Solar PV with or without battery?

Reed_Richards

Screwdriva said:

 Actually, I took the trouble of adding to OP's previous post. I'll let what I have shared above to speak for whether I have added anything to the discussion. 

Well of course you have added to the discussion by revealing details that the OP either accidentally omitted or didn't want to tell us.  @Screwdriva, you installed a new boiler and got it to work with superb efficiency.  You installed solar panels and achieved great results exporting via Octopus Flux.  You're clearly very skilled at milking every last drop of efficiency/revenue out of what you have but I wonder if this makes you something of an outlier and what you have achieved should not be regarded as typical of what the average person would manage.     

Screwdriva

As highlighted, OP had already shared their approximate location on this forum in a prior post, which I had responded to previously.

As far as me being an outlier, coming from you @Reed, I'll take that as a compliment... Thanks! It's been an informative journey, one that has made me very keen on sharing what I have learnt on my path to a more sustainable lifestyle. 

ABrass

My usage and system (size, geographic location and angles) is very close to what you're looking at. I went for a battery and am very happy with that decision. It will give a greater ROI with reasonable assumptions and in the first year the battery did even better than predicted (for reasons I can type up but it'll take a while.

My battery doesn't make it through the night by design. For me I'd be perfect at 10kWh but any larger would need a specialist tarrif to make sense, but if you're willing to set things up you can probably get an even better ROI with something like Flux.

With 8kW and a 6kW Inverter I've generated roughly 7,000 kWh this year.

Magnitio

@chris1012 You mention that the bulk of your consumption is between 4 and 9. Octopus Flux is expensive from 4 to 7, so this could prove to be the wrong tariff for you if you don't have a battery to support your usage during these hours. A flat import tariff and 15p/kWh export might be more appropriate.

Reed_Richards

Screwdriva said:

As far as me being an outlier, coming from you @Reed, I'll take that as a compliment... 

It wasn't meant any other way.  But I'm not sure I would do as well as you with the same hardware.  For one thing, I don't think I could persuade my other half to have a cooked meal only at lunch time and not use the hob and the oven during the Flex peak hours.  

Screwdriva

Reed_Richards said:

It wasn't meant any other way.  But I'm not sure I would do as well as you with the same hardware.  For one thing, I don't think I could persuade my other half to have a cooked meal only at lunch time and not use the hob and the oven during the Flex peak hours.  

If I tried that on my other half, I'd be single again!

The only changes we've made have been 1) running all cleaning appliances (washer/ dishwasher/ dryer) during the 2-5am window 2) Replacing all appliances with the most efficient option sold on the market when the time comes. 

pensionpawn

This is a complete can of worms with so many variables all aligned differently for each households installation, orientation and usage pattern. I'll have had my panels (4kWs due east, 3.12kWs due west) 8 years this Christmas and have been looking to justify a battery since. I haven't been able to, however that's an individual decision. Due to rising prices I did order a Powerwall 2 in early 2020 however lead times and costs went exponential and I binned that idea favouring moving to an EV (although our annual mileage doesn't justify one just for travelling) with a bi-directional charger in the future. In other words a mobile ~60 kWhr battery! Recently I've migrated to Octopus Flux and export payments have built a fiscal buffer for the more expensive darker third of the year. This tariff ensures that you don't waste any of your export, thus diminishing the argument for a battery, unless of course you use it predominantly for daily charge / discharge cycles / export payments. Of course a battery will still contribute to minimising import costs during the darker third, however the RoI could be lengthy. Another factor is do you what to add "island mode" to your set up allowing you to still generate / run off your battery in the event of a power cut. I see this as energy insurance and hence does not have an associated RoI. However, how often do you suffer from power cuts of more than 30 minutes? We've only had 2-3 in 27 years. My acid test is take your annual elec bill and divide that into the cost of a Powerwall. This will tell you the number of years until it pays for itself. Then of course you have to factor in that a battery will never eliminate all import so add on a percentage. Has the RoI now exceed the warranty period and for me, if it has, it's a definite no. You could probably make better use of the money, especially if you have a young family. For anymore close to 55, throw the money you would spend into your pension pot and the government will make that up by 20% and you'll have access to it very soon. As I said, a complete can of worms!

pensionpawn

QrizB said:

chris1012 said:

One of the calculations shared with me suggests: "A 7kWh system should generate 7K kWh per annum conservatively. You will sell 75% of that for export at 22p via Flux = £1150 earned. Offset 25% of your consumption = £450 saved. Total = £1600 p.a."

Highly unlikely.

The first sentence is wrong.

A7kWp system might generate 7000kWh per year if installed south-facing and unshaded at an optimised angle in an ideal part of the UK (on the south coast).

Your system is not fully south facing, partly shaded, won't be at the optimal angle and you might not be in the best part of the UK. I doubt that you will ever hit 7000kWh a year.

I would guess that you're more likely to generate 5500-6000kWh.

Without a sizable battery, most of your export will be when Flux is paying 18p.

If you export 75%, 4500kWh at 18p is £810.

If you use the other 25%, 1500kWh at 29p is £435.

Total savings £1245.

My 7.12kW installation averages around 6.4Mwhrs pa. Since moving to Flux 3.5 months ago I have exported just over 2.4Mwhrs (which is actually 74% of generation over that period!) worth around £550. With 3.12kWs facing due west 15% of my export is during the peak time (currently 31.4p). Standard rate is currently 19.3p. Export is dropping steadily from mid June and will be minimal throughout GMT. That said I have modelled the combination of Flux export and generation FiT to almost cover my annual energy bill. However it needs to be said that we're mostly retired and when convenient plan our cooked meals for noon, which of course is the whole purpose of Flux...

pensionpawn

cm4ever said:

Screwdriva said:

2) We don't have a battery and are on Flux. The T&C's don't require a battery (attached).

Thank you for being one of the few other voices on this forum that's prepared to correctly point out that you don't need a  battery to be legitimately accepted on Octopus Flux, instead of CS staff not doing their job/checks etc.

Unfortunately, too many 'regulars' of this forum will argue black is white on this simple point. 

No battery here either.

pensionpawn

Reed_Richards said:

Screwdriva said:

 Actually, I took the trouble of adding to OP's previous post. I'll let what I have shared above to speak for whether I have added anything to the discussion. 

Well of course you have added to the discussion by revealing details that the OP either accidentally omitted or didn't want to tell us.  @Screwdriva, you installed a new boiler and got it to work with superb efficiency.  You installed solar panels and achieved great results exporting via Octopus Flux.  You're clearly very skilled at milking every last drop of efficiency/revenue out of what you have but I wonder if this makes you something of an outlier and what you have achieved should not be regarded as typical of what the average person would manage.     

Not an outlier... I replaced my 26 year old boiler a year ago with a Viessmann hydrogen ready condensing model. It has almost halved my gas consumption. Replaced my 25 year old windows the year before, which also approximately halved my CH gas consumption. The next big win is a change of lifestyle to cook (electric oven / induction hob), where it's convenient, around noon. This also minimises import / maximises export (on Flux). It's a plan, over many years and not without up front cost, however the goal is to nail down my outgoings for when we're both fully retired. Not long to go!