Domestic solar PV quotes 2018

phester28

Shedmanstyle wrote: »

I got a quote from local company today. Similar to my previous post. 2.4kW with diverter. 3.5k

Is that on a tile or slate roof. Including or +vat and is it before or after the seai grant. I assume 2.4kw on one face of the roof?

Shedmanstyle

phester28 wrote: »

Is that on a tile or slate roof. Including or +vat and is it before or after the seai grant. I assume 2.4kw on one face of the roof?

Tile roof. Including vat and after the grant and one face only. A small bungalow.

phester28

sounds a bit high. i was getting quotes of 3.8k to 4k before grant for a 2kw with an east west split. So alot more work + a dearer inverter. Also mine was slate so tile should be quicker / easier. An extra panel of difference should only be 200 euro more IMO tops. actually thinking back i dont remember if that included the diverter so it could be about right.

Gumbo

Shedmanstyle wrote: »

€11,000 for a 2.4kW PV with eddi system which after the grant and a bonus comes in at €7500. If I get 6 people to sign up I get the money back. Win win for me I think. Just need to activ8 the contract with them now.

That’s really really expensive!

Charlie-Bravo

I'm shortly going to go for an east-West setup with 10 panels, diverter/Eddi. Looking for recommendations via PM.

KAGY

Shedmanstyle wrote: »

€11,000 for a 2.4kW PV with eddi system which after the grant and a bonus comes in at €7500. If I get 6 people to sign up I get the money back. Win win for me I think. Just need to activ8 the contract with them now.

That's about double the cost some other posters have. I had them out too and even with their own figures it was a15 year payback.

Imagine your relationship with your neighbours when they figure out you convinced them to pay twice the odds so you could get your one free!

thos

Have my solar install in place for 2 weeks now. 16 panel 5.2kw array facing south, 5.2kw DC battery.
28kwh generated yesterday, but 16kwh exported. The battery was charged by 11am.
Zappi just installed and first time getting it on Eco+ today, so that is currently consuming 3.6kw, which is awesome to see. Export Margin set at 100w to avoid it using the battery, seems to be working well so far. Myenergi Hub on the way also so I can use the app to monitor the Zappi.

Talking to Daikin about my heat pump and how to get that working with the solar, so will keep looking at that. Needs a LAN Adapter and a meter, and should do it's own EDDI-like dynamic consumption. If anyone has worked with that setup, I'd love to hear from them!

It's been interesting getting my head around the battery maxing out at 2.4kw charge rate, so having surplus even when battery is not yet charged. But also trying to factor the Zappi in, on the basis that it needs >1.4kw to get started.
The car is around a good bit during the day, so hoping to use Eco+ during the day, and then the Smart boost at night. The battery is not getting me through the night anyway, so at the moment I don't mind if the last of the battery is getting dumped into the car, it would get consumed over the night rate anyway. Will need to re-think that in the darker months when I'll be looking at charging the battery from the AC overnight.

Picked up a Smappee on eBay so hopefully that will replace my Efergy and help me identify specific devices/appliances, but I also want to split out EV charging costs and Heat Pump usage from general household usage (my brain still see's these as separate budgets) so hopefully it will help me do that.

ch750536

thos wrote: »

Have my solar install in place for 2 weeks now. 16 panel 5.2kw array facing south, 5.2kw DC battery.
28kwh generated yesterday, but 16kwh exported. The battery was charged by 11am.
Zappi just installed and first time getting it on Eco+ today, so that is currently consuming 3.6kw, which is awesome to see. Export Margin set at 100w to avoid it using the battery, seems to be working well so far. Myenergi Hub on the way also so I can use the app to monitor the Zappi.

Talking to Daikin about my heat pump and how to get that working with the solar, so will keep looking at that. Needs a LAN Adapter and a meter, and should do it's own EDDI-like dynamic consumption. If anyone has worked with that setup, I'd love to hear from them!

It's been interesting getting my head around the battery maxing out at 2.4kw charge rate, so having surplus even when battery is not yet charged. But also trying to factor the Zappi in, on the basis that it needs >1.4kw to get started.
The car is around a good bit during the day, so hoping to use Eco+ during the day, and then the Smart boost at night. The battery is not getting me through the night anyway, so at the moment I don't mind if the last of the battery is getting dumped into the car, it would get consumed over the night rate anyway. Will need to re-think that in the darker months when I'll be looking at charging the battery from the AC overnight.

