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

Coastalwatch

Screwdriva wrote: »

Wanted to share that today the system, by far, generated the most power since installation around 5 weeks ago. Would welcome any thoughts about generated amount and the spread across the day compared to more conventional systems.

18/1/20 yield

Hi, a similar experience to your system today here also. Looking at yours, today supplied approx 14.4% of the months total, ours was 14.9% but we're further north. In terms of generation per panel then for the month so far, ours is 5.02kWh's(295W panels) compared to 5.119 for yours. As we're seventy odd miles apart I'm not sure you can read too much into the figures, but thought they may be of interest!

Screwdriva

Coastalwatch wrote: »

Hi, a similar experience to your system today here also. Looking at yours, today supplied approx 14.4% of the months total, ours was 14.9% but we're further north. In terms of generation per panel then for the month so far, ours is 5.02kWh's(295W panels) compared to 5.119 for yours. As we're seventy odd miles apart I'm not sure you can read too much into the figures, but thought they may be of interest!

Many thanks for this! Is your spread of power during the day comparable? I ask because we tried to ensure that we could consume (vs. export) for as much of the day as possible.

Martyn1981

Screwdriva wrote: »

Wanted to share that today the system, by far, generated the most power since installation around 5 weeks ago. Would welcome any thoughts about generated amount and the spread across the day compared to more conventional systems.

18/1/20 yield

Obviously my figures won't be too relateable to you, but got over 7kWh yesterday, about 50% more than any other day so far in Jan, and our first whole O.

If you have similar weather coming to me, then looks like two whole days of sunshine, so that might help you start to get to grips with the figures.

Also note that with low temps, panels will get an efficiency boost, v's hot summer days, but sun to panel angle will also impact power figures, and of course length of daylight will impact energy figures.

Screwdriva

7.73 kWh today, eclipsing yesterday's generation. We were able to to generate usable power till around 4pm when the sun set. What I find interesting is that the peak power has yet to move past 1.68 kWh, which may be the price we pay for installing the panels across 3 aspects (E, S, W) to ensure maximum spread during each day. Do you experience higher peak power?

Martyn1981

Screwdriva wrote: »

7.73 kWh today, eclipsing yesterday's generation. We were able to to generate usable power till around 4pm when the sun set. What I find interesting is that the peak power has yet to move past 1.6 kWh, which may be the price we pay for installing the panels across 3 aspects (E, S, W) to ensure maximum spread during each day. Do you experience higher peak power?

For peak power keep an eye out in April and October when skies can be very clear, a good sun to panel angle, and cold air temps with some wind. On those occasions my individual systems can spike above 100%.

But max power as a sum of systems is nearer to late June and midday for me, when the high sun can see both of my rooves at the same time (though of course not at a great angle). At that time my system can spike to around 4.9kW, and hold 4.2kW from 11ish to 3ish, straddling 1pm (BST).

A south facing system will always generate more pa, but a mix of orientations will give a more useable power supply ....... but not in the winter, when E/W sucks!

BTW I'm personally interested in your bi-facial results as I'm ever more keen to add 4 panels in the garden at a steep, south facing direction for winter gen. As I'll be building a small frame, probably with some scaffolding poles, I'll be able to put a white and/or reflective backing up, so interested to see if they are worth it.

I'm keeping my head down for now, as I'm hoping to find a way of sorting permission for V2G with the DNO, and whilst the extra PV will go through my ESE 3.7kW capped inverter, so won't impact my DNO approval for 5.9kW, I just don't want to attract any negative attention till this is sorted.

Coastalwatch

Screwdriva wrote: »

Many thanks for this! Is your spread of power during the day comparable? I ask because we tried to ensure that we could consume (vs. export) for as much of the day as possible.

Just to confuse matters somewhat most of our panels sit facing 20degrees east of south with a just a couple vertically mounted facing 70 degrees west to catch any afternoon sunshine. With a cloudless sky yesterday the curve was not unlike yours although judging from the spikes on yours maybe there was some cloud or shading taking place after lunch.
Our peak was 4.45 kW with 4kW minimum generated for approx 2.5hrs and 3kW minimum for approx 4hrs between 10am and 2pm. As with you there was a total of approx 8 hours generation on the day.

pile-o-stone

Martyn1981 wrote: »

BTW I'm personally interested in your bi-facial results as I'm ever more keen to add 4 panels in the garden at a steep, south facing direction for winter gen. As I'll be building a small frame, probably with some scaffolding poles, I'll be able to put a white and/or reflective backing up, so interested to see if they are worth it.

I'm keeping my head down for now, as I'm hoping to find a way of sorting permission for V2G with the DNO, and whilst the extra PV will go through my ESE 3.7kW capped inverter, so won't impact my DNO approval for 5.9kW, I just don't want to attract any negative attention till this is sorted.

Snap! I'm looking at installing an export limiting device (maybe SMA) that turns off the panels when the output goes above my current 5100 watts maximum. I spoke to the local DNO rep and he said they allow export limiting devices but they have to be ENA G100 compliant.

Out of interest, does anyone know how much light the bi-facial panels let through? I have had an idea of a solar pergola in the garden for a long time but transparent solar panels are a bit pricey and have lower output. Having 400w panels providing shade but with some light getting through would be fantastic, especially as the pergola would be over part of the garden where we eat in summer and we always put an umbrella up for shade anyway.

Screwdriva

I could try explaining it but this should give you a much better idea.

I will emphasize that bifacial panels really need that white background reflection more than anything to come close to hitting that extra 20-25% yield. I've used solar reflective paint but snow, marble, granite or white pebbles will serve the same basic purpose. Without this, you're looking at a 5-8% increase over a standard mono facial panel at best.

pile-o-stone

Screwdriva wrote: »

I could try explaining it but this should give you a much better idea.

I will emphasize that bifacial panels really need that white background reflection more than anything to come close to hitting that extra 20-25% yield. I've used solar reflective paint but snow, marble, granite or white pebbles will serve the same basic purpose. Without this, you're looking at a 5-8% increase over a standard mono facial panel at best.

Perfect, thanks for posting that link. A lean-to pergola is exactly what I was looking to do and it looked really good. I'd be looking to maximise the amount of light underneath the pergola so painting the back wall, floor and any internal furnishing (i.e. table and chairs) white would help to reflect light back up through the panels. I've also seen solar pergolas with a transparent roof lining to hide the underneath of the panels and wiring, but still let light through. They were white canvas or cotton and so I guess that would bounce a lot of light back into the panels too.

Screwdriva

2nd highest generation to date today @ 7.244 kW. Would have easily topped the previous record if the clouds hadn't led to choppy generation. Interestingly, peak power hit an all time high today at just over 2 kW.

And finally, Bulb Energy has confirmed that I am now on their SEG tariff. They're trying to raise an export MPAN for my smart meter - no idea what that means!?!

Graph below:
https://imgur.com/a/BWoGnPV