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

mnbvcxz

Whoops sorry, you do you say you have a water cylinder.

And a 25 year warranty on the inverter which is something. I wonder how much labour it includes...

Still you are presumably spending about £500 a year on electric and £500 on gas. There is just no way you can offset enough of that to generate a thousand pounds a year in savings.

Screwdriva

A few additional responses/ comments to the last few posts:

1) Yes, the system is battery ready and can be scaled.

2) Yes, we have an immersion heater tank. It is a MEGAFLO Eco 250L Indirect cylinder. (not the PV ready model that has an iBoost built in). The iBoost will plug into this tank to allow for hot water and radiators into the house.

3) The Solar Edge inverter is supplied with a 25 year extended warranty, as are all major components except the iBoost, which has 10 year coverage

4) Total cost for the system is £7100/- inclusive of scaffolding, paperwork, materials and installation.

5) We spend ~£650 on electric and ~£250 on gas today via Bulb energy, and are assuming (over optimistically it would appear) 2500 kW consumption and 2000 kW of export. If the system does over perform like we expect it to, maximum export will also be 2500 kWh. We also assumed £150 of savings due to the iBoost but realize it may be lower.

Please see revised workings from installer below, thanks in no small part to your collective feedback. If you believe we're still way off, do let me know what you would change.

Income;
Assuming this system will generate 4,500 kWh If you export 44% = 1,980 kWh of the power, the Export tariff is 0.7p you get paid = £138.60p

Total income of £138.60p per year This figure is based on the SEG in January 2020

Saving’s
Assuming you use 56% = 2,520 kWh of the power per year and you are paying .19p per kWh you will save £478.80p per year on your Electric bill. Using the Solar I Boost water Heater to heat your water you will save an extra £150.00 per year on your Gas Bill
.
Total income and saving of ~£750 per year.

ABrass

You still haven't said what the Inverter is rated at?

If you don't have any shadowing then the solar edge bits are as I understand it a total waste of time and money. You might as well pay them to paint go faster stripes on the Inverter.

The iBoost may break even but it will probably save a lot less than £150 pa. If it's closer to £50 then it may be that the cost of installing it, plus the value of power fed to the grid, is greater than the savings you'll make. Or in other words it may be better not to have it at all.

It sounds like you're spending a lot of money on things that don't make a difference. £7,000 is a heck of a lot of money for a 4kw system.

How big a system could you fit now if you used the planned space and the spare space? Why not get the whole lot done in one hit. Or go without the Solar edge and go for a 5kw system? (Numbers made up)

Exiled_Tyke

I still think this is way off. A few thoughts:

1. My system has never over produced against estimate - although nearly did in ever so sunny summer of 2018
2. Usage estimates still high
3. Still don't understand why this needs to be Solar Edge
4. You haven't confirmed you have an electric immersion heater - only a cylinder
5. approx 300w panels still the best value for money. Put as many as these as possible on the roof.

Should be aiming for around £4-5k spend.

silverwhistle

michaels wrote: »

Make sure that when you are valuing 'own use' electricity you only use the electricity unit rate for electricity units saved and use the gas rate for gas units saved.

Except as a low user of gas as well my unit rate has been working out at around 6p, and if I were to remain on Ebico's new "zero standing charge" tariff with a minimum annual spend, I'd be paying about 8p(!), which is why I'm moving..


But in essence I agree with you all that the savings quoted are optimistic: think I was just trying to underline the lack of straightforwardness of the whole cost benefit calculation when it comes to individual circumstances.



I'd probably go for the simple solution too, and save money for a battery later.

Screwdriva

Yes, has an immersion heater. iBoost won't work without one.

I believe the inverter is the SE4000H but will confirm this soon.

Cardew

Screwdriva wrote: »

What would you estimate the ROI would be in a realistic scenario where we are selling unused energy to the grid during the day? Thanks again!

It seems that estimates on this thread are for a 'Return on Investment' (ROI) of 10 to 13 years.

In my book any ROI keeps the 'investment' intact. Do solar panels without FIT increase the value of a house? According to Estate Agents even with FIT they don't. During that 10 to 13 year period you are responsible for any maintenance of the system. With a xx year guarantee on the panels, who will get up on the roof to diagnose the faulty item? then remove and replace the panel.

If, say, the Bank of England came up with a scheme where you GAVE them a non-returnable £7,000 and they gave you back your money at £600 to £700PA for 10 to 13 years. How many takers would they have; even though after the 10-13 years it would be gravy time.

ABrass

Screwdriva wrote: »

Yes, has an immersion heater. iBoost won't work without one.

I believe the inverter is the SE4000H but will confirm this soon.

If it is the 4000H then that is a 4kw inverter, which means you will never be able to send more power to the grid than that. The theoretical maximum is not 5.2kw, it's 4.

The upside to having a more powerful system than the Inverter is that you'll get more power on cloudy days and earlier and later in the day when you're running below maximum. Which is not an easy thing to calculate. More than a 4kw system but less than a 5.2kw system.

Screwdriva

ABrass wrote: »

If it is the 4000H then that is a 4kw inverter, which means you will never be able to send more power to the grid than that. The theoretical maximum is not 5.2kw, it's 4.

If I understand correctly, the chances of exporting more than 4kW to the grid are nonexistent because we expect to consume ~50% of the 5.2kW generated. It is unlikely that we will add enough panels to reach 4kW of power exported to the grid, due to roof space limitation.

Hexane

Screwdriva wrote: »

If I understand correctly, the chances of exporting more than 4kW to the grid are nonexistent because we expect to consume ~50% of the 5.2kW generated.

You won't ever be generating 5.2kW - if you are only buying a 4kW inverter then the maximum you will ever be able to generate will be 4kW.

There seems to be a substantial misunderstanding somewhere. Estimates of likely consumption (and savings) only make sense in the form of "you can expect this system to generate 5000kWh in one year, and it makes sense to estimate you will self-consume 50% of that replacing existing electricity usage which you would otherwise be billed for at your current rate". (Notice the units here are kWh not kW).

It does not make sense to say "On June 1st if the weather is clear you can expect the system to be generating 4kW at midday, of which you can expect to use 2kW if you have a one million litre kettle with a 2kW heating element and you boil it continuously for as long as the sun is shining". Because you don't need that quantity of hot drinks anyway, and no-one has any idea what the weather will be like on June 1st. As others have mentioned, on June 1st if the weather is clear then your total generation on that day will be far, far more than you can use. You will struggle to use 25% on that day, never mind 50%.