Anyone Home Solar Charging?

[Fullerene]

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....

 

[kevuwk]

For fun:

Cheapest Zappi = 695GBP (ignore installation)

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

 

[Fullerene]

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

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.

 

[kevuwk]

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.

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

 

[Fullerene]

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...

 

[LukeT]

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.

 

[Fullerene]

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.

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.

 

[MrBadger]

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.

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.

 

[tsh2]

PassivHaus, as far as I can see, is expensive to achieve - if I can get close I'd be happy, more jumpers kids..

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.

 

[Epico]

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....

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

 

[Glan gluaisne]

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.

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.

 

[Fullerene]

According to one example,

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

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.

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.

I was quoted between £500 and £1100 cost to me (after the olev grant) for the install of the zappi.

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 designed and built our passive house

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.

 

[Avendit]

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.

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.

 

[Fullerene]

I also have 'invested' in a FLIR toy

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.

 

[Glan gluaisne]

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

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.

 

[arg]

Something I didn't realise until after I'd ordered (not that it would of made a difference) is that the zappi has a 1.4kw minimum it will send to the car.

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....

 

[Fullerene]

Yesterday had a decent amount of blue sky for me, I dropped the charge current in the car down so I could mop up the delta between generating and baseload. Very pleased to add my first few (30) miles of home grown solar charging

 

[Epico]

Yesterday had a decent amount of blue sky for me, I dropped the charge current in the car down so I could mop up the delta between generating and baseload. Very pleased to add my first few (30) miles of home grown solar charging

I did the same. Though didn't manage to get 30 miles from it (more like 10)

 

[WannabeOwner]

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).

Me too. In our case we made a huge attempt to upgrade the existing building, its basically poured concrete, built in the 60's, so compared to old housing stock and joists, which leak air like a sieve, it should be easy. It really really was not. So we did the best we could and put a Passive House extension on the end, into which we can hibernate in winter. In the process I discovered a lot about it ...

For a new build there is certainly no need for it to cost a lot. The figure bandied about is an extra 7% on build-cost and then a) close to £zero for heating for the lifetime of the building and also b) no wet system to need annual maintenance and boiler-replacement every 20 years or so.

Mathematically I just can't see a reason not to do it for new-build, and I remain very disappointed that Building Regs don't just require it. If we had already been doing it for a decade or two it would be massively helping the balance-of-payments with Oil States, not to mention the cost if we have to go to war once in a while to preserve supply.

I still struggle to work out a way forward

Yeah, really really hard for existing housing stock. There is a separate EnerPhit standard for refurbs, not as demanding as Passive House but aiming to get similar levels of benefit.

I have never been in a passivhaus I think it would be a shock to the system

I've had a number of people come here who's architects have told them "nah you don't want to do that, its like living in a plastic bag" and guess what? it isn't!

As @Jeremy Harris said:

the house cools at about 1°C per 24 hours

Yup, me to. Go away in depth of winter, turn everything off, houses loses 1C per day.

air quality is really good, there are never any smells

That has surprised me. We have large open plan kitchen with high ceiling. Not allowed to have extractor fan to outside (because it would puncture the air-tight layer), and we never have any cooking smells. The house does have mechanical ventilation, and there is a "one hour boost" if you want to make a stink, but I doubt we use it as much as once a year.

My view is that there is most definitely a difference between "a really well insulated house" and a "Passive House". Unless you build it completely air tight, and install Mechanical Ventilation with Heat Recovery (MVHR) you just don't get the benefit.

Certified Passive House just basically means that all components arrive on site known to perform as expected, so the outcome is assured.

Passive House has an additional health benefit. My wife and I have had no Winter Cold / Cough in 5 years (and always had one before), and that is despite my wife spending the day in an office with everyone else dying around her. The even temperature is much kinder to the body than oscillating temperatures, and having to expend energy when body is above/below optimum

I started off on a "zero energy" tack for the design. That is definitely wrong. It uses so little energy to be comfortable that planning for that outcome is a much better idea than planning to put a cardigan on, as per previous house. We heat the passive house bit (using the boiler which we already had in old part) to 22C in winter, only downstairs, we have no heating, and don't need any, upstairs (Except bathroom). I wish I had put in reversible heat pump for UFH to have cold water in Summer and cool the house. (That would need a wet system though, so more cost involved; alternative is to insulate the MVHR pipes and then put a Chiller on that). The house is so well insulated even when we had 30C_ outside for weeks on end, in 2018 (this was hottest part of the country) max temperature inside only ever hit 25C, but that's still quite warm to sit still in, and needed night-venting every night to cool the building - which is fine of course, but lets the flies in, and in particular you have to be at home to open windows, or a security risk, and so on. Just cooling the building makes more sense, particularly as cooling need coincides with time of max PV generation of course.

The extension added 50% to the total floor area, we improved the insulation in the old bit (basically just attending to any leakage and cold bridging, best we could, loft was already insulated, we added a bit more) and overall our winter fuel has dropped by 50%

We are putting in a pair of PowerWalls, and increasing our (standard 16 panel) PV to add 2x or 3x that. As has been said there is no financial justification, but I work from home and have a lot of computing gear hosted here, so I both use more power than normal, and power cuts prevent me working.

Our fall-back-car is still ICE, replacing that with BEV and thus insuring we always have a BEV on the drive, even when out at work, would perhaps be an alternative to a PowerWall.

 

[KiwiMagic]

Alas 12kWp is a mere dream for most here in UK as we are limited by 16A export install, technically 3.6kW but 4kWp is allowed (per phase). Very rare to find 3 phase, usually only commercial, so 4kWp is the typical domestic limit, assuming you have a roof big enough to even take that - many don't. Above that, you need to seek permission from DNO (power supplier) and/or use export limiting. Some cases, oversized panels on a single 3.6kW inverter is allowed, but its not the default and there is only so much you can over power an inverter by so you might get an extra kWp or so. If DNO are not happy, then you are stuck, but even if they are, you may need to prove certain things to them, including getting them to witness tests which is rather expensive. Its often very location specific so no hard and fast rules and done on a case by case basis where as under 4Wp is a retrospective notification. 4kWp also use to be a cutoff before FIT limits dropped significantly, but since FIT is negligible these days, its not so much an issue. No net metering for us, no alterations without more red tape.

I recently installed a Solaredge EV Inverter and 6.8kWh Solar system in South East England. When sunny it charges the car using both Grid and Solar and so far (weather hasn't been that great) I have seen it adding 30 miles an hour to the car. The inverter should allow me to set schdules and allow excess solar to go to the car when plugged in, however the schedule partt appears to have a bug which they are trying to fix. My install including panels and inverts was £7.5k, the inverter I think was about £1400.