Solar Power and Storage - a nerd's view

  • DISCLAIMER: this is not going to be anything about global warming, carbon taxes and how they systematically rort us all in a dystopian future, or any of that shit. So cool your jets, Baron 😉
    ALSO - please do not promote this as an article. I've shared this info here at Hooroo's request, and pretty much anything I want to say in a public environment is already out on the internet. There have been many comments on many websites (from The Australian through to gizmodo etc) that I've been itching to reply to, but have restrained myself from. When the facts and figures stack up, I'll give it a bit of jandal 😉
    And yes, this is a bit of an essay. What I'm aiming to do here is explain what it is, how it affects me, and from a technical point of view, what the dis/advantages are.
    Those of you who know me on social media will have seen some links that my name has been splashed around a tiny bit in the mainstream, but moreso around the nerd media, for the installation of the Tesla Powerwall. The first in Australia, I'm told. Maybe in the world for a domestic (non-test) install.
    Hang on a sec - the Powerwhat?
    Well, there is the official explanation of course, but in layman's terms: put a sodding great lithium battery on the side of your house. Charge it using solar panels during the day, and then use that stored power at night. 
    ("And hope it doesn't catch fire!" scream the critics - and believe me, its something I've considered).
    Yes, I'm very aware there are other battery systems out there. Some of them are cheaper per kW. Some of them have a higher capacity. But this one hit the sweet spot for me in terms of:
    Cost - one I'm willing to pay for this size storage
    Physical attributes - wall mounted instead of a big steel box filled with (effectively) car batteries taking up space in my backyard/garage
    Storage Size - enough to help reduce my power bill to acceptable levels, or eliminate it
    Prettiness - this is so NOT me when it comes to technology, but jeez its pretty to look at. And I'm a massive Elon Musk fanboi.
    Picture attached from part way through the installation process. And the box it comes in - even the BOX is pretty 🙂
    [attachment=1953:IMG_20160127_150130.jpg]  [attachment=1954:01_box.jpg]
    You can see all the official spec sheets over at Tesla, but with a rated capacity of 7kWh, a percentage of which is not usable because science, so its really 6.4kWh according to the boffins. That should be enough to provide between 25-35% of my daily power needs, and effectively "power shift" the solar I've gathered through the day into times when the sun isn't available i.e. when we're home at night or getting up in the morning.
    As per a standard solar PV (photovoltaic) install, the solar panels are also running the house at the same time they're trickling power into the battery, or feeding it back to the grid for either a provider tariff or market-led rate (see Reposit below)
    I am expecting the system to reduce my power bills by around 85% as a minimum. Depending on available sunshine, maybe close to 100%, which depends on behaviours. I spend around $1920 a year on usage alone, a lot of which is down to behaviours.
    The cost thing - let's get this out of the way now: EDIT: $15,990 inc GST, Australian dollars. Yeah, we can flag that as a "disadvantage".
    Before you mouth the word "fark!" to yourself: that is for 5kW of panels (which is about as big as my north-facing roof will support), the inverter, battery, and supporting equipment, all installed. That system is considered "large" in terms of domestic solar, but not "huge" where its getting up to the limit of what the solar subsidies provide (limit is 10kW I believe).
    And I'm not just pulling this money out of thin air or raw talent (ha!). My grandmother passed away nearly two years ago now, and her estate cleared recently. My portion wasn't quite enough to cover the whole cost, but it was enough for a good family holiday to NZ, and I opted for this, so that in future years I can afford more holidays to NZ 🙂
    Even if you take out the approximate cost of the battery as a standalone install, some of you might be asking whether I could have done the solar part more cheapky, and the answer is "probably" - but are those apples the same as my apples? I've not taken this step without doing some research, including consulting with people who have solar with and without batteries, and one of the big things is efficiency of the array as a whole unit, and how the embedded tech fits into that.
    If ever you are installing solar, consider the type of panel you're installing, and whether it has a micro-inverter on every panel. There are technical explanations in the googleverse if you want detail, but basically a micro-inverter is a device that regulates the panel's supply on an individual basis, instead of the wall-mounted inverter controlling the entire array. Why does that matter?
    On an older/cheaper style system with no micro-inverters, all the panels are wired back to the inverter as a "single string" setup. If one of the panels goes into shade, the efficiency of the whole array suffers, because the basic movement of electrons through the system is expecting balance from all panels.
    My system has micro-inverters. So if part of the array goes into shade or even if one panel just stops working, the rest of them continue on as if nothing happened, because the micro-inverter makes that panel the master of its own destiny.
    This is especially important in my case, because I didn't have one single roof area to put all 20 panels on - so they're in two arrays, facing the same direction, but one array is on a roof area slightly to the east of the other. This means that, once the sun is getting lower, array #1 starts to get shaded. In an older/cheaper system that would basically be lights out for the whole array.
