Solar install, batteries, exporting and ev tariffs

[bn8959]

You’d be restricted by the size of your inverter. So in effect the inverter is ‘unrestricted’ up to its peak output.

usually they are sized slightly under the theoretical peak output of your panels. Eg if all your panels add up to 5kW peak, you may have a 3.6kw inverter as it’s generally more efficient to run them close to full power as possible and you would lose that much when the panels are outputting more than the inverter can take.

you’d always need battery capacity to run off-grid.
Also, it’s easy to exceed the output of your battery+inverter when off-grid. The system has to instantly shut down if you do - so don’t boil the kettle!

I guess it depends how stable your supply is. In the two years I’ve had my system, I’ve had only one 15 minute grid failure (which I didn’t even notice! Which was nice I guess!). You’ll have to decide if it’s worth it.

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[Jin]

edit: sorry this turned into a long old post!

worth having a watch on YouTube of this channel.. keeps it pretty simple and great to get your head around how it all works, how to size your system, ac/dc coupled systems, pros and cons etc..

https://www.youtube.com/@GaryDoesSolar

I moved into a new build which has solar installed but on a split East/West array.. have to say having a south facing roof will make a big difference!

12 panels (4 east/8 west) and a 3.6kWh Solis inverter and then added 10kWh myEnergi Libbi battery and a zappi last autumn. decided on keeping the battery and EVSE the same brand to make sure they play ball nicely (and in an easy way!). read a few posts where people struggle to stop the batteries discharging into the car. Having it all as myenergi products means it was a simple tick box in the app to stop the Libbi discharging to zappi.. Also having one app to manage it all makes life easier. Was only able to monitor generation from May last year and it was June which was the best month for generation for me. I get a peak generation of ~2kWh and about 18kWh generated through the day.

The handover from the developer for the solar was non-existent and had a period of time last year the inverter went offline (before I was on octopus) and had no monitoring set up. Having to deal with a non-UK based company (solis) was a nightmare to get the inverter working again (ended up crawling around the loft with usb drives and software updates!) but got there in the end. I would have definitely gone down the Solax route with optimisers if I was doing this from scratch.


not had a full year yet with solar monitoring and only had the car since Dec so my data is skewed somewhat but the savings with solar, battery and OI (and load shifting washing machines, dishwashers etc) has made a significant impact to the bill. a crude example being:

May 2023 (inverter was broken so no solar, no EV back then, on standard octopus tariff) - we imported 550kWh in the month which cost £188.

June 2023 (solar running again, no EV) - we imported 270kWh which cost £91 and we exported 218kWh which I was paid £35 for. We generated 416kWh for that month so consumed ~200kWh of what the sun provided. net costs for June were £60!

saving 2/3 off my bill in one month (granted our general consumption will down down as we go into the year) has left me more than happy.

fast forward to December 2023 (solar, battery, EV and on OI) t - imported a whopping 1050kWh.. this is the worst month for 'import' for us (EV charging, cold, dark, no solar, ovens on full blast over Christmas etc) and the cost on OI was £168.. so less than what I paid in the previous May on the standard tariff when consuming 50% more!. exported 60kWh for £10 or so (generated 30kWh from Solar) - I'll explain how I exported more than I generate below



with Octopus paying 15p/kWh for export it makes no sense in putting the excess solar into the car. As others, I 'fill' the car during on OI (mostly in the off-peak hours unless they've given me extra slots in the day) and fill the battery over night too. now it's getting a little sunnier, the solar excess tops off the battery keeping that pretty much full until the sun sets and the evening consumption from the house kicks in. the battery then gets me through the evening to start it all again the next day.

what I expect of most the summer is similar to what happened on Monday (1st April).

Filled battery, ran washing machine, dishwasher between 00:00-5:30 - imported ~19kWh.
ran house the rest of the day from battery, with solar topping up now and again (generated 9kwh).

battery went down to 80% until early afternoon where the solar topped it back up... by the end of the day it was down to 50% so the next day fill was less too! no other import in the day.

cost £1.88 for the day and get 30p for the 2kWh exported (this is without me charging the car)



you can save a fair bit, does need some work to do.. load shifting etc (but our appliances have delay start functions so its a case of setting them to all start after 11.30pm). but getting access to the data is an eye opener. Having it all in the myenergi app is perfect for me too.

