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. Someone with Brave New Climate will be with you directly JQ.

    More seriously, renewable componentry is likely to be highly recyclable as well, with much lower energy inputs in reusing good wind turbine or solar sites, batteries and probably solar PV infrastucture (mounts, invertors possibly, even panel frames).

  2. I think there are great savings at the other (consumption) end of the electrical economy. Infernal Combustion Engines – misspelling intentional – have an efficiency of 20% on a good day. Electric motors have an efficiency of 80% on a bad day.

    What does this do to “apparent EROEI” as one might call it? Surely it means that a 10:1 EROEI in the new electrical economy provides as much useful work as a 40:1 EROEI did in the old oil economy.

    And this is talking about production “at the well-head” and “at the solar panel factory gate”. if people want to add in supply chains and transmission/transport costs for the electrical economy they must also add them in for the oil economy. A 100:1 EROEI claim for a new self-gushing surface oil well (very rare these days) is EROEI at the well-head not at the end of the oil supply chain.

  3. Given the profile of the buyers of battery packs, and the similarity of the products, it would pay battery makers to promise greener supply chains. Since renewable electricity now costs the same as fossil, this move is not expensive.

  4. Another way to look at it would be to assume that a battery lasts 1000 cycles (fairly typical for LiIon I think), so each day (assuming full discharge at night) 0.4kWhrs of battery manufacturing energy is required. 8% of the generated power, not counting the depreciation of the PV panels.

  5. Qld ALP determined to destroy solar:

    …Mr Bailey said a fair price for a solar energy tariff would be announced in mid-2016.

    “The independent Queensland Productivity Commission is looking at electricity pricing and will conduct a review into a fair price for solar,” he said.

    “The fair price for solar review is scheduled to report in mid-2016.”

    Mr Bailey said the uncertainty in Queensland’s solar market was due to the federal government’s position on the Renewable Energy Target, not shifting Queensland Government policy.

    “Despite uncertainty over the federal government’s Renewable Energy Target hampering the popularity of solar energy recently, demand for domestic solar has been resilient over time.”

    Mr Bailey disagreed the decision to increase the fixed energy supply charges – paid regardless of how much electricity was used – was a disincentive to take up solar power.

    “Solar users still require – on the whole – still require the use of the grid and the network,” Mr Bailey said.

    “They have to be funded and that is why there is a fixed charge,” he said.

    “Solar users will sometimes be putting energy back into the grid, they will sometimes be taking it out of the grid.

    “And depending on a number of factors, but the network still has to be fully funded.”

    The ALP and LNP are effectively identical on all policies that matter most. The ALP has no interest whatsoever in making any changes that might increase solar, decrease carbon emissions and might – possibly – save the planet. They work for the same “1%” as Abbott.

    The sooner enough real people realize that the greater our chances of survival. But while we continue the illusion that they are in ‘opposition’ to the LNP we are headed on a course of certain destruction.

  6. Tom, 1,000 cycles is low for lithium-ion home energy storage that is either on the market now or should be in the next couple of years.

    We know from years of electric car data that lithium-ion batteries can be quite durable. Currently, the 24 kilowatt-hour Nissan Leaf battery pack has an 8 year or 160,000 kilometer warranty. That many kilometers represents about 1,200 cycles, after which the battery will still have at least 80% of its full capacity and will still be useable. The Tesla electric car is warrantied for 8 years or 200,000 kilometers, or infinite kilometers for 70, 85, and 90 kilowatt-hour battery packs. The Tesla battery pack achieves this reliability not by being more durable than Nissan’s batteries, but by being bigger.

    However, stationary energy storage is considerably different from electric vehicle batteries. The 7 kilowatt-hour Tesla Powerwall, which unfortunately is not yet available, has a 10 year warranty which means it should operate for at least 4,000 cycles. And the Samsung 3.6 kilowatt-hour lithium-ion energy storage system has a 7 year warranty and so should last for considerably more than 2,500 cycles. I expect there will be a shift to more cycles and longer warranties over time and it may not take long for 10 years to become standard.

  7. John, your back of the envelope calculation looks good to me. You’ve erred on the side of caution and bumped the figure up a little for the 2 kilowatt-hour storage and that makes sense, as for stationary applications there is less incentive to keep weight down as there is for mobile applications and so it may mass more per kilowatt-hour than a car battery pack and it will still need a certain amount of electronics that will be hard to get below a certain size. However, making the energy storage module part of a solar inverter, particularly if its just 2 or 3 kilowatt-hours, will help keep its mass per kilowatt-hour down.

    And I am certain that energy and materials required to produce home and business energy storage will decline as the technology is improved. And as the world’s largest lithium producer, having just beat out Chile with its 13,000 tonnes of production, Australia can do its bit to reduce emissions from battery manufacture by minimizing fossil fuel use in lithium mining. (But note that 13,000 tonnes of lithium, soon to be 18,000+ tonnes, is likely to be lithium carbonate rather than lithium metal.)

  8. John, your EROEI calculation is good as far as it goes. The problem is that your scenario drastically understates how much battery storage would be required to make a solar system “reliable.”

