Anyone Home Solar Charging?

[arg]

if I was doing it again I would install PV instead and use a heat pump to heat the water. Bit difficult for DHW - heat Pump not great for lifting temperature to "hot", perhaps use immersion instead of heat pump? -

I believe the optimum for DHW is to have heat pump to raise it to an intermediate temp, and then direct resistance heating (ie. immersion) for the last bit. This is an excessive amount of kit if done just for the DHW, but if you are doing wet underfloor heating with a heat pump, you can have a thermal store associated with that (that you may want anyhow) and pre-heat the incoming water through that before going to your hot tank.

However, I'm not doing that myself as I have floor issues preventing me from having my originally intended UFH so have no option but go for just resistance heating - the extra kit to get the small improvement in efficiency doesn't seem justified.

So 3 bedroom house has a peak heat requirement of a 1-bar fire. For the whole house.

This does emphasise that the DHW heat requirement becomes much more significant once the space heating is so little.

Also gives another problem: I have a mega fireplace that I can't get rid of (central to the structure of the house and major feature in the living room), so the only thing to do is convert it to wood-burning stove. However, smallest stove you can buy gives out much more heat than the total requirement of the house! In my case, plan to resolve this by surrounding with thermal mass (it already has quite a lot) and only firing it for an hour or two at a time (and not using it much anyhow out of concern over particulate emissions).

 

[MrBadger]

That is typically achieved by applying loads of mastic at the leaks - e.g. under skirting boards, which the carpet fitters then cut out so they can fit the carpets under the skirting boards .

This has always confused me. You are presumably not talking about a brick house? Mind you, that could have mortar gaps I suppose - otherwise where so the spiders come from? Or do they walk around the house using the skirting boards as cover?

 

[arg]

You are presumably not talking about a brick house?

Brick walls do leak air, so if you are going for full air-tightness you plaster everywhere (ie. don't leave the gap between ceiling and floorboards above unplastered just because you can't see it). Or you use an airtightness membrane.

But a house where they aren't taking airtightness seriously and just want to bodge their way through building regulations might have dot-and-dab plasterboard rather than wet plaster so sealing round the edges will stop the leak long enough to get the airtightness test done.

 

[WannabeOwner]

you can have a thermal store associated with that (that you may want anyhow) and pre-heat the incoming water through that before going to your hot tank

Just in case anyone else goes down that route, we did that and then did a bit of a volte-face.

We put in Accumulator for old part of house (house is big, so is Accumulator), heated from biomass batch boiler (light it, let it burn completely; you then have to have somewhere to store the heat). In summer the Solar Thermal heated it, and top half got to 60C, and we heated the DHW direct from that (i.e. a DHW coil in the Accumulator). Trouble was it was touch and go to get it to 60C (2,500L tank!).

So we redid it and added a tall-thin Solar DHW tank with Solar coil. Now the Solar Thermal heats that as a priority, and then dumps heat into Accumulator. Supply to DHW tank is pre-heated in Accumulator (so, in mid Summer, the top-up water into the DHW tank is 60C )

Works well (and we have the ability to dump any excess heat from Accumulator into Pool, in addition to Solar Thermal panels which are dedicated to the pool or light the biomass boiler to heat the pool (via Accumulator). The flexibility is a boon ... I could add an ASHP into the mix if I wanted to).

This isn't for the feint hearted, and your average Corgi Plumber won't be the least bit interested in helping out ...

I have a mega fireplace ... smallest stove you can buy gives out much more heat than the total requirement of the house!

We have a tiny-ish Wood Burning Stove which is Passive House certified. Basically it draws its combustion air from outside. By trick akin to optical illusion the "body" of the stove is big, but the combustion chamber inside is very small. I expect it might still be too many kW for you, but I'll send you the details in case.

We like our Stove. At the shoulder ends of the season we light that, instead of the Boiler, and the MVHR does a good job of distributing the heat. That said, the Biomass boiler gasifies the wood, and is incredibly efficient. The Stove is very good, but it does seem that we get through quite a bit of wood (the boiler's job is to do a lot more work, so my "comparative log measurement" is very subjective!!). But we also have some feel-good of seeing the flames in the stove, through the door to that room, every time we walk down the hall ...

