Savings Calcuation: Eddi vs. Variable SEG tariff

Screwdriva

Greetings! 

I'm considering purchasing an Eddi diverter to pre-heat my 250L indirect unvented cylinder for most of the year (vs. sell to Octopus Outgoing Agile). A couple years ago, the maths didn't work in favour of diverter payback. 

Fast forward today, and assuming an:
1. import tariff of .29p
2. export tariff of .20p
3. gas tariff of .08p 

What would make more sense when the £600 cost of an installed Eddi is factored in?

QrizB

Screwdriva said:

Greetings! 

I'm considering purchasing an Eddi diverter to pre-heat my 250L indirect unvented cylinder for most of the year (vs. sell to Octopus Outgoing Agile). A couple years ago, the maths didn't work in favour of diverter payback. 

Fast forward today, and assuming an:
1. import tariff of .29p
2. export tariff of .20p
3. gas tariff of .08p 

What would make more sense when the £600 cost of an installed Eddi is factored in?

With gas at 8p/kWh and export at 20p/kWh, the Eddi will never make a profit even if it's free.

If you put 1000kWh through it, you'll have saved £80-worth of gas at the expense of £200-worth of SEG.

Check again in a year or two when energy prices might (or might not) be back to normal.

Reed_Richards

Eddi-type diverters work for many people because they are paid for deemed export so their solar electricity is effectively free.  If you get paid for your actual export and you are paid more per kW than you pay for gas then export has to be the right thing to do.  I cannot keep track of the various Octopus tariffs; £0.20 per kW would seem a fantastically generous export tariff whilst 0.20p per kW would not - but I presume is a mistake in the way you wrote your figures (thinking £ but writing p).   

Meatballs

I've mentioned the potential poor return on diverters multiple times on solar social media groups and it just tends to get drowned out in the noise of people trying to get to 0 export without realising losing SEG is a cost.

They probably were a good idea on FIT...

With a battery they make less sense as battery will often take much of the low generation that the diverter was designed to soak up.

With tariffs like Octopus Go (7.5p vs 5p SEG on SO (you can actually get 5.5p with Scottish Power)) its 2.5p/kWh saved as its cheaper to use immersion than gas to heat the cylinder. You need to divert 16,000kWh into your water cylinder to break even on a £400 Eddi (alone without harvi/hub or install costs).  To do that within the 3 year warranty period that's 14kWh diverted a day every day. How many people will have 14kWh excess every day once battery has taken its share?

Even if you did have that excess spare many people wont be using that much hot water. I seem to use about 4kWh of hot water a day... My EPC suggests 2922 kWh per year (5 bed house) comes out at about 8kWh/Day so you have to be quite a heavy hot water user. If you used 7kWh a day of hot water you could get down to 6 year repayment on £400, or 8kWh/Day to get it down to 8 year repayment for £600 install with the harvi/hub/install costs.

Many people pair them up with a Zappi which will make it even harder for the diverter to pay back if you are diverting to your car. Zappi's are also not great for returns when compared to Octopus Go - but at least if you were going to get a fast EV charger anyway its not quite so bad.

</rant>

Reed_Richards

I have a WiFi controlled switch rather than a solar diverter because I find them very expensive, probably unnecessarily so given the electronics they use.  But the advantage of solar diverters is that they incorporate a throttle so you can only use whatever excess power is available.  I have to rely on my battery to smooth out demand.    

Screwdriva

Reed_Richards said:

I have a WiFi controlled switch rather than a solar diverter because I find them very expensive, probably unnecessarily so given the electronics they use.  

I suppose you're right. This is the only WiFi switch I could find that has a fuse. Time to switch to Octopus Outgoing Agile I suppose...

Reed_Richards

The Timeguard WiFi switch is the one that I have; I have been using it for about 20 months now and it has never misbehaved.  You operate it via a phone app, in your house or anywhere else that has a WiFi signal.  I can also view my solar power generation via a phone app so if this tells me I have spare solar power when I am away from home I can switch the immersion heater on remotely.  Or I use a timed programme if I am confident it will be sunny. 

I don't know about any of these Octopus tariffs but "Agile" would seem to imply that you don't get the same export rate all the time.  Are you sure about that 20p per kWh figure?

Boffinboy24

Octopus outgoing is linked to wholesale rates, you don’t need to be on the Agile import tariff. You can’t be on Go, it can only be paired with their standard tariffs. https://www.energy-stats.uk/octopus-agile-outgoing-export/ On one of the other threads about minimising import someone has been sharing their monthly stats - I believe they were personally getting an average of around 17p export rate. 

Screwdriva

Are you sure about that 20p per kWh figure?

Not really. But I know it's quite close to 20p today and don't expect that will come down anytime soon. Plus 20p is such a nice round figure for maths

andyg9053

At the moment I’m paying 3.65p kWh gas and getting 4.1p kWh Seg from Octopus on Go. Assuming 90% efficiency on the gas boiler the numbers virtually match. However I am not burning gas which may still be coming from Russia. I’m also not creating co2. The Eddi will never pay for itself but it means my hot water is usually green

Reed_Richards

Screwdriva said:

Are you sure about that 20p per kWh figure?

... I know it's quite close to 20p today 

I've looked.  At the peak times for generation it seems to be usually in the 10p to 15p range, and occasionally below 10p.  But you are stil getting more than you pay for gas at present.