Picked up a Smappee on eBay so hopefully that will replace my Efergy and help me identify specific devices/appliances, but I also want to split out EV charging costs and Heat Pump usage from general household usage (my brain still see's these as separate budgets) so hopefully it will help me do that.

What was the quote on that system?

niallers1

https://greennews.ie/landmark-planning-rooftop-solar/

Looks like those of you who had worries about planning may find you have less to worry about now.

AlmightyCushion

niallers1 wrote: »

https://greennews.ie/landmark-planning-rooftop-solar/

Looks like those of you who had worries about planning may find you have less to worry about now.

That's actually great news. It's daft that we're trying to encourage people to install solar panels yet planning is restricting them from doing it.

Shefwedfan

It would be better if they dropped the stupid planning restriction altogether.....unless you are talking about a 50 panel installation....it is idiotic

Coltrane

@ Thos, I tried unsuccessfully to get my NIBE heat pump/UFH to soak up some of my solar-PV surplus. My HP is a NIBE2040/VVM320. NIBE sells a dedicated accessory, their EME10, which is supposed to allow you to both heat your hot water and house from PV-surplus. I expected the large cyclinder and UFH to be good capacitors.

But the accessory doesn’t work. It consumes only a few hundred Watts (measured using my Smappee), presumably on the heating element in the cylinder, no matter how large the surplus (I also have a 5.2kW PV array). NIBE offered a refund but I’m frustrated because had I known I might’ve bought a different brand of heat pump. Wish you better luck with yours.

I also have a Zappi, with hub. I’ve found the hub/app useful only for upgrading the Zappi’s firmware. I’ve no battery and so haven’t encountered your issue with conflict between car and battery. In general I find the Zappi great despite its high price. Lovely to drive home this afternoon, plug in at about 17:00 and still pick up 3kWs from Eco+.

gally74

AlmightyCushion wrote: »

That's actually great news. It's daft that we're trying to encourage people to install solar panels yet planning is restricting them from doing it.

Like every thing in ireland, where are the consequences for the council here......

Shefwedfan

Ok done a long review of system this evening, from the bills and also the Owl....currently using 13500 units per year. Last 12 month 6000 day unit and year before 6500.

If I review the Owl it gives a kWh. It doesn't really spike over 4kWh during the day. Checked even back to winter and more peaks but still under the 4 during day.

So the question is, what should I expect to pay for a ~4kW system.

If I did go battery, probably 5Kwh, based on my usage of circa 2.5 per hour it will only cover 2 hours of electricity. Doesn't really seem worth it

wexfordman2

If your going for a grant the logic of a battery increases. Also, remember you can charge the battery at night rate during low production months.

unkel

niallers1 wrote: »

https://greennews.ie/landmark-planning-rooftop-solar/

Looks like those of you who had worries about planning may find you have less to worry about now.

Great news. I wasn't aware that case was still being fought. I was under the impression the previous decision that she had to take down the panels was final.

Panels on the front of the house and all. Not that I was worried about my own system where none of my panels can be seen from the public road.

I'll most likely plaster the north facing front of my house with panels too in a year or two when panels have dropped below €50 + VAT. FIT and even bigger batteries, here we come

unkel

Shefwedfan wrote: »

Ok done a long review of system this evening, from the bills and also the Owl....currently using 13500 units per year.

Jaysus, the average house in Ireland only uses 3500 units per year! Do you run an electrically heated indoor swimming pool or something?

I'd get on with a 6kwp system pronto. And make sure you get a system where you can easily add on more batteries in a year or two.

Shefwedfan

unkel wrote: »

Jaysus, the average house in Ireland only uses 3500 units per year! Do you run an electrically heated indoor swimming pool or something?

I'd get on with a 6kwp system pronto. And make sure you get a system where you can easily add on more batteries in a year or two.

Every company I have called says the same.....but based on the owl I just seem to have a fairly constant heavy load about 2kwh but not massive peaks....so a 6kW system would be dumping a lot into grid

That’s why I am thinking if I got a 4kW system that would clean up the bulk of it?

