trial of PV with storage package, that gives the provider access to that pooled storage will be a wave of the future – some of the possibilities that I’ve noted before, like pre-empting predicted overcast conditions by charging batteries off peak and engaging in profitable trading of excess power could be tried. But I wonder if we will see more of the major encumbents engaging in heels dug in efforts to undermine PV with storage, using their political influence to lobby for regulations that allow rejecting or limiting PV input to prop up fossil fuel suppliers, disincentivising it by shifting the balance of charges away from usage, or even – as has been suggested – levelling charges for grid defection. I suspect that the very low feed in prices and sometimes rejection of feed in connections were badly thought out and failed efforts to undercut the takeup of PV. I’m not convinced going off-grid is the ideal way to go but a reasonable price structure for grid as backup for solar equipped homes is needed, and we aren’t really getting that yet.

  18. Thanks for this post on EROEI John. Its great to see increasing numbers of people thinking and discussing ‘holistic’ change in the real world that goes beyond the old model of holism as wishful thinking + chanting ‘OMMMMMMMMMMMMMMMMM’ – not that I actually mind the latter but it didnt offer the urgently needed solutions.

    Some lateral comments:

    1. A ratio of 10:1 sounds about right and in line with the analyses I’ve seen in the LCA literature and illustrates how certain aspects of an advanced steady state economy are conceptually feasible. Its probably a waste of time going further. The main point is the factor is already damn good – an it comes with all the secondary benefits – not juste reduced CO2 emissions but quietness, robustness, not ugly, individual empowerment, suitable for remote locations, use of ‘wasted’ roof space/replacement of roofs, cost efficiencies which should kill the distribution industry parasite system.

    2. There are other alternatives to battery storage on a large scale that may be much lower cost – water pumping, salt heating, air compression, flywheels etc. I expect this isnt covered above but these are more likely to improve the numbers. So all good.

    3. A complication for me is the bigger picture. Basic LCA is probably fine for small sectors – but you are talking here about the technology for powering the new infrastructure and how it operates. Conversely currently free stored energy in the form of fossil fuels effectively subsidizes the larger economy in ways PV cant and shouldnt match…including much waste, bad politics, war etc.

    Which implies all sorts of feedback cycles your LCA could not take into account – One particular issue is the problem of transport energy which is less easy to solve from my reading of it. Maybe I’m wrong but I still see the current energy system as unsustainable in its currently basic form – on the other hand getting the 4WD drivers onto pushbikes is nothing to complain about.

    For my money there is much to be gained in the future by constructing infrastructure to last for potentially hundreds of years so that after the usual 10 years of discounting we are left with essentially wealth to pass to the future rather than the crap that is currently being built following short term return principles.

    Its one limitation of current EROEI and many other models especially in economics related areas – they are lousy at dealing with time as a consideration.

    4. A different aspect of EROEI is the principle embodied of looking at feedbacks and costs and MAINTENANCE ENERGY…. illustrated by how biological systems operate and a great ecological economics concept that conventional economists continue to mostly ignore/not get yet, demonstrating their still primitive conceputalization of how the world works.

    Still overall a great post and personally I welcome this emerging feature of the brave new PV world which should indirect address an old obsession of mine – nuclear proliferation arising from going down the nuclear power station track.

  19. Just thought I would give a point in time reading (or two) to people to illustrate a point about solar power.

    Time: 9:15
    Date 21/08/2015 (still winter technically)
    Location: Brisbane
    Latitude: 27.4667° S
    Sky conditions: Complete grey overcast with some bright-ish patches. No blue sky, no direct sun.
    Precipitation: Not currently raining.

    Solar PV array nominal capacity: 5.5 kW
    Current output: 1.706 kW.

    The notion that an overcast day always produces zero solar power is completely false. If a system like mine can produce just 1.4 kW per hour average for 5 hours it can recharge a Powerwall if no power is being used. Assume the householder is at work and is careful to turn all “vampire devices” off.

    In a follow-up reading at 9:40 the sky had become a more uniform medium grey and drizzle had set in. Output reading = 0.524 kW

    Such conditions can cycle or one pattern of the other can set in for the day. These production rates are not great. Neither are they nothing. Even this “trickle charging” on gloomy days makes a significant contribution at the domestic level.

  20. To continue the above…

    Then as if to make my point, the sun comes out a bit at 11:20 and power production of the unit goes up to 3.5 kW to 4.0 kW due in part to cloud “lensing” effects. This is even though there is still much many light grey and dark grey cloud cover.

    The scenario of non-stop torrential gloomy downpours dawn to dusk is not that common even Brisbane. A week of cyclonic weather in summer might do it about once every ten years. There are plenty of options to cope with these relatively rare events.

  21. which conveniently yields about 1 tonne of CO2 per mWh … I may have made an order of magnitude mistake somewhere.

    There’s a 6 order of magnitude error there, but apparently no-one else noticed it. If coal really did put out a tonne of CO2 per milliwatt-hour solar would have eaten it for lunch back in the 1970s.

    For those concerned that PV systems might be unreliable, PVOutput has a huge collection of actual PV systems reporting live data that you can browse through. Pick the suburb you live in via google or just browse from

    In Sydney this winter we’ve had a few days under 1kWh/kW, but never all in a row.

    I’m currently running the numbers to see whether it’s cheaper to buy more panels or more batteries, once we put batteries in. PV is very cheap compared to almost anything – we can get about 2kW of extra PV for the marginal cost of a heat pump hot water system over resistive, for example. The heat pump would save 2-4kWh/day… which is less than what the extra PV generates.

    We need to split consumption into PV-time and no-gen time to get useful information. With the resistive hot water on during the day, we use about 5kWh/day during the day and another 2-4kWh/day during the night. So on a bad winter day with ~1kWh/kW and an 80% efficient battery we need 10kW of PV. To store a night worth of usage we need 5kWh of battery. That’s a battery:PV ratio of 0.5 instead of the 2 that Prof Q uses, but he seems to be assuming you need two full days on battery with zero input, so I’m guessing that’s worst case for somewhere like Hobart.

  22. FWIW, 10kW of decent PV would cost … OMG, we paid about $4500 for a 3kW system like the one on AHE’s front page which is now $3000. So, roughly $1/kW… $10k for the PV, hit Commodore for a battery kit (purely because they have prices online) and 3kW of PV with 12kWh of usable storage (24kWh PbS) is $13k, another $7k to bring that up to 10kW of PV and we have a usable system for about $20,000. realistically it’ll be closer to $30k by the time you use reputable suppliers and decent panels (LG rather than Trina panels etc).

  23. @Moz of Yarramulla

    name symbol conversion
    milliwatt mW 1 mW = 10 to the power -3 W
    watt W –
    kilowatt kW 1 kW = 10 to the power 3 W
    megawatt MW 1 MW = 10 to the power 6 W

    It seems there was a 10 to the power 9 mistake. But it was only a mistake of case really. I think everyone knew Megawatts was intended.

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