Solar - real-life experience of investment vs return

Magnitio

roadweary said:

EricMears said:

roadweary said:  When it comes to the main roof.....this angle looks more than 45 degrees (60?), which could be an issue again?

Steep roof will probably generate less in midsummer but a lot more in midwinter (relative to a 'normal' roof).  What's the problem with that ?  Most normal rooves generate more than needed in summer but never enough in winter.

Hi, no problem at all - I'm using the web and this forum to learn more.  I'd read about a 30-40 degree angle being optimal and that greater was an issue....and at a certain angle, perhaps not even possible for installation.  I also read that even 5 degrees from optimal can lead to a 10% reduction in efficiency...but that's the issue with the web.....there's good stuff, bad stuff, partially explained stuff etc.

Is there a resource you know of that shows the optimal angles at different seasons?

Thanks,
Andy

Try this:

https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html#PVP

Martyn1981

roadweary said:

EricMears said:

roadweary said:  When it comes to the main roof.....this angle looks more than 45 degrees (60?), which could be an issue again?

Steep roof will probably generate less in midsummer but a lot more in midwinter (relative to a 'normal' roof).  What's the problem with that ?  Most normal rooves generate more than needed in summer but never enough in winter.

Hi, no problem at all - I'm using the web and this forum to learn more.  I'd read about a 30-40 degree angle being optimal and that greater was an issue....and at a certain angle, perhaps not even possible for installation.  I also read that even 5 degrees from optimal can lead to a 10% reduction in efficiency...but that's the issue with the web.....there's good stuff, bad stuff, partially explained stuff etc.

Is there a resource you know of that shows the optimal angles at different seasons?

Thanks,
Andy

Hiya - straight off, the steeper the better (within reason). Yes 35-40d pitch will give maximum annual gen, but a steep roof (I think 50d is very steep), won't lose much. I've just gone to PVGIS and stuck a random pin in Gloucester. For 1kWp at an azimuth of -30d (around SSE), it suggested 1,182kWh pa for 35d pitch roof, and 1,161kWh pa for 50d pitch. Also the lowest month, December, went up from 29kWh to 33kWh, and as others have said, that's when you want as much as possible. In the summer you may have more gen than you can use anyway.

Also, regarding cleaning panels. The steeper the better, as less can land and get a hold. You mentioned moss/lichen, which can get a hold at the base of panels where the frame can hold some dirt. Newer panels, with less of a lip will help, but my panels (2011) on the roof at 30d are OK, but the same panels on a lower roof at 20d pitch, do 'grow' moss, but it's easy to reach and clean off. At 40-50d, the wind and rain will do the work for you.

Screwdriva

roadweary said:

Hi, 

Thanks - in Gloucestershire. 

I have no idea where to start in terms of manufactures or installers. 

I think batteries are a major part of the cost…but I also wasn’t sure if the power generated would be steady enough through the day so thought some kind of reservoir might make sense?

I do need to get an idea of how long the investment would take to pay for itself. 

I try to keep this thread updated with actual cost/ return on investment/ consumption/ export for our home in SE London. It should help highlight how rapidly the return equation has changed in PV ownerships favour.

I always recommend the following:

1) Always go with quality components, if nothing else than for aftersales support, warranties that are actually honoroured and the associated peace of mind

2) Check whether a battery makes financial sense by using this calculator. Hint: If you don't plan on getting an Air Source Heat Pump or an EV in the foreseeable, it won't.

The only brands I recommend are:

Panels - Sharp, Hyundai, REC, SolarWatt, Aleo, Panasonic or Sunpower 400W+ panels

Standalone Inverters - Enphase or SolarEdge (w/25 year warranty included)

Battery integrated Inverters (if #2 above makes fiscal sense for your consumption)- MyEnergi Libbi, Tesla Powerwall or GivEnergy

Alnat1

If you go with the house roof, get the maximum possible on there while the scaffolding is up. Decisions on batteries/solar diverters for hot water can always be made later if you're unsure.

