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Anyone Home Solar Charging?

Discussion in 'The UK and Ireland' started by Fullerene, Aug 2, 2019.

  1. Fullerene

    Fullerene Member

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    For fun:

    Cheapest Zappi = 695GBP (ignore installation)
    695GBP / 5p kWh = 13900 kWh
    4miles per kWh

    4*13900 = 55,600 miles
    That's a lot of miles paid for by ditching the zappi

    ~~~~

    Same miles in an ICE @45MPG
    1.20GBP/Litre
    approx 4.5 litres per gallon
    55,600 miles would be about 55,600 / (45/4.5) = 5560 Litres
    5560*1.20 = 6672GBP

    ~~~~
    Ditching the zappi you can use a 13A plug charging with UMC or more realistically a 32A command installed and the 32A Blue UMC adapter (circa 50GBP)

    overnight you'll add approx 4*7kWh = 28kWh

    If you only need to drive 28x4 approx 100 miles a day it all adds up.

    Near me a 4kWpeak array produces about 4MWh per year

    Annually that 4MWh solar will pay for 4000*4 = 16,000 miles which is approximately 44 miles a day averaged over a year - which of course means that summer peak can offset winter lows (with the 5p in / 5p out infinite battery) in a way that someone with a power wall could only dream of.

    ~~~

    I find the back of envelope maths and economics fascinating.

    I know the use electricity at source part of it makes sense - no transmission loss to worry about and if you can run your car off the sun that's fantastic. However it makes total sense for anyone who is away from home in the day and has solar.

    Really contemplating cancelling my Zappi and putting best part of 1K in my pocket, which ironically I could spend on PV panels.... :eek:
     
    • Like x 1
  2. kevuwk

    kevuwk Member

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    If you want the EVSE grant (or just some smart functionality) then you need the £85 hub as well
     
  3. Fullerene

    Fullerene Member

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    Yes - that's part of my order as well (6,800 miles at 4miles&5p/kWh..) I was planning on doing a bit of poking under the hood, I don't appreciate being forced into the cloud & I'd rather spend hours rolling my own interface. Fingers burnt with owl intuition forcing subscriptions, hacked that but at least owl had a relatively open API which made life easier.
     
  4. kevuwk

    kevuwk Member

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    There doesn't appear to be any local/direct API on the Zappi that has been exploited so far. I've only seen people access the web service "API" to control Myenergi devices
     
  5. Fullerene

    Fullerene Member

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    yes - I was planning on going down the RF route. I imagine (sincerely hope) the web interface will be quite secure. If I can get it to talk to a RPI I will be a happy zappi.

    The problem is always that anything connected to the web may well harden security overnight. I'll take a punt on it not needing to talk back to HQ to remain active. That's the exact reason I firewalled off my Owl Intuition - I've put the time into hacking it and I don't want to be locked out of it, just because I refuse to pay the subscription - which was never on the radar of the original product. Cheeky monkeys...
     
  6. LukeT

    LukeT Member

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    I was intending to buy a charger anyway, whether zappi or another, so up front cost is pretty neutral across the options. Even if that's just for the capability of faster charging if needed and the convenience of a tethered cable and the UMC left permanently in the car.

    However the point about export price and nighttime buy price being about the same is good if you can get it. I never understood folks' desire to be "off grid" - the grid is an excellent battery in principle, so long as you can sell your export OK.
     
  7. Fullerene

    Fullerene Member

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    I think apart from being in the middle of nowhere going full off-grid is a bit odd. I would love to have a battery to avoid loading the grid at peak times & be smug during any outages. I am planning to install a second big solar array, and I would feel gutted if the DNO wouldn't let me export surplus. My plan is to achieve net zero carbon at home for the house and our transport. If I can export surplus it would be great. I also want to disconnect the mains gas and be entirely renewable. PassivHaus, as far as I can see, is expensive to achieve - if I can get close I'd be happy, more jumpers kids..

    Ditching the ICEs and buying a Tesla is a doddle compared to overhauling the insulation at home. Economically then sensible thing would be to maintain the status quo and keep the boiler but I would like to prove it can be done.
     
