Solar Panels to Batteries - a Poor Mans Tightarse Tesla battery

Hi All,

I recently decided to go ahead with solar panels and so I'm now considering how best to harness my day time energy.

Obvious ones - Dryer/Washing machine/dishwasher seem easy enough, but I was thinking about how to manage my night time usage with some balance of tight-arsedness to ease.

What I've come up with is the following:

We currently have a power board with 3 chargers next to the bed which charge on rotation either phones, tablets or other electronics - typically at night.

I was thinking of replacing this with xiaomi smart plug that the home assistant turns on in the middle of the day to power a decent capacity power bank (either or even some of the smallish ones I already have to minimise outlay). The phones then charge from this overnight (not as fast as the chargers with USB-PD but they'll be around for quick top ups as needed. I know it won't save much, but it also won't take much to set up

This special 'power board' can also have the eneloop charger (you know it had to) and anything else that needs a bit of charge or power but doesn't really matter then.

Does anyone have any good suggestions on this or others ways to maximise solar? Do YOU have something even more pennypinching?


  • +1

    Maybe a few more powerbanks.. and then use lamps at night instead of the main lights.

    • +1


    • +3

      Those lamps better be hella bright, or what OP saves in electricity they'll end up paying in optometrist appointments and glasses prescriptions…

      • +3

        I already have glasses - sunk costs right?

        • +3

          LOL! I'm not sure how valid that logic is, but I don't know enough about eyes to say that's wrong haha.

          Ok, real talk though - work out your ROI. I don't know how long power banks last if you're going to be using them as regularly as basically 1+ discharge cycles per day, and you might end up spending more on those than you get back in saved electricity bills because powerbanks don't last forever.

        • @HighAndDry: Fair point, but the power banks have been sitting in my draw for the last few months so they aren't adding a pile of value as it is. Whether or not I 'invest' in more is definitely a bigger issue.

          I think I read somewhere that a full mobile or tablet charge can be up to 50c each but I can't work out how to determine the amount of power a phone needs with how much they cost (mAh to KwH)

        • @ewanw: You can estimate it from the capacity of the battery. Say you have a 3000 mAh battery. That's 3 Ah @ say 4V = 12 Wh. 1 kWh is say 30c. Allow some factor for inefficiency but you can see that it's only a few cents to do a full charge from zero. That's insignificant compared other appliances in the house.

          What about solar hot water do you have that? Or can you turn off the water heater at night?

        • @greenpossum:

          Sorry, as per other post it's gas hot water.

        • @greenpossum: actually you only save 6c per hWh (difgerence between feed in and feed out). So you'd stand to make 6c after 100 days if you were lucky.

  • +1

    next is hooking up deep cycle batteries

    not sure if diy-able

  • +2

    I doubt if you can save enough energy to repay for the smart plug. If you have one of those mechanical 24 hour timers lying around, I'd just use that. Maybe you could turn on an electric heater in the afternoon to warm up the house before you arrive home.

    • Sorry I already have home assistant going so the existing batteries + the smart plug are a sunk cost.

      However the raspi running home assistant runs 24 hours so is a possible candidate for this solution. The battery could become a 'UPS'

      • The biggest consumers of energy in a home are generally heating and cooling. Problem is you can't get at the controls of water heaters and fridges. What about cooking your dinner in a slow cooker during the day?

        • Hah - now we're cooking with…. solar power! Honestly though we have gas for the stove and hot water, oven is electric though and we do have a slow cooker. Time to start having dinner for lunch

  • +1

    Im bored so lets try this out. The thing about those batteries is they advertise the Ah of the internal batteries rather than the usb power so that $26, 10,000mAh battery can output about 35Wh before it gives up the ghost. Teslas powerwall costs $9,600, but stores around 13.5 kWh, (385 powerpacks). While 385 powerpacks cost just over $10k they lack the charging and 240v conversion gear that the powerwall incorporates. So yeah use them for small things like charging your phone or led lights but after battery conversion and keeping it trickle charged will probs drain more than just charging at night offpeak.

    • Well first issue is I only have a single rate. To have off peak do I need a whole 'nother meter installed or otherwise how does it happen? (I have a smart meter at the moment which records electricity at time of day)

      • For all that trouble you go through, I think growing vegetables may offset your grocery bill more than your efforts to offset your electricity bill.