OI has made the biggest different in cost.. Octopus is also good for paying out during saving sessions (reduce usage for 30mins/1hour) if you have batteries, you can 'dump' energy to the grid and get paid anywhere from £1.25/kWh up to a session where they even paid £2.50/kWh!..

from not knowing anything about this call a year ago, to then ordering a Taycan opened my eyes to all this.. and it can be a little addictive too! now into the wider world of home automation with home assistant! (idea is the fully automate me plugging the car in and been given a charging slot outside the standard 23:30-5:30 and topping up the battery etc in these additional windows!)

but most importantly, I made the man maths work and the missus signed off on the car!

 

[Midlifecrisis]

Interesting to see all of the different software/setups people have.

For the inverter, the headline figure (5kW, 3.6kW, 7.5kW) is the amount of power that it can convert from DC to AC. So our 5kW inverter can convert 5kW of DC power from either the solar panels or the panels + battery into AC for the house or export to the grid. Our panels all face East, so in the morning can produce in excess of 5kW (19 panels, up to 7.4kW). The inverter can however manage this IF there is some spare "empty" battery to put the excess into. So provided the battery is <95% charged it will take at least 2.5kW power (remains as DC off the panels going into DC in the battery). If the battery is full, the power usage is clipped at 5kW. It makes no difference if we use this or send it back to the grid.

There is a separate limit on the battery - I have a GivEnergy gen 2 inverter, so this will allow 3.7kW to go into or out of the battery. It looks like @Dabz has a gen 1 inverter which allows only 2.5kW in and out of the battery. This is a separate limit to the ability to convert DC to AC.

To be honest, I don't think you will really understand it until you have it and use it. I think most larger houses probably need at least a 5kW inverter. We have 16.4kWh battery capacity and sometimes use it. It is also a huge money saver if this can be charged over night in the winter... our day rate usage is only 1.5% of our total usage which is almost exclusively at OI 7.5p rate over night due to the ability to charge the house batteries during this period.

 

[Nickj]

edit: sorry this turned into a long old post!

worth having a watch on YouTube of this channel.. keeps it pretty simple and great to get your head around how it all works, how to size your system, ac/dc coupled systems, pros and cons etc..

https://www.youtube.com/@GaryDoesSolar

I moved into a new build which has solar installed but on a split East/West array.. have to say having a south facing roof will make a big difference!

12 panels (4 east/8 west) and a 3.6kWh Solis inverter and then added 10kWh myEnergi Libbi battery and a zappi last autumn. decided on keeping the battery and EVSE the same brand to make sure they play ball nicely (and in an easy way!). read a few posts where people struggle to stop the batteries discharging into the car. Having it all as myenergi products means it was a simple tick box in the app to stop the Libbi discharging to zappi.. Also having one app to manage it all makes life easier. Was only able to monitor generation from May last year and it was June which was the best month for generation for me. I get a peak generation of ~2kWh and about 18kWh generated through the day.

The handover from the developer for the solar was non-existent and had a period of time last year the inverter went offline (before I was on octopus) and had no monitoring set up. Having to deal with a non-UK based company (solis) was a nightmare to get the inverter working again (ended up crawling around the loft with usb drives and software updates!) but got there in the end. I would have definitely gone down the Solax route with optimisers if I was doing this from scratch.


not had a full year yet with solar monitoring and only had the car since Dec so my data is skewed somewhat but the savings with solar, battery and OI (and load shifting washing machines, dishwashers etc) has made a significant impact to the bill. a crude example being:

May 2023 (inverter was broken so no solar, no EV back then, on standard octopus tariff) - we imported 550kWh in the month which cost £188.

June 2023 (solar running again, no EV) - we imported 270kWh which cost £91 and we exported 218kWh which I was paid £35 for. We generated 416kWh for that month so consumed ~200kWh of what the sun provided. net costs for June were £60!

saving 2/3 off my bill in one month (granted our general consumption will down down as we go into the year) has left me more than happy.

fast forward to December 2023 (solar, battery, EV and on OI) t - imported a whopping 1050kWh.. this is the worst month for 'import' for us (EV charging, cold, dark, no solar, ovens on full blast over Christmas etc) and the cost on OI was £168.. so less than what I paid in the previous May on the standard tariff when consuming 50% more!. exported 60kWh for £10 or so (generated 30kWh from Solar) - I'll explain how I exported more than I generate below



with Octopus paying 15p/kWh for export it makes no sense in putting the excess solar into the car. As others, I 'fill' the car during on OI (mostly in the off-peak hours unless they've given me extra slots in the day) and fill the battery over night too. now it's getting a little sunnier, the solar excess tops off the battery keeping that pretty much full until the sun sets and the evening consumption from the house kicks in. the battery then gets me through the evening to start it all again the next day.

what I expect of most the summer is similar to what happened on Monday (1st April).