    In addition, I've got warranty from my installer as follows:
    Powerwall - 10 years for grid-connected systems (Tesla-backed)
    Panels - 25 years (installer-backed) performance, 10-year product
    Workmanship - 12 years (installer-backed)
    If anything goes "pop" I've got that to fall back on. In addition, the installation company has been around for years and doesn't look to be going away soon. The panels are made by what they call a "Tier 1" provider, so a bit of assurance there as well.
    So what are the "hard" numbers. When do I expect to make that money back/ROI? I've looked at the consumption figures across the last 12 months, where our house consumes approx 22kWh per diem across the year, with a rate of approx 23.5c ex GST (I don't have off-peak power). The answer is:
    Approximately 8.4 years. 
    Some thoughts around this:
    The rated lab-tested output for a 5kW array at Sydney's latitude is 19.5kWh per day - which will be an average across the year I suppose. Being in less than a week, my daily readouts so far with weather conditions have been:
    22.521 kWh - light overcast
    21.077 kWh - light overcast
    25.148 kWh - light, occasional overcast
    29.540 kWh - clear
    14.506 kWh - overcast day up until about 5PM
    17.580 kWh - up until about 1350 hours AEDST today - mostly sunny
    I realise this is summer, but those are pretty good numbers. It isn't going to necessarily give me 100% coverage. What if we have some particularly overcast weeks? The battery will struggle to top up, and I'll be yanking power from the grid. In winter, the sun will be further north, and my array faces just west of north, so might lose a little there as well, with the shorter days considered.
    So, some behaviours have to change. I've already informed the wife that boiling a litre of water to make 1 cup of tea needs to change (and makes subsequent cups taste poor due to deoxygenation or some such). Running the air conditioning full blast because it is outside the 21.3-21.35 degrees Celcius range she likes in summer (add 2C for winter) is just ridiculous. I accept we need to live comfortably, but be a bit smarter about it.
    Similarly, when we're running "big" appliances like washing machine, dishwasher, etc. we need to use the timer functions they have, to let them suck power from the solar panels, and not use the battery or grid. Ironing will now have to be done during daylight hours where possible, and I've set the pool pump to run the minimum required time per day, starting from when the sun is well overhead.
    Go look at the power ratings of various devices in your house and you'll see where the power is going.
    There are still unknowns - how much power ARE we using at night? Do we need to replace some appliances that are just too old and inefficient? What will that add/substract from the ROI overall? Do I run the air con on low all day on hot days, so I don't need to use it at night when the battery will be running the lights/TVs etc?
    I'm not stressing too much about it, but I am whacking a lot of moolah into this, and want to see good returns out of it. I want the running costs of the household to go down correspondingly. But there are also opportunities with other startups...
    The battery is rated to give "5 hours household power" but I won't know whether they mean something the size of mine, or something smaller. Maybe, being American, it'll keep my house running until The Walking Dead actually happens because their average house is megawatts bigger. All that will be found out in the future.
    Speaking of the future - if prices move up 10% - which is only a couple of cents per kilowatt hour, the ROI drops by approx 9 months. Throw in a carbon tax, and you're going another leap. So I take a bit of surety there, and in other technologies like this:
    Reposit (
    My provider has a net metering feed-in tariff of 5.1c / kWh that I export to them. So if I left things sit the way they are, after my solar panels are running the house during the day and topping up the battery, I will export a few kWh and make a few cents on any given day. But by the time I pay the daily grid connection fee of 77 cents, that isn't going to amount to much (and some providers are over 90c/day!)
    Reposit is a startup, from Canberra, who are looking to do a bit of their own disrupting in the electricity market. They attach a device to your battery, that analyses your usage and input/output to battery and grid use as well as weather patterns, and wider grid use from power companies. At a given point in time, it can then sell your stored power into the open market at a higher rate than the provider feed-in tariffs, and help increase the value of each kWh.
    e.g. if I generate 25kWh on a given day, use 6 of it to top up the battery, and another 15 to run the house, I've got 4kWh fed into the grid. That's 20.4c return my electricity provider.
    On the other hand, Reposit's software might analyse my patterns, decide I've got 3kWh in the battery to spare in peak time, and sell it to the grid for a peak value of 40c/kWh. That's $1.20 for me, which pays for my connection fee with a little left over.
    Some people (like these guys) are making up to $1 per kWh, but I haven't set my sights that high 🙂 What this does offer is the ability to sell power back and forth and establish "micro-grids" which reduce reliance on distant power stations (be they coal, nuclear, hydro, etc).
    So there you have it. A discussion based on financials, that is flavoured with a tech-interest and green, touchy-feely side of things. Fire away with any questions you might have.