Or am I talking gibberish

unkel

it costs very little extra to go from 4kwp to 6kwp, about EUR1200 or so. Might as well go for it if you have the roof space as it would cost a lot more retrofitted later

Then add on batteries later when / if they become substantially cheaper and or just wait for the FIT. Worst case scenario with a low FIT of say 6c/kWh, and you not able to use a single kWh of the added output, so it will all go back to the grid unused, for the lousy fee of 6c, the additional 2kwp generating 2000kWh extra per year, the extra panels will fully pay for themselves in 10 years. In practice it will be only a fraction of that, maybe 4-5 years as you will use quite a bit of the extra power directly and or it will go through your battery and or it will charge your car. It's the financially best performing part of your system

And even if we don't get a FIT, get an immersion diverter. Also worth no more than 6c/kWh, but it costs just €500 and it will heat a lot of water...

Shefwedfan

unkel wrote: »

it costs very little extra to go from 4kwp to 6kwp, a bit more than a grand. Might as well go for it if you have the roof space as it would cost a lot more retrofitted later

Then add on batteries later when / if they become substantially cheaper and or just wait for the FIT. Worst case scenario with a low FIT of say 5c/kWh, and you not able to use a single kWh of the added output, so it will all go back to the grid unused, for the lousy fee of 5c, the additional 2kwp generating 2000kWh extra per year, the extra panels will fully pay for themselves in 10 years. In practice it will be only a fraction of that, maybe 4-5 years. It's the financially best performing part of your system

The batteries are too expensive and you only get 1k grant from the looks of it....

unkel

Nope. If you go for a 4kwp system, the battery is free.

If you go over the 2kwp with the grant scheme, you only get the subsidy for the additional 2kwp if you install a battery. So basically the subsidy for the battery is 2kwp * €700 per kwp + €1000 grant for the battery, so €2400 additional subsidy

A 2.4kWh battery is about €1200 incl VAT, the additional cost of a hybrid inverter (over a standard inverter) is about €900 incl VAT and the install cost of the battery is two hundred quid max, so basically a small battery is completely free

KCross

unkel wrote: »

Nope. If you go for a 4kwp system, the battery is free.

If you go over the 2kwp with the grant scheme, you only get the subsidy for the additional 2kwp if you install a battery. So basically the subsidy for the battery is 2kwp * €700 per kwp + €1000 grant for the battery, so €2400 additional subsidy

A 2.4kWh battery is about €1200 incl VAT, the additional cost of a hybrid inverter (over a standard inverter) is about €900 incl VAT and the install cost of the battery is two hundred quid max, so basically a small battery is completely free

We've had this discussion before unkel. The battery isnt free. You cant say you have a free battery unless you are willing to say you have very expensive panels as you cant double count the grant against the battery and the panels!

If it was free you'd have done it already!


Your prices are also direct buy prices, not the prices that you will get quoted by an SEAI registered installer, which you need to use to draw the grant.


I think you are misleading people with the "battery is free" angle.

unkel

Some installers quote very reasonable parts prices in their SEAI grant quotes. But I agree, a lot of them rip you off. If I had no solar at all when the subsidy system came in, I would have gone for a large system with small battery under the SEAI scheme. From a decent installer like save me money wind and solar who knows what they are at and won't rip you off. The subsidy scheme itself is extremely generous.

As I already had solar PV, going with the grant scheme did not make financial sense for me unfortunately

thos

ch750536 wrote: »

What was the quote on that system?

I paid €10,500 inc VAT for 16 panels 5.2kw array, 5.6kw battery, 5kw hybrid inverter.

Coltrane wrote: »

@ Thos, I tried unsuccessfully to get my NIBE heat pump/UFH to soak up some of my solar-PV surplus. My HP is a NIBE2040/VVM320. NIBE sells a dedicated accessory, their EME10, which is supposed to allow you to both heat your hot water and house from PV-surplus. I expected the large cyclinder and UFH to be good capacitors.

But the accessory doesn’t work. It consumes only a few hundred Watts (measured using my Smappee), presumably on the heating element in the cylinder, no matter how large the surplus (I also have a 5.2kW PV array). NIBE offered a refund but I’m frustrated because had I known I might’ve bought a different brand of heat pump. Wish you better luck with yours.

It's unfortunate if these systems aren't going to work well together alright. Daikin don't seem to have done one yet, and didn't know much about it, which has me nervous. The unit needs some firmware updates too before I can add this LAN adapter, so doesn't sound like a DIY job either.

