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

Screwdriva

Waywardmike said:

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.

Yes and that's exactly what I've measured with our immediate neighbouring systems (all 3 of them are SolarEdge done via me). The incremental generation on the West/ East aspect panels ranged between 8-11% in favour of the bi-facial panels on all but the hottest of days (I'm on the only one with South facing panels).

Martyn1981

Screwdriva said:

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.

Thanks, forgot about the paint (Doh!), you mentioned it before. It got me thinking that if I ever get round to the garden ground mount, I might deliberately build it with a larger offset from the backing, and use a reflective paint plus bifacials. I was planning to board out the structure anyway, so that it's a 'ladder store', as the permitted planning rules are a bit limiting otherwise (max 9m2, max 3m on any side).

Alternatively, I wonder how my neighbour to the south would feel about me replacing the communal fence with a vertical mounted bifacial PV fence, as per the agro-voltaics idea? Think I may be more than overthinking this now. 

Waywardmike

Screwdriva said:

Yes and that's exactly what I've measured with our immediate neighbouring systems (all 3 of them are SolarEdge done via me). The incremental generation on the West/ East aspect panels ranged between 8-11% in favour of the bi-facial panels on all but the hottest of days (I'm on the only one with South facing panels).

I suppose the question then is whether the panels were 10%+ more expensive (with paint costs/painting etc).  If not then definitely worth doing, if more, probably not worthwhile as you won't see the ROI over 'standard' panels?

Screwdriva

Waywardmike said:

I suppose the question then is whether the panels were 10%+ more expensive (with paint costs/painting etc).  If not then definitely worth doing, if more, probably not worthwhile as you won't see the ROI over 'standard' panels?

Hard to compare really. They cost us the same to install in 2019 as my neighbour paid in 2022 for their "standard" 400W Hyundai black panels, probably due to the inflationary effect. Given our limited roof space, three aspects, shading and the eventual goal to electrify our heating, I see the performance improvement as very useful. 

Waywardmike

Screwdriva said:

 I see the performance improvement as very useful. 

Any performance gain is useful, doesn't mean it makes sense financially!  If they cost you £1000+ more to install, yet make/save you £30-£50 a year extra, I'd argue they're not worth it!

JKenH

Waywardmike said:

Screwdriva said:

 I see the performance improvement as very useful. 

Any performance gain is useful, doesn't mean it makes sense financially!  If they cost you £1000+ more to install, yet make/save you £30-£50 a year extra, I'd argue they're not worth it!

But you are ignoring the satisfaction element - that has to be worth something. Without it we would hardly ever buy anything other than food. Most of the clothes we buy are hardly essential and certainly not value for money so why do we need to buy them? Why would we eat out when it is cheaper to cook at home? Maybe you don’t, but I do buy things that give me satisfaction beyond their monetary value. 

Waywardmike

JKenH said:

But you are ignoring the satisfaction element - that has to be worth something. Without it we would hardly ever buy anything other than food. Most of the clothes we buy are hardly essential and certainly not value for money so why do we need to buy them? Why would we eat out when it is cheaper to cook at home? Maybe you don’t, but I do buy things that give me satisfaction beyond their monetary value. 

I agree wholeheartedly....  If you look at previous posts by the OP though you'll see that's normally a stance taken by them.

I find it strange that @Screwdriva will adamantly claim batteries are a waste of money that you'll never see a ROI on, yet advocate paying for a panel type that's arguably a bigger waste?

Martyn1981

Waywardmike said:

Screwdriva said:

 I see the performance improvement as very useful. 

Any performance gain is useful, doesn't mean it makes sense financially!  If they cost you £1000+ more to install, yet make/save you £30-£50 a year extra, I'd argue they're not worth it!

I agree that a balance is needed, but had to chuckle at your example, as it's fun how different people look at things. That's probably exactly the point that I'd suggest they are worth it, after all that's a 3-5% annual return, and it's index linked.*

Obviously everyone will have a different ROI that makes them jump in, or not. So thanks for the thought exercise.

Personally, I'm somewhat doubtful that bifacial are worth it, if mounted close to a barrier, which tbf isn't what they are specifically designed for. But Screwriva's findings are interesting, and hopefully my gut feeling is wrong, and they have a wider role.

Just spitballing now, and pondering the various benefits. Back in the early days of PV (circa 2010-12), folk were paying quite a premium for higher efficiency panels from Panasonic. These were 240Wp (v's normal 250Wp panels) but only 800mm wide, so you could fit more. Obviously as panels got more efficient, then roof limitations eased. But it is a genuine issue, where space is limited.

For instance it has occured to me that installing 4 panels portrait in the garden will be around 4.5m long, as many are 1.1m wide now (plus panel gaps). But 3 2m tall panels would be a nicer fit at about 3.5m, but similar area. Is it worth going to a higher efficiency, at a higher price, I don't know. As they say, when you are at the cutting edge, you bleed. But it might be worth the extra.

Back to your £1,000 example, I know it was just an example, but it may be quite accurate. At 2m2 to 2.5m2 for larger panels, then 10 panels may be a typical install. So £1,000 would be £100 extra per panel, which may be comparable, not sure. Trade prices for normal 400Wp panels are about £150 + VAT, so a larger panel, that's also higher efficiency, may be £250, or will be as the technology beds in.

[Edit - that's wrong, I was thinking £100 proportionately, so let's assume the larger panel by size is £200, so the high cost of achieving those last extra bits of efficiency, may mean the larger bifacial panel is £300. M.]

So many guesses and thoughts here, please don't take any too seriously. Maybe something to watch for a year or two, and see how it shakes out?


*Index linking itself is a minefield today, as the income from the panels may actually drop over the next few years as gas/leccy prices go back to normal. But I'm thinking of normal leccy price rises in line with 'normal' inflation. If we ever see normal again.

Screwdriva

Waywardmike said:

I find it strange that @Screwdriva will adamantly claim batteries are a waste of money that you'll never see a ROI on, yet advocate paying for a panel type that's arguably a bigger waste?

Ah but that's the beauty of PV only system! Satisfaction and sentiment aside, adding 2.3 kW of the lucrative West facing aspect  to a 4kW system is expected generate an incremental 2000+ kWh p.a. for us. Assuming we are paid .26p per kWh (a highly conservative blend of the Flux tariff, which pays 50% more during the 4-7pm window), at a total cost to install of £1K, I expect to earn ~£525 p.a. Or in ROI terms, a full payback in < 2 years. 

Find me a battery that can do that!?! 

Waywardmike said:

Any performance gain is useful, doesn't mean it makes sense financially!  If they cost you £1000+ more to install, yet make/save you £30-£50 a year extra, I'd argue they're not worth it!

The numbers shared don't lie. And they don't lie with batteries either. They (& I) argue that few things are more worth it! 

ispookie666

@Screwdriva the modelled generation for a west facing seems to be high, but we all know that most of our systems regularly beat the predicted numbers. 
I have panels on 4 roofs and have varied shading during the day. The west facing one (with variable shading) to the best performing south facing (variable shading) has a performance deficit of 20%, actually worse than my NE roof 
Have you had the export limit lifted?