You are presumably not talking about a brick house?

Yup. Needs an air tight membrane/layer as well. Turns out that Breeze blocks are ... just that. Amazes me.

Not sure I can easily describe this, but I'll try.

We were at the point of having an outside wall - brick outer, cavity (full of "fluff") and block inner. At right angles to that a block internal wall was being built, butting up to the inner-skin of the exterior wall. It had a "hole" knocked into it where a socket was going to go; probably 2~3M in (from the joint with the exterior wall). Passive House consultant rocked up for one of his regular visits. "Was the [inner surface of] that external block wall parged before the inner block wall was built?" ... builder had no idea that was needed, so "No".

Passive House guy say "Air will go in to that power socket, along that 3M of wall, and out through the exterior block wall". He got some pretty surprised looks!

If you plaster the wall then that is air tight. But of course when a plasterer does that he doesn't bother with all the bits behind pipes that are going to be covered with a "vanity board" and so on. And that's where the problems start. We needed to have "plastered" (parged) the wall where the internal wall was going to meet it. normal block-laying just has some hit-and-miss mortar in the joints. Every house ever built has that problem, so in converting existing houses to "air tight" it is ... really really hard, as we discovered trying to do ours.

Passive House has to be built right. It can't be sorted out at Snagging, as UK builders tend to fix (as in "bodge") everything. They may need to learn some new stuff, but there is nothing onerous.

 

[elecTED]

Hey peeps

Surviving fine at the mo without a home charger but considering one for the future.

I’ve skim read this thread but couldn’t work out if a home charger that can make use of solar PV (eg, zappi) makes economic sense.

We have a 7.2KW solar PV system.

Not sure how much of what we generate we can in real life make use of to charge car.

If we can make use of around 10% of what we generate that’s around £100 in electricity savings. Over 5 years that’s £500. If the initial cost of supply and install of zappi is around £500 more than a basic home charger then the RoI is 5 years.

Does my back of the fag packet maths stack up?

Any fundamental flaws in my computations and assumptions?

 

[tsh2]

You have to be using power during the day, but offset it against night rate. I expect it will make sense if you can do this, since the storage is paid already. I recon that buying storage today is only holding future electricity cost at todays rate, so minimal financial gain.

If export metering comes, the benefit is very small.

 

[WannabeOwner]

if a home charger that can make use of solar PV (eg, zappi) makes economic sense.

Stating the blinking obvious here, so i'm sure you have it in hand, but using your own solar PV only works if the car is at home during sunshine hours.

Winter PV in UK is 90% less mid Winter than mid Summer ...

As a twist we are considering replacing our 2nd car, ICE (rarely used) with an EV and then going to work in alternate cars each day so that each car is charging from PV every other day.

We have been considering a second PowerWall to store PV and shift Off Peak purchase of electricity into Peak Period. My man maths says that if we had 2nd EV, and thus always one parked at home, we could "dump" all PV into Car, avoid exporting any, still get the FIT on teh 50%-assumed-export, and avoid having to pay £7,500 for the PowerWall

(We are installing significantly more PV than the standard 16-panel setup)

 

[MrBadger]

If we can make use of around 10% of what we generate that’s around £100 in electricity savings. Over 5 years that’s £500. If the initial cost of supply and install of zappi is around £500 more than a basic home charger then the RoI is 5 years.

Does my back of the fag packet maths stack up?

Not according to my back of envelope calculations.

Say you generate twice what we generate - assumption your PV is not quite ours but we have some shading. We generate average 3500kWh/year, so lets say you generate 7000kWh. Then your 10% is 700kWh/year. So, at 15p/unit, thats £105/year or £525 over 5 years, so looks like my assumption holds true.

However, you can get tarrifs at 5p/kWh, so if you can charge using that (its pretty much all built into the car to achieve if your circumstances are right) your saving is then only £35/year, or £175 over 5 years, ROI pushing 15 years. Plus you have allowed the PV that you have generated to be used elsewhere on the grid and reduce marginal grid generation emissions, typically gas. Your overnight charge then comes when grid usage is currently much lower, and a better chance that marginal grid production comes from low carbon sources.

