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

Screwdriva

The highest August solar yield so far, over 10% higher than the previous best of 440 kWh in 2020. In fact, August '22 had a higher yield than any month in 2021, which is incredble!

Six out of the eight months have hit their all time high this year.

Whitworth789

As someone totally new to the whole subject of solar panels I would like to thank both the OP and all contributors to this thread. The information has been very helpful and I have learned so much that I now feel able to make the right decisions

Screwdriva

Whitworth789 said:

As someone totally new to the whole subject of solar panels I would like to thank both the OP and all contributors to this thread. The information has been very helpful and I have learned so much that I now feel able to make the right decisions

Great to hear this has been useful! 

Another record generation month in 2022 (the 6th so far). At 255 kWh, a full 22% more generation this October compared to previous years.

Screwdriva

And that's a wrap for 2022, an above average year in terms of PV generation (& not much else). A couple highlights:

1) 7 out of 12 months yielded more power than any prior year, as displayed by the graph below. 

2) We were able to increase household PV consumption to ~32% (up by ~27% YoY) during solar generation hours, primarily by using the immersion element to heat hot water during the summer months. £ savings in gas are not reflected below.

2022 Analysis below:

Consumption:
A. Smart Meter reading on 1st Jan 2022: 10765 kWh
B. Smart Meter reading on 1st Jan 2023: 12385 kWh
Total import over 12 months is (B-A): 1620 kWh (slightly below 2021's 1645 kWh). 
Avg. Cost per kWh is ~0.30p (up ~33% YoY and still rising!!)

Generation:
A. Total generated as of 31/12/22 is 3928 kWh (via Solar Edge)
B. Est. total exported to the grid as of 1st Jan is (8259-5594): 2665 kWh (via Smart Meter, up slightly from 2519 kWh in '21)
Total solar energy consumed would be (A-B): 1263 kWh (an increase of over 27% YoY from 2021's 996 kWh consumption)

Bulb's SEG tariff was 5.57p per kWh till 4/22. Octopus Outgoing Agile has averaged well in excess .20p per kWh since. I have used 0.20p per kWh as a conservative blended SEG tariff paid for 2022

Amount saved  = £375
Amount earned = £535

Total savings + earnings for 2nd year since installation i.e. 2021 = ~£910. At the current rate, it will take < 8 years to recover the investment in a £7K solar panel system. 

(2021's results are on Page 21)

Screwdriva

With LG no longer in the Solar PV business, we were able to convince SHARP (Düsseldorf) to ship over a half dozen of their 570W Bifacial Panels.

We plan on moving the 2 existing visible LG panels over to the East aspect (West visible) and replace them with the Sharp panels around the area marked in red (reserved for a Velux Cabrio folding balcony). If we manage to get 4 to fit, that’s an incremental 2.3+ kWh of lucrative West facing generation added to the system. Can’t wait! 

Martyn1981

Can I ask why you would choose bifacial for a roof install?

Screwdriva

Martyn1981 said:

Can I ask why you would choose bifacial for a roof install?

I get that one alot! 

Based on the generation comparisons with immediate neighbouring households (3 of them), the LG bifacial panels are outperforming their standard 400W counterparts on all but the warmest of days. I use a white, solar reflective paint to maximize the bi-facial effect.  I have no way to prove this but believe the rear side generation capability is generating as the sun moves from strings (aspects) 1(E) to 3(W).  

I'm not seeing the 13-19% incremental gain seen here (but estimate around 8-10% as seen here). Previous years generation #'s, despite shading on between 1 to 2 South facing panels due to our chimney, should highlight this.

JKenH

I apologise if this is taking the thread slightly off topic but I have been experimenting with a reflective panel in front of my free standing solar panel (see this link for my set up https://forums.moneysavingexpert.com/discussion/6360585/portable-power-stations ).

I am still at the experimental stage so it is, currently, simply a large sheet of cardboard to which I have glued kitchen foil. I place it in front of the panel, at an obtuse angle (almost on the ground) during strong sun but propped up closer to a right angle when overcast. Unfortunately it’s not the old style shiny aluminium foil, rather a matt embossed finish, but that’s all that we had in the kitchen. Nevertheless in overcast conditions I am seeing a gain of 20%. With the right foil I could probably get this up to 50%. I intend to refine my reflector by using a more robust plywood backing (recovered from old garage doors) but retaining the foil. (I am kicking myself now for giving away three 2m x 1m sliding wardrobe mirror doors which would have been perfect for my set up.)

Although employing a different approach, as with the bi-facial panels, the objective is to enhance generation by making use of ambient light.  In the case of bifacial panels, though, no additional roof area is needed whereas my approach is very space inefficient but minimal cost. I would probably have been better off starting with a bi-facial panel for my set up with a reflector on the pallet underneath. 

At the end of the day it is about return/cost. With a full solar installation a big part of the cost is labour, fittings and scaffolding so even a minimal uplift in generation from bi-facial panels would probably be cost effective where roof space is limited. The cost of a conventional solar panel itself is around £250/kwp out of a domestic roof solar installation cost of, say, £1200 per kwp. Upgrading to bi-facial would probably add £50/kwp to the cost - that’s less than 5%. It makes sense if you can get a 10% uplift. It would probably make even more sense for flat roof installations where the panel is mounted at an angle. 

Screwdriva

JKenH said:

At the end of the day it is about return/cost. With a full solar installation a big part of the cost is labour, fittings and scaffolding so even a minimal uplift in generation from bi-facial panels would probably be cost effective where roof space is limited. The cost of a conventional solar panel itself is around £250/kwp out of a domestic roof solar installation cost of, say, £1200 per kwp. Upgrading to bi-facial would probably add £50/kwp to the cost - that’s less than 5%. It makes sense if you can get a 10% uplift. It would probably make even more sense for flat roof installations where the panel is mounted at an angle. 

If I do have a regret, it's that I did not maximize my roof coverage during the initial installation back in 2019. The goal then remains the goal now - squeeze every watt of generation from available roof area. That said, should the Barclays Green Reward come through, the cost for this system expansion will be substantially lower. 

Waywardmike

Are the five panels on the left a neighbour?

What would be interesting, is to match their panels (wattage), but bifacial, and see the difference, assuming everything else being equal, SE and shading etc., then you'd know for sure.