    Take the 7 kwh Tesla Powerwall battery. It gets about 5000 charge/discharge cycles, and assuming an 80 percent depth of discharge, that’s about 28,000 kwh of storage over a lifetime. Per your estimate, its energy input is about 1200 kwh, so the EROEI is 23, which is great. (Assuming we should even calculate a separate EROEI for a battery, which doesn’t actually generate electricity. It might make more sense conceptually to just aggregate the battery’s energy input with the solar system’s.)

    But here’s the rub. Your scenario of 2 kw of battery for ever kw of solar panel (I guess you mean 2 kwh of battery storage?)—seems wholly inadequate for a reliable solar-plus-battery system. Estimating from “average” daily solar output is meaningless, because solar output is anything but average, with deep droughts that can last for weeks. To bridge the gap between average and real-time output requires a battery system with huge redundant capacity, much larger than you have allowed for.

    For example, a typical American home’s daily electricity use is 30 kwh (much more during extreme weather), of which a Powerwall can supply just 7 kwh. The best a Powerwall can do is extend the hours of solar supply into the evening after a sun-drenched day’s storage. If the next day is overcast, the battery is dead along with the PV panels and it’s back to the grid. If you want a solar-plus-battery system that’s reliable enough for a single winter week of overcast, you would need 20 Powerwalls worth of storage.

    Calculating the EROEI on that kind of redundant overbuild is tricky; the system would have a much lower depth of discharge, which would give it more cycles, but the scaling isn’t linear. But realistically the EROEI for a reliable solar-plus-battery system would be much lower than the naïve estimate above. And even a week’s worth of Powerwall storage is nowhere near enough for the kind of solar droughts that are routine in, say, Germany.

    It all boils down to what task you want batteries to accomplish. If you limit your ambitions to storing some solar power that would otherwise be wasted, and extending solar operating hours into the evening on some days (but not on many others), that’s perhaps a feasible goal in terms of cost and EROEI. But it’s not feasible to add enough battery storage to support a truly reliable system of intermittent generators, one that’s not dependent on backup from the grid and dispatchible power plants; the result would be huge costs, a major hit to EROEI and only modest improvements in reliability. See my article here for more.

  9. The other way to look at it is that the battery pack can also store power from the grid during off peak periods reducing the need for big generators to meet peak demands.

  10. @Will Boisvert A typical American home can be in Alaska or Florida or California…enjoying a vast range of weather conditions. Could excess solar from California be redirected to Chicago?

  11. There are two important points in this debate;

    (1) Energy storage at the household level is not limited to batteries.

    (2) Energy storage is not limited to the household level.

    Point 1 – My house stores energy (and another useful energy gradient) without batteries. Every house can do this. Any solar hot water system stores solar energy with batteries. It stores heat energy which of course is the exact form of energy required for that application. There are no re-conversion costs to another form of energy.

    My house “stores” or maintains a useful energy gradient when I aircon a well-insulated room with solar power by day and then turn off the aircon by night. The room stays adequately cool and de-humidified for 10 to 12 hours.

    There is great scope for increasing the ways in which houses are passive-designed, insulated and able to store heat energy as required or maintain energy gradients to maintain comfort in the house. These approaches will all considerably reduce the need for battery storage at the domestic level.

    This approach is not limited to tropical and sub-tropical climates. These is great scope for seasonal thermal energy storage in colder climates. See the Wikipedia article.

    Point 2 – The grid can store energy at industrial levels with or without batteries. There are many approaches. See the Wikipedia article on energy storage.

    Energy storage engineering is arguably less difficult than nuclear engineering. There are also systems which lose little energy in the actual storage phase. More energy is lost in the re-conversion phase but this loss needs to be balanced against the energy wasted when so-called “base load generators” are kept spooled up for periods when the demand is not there.

  12. Correction: I meant;

    “Any solar hot water system stores solar energy (as heat energy) WITHOUT batteries.”

    This blog needs a user edit function. Heck, the computer game blog I frequent has edit capacity and many other more sophisticated user functions than this blog. I guess it’s a matter of money though.

  13. I’ve been looking for a production watts per watt of output. This is as close as i have come so far

    Click to access 37322.pdf

    Pretty well every source highlights the moving target nature of the production as technology is moving so fast. See next comment for an illustration of where the technology is.

  14. A potentially controversial thought. Our host has noted a few times that the cost of solar, batteries, wind, etc is falling rapidly and is likely to continue to do so.
    Does this actually weaken the case for setting strong renewables/ carbon targets now, since there is a reasonable case that it will be cheaper to convert more rapidly in the future? A lot of the case for early adoption is about warding off huge costs in the future – but what if technological advance is causing those huge costs to melt like icebergs?

  15. Where the technology currently is

    The commonly installed panels are around 17% efficient. Anyone bothering to read my comments should notice that I recommend PVT’s over PV’s as the future of rooftop solar.

    See Solimpeks for an early example though not yet optimal but will convey the idea.

