31% PV efficency

[Stinsy]

Common misconception!

DNO cares only about inverter power. You can have as much solar as you like!

I appreciate this is a further digression from the OP, but on that subject, I'm still hoping to add some more PV (steep pitched south facing for winter gen), via a zero export battery addition. Been chatting with a company, and the use or not of the PV input (hybrid inverter but not linked to my existing PV) may not be an issue. But my gut tells me that the DNO may still get funny, even if the PV isn't mentioned*, as they've already said my current 5.9kW limit shouldn't have been granted.

So I have to gamble on rockin the boat, with a battery application, even if it's zero export.

Difficult decision. Probably end up tossing a coin.


*Anyone know if you need to tell the DNO about PV that feeds into a battery, for domestic consumption? I can see why it might be irrelevant, but at the same time it's grid connected ..... sorta? [Edit - Just to be clear, a battery whose inverter has DNO certification confirming it meets the zero export requirements.]

No need to tell them! It isn’t connected to their grid so in none of their business.

[Krill]

Interesting discussion. As an example:

I'm currently getting quotes for a 6.4kw ish solar array (SSW rooftop, 16 panels) and wondering what I'll get away with on an inverter, given a likely 10kish battery (ie 2 pylontech 5000s etc). Having read this forum I'm aware of the issues with having a larger inverter fitted (plus the DNO sign-off off). But yhe kicker is I'm building a pergola to the north of the house, mostly hidden from view, and it would allow another 12 panels (pergola would be almost 5 metres by 5 metres and the panels would be raised to about the first story height of the house to the direct south). It would still be unshaded at that height foe most of the day even in early November and very late January.

Anyway, to the topic at hand. That would be a few years down the line, when I had to get an airsource heatpump and unvented cylinder and there was an electric car but it would be entirely for domestic consumption. If the inverter is already fitted, what is to stop a new MPPT being fitted to charge the already in situ battery bank which could also be expanded?

My understanding is as Stinsy said, its hidden behind the inverter so the DNO can GFT. The issue is that the battery bank would need to be one he'll of a reservoir if this tactic was pushed to the extreme....

And to bring the post back on topic, I wonder when we will start seeing 25% and these 31% efficiency panels available? Not like it is a solution to current problems, but always nice to plan.

[nowty]

If the inverter is already fitted, what is to stop a new MPPT being fitted to charge the already in situ battery bank which could also be expanded?

Nothing.

My understanding is as Stinsy said, its hidden behind the inverter so the DNO can GFT. The issue is that the battery bank would need to be one he'll of a reservoir if this tactic was pushed to the extreme....

No issue as the DC Charge Controller (MPPT as you say) simply throttles back to zero as the battery becomes full, no need to have "one hell of a battery reservoir", but it does help. The trick is to keep the EV charger or the immersion heater on to keep the battery from being full, so you keep generating. Several on here do this.

And to bring the post back on topic, I wonder when we will start seeing 25% and these 31% efficiency panels available? Not like it is a solution to current problems, but always nice to plan.

Too long in the future to delay sticking as much PV in as you can now.

[Mart]

Thanks everyone, really interesting stuff.

The solar pergola, and similar things, like car ports, have fascinated me for years - the ability to add significant amounts of PV, separate to roof limitations, opens up so much more potential for folk. Add in the rising efficiencies, which in my example just at 20% would take me from 5.58kWp to 7.44kWp, really makes PV more and more viable every day.

And for an all year package, given the huge issues with domestic wind turbines, I think Ripple (or similar) offers a great way forward.

Fun times.

[Joeboy]

Thanks everyone, really interesting stuff.

The solar pergola, and similar things, like car ports, have fascinated me for years - the ability to add significant amounts of PV, separate to roof limitations, opens up so much more potential for folk. Add in the rising efficiencies, which in my example just at 20% would take me from 5.58kWp to 7.44kWp, really makes PV more and more viable every day.

And for an all year package, given the huge issues with domestic wind turbines, I think Ripple (or similar) offers a great way forward.

Fun times.

Pergolas, carports, covered walkways, ladder stores, bi facials. Its a growing list!

[Joeboy]

Thanks everyone, really interesting stuff.