  • I'll be really interested in the actuals re your power bill Nick. If i do end up building this year, given where i live, this kind of tech could be pretty handy.

  • THis is probably going to be the dumbest question....
    At night if the Tesla battery runs flat, will you notice the switch back to grid/paid for power or do you get a warning and you have to switch back to grid yourself? How does that transition happen?

  • On a spend side of things, I'm not sure you should even bother working out the pay back as a source of satisfaction/ worry if right thing to have purchased. You had that money burning a hole in your sky rocket. Sometimes it's just nice to spend knowing that you won't have to spend in years to come.
    Good for you, I say.

  • Its funny you mention that, Hooroo - because while I was in the process of getting the install done, I've been looking at other energy providers, and found someone cheaper by a double-digit percentage, so the ROI I calculated originally is not relevant once I change over. 
    But, as you say, I've got the money to do it, and I want to do it. Some people would have spent it on a car, holiday, hookers n blow 😉 I decided to be a bit sensible, a bit nerdish, and a bit future-thinking.
    Now that it is spent, I'm not beating myself up about the ROI. But there are a LOT of critics* out there that are waiting to see this fail, so the ROI I've got worked out will be the test case for me sticking it up the fluffybunnies.

    • So far, the articles in which I've appeared - from esteemed publications like The Australian, down to the tech sites, have contained a fairly equal balance of "good on you! Well done!" people looking at this tech for themselves, compared to "too expensive, will wait until early adopters like this bloke drive it down" to the utter shitwits with stuff like:
      "Ha! Interview them in 25 years when they've finally paid it back!"
      "Rich people like this suck up subsidies, and will force providers to drive up prices, and only hurt poor people!"
      "Look at this bloke - huge house, heated^ pool, 2 kids - profligate Western lifestyle and thinks reducing his carbon footprint 0.5 percent makes the world right!"
      ^ Pool isn't heated, btw 🙂 That is madness - I have a blanket to trap heat.
      Various things in between. Lot of comment from people who are clearly baby boomers and/or climate change deniers, and have a real problem with any form of progress like this. At one point I had to question whether I was an elitist white Tesla shill, crushing the poor under the heel of my jackboots while worshipping at the altar of the money god. Never mind that the poor are tax neutral to the government, and I pay a fair share.
      I am actually planning a follow-up in a few months with some of the outlets I spoke to, just to give them a progress update - and to get those fuck knuckles to eat crow 😉

    THis is probably going to be the dumbest question....
    At night if the Tesla battery runs flat, will you notice the switch back to grid/paid for power or do you get a warning and you have to switch back to grid yourself? How does that transition happen?

