Bad month for solar generation

[Everest]

December 23 was 104 KW
December 24 was 85.6 KW (82.3% previous year)

2023 was 5490 KW
2024 was 4810 KW (87.6% previous year)

OMG - those seem very low for 15kWp of panels! Do you have lots of shading, or is it really that wet and cloudy in Wales?

On the bright side when we were without power for nearly 4 days in December due to storm damage we were able to keep the house running all the time due the benefit of 15Kw of solar and the Tesla Powerwall

 

[Tangoed Man]

I think all of us with solar PV expect winter to be a poor season for generation. However, even as I type this on a dull, cloudy day, my panels are generating 400 Watts and the house is only using 200, the extra is trickling into the battery.

I've been looking at the stats for the year and my panels have generated a total of 3941.5kWh and the battery supplied 2891.8kWh. We've used 9681.2kWh of off peak, and 626.69kWh peak.

Putting all that together, without any solar or battery it would have cost us £2260.23! Adding solar and a battery brings it down to £1039.20, so well worth the investment.

Yes, but minus about £400-500 a year for the cost of capitalising the installation, and minus the writing down costs of the capital.

 

[Everest]

Yes, but minus about £400-500 a year for the cost of capitalising the installation

Interested how you arrive that figure?

, and minus the writing down costs of the capital.

Of course, but with PV panels having working lifetime of 30 years and LFP battery of 12 - 15 years, these costs are minimal.

 

[Tangoed Man]

Interested how you arrive that figure?


Of course, but with PV panels having working lifetime of 30 years and LFP battery of 12 - 15 years, these costs are minimal.

They are not minimal. You are also failing to include replacement inverters, around £2,000 each so possibly two inverters for larger installations every 8-10years. Everyone forgets to write off the installation and maintenance costs. The sales people often tell you, "....solar is an investment"; it is not because you never receive back the original lump sum invested and a typical installation price can yield £500 per year if invested elsewhere. I am not trying to 'dis' solar, but all the arithmetic needs to be included. Also, the performance of panels over 30-years will significantly degrade. That needs factoring in to any statement regarding real returns on the investment.

 

[Everest]

For sure you need to do the sums, though increasing price of electricity is obviously an unknown and being able to power your essential house loads (light, computer, fridge, freezer, kettle and, of course, the coffee machine) during a power outage is, to quote Mastercard, "priceless".

You are also failing to include replacement inverters, around £2,000 each so possibly two inverters for larger installations every 8-10years.

Possibly, but not at that price. We have two hybrid inverters, price approx. £900 each. Like any complex electronic equipment, they may fail, but equally, I am aware of many inverters that were installed when solar first became popular around 2010 that are still running fine. It is not a given that they will fail at regular intervals - though of course, you could be unlucky and have one fail after 5 years or so.

Also, the performance of panels over 30-years will significantly degrade

Degrade, yes. Significantly degrade, no. Typical modern mono-crystalline panels will have a first year degradation of about 1%, with 0.5% degradation per subsequent year. Hence will still generate approx. 85% of their output after 30 years.

Our ROI will be around 4.5 years prior to getting an EV - hopefully even less when we can use spare production to charge the car.

 

[Tangoed Man]

For sure you need to do the sums, though increasing price of electricity is obviously an unknown and being able to power your essential house loads (light, computer, fridge, freezer, kettle and, of course, the coffee machine) during a power outage is, to quote Mastercard, "priceless".


Possibly, but not at that price. We have two hybrid inverters, price approx. £900 each. Like any complex electronic equipment, they may fail, but equally, I am aware of many inverters that were installed when solar first became popular around 2010 that are still running fine. It is not a given that they will fail at regular intervals - though of course, you could be unlucky and have one fail after 5 years or so.


Degrade, yes. Significantly degrade, no. Typical modern mono-crystalline panels will have a first year degradation of about 1%, with 0.5% degradation per subsequent year. Hence will still generate approx. 85% of their output after 30 years.

Our ROI will be around 4.5 years prior to getting an EV - hopefully even less when we can use spare production to charge the car.

You have no ROI because you do not get back the lump sum invested. The costs are still about £500/year plus the amortised capital write off plus inverter replacements. Degradation will almost certainly be more than than 0.5% per year.

 

[Everest]

You have no ROI because you do not get back the lump sum invested. The costs are still about £500/year plus the amortised capital write off plus inverter replacements.

I disagree. ROI = Net Investment Gain/Cost of Investment x 100. My Net Investment Gain (money not spent on buying power) is approx 0.25 of the Cost of Investment, per annum, taking into account interest lost on capital.

Degradation will almost certainly be more than than 0.5% per year.

What is your reference for that? It doesn't concur with my experiences & observations and not from top-tier panel manufacturer's warranty terms, either.

 

[Gadget Geek]

I disagree. ROI = Net Investment Gain/Cost of Investment x 100. My Net Investment Gain (money not spent on buying power) is approx 0.25 of the Cost of Investment, per annum, taking into account interest lost on capital.