I had a PV system installed last March, 5.25kWp on the roof and 4.8kWh of battery. Our annual leccy use is fairly low, around 3000kWh (around 11,000kWh gas for CH & DHW) so any more battery didn't really add up for ROI. Battery was more than enough to cover the overnight load Mar-Sep and is handy during the darker, dreary months to cook dinner after sunset and then fill from the grid overnight when Octopus Agile has cheap rates.

I switched energy to Octopus in April and set up the SEG payments with them. I opted for variable DD, to pay monthly bills in full. So far I've only paid £1 (to activate the referral £50 ) and haven't needed to pay anything else as the export credits and now government £67s have covered the cost of all gas and electricity used.

Still £230 in credit as at 20th December, Jan-Mar £67s to add, hoping that might just see us through until the sun starts shining a bit more in March if we don't get another cold snap.

Don't think this year's prices will be repeated again but very happy with the solar/battery choices we made.

ABrass

My annual consumption is similar to yours and I also work from home.

I've had my system up since mid September, it has generated 1,200 kWh over that time, of which I used 75%. Without a battery I'd only have used around 37%.

My battery isn't enough to make it through the night, but since mid October I haven't been able to fully charge it either. With larger systems you are nearly always generating far more than you need or not enough. The battery helps smooth that out during the day and then cover some of my evening.

It has saved me around £300, SEG took a while to set up but that should have been another £50. Over the next year I should be saving in the region of £1600-2000. At the lower end that will pay back my (£12,000) investment in 7.5 years. Which is a testament to how expensive electricity has gotten. What's more likely is that prices will ease in a year or two and I'll reach payback closer to 10 years in.

roadweary

I'm conflicted.....one possiblity is to 'dip my toe' - though not sure how over £7k is dipping my toe - with solar panels only....hoping that better / cheaper batteries come available by next winter.  In either case, with the time it'll take me to make a decision, get quotes, get it done....it won't be in till the summer......and it's really our super high usage in the winter where I think the solar panels....and possibly the batteries too would come into their own.  But TBH I'm still at the early research stage.

ABrass

You'll have too much in the summer, enough but at the wrong times in autumn and spring and no where near enough in winter.

Reed_Richards

roadweary said:
... it's really our super high usage in the winter where I think the solar panels....and possibly the batteries too would come into their own.  

Lots of people think this when first contemplating getting solar panels but it's completely wrong.  Think about why it's cold in winter.  It's because we have short days with weak sunshine.  There isn't much solar energy to warm things up and there isn't much solar energy for your panels.  So you'll get the least electricity when you need it the most.

roadweary

Reed_Richards said:

roadweary said:
... it's really our super high usage in the winter where I think the solar panels....and possibly the batteries too would come into their own.  

Lots of people think this when first contemplating getting solar panels but it's completely wrong.  Think about why it's cold in winter.  It's because we have short days with weak sunshine.  There isn't much solar energy to warm things up and there isn't much solar energy for your panels.  So you'll get the least electricity when you need it the most.

So based on the majority of my usage being in the winter months, isn't that massively reducing the likelihood of solar being a viable option for me in terms of ROI?

1961Nick

roadweary said:

Reed_Richards said:

roadweary said:
... it's really our super high usage in the winter where I think the solar panels....and possibly the batteries too would come into their own.  

Lots of people think this when first contemplating getting solar panels but it's completely wrong.  Think about why it's cold in winter.  It's because we have short days with weak sunshine.  There isn't much solar energy to warm things up and there isn't much solar energy for your panels.  So you'll get the least electricity when you need it the most.

So based on the majority of my usage being in the winter months, isn't that massively reducing the likelihood of solar being a viable option for me in terms of ROI?

That's why you'll only manage self use of 30-50% without batteries. The good news is that you can get 15p/kWh for your export which helps the ROI.

You mentioned £7000 so I'm assuming a 5kWp system generating 5000kWh/annum...

Self use say 40% - 2000kWh @ 34p/kWh saves £680
Export 3000kWh @ 15p saves £450

£7000/£1130 = 6.2 year ROI.

Even with a poor orientation & some shading a 5kWp system is unlikely to produce less than 4000kWh. That would still save £904 per annum & give you an ROI 7.75 years.