Solar diverter - flawed return on investment calculations

JKenH

Grandad2b said:

JKenH said:

so far this month (and it hasn’t been a sparkling one so far) I have exported 142 kWhs and imported 69 kWhs so have stored 73kWh worth for future use. With a battery after covering the 69kWh imported those 73 kWh would have been lost 

If you were off grid those 73kWh would be 'lost'. Surely if you remain on grid you are still able to export?

Yes, you are right. What I should have said was you lose the value of the 73kWh exported. I received credit for exporting 142kWh but used up 69kWh of that credit offsetting import. Yes, there is a difference in rate between import and export so you lose some of the value of that export but with batteries you also lose some of the value of what you store in cycling. My average import cost under Flux last week was 25p (see below) I can’t give you the exact figure for export as my app isn’t yet showing it but while most of my export will have been at 22p there will have been some at 35p so at the moment I’m not losing much in Flux cycling losses.

The saving figure shown is against SVT. The daily spend figure includes the standing charge.

Alnat1

@JKenH The average price you've paid for each kWh of import is 24.928p 

With a battery my import price is 20.66p for an average of 2.48kWh/day this last 7 days. I need to import less because the battery helps power the oven for dinner and runs the evening and overnight load.

I probably get paid slightly more per kWh on average than you too, as I discharge my battery down to 50% by 7pm.

Whether this is enough to justify the cost of the battery..........my maths isn't good enough to do the sums 

JKenH

Alnat1 said:

@JKenH The average price you've paid for each kWh of import is 24.928p 

With a battery my import price is 20.66p for an average of 2.48kWh/day this last 7 days. I need to import less because the battery helps power the oven for dinner and runs the evening and overnight load.

I probably get paid slightly more per kWh on average than you too, as I discharge my battery down to 50% by 7pm.

Whether this is enough to justify the cost of the battery..........my maths isn't good enough to do the sums 

My figures are for summer of course and in winter I will import far more and pay a higher average price but at the moment Flux is working for me and for you. Your batteries will be even more useful in winter. Whether I go back to something like Go in the winter is something I will need to think about.

I am not suggesting batteries don’t work with Flux - they do, you get the best of both worlds. I think the argument that @Screwdriva was making is that if you don’t already have batteries, Flux is a good alternative at no capital cost and the question anyone now considering batteries needs to ask is once I have Flux, how much more will batteries benefit me?

I very much understand the satisfaction of being more self sufficient and batteries storing energy are more satisfying than just saving money. You obviously appreciate Flux but others having spent money on a battery system (and seeing the higher overnight rates on Flux) are happy to just minimise overall draw from the grid (their import bill) rather than look at the net bill after taking export into account. 

On a good day, if I try, I can get my import down to around 2kWh per day using solar for my DHW but it is cheaper overall for me to import 4kWh, heating my hot water between 2 and 5am, because I am paid more for export. Same for you with a battery - you import more than you need to export it at a profit.

I think it will be a challenge for EV owners, who with IO/Go have been able to pay 7.5p/kWh or charge their car for “free” using their own solar, to now mentally accept it may overall be cheaper to pay 19p/kWh to charge the car and not use their Zappi.

iotum

orbit500 said:

Interesting. I’m on old style FIT. If I switched then I would lose my deemed export of about 2.5p/kWh but keep the 5p generation payment.
I have 12kWp solar and 30kWh battery. I’m a heavy user at 16000kWh and a heated pool. Current setup is EDF goelectric35 with 4.5p night rate and 46p day.
I’m going to run some numbers!

Yes I was wondering if switching from FIT would make sense. But Octopus could change their rates at any time. The Government "should" stick to the index linked increase in the FIT payments for 20 years. Although it wouldn't surprise if they somehow ditched it early.

With the current uncertainty in the energy markets it would be a gamble to leave the certainty of FIT but then maybe I should just check the numbers as well. Just to be sure.

mickyduck55

iotum said:

orbit500 said:

Interesting. I’m on old style FIT. If I switched then I would lose my deemed export of about 2.5p/kWh but keep the 5p generation payment.
I have 12kWp solar and 30kWh battery. I’m a heavy user at 16000kWh and a heated pool. Current setup is EDF goelectric35 with 4.5p night rate and 46p day.
I’m going to run some numbers!

Yes I was wondering if switching from FIT would make sense. But Octopus could change their rates at any time. The Government "should" stick to the index linked increase in the FIT payments for 20 years. Although it wouldn't surprise if they somehow ditched it early.