I also have a Zappi, with hub. I’ve found the hub/app useful only for upgrading the Zappi’s firmware. I’ve no battery and so haven’t encountered your issue with conflict between car and battery. In general I find the Zappi great despite its high price. Lovely to drive home this afternoon, plug in at about 17:00 and still pick up 3kWs from Eco+.

Hub arrived yesterday and Zappi firmware updated. Previously the Zappi was only charging at 7A overnight, so that is fixed now.
So far unimpressed with the app alright, I wanted the charge history and it's not returning much, I'll give it a day to see if it needs to build the history, but a bit clunky so far.

thos

34kwh generated yesterday, 17kwh exported. Battery charged by 10.30.
After getting the Zappi fixed, I managed to get about 1.5hrs on Eco+, which gave me 5kwh in the car, first time and it felt pretty cool!

My panels are just off south facing, 160degrees. On a clear day like yesterday they are generating 1kw from 7.30am, but are typically back down to 1kw by 6pm. The battery is currently getting me through to midnight but I have some off west facing, 250degrees roof space to the rear, which seems like a good bet next to help fill some of those evening hours.

How would my 5kw inverter work here? If I'm adding more panels, but at different orientation, I'm assuming the peak generated wouldn't really change? How do the ESB determine your max generation, if I have 6-7kw of panels in total, but still only a 5kw inverter, I'm assuming the inverter is the determining factor?

Stefs_42

thos wrote: »

34kwh generated yesterday, 17kwh exported. Battery charged by 10.30.
After getting the Zappi fixed, I managed to get about 1.5hrs on Eco+, which gave me 5kwh in the car, first time and it felt pretty cool!

My panels are just off south facing, 160degrees. On a clear day like yesterday they are generating 1kw from 7.30am, but are typically back down to 1kw by 6pm. The battery is currently getting me through to midnight but I have some off west facing, 250degrees roof space to the rear, which seems like a good bet next to help fill some of those evening hours.

How would my 5kw inverter work here? If I'm adding more panels, but at different orientation, I'm assuming the peak generated wouldn't really change? How do the ESB determine your max generation, if I have 6-7kw of panels in total, but still only a 5kw inverter, I'm assuming the inverter is the determining factor?

I would love to know that too from tech heads. If im adding more panels to an existing inverter. is the surplus of generated power not going to fry my inverter? or inverter needs to be swapped out for more powerful one?

Evd-Burner

Stefs_42 wrote: »

I would love to know that too from tech heads. If im adding more panels to an existing inverter. is the surplus of generated power not going to fry my inverter? or inverter needs to be swapped out for more powerful one?

The spec-sheet for the inverter should list the maximum DC input. As long as you don't go over that it should be fine.

quentingargan

Stefs_42 wrote: »

I would love to know that too from tech heads. If im adding more panels to an existing inverter. is the surplus of generated power not going to fry my inverter? or inverter needs to be swapped out for more powerful one?

It depends on your inverter, but for most inverters there are two MPPT channels for different orientations. Generally the absolute max is 600V which is 13 panels, but you would need to check data sheet of both the panel and the inverter. Add 15% to open circuit voltage per panel to allow for cooling.

You also generally need a minimimum of 4 panels on the second orientation to fire up the inverter.

If you have 14 panels already, they are probably 7 + 7. You could take one of these on optimisers with the second orientation.

Lastly, if you put additional panels on a small second inverter, say a 1kw mini, the battery inverter will usually treat this second inverter the same as if it had more capacity itself.

As far as ESB is concerned, you can have as many panels as you like. It is the inverter that counts.

Lastly, inverters have a max DC total input and max input per string. Again, check the data sheet

AidenL

quentingargan wrote: »

It depends on your inverter, but for most inverters there are two MPPT channels for different orientations. Generally the absolute max is 600V which is 13 panels, but you would need to check data sheet of both the panel and the inverter. Add 15% to open circuit voltage per panel to allow for cooling.

You also generally need a minimimum of 4 panels on the second orientation to fire up the inverter.

If you have 14 panels already, they are probably 7 + 7. You could take one of these on optimisers with the second orientation.

Lastly, if you put additional panels on a small second inverter, say a 1kw mini, the battery inverter will usually treat this second inverter the same as if it had more capacity itself.

As far as ESB is concerned, you can have as many panels as you like. It is the inverter that counts.