Filled battery, ran washing machine, dishwasher between 00:00-5:30 - imported ~19kWh.
ran house the rest of the day from battery, with solar topping up now and again (generated 9kwh).

battery went down to 80% until early afternoon where the solar topped it back up... by the end of the day it was down to 50% so the next day fill was less too! no other import in the day.

cost £1.88 for the day and get 30p for the 2kWh exported (this is without me charging the car)



you can save a fair bit, does need some work to do.. load shifting etc (but our appliances have delay start functions so its a case of setting them to all start after 11.30pm). but getting access to the data is an eye opener. Having it all in the myenergi app is perfect for me too.

OI has made the biggest different in cost.. Octopus is also good for paying out during saving sessions (reduce usage for 30mins/1hour) if you have batteries, you can 'dump' energy to the grid and get paid anywhere from £1.25/kWh up to a session where they even paid £2.50/kWh!..

from not knowing anything about this call a year ago, to then ordering a Taycan opened my eyes to all this.. and it can be a little addictive too! now into the wider world of home automation with home assistant! (idea is the fully automate me plugging the car in and been given a charging slot outside the standard 23:30-5:30 and topping up the battery etc in these additional windows!)

but most importantly, I made the man maths work and the missus signed off on the car!

Hi, sorry, not checked in for a few days so hadn’t seen your fab and informative post! Very interesting. I have been watching Garydoessolar so will watch a few more vids.

I’ve been doing the saving sessions with OVO and saved some good £££. Do octopus advise what the rate is for you to export back in. Presume this would be more of Winter thing?

 

[Nickj]

Interesting to see all of the different software/setups people have.

For the inverter, the headline figure (5kW, 3.6kW, 7.5kW) is the amount of power that it can convert from DC to AC. So our 5kW inverter can convert 5kW of DC power from either the solar panels or the panels + battery into AC for the house or export to the grid. Our panels all face East, so in the morning can produce in excess of 5kW (19 panels, up to 7.4kW). The inverter can however manage this IF there is some spare "empty" battery to put the excess into. So provided the battery is <95% charged it will take at least 2.5kW power (remains as DC off the panels going into DC in the battery). If the battery is full, the power usage is clipped at 5kW. It makes no difference if we use this or send it back to the grid.

There is a separate limit on the battery - I have a GivEnergy gen 2 inverter, so this will allow 3.7kW to go into or out of the battery. It looks like @Dabz has a gen 1 inverter which allows only 2.5kW in and out of the battery. This is a separate limit to the ability to convert DC to AC.

To be honest, I don't think you will really understand it until you have it and use it. I think most larger houses probably need at least a 5kW inverter. We have 16.4kWh battery capacity and sometimes use it. It is also a huge money saver if this can be charged over night in the winter... our day rate usage is only 1.5% of our total usage which is almost exclusively at OI 7.5p rate over night due to the ability to charge the house batteries during this period.

yes, agree, still read post and sound a bit gobbledegook! On my install it includes a 7.5kw inverter so hopefully should cover al bases.. I’m now back with octopus so when the install goes in, in early may I will be fully utilising Ol off peak rate!

 

[Jin]

Hi, sorry, not checked in for a few days so hadn’t seen your fab and informative post! Very interesting. I have been watching Garydoessolar so will watch a few more vids.

I’ve been doing the saving sessions with OVO and saved some good £££. Do octopus advise what the rate is for you to export back in. Presume this would be more of Winter thing?

octopus pay in ‘octopoints’ for the saving sessions. It’s 800 points = £1. Usually, the saving sessions are at 1800 points per kWh saved. (There was a couple of sessions last year where they gave 3200 points.)

So if your usual usage at the time of the session was say 1kWH but during the session you exported 4kwh.. you would have saved 5kwh = 9000 points = £11.25.

you can redeem points as credit to your account or pink fluffy stuffed octopus toys ?

 

[Midlifecrisis]

octopus pay in ‘octopoints’ for the saving sessions. It’s 800 points = £1. Usually, the saving sessions are at 1800 points per kWh saved. (There was a couple of sessions last year where they gave 3200 points.)

