7.3 kW Bi Facial Rooftop Panels: ~7 year ROI: Fact OR fiction?

Screwdriva

Looks like the latest crop of bifacial panels have arrived. An increase of 10% more power generation (440 vs 400W) in < 24 months 

https://www.lg.com/us/business/neon-2/lg-lg440n2t-e6

arty688

Yes but they tend to get 10% more power by making them 10% bigger . So depending on your roof bigger might not be better.

QrizB

arty688 said:

Yes but they tend to get 10% more power by making them 10% bigger . So depending on your roof bigger might not be better.

This year's panels are definitely a little bigger, but thast's not the whole story.

Comaring this 2019 data sheet to this 2021 one, they've changed from 72 full cells to 144 half cells and as a result the panel has grown from 2,024mm x 1,024mm to 2,130mm x 1,042mm; an increase in area of 7%. Some of this will be down to the construction style which adds an unproductive strip across the middle of 144 half-cell panels.

Module efficiency has increased by around 2.5%, from 19.3% in 2019 to 19.8% in 2021.

Screwdriva

And that's the end of 2021, a mediocre year in every sense of the word. Speaking Solar generation, a couple of observations for 2021:

1) 10 out of 12 months produced less power than 2020 as displayed by the graph below. 

2) We were able to optimize consumption, up 5% YoY, to 28.3% during solar generation hours , thereby increasing our savings (vs. export). I'm not sure how many are able to achieve >30%, but we're struggling to think of ways to increase this further without storage.

2021 Analysis below:

Consumption:
A. Smart Meter reading on 1st Jan 2021: 9120 kWh
B. Smart Meter reading on 1st Jan 2022: 10765 kWh
Total import over 12 months is (B-A): 1645 kWh
Avg. Cost per kWh is ~0.20p (up 25% YoY and still rising!!)

Generation:
A. Total generated as of 1st Jan is 3515 kWh (via Solar Edge)
B. Est. total exported to the grid as of 1st Jan is (5594- 3075) 2519 kWh (via Smart Meter)
Total solar energy consumed would be (A-B): 996 kWh (an increase of over 10% YoY)
Bulb's SEG tariff is 5.57p per kWh exported.
Amount saved  = £200
Amount earned = £140

Total savings + earnings for 2nd year since installation i.e. 2021 = £340. At the current rate, it will take 20 years to recover the investment in this solar panel system. 

Solarchaser

Well done in increasing your usage by 10%

In sunny Glasgow 2020 generation was 3200 and in 2021 generation was 3450 for 7 year old 250w panels at sse orientation. 

Dam shame about your 20 year payback.
I wonder how the economics would be for you moving to octopus agile and agile export bearing in mind you generate more than you use and more than you then buy as well.

Screwdriva

Solarchaser said:

Well done in increasing your usage by 10%

In sunny Glasgow 2020 generation was 3200 and in 2021 generation was 3450 for 7 year old 250w panels at sse orientation. 

Dam shame about your 20 year payback.
I wonder how the economics would be for you moving to octopus agile and agile export bearing in mind you generate more than you use and more than you then buy as well.

Cheers SC - I'm sure we can hit 30% usage next year. 

I've been wondering the same. Probably best to wait till the government's sponsorship of Bulb Energy's insolvency concludes first. 

arty688

I think the figures maybe show a few things 

if you are a low to average electricity consumer then just panels might not make financial sense as you will never use a high portion of the generated electricity. If you throw a battery into the mix then maybe but would probably mean moving to TOU tariff.

Probably not worth going for premium panels if payback is your main concern. The LG panels probably cost an extra £1K to £1.5K

if you don't suffer shading issues then you probably won't get the payback from solar edge.

QrizB

Screwdriva said:

And that's the end of 2021, a mediocre year in every sense of the word. Speaking Solar generation, a couple of observations for 2021:

1) 10 out of 12 months produced less power than 2020 as displayed by the graph below. 