The solar pergola, and similar things, like car ports, have fascinated me for years - the ability to add significant amounts of PV, separate to roof limitations, opens up so much more potential for folk. Add in the rising efficiencies, which in my example just at 20% would take me from 5.58kWp to 7.44kWp, really makes PV more and more viable every day.

And for an all year package, given the huge issues with domestic wind turbines, I think Ripple (or similar) offers a great way forward.

Fun times.

How long has your pv system been in Mart and what efficiency did they come with? Majority of mine are 19 to 20%. Not seen any performance drop off in 6 years of installation which has been excellent.

[Mart]

Thanks everyone, really interesting stuff.

The solar pergola, and similar things, like car ports, have fascinated me for years - the ability to add significant amounts of PV, separate to roof limitations, opens up so much more potential for folk. Add in the rising efficiencies, which in my example just at 20% would take me from 5.58kWp to 7.44kWp, really makes PV more and more viable every day.

And for an all year package, given the huge issues with domestic wind turbines, I think Ripple (or similar) offers a great way forward.

Fun times.

How long has your pv system been in Mart and what efficiency did they come with? Majority of mine are 19 to 20%. Not seen any performance drop off in 6 years of installation which has been excellent.

Hiya. Rear ESE roofs were 2011, with 235Wp and some physically smaller 185Wp's. Then front WNW roof in 2012 with 250Wp's, so around 14-15% efficient. Plenty of power for the summer, but being E/W the winter drop off is magnified. In fact most of the 20% loss, v's south facing PV, is in the winter.

Just 2kWp of 70d pitch, south facing ground mount would match our Dec generation, so a significant increase.

Regarding degradation, this is something I find really interesting. I can't see any reduction across the whole 10yrs ..... honestly!

There was a detailed report out by NREL (I think), probably 10yrs ago, and they suggested an annual degradation of 0.8%. But that was based on all PV technologies, and all ages, in the report. For post 2000 monosilicon, the number was about 0.4% (I forget). So I assume things keep improving.

Just to be clear, I'm not suggesting there's been no drop off for my panels, but I simply can't see it yet in the figures. The annual gen fluctuates with weather, of course, but has been between 97% to 110% of PVGIS target, ironically with the worst year in 2012, and the best in 2020. This year on course for 107%.

Never say never, but after 10yrs, a 0.3% degradation would be 3%, and I suspect that I'd notice the declining trend, so it must be less than that. Suggests to me that new PV now should be good for 95%+ after 20yrs, perhaps 90%+ after 30-40yrs. So effectively, degradation is a non-issue. Does that makes sense?

I'm actually a bit worried to suggest such good figures, as I don't want to mislead anyone, and I'm sure it should be worse than I'm seeing, but I honestly can't see a downward trend yet, so it would have to be tiny, 1% or 2% (after 10yrs). Too good to be true?

[Stinsy]

Interesting discussion. As an example:

I'm currently getting quotes for a 6.4kw ish solar array (SSW rooftop, 16 panels) and wondering what I'll get away with on an inverter, given a likely 10kish battery (ie 2 pylontech 5000s etc). Having read this forum I'm aware of the issues with having a larger inverter fitted (plus the DNO sign-off off). But yhe kicker is I'm building a pergola to the north of the house, mostly hidden from view, and it would allow another 12 panels (pergola would be almost 5 metres by 5 metres and the panels would be raised to about the first story height of the house to the direct south). It would still be unshaded at that height foe most of the day even in early November and very late January.

Anyway, to the topic at hand. That would be a few years down the line, when I had to get an airsource heatpump and unvented cylinder and there was an electric car but it would be entirely for domestic consumption. If the inverter is already fitted, what is to stop a new MPPT being fitted to charge the already in situ battery bank which could also be expanded?

My understanding is as Stinsy said, its hidden behind the inverter so the DNO can GFT. The issue is that the battery bank would need to be one he'll of a reservoir if this tactic was pushed to the extreme....

And to bring the post back on topic, I wonder when we will start seeing 25% and these 31% efficiency panels available? Not like it is a solution to current problems, but always nice to plan.

You are correct, perfect plan!

And in any case I don’t think you need an inverter bigger than 5kW, and only that big because of the HP. The point of an oversized array is to provide enough power from solar on the “shoulder” days when you only get 1-2x your kWp in kWh. So you don’t need a battery bank bigger than 50% of your typical daily demand and you don’t need a bigger inverter. On sunny days in August you’d have more power than you can use and you can power a hot tub, crank the AC, or whatever without costing a penny.