So if your usual usage at the time of the session was say 1kWH but during the session you exported 4kwh.. you would have saved 5kwh = 9000 points = £11.25.

you can redeem points as credit to your account or pink fluffy stuffed octopus toys ?

In addition to this you will also get 15p/kWh that you export. Our usage at these times is normally zero but we were paid for export. Approx £100 total plus the export payment

 

[Nickj]

octopus pay in ‘octopoints’ for the saving sessions. It’s 800 points = £1. Usually, the saving sessions are at 1800 points per kWh saved. (There was a couple of sessions last year where they gave 3200 points.)

So if your usual usage at the time of the session was say 1kWH but during the session you exported 4kwh.. you would have saved 5kwh = 9000 points = £11.25.

you can redeem points as credit to your account or pink fluffy stuffed octopus toys ?

I will keep the fluffy toy info to myself as i fear I would be coerced into this if wife/ daughter were aware! The excitement the little octopus toy created the first time we joined was unparalleled..

 

[Nickj]

In addition to this you will also get 15p/kWh that you export. Our usage at these times is normally zero but we were paid for export. Approx £100 total plus the export payment

Wow, that’s nuts and a handy credit !

 

[Nickj]

So, the DNO results are in….



And I’m not the dad!

And even better I can export at 7kw! Im fairly happy with that as was worried it would be restricted to 3.6kw. I’m presuming my peak system panel capability is the 7.74 so just 10% short of peak.

So, all booked in for the first week of may to install. It’s the bank hol week so will start on the Tuesday.

7.74kwh 18 panels, 7.5kw inverter and 11.6kw battery. The in roof installation is £1200 and a new zappi to replace my podpoint £720. Going to give the chap a call to discuss the battery back up option and if it’s worth the £600 to £800 extra.

Anything I’m missing? Back with octopus OI now in preparation.

Roof is south east facing so I’m hoping for some good returns during the summer and looking forward to learning about it more! Install will be flush centralised from left up to the skylight.

 

[bn8959]

So, the DNO results are in….



And I’m not the dad!

And even better I can export at 7kw! Im fairly happy with that as was worried it would be restricted to 3.6kw. I’m presuming my peak system panel capability is the 7.74 so just 10% short of peak.

So, all booked in for the first week of may to install. It’s the bank hol week so will start on the Tuesday.

7.74kwh 18 panels, 7.5kw inverter and 11.6kw battery. The in roof installation is £1200 and a new zappi to replace my podpoint £720. Going to give the chap a call to discuss the battery back up option and if it’s worth the £600 to £800 extra.

Anything I’m missing? Back with octopus OI now in preparation.

Roof is south east facing so I’m hoping for some good returns during the summer and looking forward to learning about it more! Install will be flush centralised from left up to the skylight.

Sounds mega!

 

[Nickj]

So, chatted through back battery options with installer yesterday, and we have a new twist….

Tesla Powerwall 2 option added to the mix!

They have just become an Tesla approved installer, and when we were discussing the battery back up options TPW was suggested as may not be that more expensive. To get current system to have battery back up was £6-800 more on my basic quote of 13050. So let say 13750 if we split the difference.

Had a new quote for the 18 panels and TpW 2 for £14480 so under £750 more for the Tesla battery pack and also has 13.5kw storage instead of my original 11.6kw battery storage.

I’m thinking it’s a no brainer, and am a bit more excited about the Tesla pw2…

Any differing views or am I making the right option paying a bit more for the Tesla battery?

 

[bn8959]

Powerwall 2 is amazing. I love mine. It very cleverly optimises how it charges to ensure you just have enough battery to see you through, yet leave room for charging from solar if it predicts the weather will be good.

We've found the most reliable weather forecast for the day ahead is how much the PW charged up overnight! Definitely worth if you are on a low rate tariff overnight.

Only downside is that its AC coupled, so cant soak up any lost excess, where your panels are generating more than your inverter can convert.

 

[Midlifecrisis]

Only downside is that its AC coupled, so cant soak up any lost excess, where your panels are generating more than your inverter can convert.

This would be a problem for us, but if your inverter can handle all of the power from your panels then it won’t be a problem for you

 

[Nickj]

This would be a problem for us, but if your inverter can handle all of the power from your panels then it won’t be a problem for you

oh, I thought this system ditched the inverter and that’s where the saving came?

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