    • Like x 1
  8. VanillaAir_UK

    VanillaAir_UK Waiting patiently for a tow

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    Under FIT scheme, you got paid for export whether you exported or not. They deemed that 50% of your generation would be exported, so you got paid 4p ish for 50% of your generation (or 2p ish for your generation kWh depending on how you looked at it). For us, 50% is a fair figure on our actual usage, but I know that some will try and minimise export and will only get more prevalent as EV's and batteries become more common.

    I've not followed the FIT now, other than knowing that it is not what it once was and some electricity suppliers will pay export in return for giving up the export part of the Fit.
     
  9. tsh2

    tsh2 Member

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    According to one example, about £20k does a good enough job. There are some numbers in the middle of these slides http://wookware.org/talks/retrofit.pdf

    Not sure how much DIY is factored into these numbers, but hes taking a 'realistic' approach.
     
    • Informative x 1
  10. Epico

    Epico Member

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    I was quoted between £500 and £1100 cost to me (after the olev grant) for the install of the zappi. Needless to say I told the guy trying to charger £1100 his services wouldn't be needed
     
  11. Jeremy Harris

    Jeremy Harris Member

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    I can add some data points, as I designed and built our passive house, which also has a reasonably sized PV array (6.25 kWp) and I've been charging cars using that for the past five years.

    Designing and building to the Passivhaus standard need not cost any more than just building a house to our pretty poor building regs standard. You spend a small amount more on doors and windows, a a very small amount more on additional insulation, but you save a fair bit from needing barely any heating (our house has no heating system at all on the first floor, and definitely doesn't need it).

    We're semi-off-grid, as being in a rural area I needed to drill a borehole for a water supply and install a treatment plant to deal with sewage, but we do have a normal single phase electricity supply. The house is all electric, for heating, hot water and cooking. We use no other energy sources.

    Our annual electricity bill is about £500, for a 130m² house (roughly 1,400ft²). We generate more than twice as much electricity as we use in a year, so are net exporters and effectively "negative CO2". Our CO2 "emissions" were assessed as being -0.9 tonnes of CO2 per year, which is roughly the same as that sequestered by around 40 mature trees in a year (although 40 trees wouldn't fit on our plot).

    We get paid FiT and export payments that are around £1,000 a year, so our net electricity "bill" is about -£500 a year. The only bills we pay are council tax and the phone/internet charges, and part of those costs are offset from the electricity payments. The bill payment savings we've made since building this house pay for at least one of our holidays each year.

    Getting back on topic, I charge using the excess PV generation pretty much all the time for about 6 months of the year. I built a pretty simple charge point that senses when we are exporting, and by how much, and adjusts the charge rate accordingly, within the limits allowable (6 A being the lowest it's possible to charge at normally). The charge point turns itself on or off, with a fair bit of hysteresis, if it can't sustain charging without importing above a set threshold. I've set the threshold to be equivalent to the off-peak rate electricity tariff, so the car will charge during the day if the cost is equal to, or less than, the cheap rate.

    I will probably be installing a battery storage system in the near future, and have already put in the wiring for it. The return on investment will be marginal, what we save from being able to better use self-generated energy, and from time-shifting off-peak electricity for day time use, will only just cover the investment after about 9 years, which is probably when the batteries will be close to their end of life. The thing that has swung the balance in favour of battery storage is really the ability to use the battery system as a standby generator if there is a power cut. The system I'm looking at has a separate output that is always on, and can be used for essential services, like our water pump, some lights in the house etc. Being in a rural area, power outages are fairly common, so there is a value to us in having a backup system, about the same as the cost of a small generator, in my view.
     
    • Informative x 3
  12. Fullerene

    Fullerene Member

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    Thanks for this link, it was really interesting. I immediately disappeared off with a calculator!

    I followed FIT and panels from the early days and got a system installed when the capital price took a tumble and the FIT payment had not caught up. At the time it felt like a no brainer decision. I get 52GBP Per Month averaged across the year in FIT payments, index linked. I am staggered at how much more efficient the newer panels are compared to my 5 year old panels. The loss of FIT this yeas as well as the October 1st hike in PV VAT from 5% to 20% is a poor move. The FIT replacement scheme, SEG (Smart Export Guarantee) is sure to emphasise balancing not just exporting, but it's yet to surface. Well done to Octopus for what looks like the direction things will be heading.