In addition, do you want to charge your car because it is 'free' or because you need it. If it is because you need it, then turn down charge rate to 6A, so approx 1500W, which during non winter months and choosing your charge days sensibly, will guarantee a charge and allow a high percentage to come from your solar. It won't track the clouds or your insolation curve automatically, but wont cost you anything either.

 

[arg]

10% of your total generation seems an odd figure to start from, unless you have lots of other consumers and only have ~10% left over that you currently send to the grid. In that scenario, solar charging seems highly unlikely to work out.

Perhaps another way to look at it is to start with your mileage. If you assume you will have opportunities to do most of your charging with solar during the sunnier months, how much is that? Let's say you do all your charging from solar during the best 6 months of the year, and counter the optimism of that by saying you will not solar charge at all during the other 6 months. Say 9K miles/year, 4500miles/half-year = 1500kWh (more miles or less kWh if it's a Model 3). So your saving is that 3000kWh for free vs. what you would have paid to charge from the grid - about £250/year if you are forced to charge at peak rates, or £100/year at a typical E7 rate, or £75/year on the best possible EV tariff.

Is that estimate feasible to even achieve? We are saying that during the sunny months you are charging an average of 8.2kWh per day, so 1kW for 8 hours or 3kW for nearly 3 hours. With a typical 4kWp installation, you will beat the average on 'good' days, but struggle on other days; since this only needs to be on average and we assume you don't need your car to be full every day, it's maybe just about possible if you have no other loads using up your solar and you were otherwise sending nearly all of it to the grid. Likewise, if your annual generation is 3500kWh, most of which is during the summer, then managing to get about half of it into the car is just about believable.

So, it's hard to argue that there's more than £100/year to pay for your charge diversion unless you have a very large solar install. If you do have an enormous array of panels, the upper bound might be to say you do all of your charging for 10 months out of they year, which by the above logic is 2500kWh, so £125-£375 saving. Your mileage might be higher, but most people on high mileage will be doing it on long trips which means charging away from home and so no extra opportunity to solar charge.

Obviously if you aren't at home during the daytime or you already use most of your solar generation to heat DHW, run a server farm etc. then there's no saving to be had at all - just charging at the weekend when you happen to be home and the sun is shining will only save pennies.

So as a very rough budget, ordinary person with a 4kWp install and some existing consumption from it might save £50/year, someone with ideal circumstances for charging and a standard install might save £100/year, someone with a very big solar installation (that they put in just for the hell of it rather than because it was going to get used) might save £200/year.

So on traditional chargepoint economics it's very hard to see how to make it pay. One possible saving grace is that the OLEV grant scheme now requires 'smart' chargepoints, inflating the cost of a basic chargepoint but meaning that one with solar capability shouldn't cost much extra.

 

[WannabeOwner]

Dunno how it comes into play, but with PV your costs are fixed, whereas price of Leccy is likely to go up over time.

 

[MrBadger]

Dunno how it comes into play, but with PV your costs are fixed, whereas price of Leccy is likely to go up over time.

Not necessarily. As people come off of deemed export FiT, either by choice, or not, then the amount they will get paid for export will be reduced if they use more of their generated solar. I could imagine that this figure will increase over time as wholesale prices rise over time. As an example you could get paid 5.5p/kWh for export, but theoretically buy back at 5p/kWh should you find a supplier that allowed paid export and cheap import. Before anyone goes looking at Octopus, I do not believe that their 'Outgoing' tarrif supports reduced price 'Go' import but does 'Agile'. However, the reality is, you get paid for export even if your car is not at home, and pay for import, when it is.

 

[LukeT]

... Plus you have allowed the PV that you have generated to be used elsewhere on the grid and reduce marginal grid generation emissions, typically gas. Your overnight charge then comes when grid usage is currently much lower, and a better chance that marginal grid production comes from low carbon sources.

A side note/question on marginal grid generation...