Lastly, inverters have a max DC total input and max input per string. Again, check the data sheet

I thought the ESB only allowed 6kw maximum?

wexfordman2

AidenL wrote: »

quentingargan wrote: »

It depends on your inverter, but for most inverters there are two MPPT channels for different orientations. Generally the absolute max is 600V which is 13 panels, but you would need to check data sheet of both the panel and the inverter. Add 15% to open circuit voltage per panel to allow for cooling.

You also generally need a minimimum of 4 panels on the second orientation to fire up the inverter.

If you have 14 panels already, they are probably 7 + 7. You could take one of these on optimisers with the second orientation.

Lastly, if you put additional panels on a small second inverter, say a 1kw mini, the battery inverter will usually treat this second inverter the same as if it had more capacity itself.

As far as ESB is concerned, you can have as many panels as you like. It is the inverter that counts.

Lastly, inverters have a max DC total input and max input per string. Again, check the data sheet

I thought the ESB only allowed 6kw maximum?

Ac though, they prob dint care about what level of DC you put in to your inverter as long as the inverter is limited to 6kw.

Was thinking in a similar vein myself, about putting another 2 strings on a different side of the house to better catch late evening generation.

Was musing about how it could be done, was even thinking of a switchable array that was time based or something.

air

If you can put identical strings on each face of the roof you don't need any switching, you can just connect them in parallel to the same inverter input.
A series diode on the end of each string would be advisable however.

unkel

wexfordman2 wrote: »

Was thinking in a similar vein myself, about putting another 2 strings on a different side of the house to better catch late evening generation.

Was musing about how it could be done, was even thinking of a switchable array that was time based or something.

How many strings (and what direction facing) have you now and how many strings can your inverter handle? Many 5-6kW inverters have 2, 3 or even 4 input strings these days

quentingargan

air wrote: »

If you can put identical strings on each face of the roof you don't need any switching, you can just connect them in parallel to the same inverter input.
A series diode on the end of each string would be advisable however.

Just be careful with parallelling strings. Many MPPT inputs on smaller inverters have a max rating of 10 amps which is one string.

unkel

quentingargan wrote: »

Just be careful with parallelling strings. Many MPPT inputs on smaller inverters have a max rating of 10 amps which is one string.

And you probably can't use the standard solar cable either but have to use thicker ones?

Gumbo

gally74 wrote: »

Like every thing in ireland, where are the consequences for the council here......

The council don’t make the regulations, that’s the department of environment. The council only enforce them.

gally74

kceire wrote: »

The council don’t make the regulations, that’s the department of environment. The council only enforce them.

Something like common sense rather than take the person to court ???

Shefwedfan

These are my current prices

13 panels(4.2kw) = €7378 - €1400 = €5,978
13 panels(4.2kw) + Battery(2.8kWh) = €10,215 - €3,800 = €6,415
13 panles(4.2kw) + Battery(6.3kWh) = €11,918 - €3,800 = €8,118

I have pricing for bigger system but way over budget

beertons

Can you pm me who those are with?

pale rider

Shefwedfan wrote: »

These are my current prices

13 panels(4.2kw) = €7378 - €1400 = €5,978
13 panels(4.2kw) + Battery(2.8kWh) = €10,215 - €3,800 = €6,415
13 panles(4.2kw) + Battery(6.3kWh) = €11,918 - €3,800 = €8,118

I have pricing for bigger system but way over budget

I’m finding that on a reasonably good day I am almost fully charging my 6 kw odd battery resulting in grid free power in the evenings and overnight, I have a diverter which adds hot water.

I last used the grid about a week back.

For me the larger battery makes sense, on good days the array is showing over 4kw production.

Your quotes can be beaten with negotiation, don’t accept the first number which is given to everybody.

choose a company that has a history and a decent set of accounts, www.cro.ie is an important check, this is a lot of money with new technology and a solid company history suggests they will be around in a few years if you need them and not fold up when or if the grant is pulled.

I’m curious why people who have quotes have not moved forward, a lot of posters have made enquiries but not yet pulled the trigger, is it a cost issue ?

Gumbo

gally74 wrote: »

Something like common sense rather than take the person to court ???

Their hands are tied. Someone made the complaint so they are legally obligated to follow the same process if you or me complained about a small extension on a small house or an additional storey on an apartment block.

Once the member of public made the complaint, they had to follow due course. They are not legislated to relax the laws or regulations without the departments guidance. I feel your gripe but your anger is directed at the wrong group of public servants.

