Solar PV with or without battery?

chris1012

Greetings, everyone,

After dedicating over a month to researching Solar PV systems, I'm nearly ready to make a decision. I owe my progress to some wonderful individuals who generously shared their time and solar expertise with me, especially one from on here!

Currently, my inclination is towards a 7kWh optimized system. However, I'm grappling with the decision of whether to invest in a battery now or wait a few more years, as I have a budget of up to 3k for a battery.

My yearly energy consumption stands at 6000kWh, with daily averages of 12-13kWh in the summer and 20-25kWh in the winter.

My setup will include 16 panels, with 12 facing South (185 degrees) and 4 facing South West (247 degrees). Some of these panels will experience morning shading, but they're unobstructed from 10am to 6pm.

I'm curious about estimating my annual energy generation and export? During summer nights (midnight to 8am), our maximum grid import is 2.5kWh.

The bulk of our energy usage occurs on weekdays from 4pm to 9pm, and during weekends. I anticipate a significant increase in consumption during the winter due to our gas central heating and reluctantly using a tumble dryer from time to time.

Based on my understanding, if I export 75% of my generated power (likely via Octopus Flux), it might make more financial sense to delay the battery investment until I can afford a 13kWh+ battery.

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."

Any suggestions and advice on this matter would be greatly appreciated.

Screwdriva

Inputting your actual usage / system size and flux tariffs into this calculator should help you generate a realistic ROI timeframe. 

https://garydoessolar.com/utilities/dailymodellingutility/

Reed_Richards

Your DNO will allow you to export a maximum of 3.68 kW of power without question.  If you want to export more than this you need special permission.  I gather that this is usually granted but not always, as in this instance: https://forums.moneysavingexpert.com/discussion/6467206/g99-knocked-back-by-dno-trying-understand-proposed-reinforcemen/p1

Have you approached your DNO to verify that you would be allowed to export your full output capacity (which I presume is a maximum of 7 kW, i.e. 7 kW peak output, 7 kWp )?  Then if you add a battery, which exports at the same time as your panels the figure could be even greater.  And many inverters will limit your power output to less than you are actually generating.  Have you covered these issues in your one month of research?  These must affect the numbers in your calculations.

Also, don't you need a battery to make best use of Octopus flux? https://octopus.energy/smart/flux/  Octopus say:

Power your home with 100% renewable energy on this Octopus Energy electricity tariff designed exclusively for solar and battery owners.

I can't find any reference to your 22p per kWh, it looks like the vast majority of your exporting would be done at 18.67 p per kWh and you would have to change your usage pattern to avoid importing between 16:00 and 19:00 (although your south west panels would help a bit).

QrizB

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.

1961Nick

For around £1800 you could add a Pylontech US5000 to a hybrid inverter. This would cover most of the consumption during the expensive Flux period 4.00pm - 7.00pm.

Screwdriva

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.

I beg to differ based on my actual use case. 

1) We have a 4kWh system in London, which isn't too far from OP's location. We have averaged ~3.81 kWh p.a. across the past 3 years, despite utilizing 3 aspects, are not fully South facing or in the "best part" of the UK and being partially shaded. It can be argued that OP's address is better suited than ours and will likely exceed our performance, especially in the 2nd half of the day's generation.

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

3) So far, we have been paid an average rate of 21.7p for export, including the more lucrative window.

Reed_Richards said:

Your DNO will allow you to export a maximum of 3.68 kW of power without question.  If you want to export more than this you need special permission.  I gather that this is usually granted but not always, as in this instance: https://forums.moneysavingexpert.com/discussion/6467206/g99-knocked-back-by-dno-trying-understand-proposed-reinforcemen/p1

4) I'm yet to hear of a London address not being G99 approved for export by UKPN. 

Reed_Richards

Screwdriva said:

1) We have a 4kWh system in London, which isn't too far from OP's location. 

The OP did not reveal their location in public so I presume you have been communicating privately.  In which case I surmise that you provided the quoted figures and the OP is now seeking a sanity check on those.  If so, you saying that you think you are right adds little the discussion.

Screwdriva

Reed_Richards said:

The OP did not reveal their location in public so I presume you have been communicating privately.  In which case I surmise that you provided the quoted figures and the OP is now seeking a sanity check on those.  If so, you saying that you think you are right adds little the discussion.

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. 

Qyburn

chris1012 said:

My setup will include 16 panels, with 12 facing South (185 degrees) and 4 facing South West (247 degrees). Some of these panels will experience morning shading, but they're unobstructed from 10am to 6pm.

...

Any suggestions and advice on this matter would be greatly appreciated.

Have you had actual quotes, from installers open to actually doing the work? Just checking because some of the "shouldn't cost more than £xxxx" comments on here can wildly underestimate what you would have to pay in reality.

cm4ever

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. 

Screwdriva

A pleasure. In my experience, most on these forums mean well and are genuinely helpful, if a tad passionate