As you say, marginal grid generation is typically gas. I suspect (but I don't know) it's pretty much always gas. Suspect also it'll stay this way for a good few years, although I hope not. It could therefore be argued that whatever one generates is in replacement of gas rather than in replacement of grid average power.

However it could equally be argued that it makes no difference in sustainability terms whether the EV on the drive uses kWh out of the solar panels or the grid, so long as the whole lot is connected.

So for me, I do intend to install zappi/similar but with expected export rates (my PV won't be in for a while) the financial case relies on it being pretty competitively priced vs normal chargers and the sustainability case is marginal too. However it doesn't cost much extra and as part of a wider package is a 'nice to have'.

 

[WannabeOwner]

As people come off of deemed export FiT, either by choice, or not, then the amount they will get paid for export will be reduced if they use more of their generated solar.

Good point, thanks. I have no idea when my FiT contract runs out !

I was actually thinking more simplistically which is that if the sums are done on the basis of bought-power costing 5p today, it might cost 6p tomorrow, whereas the cost of self generating is fixed, for the lifetime of the panels (less efficiency loss etc)

 

[NoUserName7]

Hi guys,

My house has a 1.5 kW solar power, but I remember that someone said a solar panel needs to generate a minimum 1.5 kW power to charge an EV car (Is this only for a Zappi case?). In this case, is it still worth to install a smart EV charger, which connects to my solar panels (e.g. Andersen, Zappi, EO mini Smart Home, etc.)?

 

[WannabeOwner]

is it still worth to install a smart EV charger,

Doesn't sounds like it. Do you have anything else that could soak up spare PV self-generated electricity? Immersion heater perhaps?

 

[NoUserName7]

Doesn't sounds like it. Do you have anything else that could soak up spare PV self-generated electricity? Immersion heater perhaps?

No, I don't have such things. Thanks for the tip. Then, Zappi is surely out of my choice.

 

[WannabeOwner]

What we need is a really heavy weight and hydraulic lift that can "store" excess energy ... cheaply ...

Or a Tesla PowerWall

 

[tsh2]

Hi guys,

My house has a 1.5 kW solar power, but I remember that someone said a solar panel needs to generate a minimum 1.5 kW power to charge an EV car (Is this only for a Zappi case?). In this case, is it still worth to install a smart EV charger, which connects to my solar panels (e.g. Andersen, Zappi, EO mini Smart Home, etc.)?

I think it's unlikely in any sense (cash or carbon) to pay off. Do you know your actual daily generation? Here is my generation from a 3.4 kW system from two days ago (yesterday was almost nothing, today it is not yet powered up):

300W barely covers the base load (fridge, internet, pond, etc.), and you can see there is a significant and fairly rapid variation which makes it difficult to adapt anything to absorb the excess. Best case, you only have about 1 kW headroom for a few hours over 6 months of the year.

If you haven't got real-time metering, look at pvoutput.org and find a local system to get an idea of month to month performance.

Exporting your excess generation is efficient, getting any pay-off from your generation will need a very low incremental cost (considering you can manually schedule on the sunny days for free).

 

[elecTED]

Not necessarily. As people come off of deemed export FiT, either by choice, or not, then the amount they will get paid for export will be reduced if they use more of their generated solar.

Do you mean when ‘smart’ meters actually behave like smart features and can work out the excess you’re giving back to the grid?

Is there any current gov guidance when smart meter infrastructure and installations should be able to work out what customers are exporting back to the grid and pay them accordingly?

 

[MrBadger]

Do you mean when ‘smart’ meters actually behave like smart features and can work out the excess you’re giving back to the grid?

There are tarrifs there now. Octopus Outgoing is one such tarrif. You can decide to swap your deemed 50% export part of FiT for actual export. The generated part of FiT remains the same. Introducing Outgoing Octopus: The UK's first smart export tariff So if you export more than 50% nof your generation, a plan such as Octopus Outgoing may be worth looking at. However, if you use your energy from your solar, you miss out on the 5.xp/kWh, ie your generated energy effectively costs 5.xp/kWh to use.