    Assuming your install was nothing out of the ordinary then this seems silly when you take into account the relative cost of the electricity consumed. Home charging EVs is about as free as fuel will ever be. The fact that EVs are now being marketed at or lower (thinking Electric Mini as an example) than the ICE equivalents makes the overall saving significant.

    I applaud this and hope to head down a similar route and become a net exporter! Thank you for taking the time to write this up, the numbers sound great. I am wary that I could go on a massive tangent here and fear the wrath of the moderators, so I will try and keep it in check.

    I'm really pleased to hear what I always suspected, that passivhaus is more about attention to detail rather than the need to spend a lot of money. I purchased a low cost IR camera (Flir 1 for my phone was on special for 100GBP) and went around my house and found lots of issues with construction that I remedied. I spent no more than 100GBP on materials and a couple of weekends crawling in voids, the heat input required to the house fell by just over 20% in the following 12 months. Upgrading the UK housing stock seems a very difficult ask - I want to do this to my house - I'd rather do this than replace my perfectly serviceable 35 year old kitchen, but I still struggle to work out a way forward. I imagine for the majority of people the less disruptive, just pay the gas bill option is much more sensible on a personal level compared to cost and disruption.
     
  13. Avendit

    Avendit Member

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    The main message I took from https://www.lboro.ac.uk/microsites/enterprise/calebre/project-calebre-summary.pdf too was that attention to detail really matters when aiming for efficient heating. I also have 'invested' in a FLIR toy, just waiting for it to get cooler so I can whack the heating up to max and take some photos.
     
  14. Fullerene

    Fullerene Member

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    In fairness they are great:
    Determine if the washing is dry on the clothes rack without fondling it
    My kids adore making heat foot print trails on the carpets
    I was able to find a central heating leak with it
    No need to touch radiators to see if they need bleeding
    Handy for locating the cat when it's hiding in the back of cupboards
    I could drill a hole in my concrete slab with confidence I wasn't going to hit the water pipe
    Quickly assess the log pile without jabbing with the moisture meter

    When I went on my remedying the house issues campaign the before and after pictures were amazing. Even something as simple as filling in a 5mm gap around a waste pipe going into a cavity wall made a staggering difference, the cold air flow could be seen falling down the inside of the wall, under the kitchen cupboards and chilling the floor near the sink. It made a noticeable difference.

    I have never been in a passivhaus I think it would be a shock to the system.
     
  15. Jeremy Harris

    Jeremy Harris Member

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    One of the most noticeable things about a passive house is that there are never shocks to the system, as any changes are pretty slow, and small in magnitude. With no heating, in cold weather, the house cools at about 1°C per 24 hours (sometimes it's slower than this if it's not very cold outside).

    The other very noticeable thing is that the air quality is really good, there are never any smells, and the house stays pretty much dust-free, as all the air in the house is changed around once every couple of hours, with all incoming air filtered through a pollen filter before passing through the ventilation system heat exchanger.
     
    • Like x 1
  16. arg

    arg Supporting Member

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    Just to be clear, this isn't a Zappi limitation, it's a car limitation (or strictly speaking, the comms between chargepoint and car): you can't signal a charge rate lower than 6A (apart from zero), so that's 1.38kW at 230V.

    Another issue is that the car will charge less efficiently at lower rates, due to the fixed overhead of running the computers, water circulation etc. With a Model S, practical results suggest a rough estimate that 1A (~250W) of the input current is used up on overhead, so at 6A charging to fit within available solar, about 1/6 (17%) lost, compared to only 1/32 (3%) lost charging at full rate.

    Then there's the question of what your motivation is for doing solar charging. If you are trying to be 'green', you are maybe better exporting your solar to the grid in the daytime when there's high demand and lots of fossil generators running, then charge at night when wind is available. Or if you are doing it to save money, the actual amount of savings available are so low that you can't justify spending money on the kit to do it.

    But it does feel like a good idea....
     
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