With the current uncertainty in the energy markets it would be a gamble to leave the certainty of FIT but then maybe I should just check the numbers as well. Just to be sure.

You do not need to leave FIT to signup for Flux, you have to change from deemed export to measured export.  The total generation payment remains the same.

Petriix

JKenH said:

I think it will be a challenge for EV owners, who with IO/Go have been able to pay 7.5p/kWh or charge their car for “free” using their own solar, to now mentally accept it may overall be cheaper to pay 19p/kWh to charge the car and not use their Zappi.

There's a bit more to it than that. I'd have to give up my deemed exports permanently (plus scratch around for the requisite paperwork to get an export MPAN). That would be fine if SEG payments stay high, but could well be a long-term loss if prices return to 'normal'.

Then there's the faint hope that battery prices come down and make the ROI more reasonable. Losing export payments for self consumption is more of a psychological hit than not using the Zappi during the day. 

silverwhistle

Alnat1 said:

Whether this is enough to justify the cost of the battery..........my maths isn't good enough to do the sums 

I was never any good at simultaneous equations either! I'm on original FIT (2013) and am very happy with my decision and getting an iboost. The 10000~ units to hot water would be more but it's a single person household with an electric shower. Heating by PV means I don't use the boiler for 6 months of the year so saving on boiler servicing, but overall it's the peace of mind I have in reasonable and predictable bills which has a value for me.

I do keep an eye on tariffs: currently on Intelligent Octopus, average price over the winter 17-18p/kWh, but keeping an eye on Agile and wondering whether new wind coming onstream this year will impact prices. But I don't spend too much of my valuable time worrying about it.

I do have a battery, in my MG4, and if things get desperate I can always use the V2L capability!

JKenH

Deemed export is worth around 3p for every kWh generated. Flux export is a minimum of 22p/kWh. You only need to export 14% of your solar generation to be better off on Flux. 

We don’t know what future export payments will be worth so can only make decisions on prices now and where we think they might be. I seem to recall 4 or 5 years ago solar companies being pilloried for suggesting electricity prices would continue the trend of 6% pa increase. No, it was claimed RE will make prices cheaper, and look where we are now. If electricity prices go up then so will export prices. If electricity prices fall we all win. Look at Flux export as a hedge against inflation. 

Screwdriva

JKenH said:

I am not suggesting batteries don’t work with Flux - they do, you get the best of both worlds. I think the argument that @Screwdriva was making is that if you don’t already have batteries, Flux is a good alternative at no capital cost and the question anyone now considering batteries needs to ask is once I have Flux, how much more will batteries benefit me?

I very much understand the satisfaction of being more self sufficient and batteries storing energy are more satisfying than just saving money. You obviously appreciate Flux but others having spent money on a battery system (and seeing the higher overnight rates on Flux) are happy to just minimise overall draw from the grid (their import bill) rather than look at the net bill after taking export into account. 

To further highlight JKenH's above point, here are two scenarios of Flux (one with and one without a 10 kWh battery), using our actual consumption pattern, generation and export. (Highly recommend Gary's new Solar Calculator)



vs. Battery (set to charge fully from 2-5am and discharge during 4-7pm)



Without drastically increasing our consumption, it's unlikely we will recover the cost of the battery within the warranty period. 

Waywardmike

Here's my experience with an iBoost...

Old FIT scheme so deemed export, made sense to have one.  It broke within the two year warranty period!  In Marlec's defense they changed no problem and it's been fine since.  Have had it maybe 5 years now

I didn't have it fitted when the solar went in as I had a Combi at the time but later changed to a system boiler and cylinder as part of a much larger renovation.  Worcester bosch boiler, the 'Rolls Royce' of boilers I was told, we had nothing but problems with it so was thankful for the change, but that's another story.

It cost me £200 and I fitted it myself.  It provided hot water from ~Mar-october pre battery, and now with the battery which takes priority it's looking more like late Apr to October, but that might just be because we've not had a great start to the year.

If it broke would I buy another?  No.  Not least because they're more than double what I paid now, but I just don't think the savings are there to be had especially with a battery.  I don't trust any diverter (Eddi included) to pay for itself within it's warranty period.  I think you're better off just getting a WiFi switch and putting it on timer or doing it yourself.  The battery will pick up the slack if a cloud rolls over and continue to charge once the tanks hot.  They cost very little.