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

GreatApe

Screwdriva wrote: »

As with nearly every financial decision we make in our household, we prioritize economic risk/ reward and a focus on the environment. For example, our cars are made pre-1997, consume little fuel, even by modern standards, and are reliable enough to last for many more decades with proper care. They also appreciate over time, get loads of praise on London roads and are exempt from all taxes and testing. In other words, exceptions to the planned obsolescence that is endemic in modern culture.

How much of the savings have you put aside to pay for the medical expenses and lost earnings when you get in a medium/high speed accident in a 40 year old metal bucket?

This approach is a remnant from when our family didn't have much, and has been passed down over the past 3 generations. Even though we are definitely comfortable today, we try not to deviate from it. So while we can easily afford these panels upfront, a < 10 year ROI is difficult to argue against.

Hobbies cost money see it as a hobby
Unless your hobby is to be a penny pincher in which case more power to you nothing wrong with that so long as it doesn't make those around you unhappy

Screwdriva

GreatApe wrote: »

How much of the savings have you put aside to pay for the medical expenses and lost earnings when you get in a medium/high speed accident in a 40 year old metal bucket?

My cars are incredibly safe and are built like Panzer tanks. They have a reputation in the automotive industry for being overly engineered.

GreatApe wrote: »

Hobbies cost money see it as a hobby

I typically don't spend this kind of money on hobbies in one go. But I am looking at this as long term investment. Thanks for the advice - I'm looking for inputs/ suggestions on the system and its cost, not my overall life decisions.

pinnks

I think the proposed own consumption figures are a little off the mark. I generate about 4,500kWh per year from an ESE array (1750Wp) and an WSW (3500Wp), both with some shading. I have a diverter which powers hot water and underfloor heating/radiators.

My gas bills are around £70 to £80 per year lower than they were without diverter (this is based on gas bill records and suggests that with my system with inefficiencies of using the boiler in the summer including round trip losses in the pipes I can equate savings to electricity prices, not gas prices) and I have the boiler off between mid April and mid October.

I have 2 diverters and have calculated (from monitoring records) that ignoring the inverters I consume about 40%, so would export about 60%. Diverting only to the immersion heater I consume about 55% and using both diverters, so hot water, underfloor heating and some radiators i manage to self-consume about 63%. Why not more? Because the max generation in the summer could only be used if I had an electric vehicle or battery...

So, if you propose to divert only to hot water, I would base your calculations on total own consumption of max 55%. Depending on how far you have between boiler and tank (my round trip is about 20m) you may chose to use electricity rates for your savings calcs, though I am sure others on here will scream at me for saying that!

I also agree with Mart that going lower Wp on the panels but using more roof to get your kWp would be economically sensible. When I installed my system, 330Wp panels were the bee's knees but would have cost about 30% more for the same net output.

HTH

Exiled_Tyke

As is always the case Martyn's advice is the best. I agree with everything he says.

My observations:

1. I really can't see that painting the roof white will give much benefit? And regardless, as others have said 300kW seem to be the best value for money panels currently.
2. You've said that water is heated by gas boiler. I may have skimmed too quickly to spot it, but I can't see that you've explicitly stated that you have an electric immersion heater. If this needs installing then the return on the hot water system will be pretty much wiped out.
3. Why does this system need a Solar Edge system with optimisers? You need to be sure that the premium cost of this set up is outweighed by the benefits.
4. The figures seem woefully optimistic: surely nobody needs to be paying 19p/kWh for electricity? And is it really possible to get paid 10p/kWh for export (I wouldn't know as I've never looked into these tariffs). I think the self-consumption figures may also be unrealistic. Others on here (especially those with Solar IBoost) will know better but in Summer my 3.3kW system can produce (each day) three to four times the electricity that I consume.

michaels

19p/kwh We currently pay 11.7 and would be looking to renew at less than 13. I also think that own use of more than 50% unless you are home all day is hopeful (excluding any iboost units which should be valued at the price of gas displaced 3.5p and with a max summer day output probably in the 30+kwh rate you will not actually be able to soak up all your spare capacity in this way) We value our iboost use at about £30 pa which made sense on the extra cost of £250 on our quote.

Output - we are just n of London and have 4kw W facing panels, same quantity and over 4 years have generated between 3500 and 3800 pa so I guess with super efficient panels 4500 is not impossible.

But do the sums again with leccy at 13/14p per unit and 50% own use plus 30 for the iboost and see what you get.

Then possibly think about batteries and export tariffs if the maths doesn't work without.

Edit - although our panels were less fancy we do have solar edge optimizers and our system cost 4800 to install 4 years ago.

Screwdriva

Many thanks for the advice on the panels. The reason I'm choosing the best panels I can for our climate is because I plan to add additional panels in the future and roof space is limited. So while I could take up an additional 3 precious panel spots if I went with 310W Panasonic panels, I would lose out the ability to scale the proposed system in the future, as I wouldn't want to try to sell or scrape purchased panels after 5-10 years of use.

A quick Google on "LG Bifacial white TPO" should highlight the added gains that these panels are known to deliver.

pinnks

Scaling the system is a good option but don't forget that if you can export more than 16A (3,628W or something like that) you need approval, which is not guaranteed and can come with a very hefty cost if it would only be given with grid-side works.

I and many on here have been lucky and received approval at no or small cost (I recall having to pay £150 or something) but others have been denied or quoted eyewatering amounts.

If you propose going over that limit now then you will need approval and I am not sure how the authority views subsequent further extension applications from the same address. It might therefore be worth doing some research to see how that works in your location.

joefizz

Screwdriva wrote: »

.
A quick Google on "LG Bifacial white TPO" should highlight the added gains that these panels are known to deliver.

Id also recommend martyns advice.

Primarily for the simple reason is the amount of green algae built up under the frame of my additional panels. Any white undercoating that close to the panels is going to get algae covered within a year or two and diminish the output. If the panels are close to the surface then any splashes could also put algae on the underside of the panels.
Ive four panels on a frame over a transparent roof and at the minute Im looking up at them thinking I really should clean them over winter...
It will depend on your roof, distance between panels and roof and slope of the roof (level of rainfall etc), so dont take the reflective capability as gospel as cleaning will be an issue.



For the difference in price you could utilise your space now with more lower output panels then at some point in the future upgrade/replace.


I have more panels than my rated output but I have east, west and south facing planes so maybe one or two days in june I'll max out the inverter.

Screwdriva

Point taken on the Algae - we will plan to use algae resistant white paint to try to address this. Any recommendations on the best roof paint options are welcome.

It is unlikely that we will exceed 3600 kWh of exported power in the foreseeable. Current estimates for our export are 2500 kWh +/- 10%. We would need to add 3 additional LG panels rated at 400W to exceed this limit, or two 500W panels when they eventually invent and market them.

1961Nick

Screwdriva wrote: »

Point taken on the Algae - we will plan to use algae resistant white paint to try to address this. Any recommendations on the best roof paint options are welcome.

It is unlikely that we will exceed 3600 kWh of exported power in the foreseeable. Current estimates for our export are 2500 kWh +/- 10%. We would need to add 3 additional LG panels rated at 400W to exceed this limit, or two 500W panels when they eventually invent and market them.

I could be wrong ... but I seem to remember that it's the rated output of your array that's required to be under 16A (unless you have DNO approval for a higher export).

What is the theoretical maximum output of this system - 4kWh, 5kWh ... or is it limited by the inverter?