    That bit I don't know, but it is an interesting concept. I expect, over time, I'll become accustomed to what works, and aim for that at all times. Wife is the problem. Gets out of air conditioned car into hot garage, dressed in work clothes (long dress, pantyhose, middle of summer), staggers into reasonable temp house and starts lowering the thermostat on the ducted. Sheesh!
    I have monitoring sites available to me through the inverter that can tell me how much I'm generating - it is connected to the WiFi at home and sends stats updates to the manufacturer every few minutes. So I can see in the hour since I put that post up, I've hit 22.52kW as the sun is out here and blazing away in the peak of the day. 
    Funny thing about solar panels is their output is determined in lab tests - so 25C, basically. The hotter it gets, the efficiency rating starts to dip just a little bit. And considering atmospheric temperature is often 20C lower than up on the roof here, you don't need hot days, just sunshine. So what you're after is a bright day, no cloud, in the high teens or low 20s. Which is basically Sydney three seasons of the year!

    I'll be really interested in the actuals re your power bill Nick. If i do end up building this year, given where i live, this kind of tech could be pretty handy.

    Fo shizz. A bloke I know in Brisvegas gets peaks of 32kWh / day so up there you'll be laughing all year round. By the time you get built, the cost might even have crept down a little, or other battery manufacturers will have started the price war.
    Adding $16K to a build is nothing.

  • I
    Fo shizz. A bloke I know in Brisvegas gets peaks of 32kWh / day so up there you'll be laughing all year round. By the time you get built, the cost might even have crept down a little, or other battery manufacturers will have started the price war.
    Adding $16K to a build is nothing.

    A client said to me I was up to my eyeballs in debt anyway with the build, this just takes me to the eyelids.
    Do ask around about the installers though, when something like this comes up they appear out of nowhere and a lot of them hire muppets. The one I just mentioned had five guys turn up and then they tramped mud and gravel all over the roof and left it covered in scratches and dents, its cost $1500 to put right which they agreed to pay and then went into receivership a fortnight later.

  • Yeah definitely. Can make all the difference. I've done about a dozen media outlets now, and all bar one mentioned the installer by name (installer not happy with that one). It has generated business for them so they're unlikely to tank, given their history as well.
    All their "sales" guys are engineers, too.

  • I'll be really interested in the actuals re your power bill Nick. If i do end up building this year, given where i live, this kind of tech could be pretty handy.

    Oh another thing on this: one of the big points I made to Mrs TA on this was the usefulness of the cash.
    At current interest rates (under 5%), that sort of money is worth about $640-820 a year in a mortgage offset, depending on exact rate.
    Compare that to about $1500 in power bills, and that's just minimum estimated savings. Wipe out my $1920 from last year and I'm ahead of the bank by about $1200 with enough sun and smarts.

  • The temp thing is not something i had considered, and could be an issue. Sun? No worries for the vast majority of the year. Even during the wet season we get extended sun. Winter is prime obviously.
    But the temp in the depot today is about 38, and it's humid as fuck (storm tonight no doubt) so i wonder if summer conditions will have a negative impact on output (and lifespan)

  • The unit is rated to the appropriate IP weatherproof reading - in fact the fancy casing isn't as waterproof as the innards. So as far as being outside goes, it is covered

    I think humidity will be a factor, but its effectively a sealed lithium battery. So provided you're not buggering up the temperature factor too much - 50C max operating - you should be fine.

  • Apparently this can be retrofitted to an existing system which should make my parents happy. Their solar system and associated tariffs provides free electricity, which isn't bad considering multiple widescreen tvs, aircon and pool. Father wanted to store the energy rather than feeding it back into the grid.