What is your reference for that? It doesn't concur with my experiences & observations and not from top-tier panel manufacturer's warranty terms, either.

I think he has a bad case of NFBO.

 

[T1 Terry]

NFBO

Not even Google knew what that one was

Back to this one

OMG - those seem very low for 15kWp of panels! Do you have lots of shading, or is it really that wet and cloudy in Wales?

Maybe they are dirty, poorly aligned or get coated with snow/ice. I've seen a few top of the line solar controllers that actually monitor panel temp and if it drops low enough for ice to form, it back feeds from the battery at a limited current to turn the solar panels into heaters. Once they are warm enough that the ice/snow would have melted or slid off, programming returns to normal.

We do get a lot of grunge build up on panels over here, a bit of dew over night and some dust blowing over in the early hrs, then baked on during the day, repeat a few days later and the efficiency really suffers.

On RV installations, we polish the panels with a coat of good quality car wax when new and a wash and cut & polish every 12 mths or so, as required. It helps the water to ball up and slide off rather than create a wet layer for the muck to adhere to and form a coating.
We find the biggest issue is often the border around the panel; it tends to hold in extra layers and that slowly edges out to the active area of the panel ...... it doesn't take much to seriously affect the panel efficiency with a film just reaching the active area.

The whole nonsense about not making solar panels reflective, is just that, nonsense, the only light reflected is the light it can't use, hence the colour, if it can't use the blue spectrum, then they look blue, if they have a whitish look, that is a dirt film blocking the light from penetrating and needs to be removed ..... if they are black, add a layer of poly swimming pool heater tubing under the panels and use the waste heat to warm parts of the home or glasshouse, I've even seen it used for hydroponics to keep the soil matrix above freezing to save sensitive "vegetables", even ones that do actually produce tomatoes

T1 Terry

 

[Gadget Geek]

Not even Google knew what that one was

Non Factual Based Opinion.

 

[T1 Terry]

I've added that one to the collection, love it

T1 Terry

 

[Tread Softly Terran]

My 2 penny's worth. December near Gatwick was 106% of my last years 'harvest'. Although the whole year was down about 20%.
My solar investment in 2011 has more than paid for itself in costs not incurred & has FIT too. Also inverter is still going strong, although will need replacing at some point soon.

 

[SteveRW]

I’ve noticed that bright sunny days plus fluffy white clouds seem to give me a higher peak than just a cloudless bright sky.
I’m in year 14 of my 4kW ground array and agree it’s been a poor start to the year.

Not had to replace my inverter yet. Get around £2000 year FIT payments (currently 72p). Get paid for generation whether I use it or not so double bubble. Lots of naysayers when I first started but it’s been a no brainer.

 

[Bam Bam]

I’ve noticed that bright sunny days plus fluffy white clouds seem to give me a higher peak than just a cloudless bright sky.

You're getting bonus production because the clouds are refracting light in addition to the direct sunlight.

Tim noticed it happening to him as reported:

 

[Everest]

I’ve noticed that bright sunny days plus fluffy white clouds seem to give me a higher peak than just a cloudless bright sky.

Likely due to "cloud edge effect". Also lower temperatures will increase output; typical temp coefficient will be around -0.25% per degree C.

Edited... BB beat me to it

 

[SteveRW]

Ah missed that, thank you. Also remember my solar installers offering some sort of prize if anyone could prove just one watt generated by moonlight. Never claimed as far as I know.

 

[Everest]

Also remember my solar installers offering some sort of prize if anyone could prove just one watt generated by moonlight.

- full moon luminosity is about 1/100000 to 1/400000th of the sun, so you'd need a large PV array to get 1W.

But one can observe some open circuit voltage on the panels on a clear night as someone posted in this thread...

Lunar energy? ;)

Tracking the moon phase with PV panel voltage: I'm getting up to 1.5V (Oct 17) from the trailer's single 300W PV panel at night from the moon, as it approaches full.

diysolarforum.com

 

[Rolfe]

On Ne'erday, the day I knew I'd need a lot of electricity, my panels produced the magnificent total of 360 watt-hours.

 

[Everest]

typical - it wasn't the best day, was it - you need a nice EV with a V2L output so you can top up those batteries with cheap electricity

 

[Fokmg]

It has been very up and down here in sunny West Wales on 25/01/25 we had 17kWh and on 26/01/25 we had 1.42 kWh ! this morning 28/01/25 is looking at 152 Wh ! and 1.6 inches of rain !!!
I think a water wheel may be the way to go !
On the positive side January 2025 looks to be on target to match January 2024 for power generation its just been a bit variable.

Fortunate battery storage and octopus Go intelligent means the cost of power does not exceed 7p/ kWh (ok I did buy a total of 31 units at 26.5 p ) but managed to generate 4800 kWh of solar, all of which I used.

It's a bit like swings and roundabouts but I certainly find the solar panels a worthwhile buy.