You need to lobby the civil servants that create these rules and regulations in the department.

reni10

pale rider wrote: »

I’m finding that on a reasonably good day I am almost fully charging my 6 kw odd battery resulting in grid free power in the evenings and overnight, I have a diverter which adds hot water.

I last used the grid about a week back.

For me the larger battery makes sense, on good days the array is showing over 4kw production.

Your quotes can be beaten with negotiation, don’t accept the first number which is given to everybody.

choose a company that has a history and a decent set of accounts, www.cro.ie is an important check, this is a lot of money with new technology and a solid company history suggests they will be around in a few years if you need them and not fold up when or if the grant is pulled.

I’m curious why people who have quotes have not moved forward, a lot of posters have made enquiries but not yet pulled the trigger, is it a cost issue ?

Just wondering what your base load in watts is?

Mine is nearly always under 300w so with sizing the battery I need to have it sized so that in the summer I will be grid free with the battery fully charged during the day and then in the winter being able to get at least some coverage from the battery when the sun goes down.

Alkers

pale rider wrote: »

I’m finding that on a reasonably good day I am almost fully charging my 6 kw odd battery resulting in grid free power in the evenings and overnight, I have a diverter which adds hot water.

I last used the grid about a week back.

For me the larger battery makes sense, on good days the array is showing over 4kw production.

That extra €2,000 pays for a lot of electricity, especially at night rate!

pale rider

Alkers wrote: »

That extra €2,000 pays for a lot of electricity, especially at night rate!

It does....up to some point in the future and then the solar will overtake but it is missing the point of installing a PV system with a decent battery.

I'm playing with the system to extract the best from it without recourse to grid, I'm also saving on the vat costs and carbon charges none of which are likely to be reducing, Energia have increased electricity costs three times in the last 18 months.

It's not for everyone, it might not be for me either but time will tell, for now it's giving me between €5 - €7 a day in savings, a return you won't get from a Bank.

My base load is around 300w.

Shefwedfan

pale rider wrote: »

It does....up to some point in the future and then the solar will overtake but it is missing the point of installing a PV system with a decent battery.

I'm playing with the system to extract the best from it without recourse to grid, I'm also saving on the vat costs and carbon charges none of which are likely to be reducing, Energia have increased electricity costs three times in the last 18 months.

It's not for everyone, it might not be for me either but time will tell, for now it's giving me between €5 - €7 a day in savings, a return you won't get from a Bank.

My base load is around 300w.

The problem I have with the batteries is they are horrendously overpriced at this time......

unkel

pale rider wrote: »

it's giving me between €5 - €7 a day in savings

How did you get those figures?

pale rider

unkel wrote: »

How did you get those figures?

I've done my math based on my usage cost from bills versus no grid use and monitoring the meter, I added vat/carbon tax to unit costs not purchased to arrive at my average daily savings, weather has been good for all but one or two days since install.

That's a hell of a saving if calculated correctly

Agent_47

pale rider wrote: »

I’m curious why people who have quotes have not moved forward, a lot of posters have made enquiries but not yet pulled the trigger, is it a cost issue ?

Cost, component specification and information but mostly the cloak and dagger approach of the Firm providing the supply and fit. Some companies operate on a no names basis, there are no people profiles on websites, names on quotes etc. That's a real turn off. When it is installed and you have a problem, who can you call and look for....

Shefwedfan

pale rider wrote: »

I've done my math based on my usage cost from bills versus no grid use and monitoring the meter, I added vat/carbon tax to unit costs not purchased to arrive at my average daily savings, weather has been good for all but one or two days since install.

How much electricity do you use? 5-7 Euro per night is even more than I burn up and I’m charging a car with it....

unkel

pale rider wrote: »

I've done my math based on my usage cost from bills versus no grid use and monitoring the meter, I added vat/carbon tax to unit costs not purchased to arrive at my average daily savings, weather has been good for all but one or two days since install.

Sounds extremely optimistic if I'm honest. A 4kwp system is producing about 20kWh per day on relatively good days like the last few days

If you use all of this for daytime consumption (that you could not have used night rate electricity for) and nothing goes to heat your water and nothing goes back to the grid, your saving is 20 kWh * 18c (unit price) = €3.60

In practice a lot of electricity would have gone to the grid even with a 6kWh battery. And you said you also use immersion? That's only worth 5c (unit price)

With your system you'd do very well to save €2 per day on a good day