    PVT’s deliver up to 3 times the energy throughput of a straight forward PV with the balance after the electrical output being thermal energy at a level suitable for water heating and space heating. Obviously the higher the electrical conversion efficiency of a panel the lower the amount of thermal energy there is left to take away as heat. A 45% PV panel would be an awesome piece of hardware, but not likely in the very near future for houses unless it is as a concentrating system.

    Conclusion: the EROEI aguement is a total crock.

    Batteries: The last mainstay of the anti renewable brigade is that you would need huge banks of batteries to cope with a week of clouds. That is largely true if that were the only option, but it is not the only option by a long shot.

    Backup: Though not yet available as a system the Liquid Piston engine generator set is the ideal technology here. This is an generator set that will be around 160mm and 450mm long to produce 2.5 Kw continuous and 3.5 Kw peak plus provide 5 Kw energy equivalent output as hot water from its cooling jacket. The system runs quietly with very low vibration, requiring minimal muffling to produce as low noise as a split cycle air conditioner unit. The generator will run on CNG or synthetic methane produced from recycled municipal refuse. I calculate that such units will operate for around 600 hours per year to deliver continuous energy access for a 4.5 kw PVT rooftop solar system. The LPG gas consumption will be around 1.2 litres per hour at 2.5 Kw output, I have not done the CNG calculation yet. The engine will have a 3 to 4 year life and be a plug on replacement. These 70cc engines are designed to cost competitive with whipper snipper type products so will not be prohibitively expensive to replace and recycle.

    Final Conclusion: Though all of the components are not yet readily available for completely modular renewable energy life as usual replacement, the technologies are all proven and in the process of working towards high volume production.

    Warning to Grid energy operators: Learn to speak nicely to your customers and develop renewable energy complementary technologies or you will become substantially redundant.

    Warning to Nuclear Energy developers: get on with designing practical Nuclear Power Plants for shipping or you will become substantially redundant.

  16. @BilB

    Basically, I agree. I could embroider round the edges and add a few more of my own arguments but it wouldn’t alter the fundamentals of what you are saying.

    Old school grid energy generators (coal and nuclear mainly) are indeed showing extreme arrogance and stupidity in their business models and treatment of the public. They will rapidly obsolete themselves if they don’t change their ways. As macro generators, they can move into macro solar and wind or they can die. If people think very large companies can’t be rendered obsolete by failing to properly move with new technology and then die very, very quickly they ought to look at Kodak.

  17. Ikonoclast, I’m not one of those hoity-toity people who uses “washing machines” or engages in “clothes hygiene” so I didn’t know what you were referring to with regards to Samsung washing machines. But after reading about it, in answer to your question would I buy anything from Samsung, well of course I would if, all things considered, I decided it was better than the next best alternative. In fact, I would even look up someone whose washing machine caught on fire, befriend them on facebook, and then say to the Samsung salesperson, “Look, I like your product, but I am concerned about safety because my friend’s Samsung washing machine caught on fire. So I’m not going to buy it unless you give me a discount equal to the cost of at least a couple of fire extinguishers.”

  18. @Ronald Brak

    Better make that an automatic sprinkler fire system. 🙂

    More seriously, I don’t ever give businesses second chances after dodgy products or services. (Dodgy = dishonest or unreliable).

    There are quite a few businesses in my nearby suburbs whose doorstep I will never darken again. Equally, a city dweller always has more options to try until he or she actually finds a good business or trades-person or professional, relatively rare as such entities are.

  19. @Will Boisvert
    You seem to be using a worse case scenario. Where I live – Hobart, Tasmania – there are plenty of clouds but a fully overcast sky is unusual, a full day of overcast sky is a rarity and an overcast week would be a 20 or 50 year event – I guess, I’ve never seen one. (I have a meteorology background and I watch the sky.)

    That’s here. Other places are different. It should be possible to combine site information and sunshine records to optimise panel capacity, panel type, and battery capacity to risk and cost of shortfall. All this can be calculated and is location and application dependent. While, there will obviously places where solar doesn’t work, and entities that need more power than can be generated on site there are going to a lot more places where it does. I’m not sure if you are strawmanning, but the objective is not achieve an individualistic dream of complete energy self-sufficiency but rather to substantially reduce coal/CO2 at low economic cost – or, as now appears to be the case, at significant economic benefit. So far, no one is proposing to rip out the grid in a fit of spite so this remains a component of the solution.

  20. @rog

    That’s right. Distributed storage capacity greatly reduces the amount of backup grid generation capacity that’s needed for any given level of reliability. I’ll try to do an illustrative post on this when i get time, but, as a first approximation, backup generation capacity only needs to match average use over the course of the day, not peak use, even assuming zero contribution from distributed solar and no use of demand management.

  21. @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.

  22. 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?

  23. 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.

  24. @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.

  25. 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.

  26. @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.

  27. 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.

  28. 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.

  29. @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.

  30. @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.

  31. 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.

  32. 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.

  33. @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.

  34. @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.

  35. 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.

  36. 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.

  37. 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.

  38. 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.

  39. 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.

  40. 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.

  41. 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.

  42. 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).

  43. @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.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s