        • +1

          Hah, solar powered hydroponics, I hear ya

        • @ewanw:
          Yeah. With that, you can also offset your recreation bills. ;)

      • You should have another meter installed when you connected your solar, if not then it must just be net metering. Usually your retailer switches you over to a different tariff and installs another meter for you to buy your solar back. you can test this one sunny day by turning off everything and seeing if your meter goes backwards. If you just have net metering dont bother storing any power as the losses will outweigh any benefits.

        • My understanding was that modern smart meters record the import and export, it definitely doesn't have one of the old spinning disks.

        • +1

          If your daily usage with solar is less than the solar you generate, 1 quick win is to move to the provider who gives the largest feed-in tariff. For example, I live with my partner and both of us work so there's no one at home during the day. With the excess solar, I found out its better for me to move to AGL's 20c feed in tariff with no discount compared to other providers with less feed-in rate but with 20+% discounts (discount is useless if your bill runs in credit) … I should mention this is in QLD

        • +1

          how much solar are you generating per day?

        • +1

          @Archi: 38kW on a clear day for now … hoping to hit 40 in summer … one can dream :D :D

        • +1

          8kw system

        • +1

          @Archi: 5kW with 6.6kW panels

        • +1

          ahhh sunny Queensland, so much sunshine.

  • +7

    You're not going to save any money hitting really small targets like USB powered devices.

    • +2

      Just to add to that I was doing a power audit of my house and tried to measure the consumption of my phone charger, and it didn't actually register so it was less than 1w. So to charge that for 1000 hours I would use 1 unit (kw/h) of electricty for which I pay 24c. There is about 750 hrs in a month.

      People who think they are saving power unplugging devices when not in use are kidding them selves that it is going to make a noticable difference on their power bill.

      • -1

        There were (and may still be) devices that have a high standby draw. I'm thinking of those set top boxes that ran palpably warm. I guess 10-20W dissipated there.

      • Just because you haven't encountered one because your experience with consumer electronics started with mobile phones doesn't mean those vampire devices don't exist. Some panel TVs were culprits in this area.

        However the sheer number of mobile devices is consuming a significant amount of power generation for the supporting infrastructure.

        But that's outside the scope of OP's query.

        • Thats a 4 year old article and technology has evolved a lot and standby power is a big thing. If you dont believe me, then do a power audit on your house using a power consumption plug.

          I'm not saying it doesn't exist but it's not going to make a meaniful (cost of beer) difference in the average power bill.

        • @seano2101: Actually it looks like you haven't actually read the article. It's not about standby power as such. As I said it's not directly related to OP's query, but pointing out that mobile usage is causing large increases in power drawn by the infrastructure, the towers, the backend servers and so forth. So nothing to do with your or my monthly bill.

  • +2

    A USB power bank will cost you more than you would ever pay in a lifetime for charging the device.

  • You mean something like a DIY Powerwall? (Not sure if legal though)

  • +1

    Best thing you can do is switch to Tango or other cheap retailer. Power is 19c and feed in is 12 or 13c. So you really just use the grid as an approx 60% efficient battery. A power wall is only 85% efficient. Lithium batteries of any sort for home power savings are a total and utter waste of money at the moment. The high feed in tarrif kills any possibility of them saving you money. Payoff is around 25 years after which the battery will likely be dead.

    • +1

      Thanks. I'm in NSW so no tango. I'm currently with PowerShot but I think they recently dropped their FIT which makes their overall offering less good.

      • +1

        If you mean PowerShop, get away from them, they are dodgy af.

        • I did but got autocorrected.

          What problem have you had? I've been with them for a while after finding agl/origin and the rest of those guys dodgy af

        • @ewanw: my main problem was you couldn't have it go to direct debit without getting penalised. In order to get the discounts you had to make manual payments. Then even after going to all that effort it was something like 50% more expensive than tango. To me their app and billing system was deliberately setup to be confusing. The 3 levels of discount is deliberately misleading

        • @ewanw: you are right, AGL are even more dodgy

  • +1

    How about charging a 12v deep cycle battery of your solar. Then use car chargers during the night.

  • +2

    This is a false economy. A regular phone costs 50c A YEAR to charge, nightly. The only things its worth being clever about in your household is heating/cooling, and to lesser extents your tv, washer, dryer & fridge. Everything else (LED lights, sound systems, other kitchen stuff, laptops) use a pittance in comparison

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