2) We were able to optimize consumption, up 5% YoY, to 28.3% during solar generation hours , thereby increasing our savings (vs. export). I'm not sure how many are able to achieve >30%, but we're struggling to think of ways to increase this further without storage.

2021 Analysis below:

Consumption:
A. Smart Meter reading on 1st Jan 2021: 9120 kWh
B. Smart Meter reading on 1st Jan 2022: 10765 kWh
Total import over 12 months is (B-A): 1645 kWh
Avg. Cost per kWh is ~0.20p (up 25% YoY and still rising!!)

Generation:
A. Total generated as of 1st Jan is 3515 kWh (via Solar Edge)
B. Est. total exported to the grid as of 1st Jan is (5594- 3075) 2519 kWh (via Smart Meter)
Total solar energy consumed would be (A-B): 996 kWh (an increase of over 10% YoY)
Bulb's SEG tariff is 5.57p per kWh exported.
Amount saved  = £200
Amount earned = £140

Total savings + earnings for 2nd year since installation i.e. 2021 = £340. At the current rate, it will take 20 years to recover the investment in this solar panel system.

Thanks for the annual summary. A smattering of thoughts:

• ~30% self-consumption is what most of us seem to get unless we have small systems, batteries or similar.
• A return of £340 on 3500kWh generated sounds about right, too.
  
• Your total annual consumption of 2641kWh is quite a lot less than the 3200kWh you stated in the opening post of this thread. do you know how you've made this reduction? (Edit: last year's consumption was also ~2600kWh.)
  
• Your 20-year payback period is a reflection of the premium-quality equipment you've chosen (no criticism implied; you explained earlier in this thread that you actively selected these, for clearly-stated reasons). Chinese panels without SolarEdge might have saved you £3k on the price and 9 years on the payback period.

My system is ten years old in a week or so. I don't have fully detailed records for the whole period but I'll try to put up a reasonable retrospective of my own.

Screwdriva

QrizB said:

• ~30% self-consumption is what most of us seem to get unless we have small systems, batteries or similar.
• A return of £340 on 3500kWh generated sounds about right, too.
  

Thanks for this - it helps validate that things are running as expected.

• Your total annual consumption of 2641kWh is quite a lot less than the 3200kWh you stated in the opening post of this thread. do you know how you've made this reduction? (Edit: last year's consumption was also ~2600kWh.)

Three reasons: 1) Our initial estimate was based on a previous residence's consumption as we had only just moved in when we installed our solar system. 2) Since doing so, we've made a conscious effort to use energy efficient appliances, which appear to have also made a difference. Here's a great example of an A rated dishwasher which uses far less energy than our previous one 3) Our stove top cooking is now gas powered vs. induction

• Your 20-year payback period is a reflection of the premium-quality equipment you've chosen (no criticism implied; you explained earlier in this thread that you actively selected these, for clearly-stated reasons). Chinese panels without SolarEdge might have saved you £3k on the price and 9 years on the payback period.

Skipping on the SE 505 optimizers was not an option as we have shading on our south facing roof thanks to a chimney. It only affects one panel at any time but that would have negatively impacted performance from 60% of the system. We could have considered micro inverters vs. a single HD wave inverter but the 25 year SE warranty and easier access/ serviceability made more sense at the time.

On Chinese components, this is one compromise I would never accept, simply because I have never seen any Chinese brand's device last the full length of its warranty term without issue. Chinese brands appear bankrupt when it comes to reliability, quality and customer service based on my observation. I have had the opposite experience with Japanese and Korean (specifically LG) products and would have gladly considered a Panasonic/ Sanyo or Samsung panel if a comparable option existed but an alternative that could compete with the LG bifacial panels didn't seem available.

I take your point on the upfront savings and will be following other users feedback on Chinese panel performance in the decade ahead. 

Spies

Not every budget panel is Chinese, Eurena are Spanish...