  • Cost will also depend on how their inverter stacks up - may need to replace it.

  • And in other news: fuck.

    ast year saw the introduction of the Tesla Powerwall â€“ a wall-mounted rechargeable lithium ion battery with the ability to power your entire home, powered entirely by solar energy.
    And while the first version of the Powerwall has only recently gone to market, just like Tony Stark and his various armors, Musk is already working on a next-generation model of his zero-emission power solution.
    Speaking at an event for Tesla car owners in Paris, Musk told attendees that plans for a second version of the Powerwall are already on track for a 2016 launch.

    Elon story short

    “We are coming up with the version two of the Powerwall probably around July or August of this year, which will see further step changes in capabilities,” said Musk.
    Though Musk did not elaborate on what these changes are, he did reveal thatTesla’s Gigafactory will now be producing its own battery cells, instead of using the ones manufactured by Panasonic the first time around.
    “Moderate improvements” to the technology were teased, and it is expected that the second generation Powerwall will boast a longer lifecycle.
    You can watch the full video of the Musk’s talk in Paris below.

  • Great podcast here with Lyndon Rive talking about the economics and business of SolarCity in the US.

    I was thinking of a similar business plan a few years back - should have got off my arse and done something about it

  • You'd assume most of Australia & a lot of NZ the eventual home setup will be really good solar units, a powerwall & effectively zero input from the grid. Even more so once you tie it all into well designed houses with great insulation, underfloor heating etc.
    Whats the insulation like on your house Nick? Double glazed etc?
    Thats weirdly the bit that always makes me go "maybe next year" when I look at building a self suffecient home. The powerwall tech is more or less there, Solar has come way down, but I'd want to incorporate REALLY good insulation & yet I have a thing for full length glass. And fuck me, double or triple glazed glass will do very bad things to your budget.

  • Unfortunately no double glazing - don't get it a lot in Australia except for noise related reasons, or architect designed bespoke jobbies.
    However, I have ensured the insulation in the ceiling (batts) are of suitable size and coverage. The original owner didn't put batts over the garage, so that was a massive suck hole for the thermal status of the house, which I corrected. I also insulated the inside of the garage door, which faces west, to limit heat transferred into the house from the metal surface late in the day.
    The house was built with wide eaves - very important in Australian heat - and the roof (corrugated steel) had a pretty big pitch on it. I installed a solar powered extractor fan that keeps it pretty nice up there and on the hottest days, the fan works hardest, so it balances things nicely and stops more reflective heat against the ceiling.
    The air con is a ducted system in the whole house, which isn't the most efficient, but is zoned to do either the east or west (roughly), so that minimised wasted energy to as large a degree as can be expected as the sun moves.
    I can take it a step further and get exterior blind or shutters, but I think I've spent enough money for now 🙂

  • Have just seen consumer group CHOICE Australia say the payoff time for the PowerWall, with 4kw solar panels, of 23 years.
    LOT of assumptions made. Look forward to proving them wrong.
    Today was a new record for my solar panels: 32.68kWh generated. Wish my fucking meter was changed over so I could at least get some cash for that

  • Have just seen consumer group CHOICE Australia say the payoff time for the PowerWall, with 4kw solar panels, of 23 years.
    LOT of assumptions made. Look forward to proving them wrong.
    Today was a new record for my solar panels: 32.68kWh generated. Wish my fucking meter was changed over so I could at least get some cash for that

    Setup a website detailing stuff you are doing. Have links to retailers. You can get that down to 15 years with click thrus. This stuff is going to get more & more mainstream & folks will always want to have a read about what people are doing with their houses, I've book marked half your stuff & I'm probably not building for 5 years

  • Yeah the inverter comes with an API feed off the manufacturer's website. I'm assuming the Reposit stuff does too, so I can wire that all up and spit out some metrics n shit. Add comments and such

  • Need a bit if time to get my head around it and get the peak (summer) dusted to see where I go next

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