I get by with a 3.6kW inverter. I have a 5-bed house wit 4-people, a dog, marine aquarium, PHEV, garden office, and everything else you can imagine.

[Stinsy]

How long has your pv system been in Mart and what efficiency did they come with? Majority of mine are 19 to 20%. Not seen any performance drop off in 6 years of installation which has been excellent.

Hiya. Rear ESE roofs were 2011, with 235Wp and some physically smaller 185Wp's. Then front WNW roof in 2012 with 250Wp's, so around 14-15% efficient. Plenty of power for the summer, but being E/W the winter drop off is magnified. In fact most of the 20% loss, v's south facing PV, is in the winter.

Just 2kWp of 70d pitch, south facing ground mount would match our Dec generation, so a significant increase.

Regarding degradation, this is something I find really interesting. I can't see any reduction across the whole 10yrs ..... honestly!

There was a detailed report out by NREL (I think), probably 10yrs ago, and they suggested an annual degradation of 0.8%. But that was based on all PV technologies, and all ages, in the report. For post 2000 monosilicon, the number was about 0.4% (I forget). So I assume things keep improving.

Just to be clear, I'm not suggesting there's been no drop off for my panels, but I simply can't see it yet in the figures. The annual gen fluctuates with weather, of course, but has been between 97% to 110% of PVGIS target, ironically with the worst year in 2012, and the best in 2020. This year on course for 107%.

Never say never, but after 10yrs, a 0.3% degradation would be 3%, and I suspect that I'd notice the declining trend, so it must be less than that. Suggests to me that new PV now should be good for 95%+ after 20yrs, perhaps 90%+ after 30-40yrs. So effectively, degradation is a non-issue. Does that makes sense?

I'm actually a bit worried to suggest such good figures, as I don't want to mislead anyone, and I'm sure it should be worse than I'm seeing, but I honestly can't see a downward trend yet, so it would have to be tiny, 1% or 2% (after 10yrs). Too good to be true?

I’ve seen a study of some of the very early domestic solar installations showing much less than expected deg. It is possible that deg will speed up as the panels age, however the expected lifespan of an array is now 30-35 years.

[Krill]

Interesting discussion. As an example:

I'm currently getting quotes for a 6.4kw ish solar array (SSW rooftop, 16 panels) and wondering what I'll get away with on an inverter, given a likely 10kish battery (ie 2 pylontech 5000s etc). Having read this forum I'm aware of the issues with having a larger inverter fitted (plus the DNO sign-off off). But yhe kicker is I'm building a pergola to the north of the house, mostly hidden from view, and it would allow another 12 panels (pergola would be almost 5 metres by 5 metres and the panels would be raised to about the first story height of the house to the direct south). It would still be unshaded at that height foe most of the day even in early November and very late January.

Anyway, to the topic at hand. That would be a few years down the line, when I had to get an airsource heatpump and unvented cylinder and there was an electric car but it would be entirely for domestic consumption. If the inverter is already fitted, what is to stop a new MPPT being fitted to charge the already in situ battery bank which could also be expanded?

My understanding is as Stinsy said, its hidden behind the inverter so the DNO can GFT. The issue is that the battery bank would need to be one he'll of a reservoir if this tactic was pushed to the extreme....

And to bring the post back on topic, I wonder when we will start seeing 25% and these 31% efficiency panels available? Not like it is a solution to current problems, but always nice to plan.

You are correct, perfect plan!

And in any case I don’t think you need an inverter bigger than 5kW, and only that big because of the HP. The point of an oversized array is to provide enough power from solar on the “shoulder” days when you only get 1-2x your kWp in kWh. So you don’t need a battery bank bigger than 50% of your typical daily demand and you don’t need a bigger inverter. On sunny days in August you’d have more power than you can use and you can power a hot tub, crank the AC, or whatever without costing a penny.

I get by with a 3.6kW inverter. I have a 5-bed house wit 4-people, a dog, marine aquarium, PHEV, garden office, and everything else you can imagine.

Call me greedy, but I suspect that the shoulder days are just one part of it, ie there are shoulder days when not reliant on electric to heat, and shoulder days when you do. When starting from scratch, the order of installation is a new challenge, especially for those of us starting now.

For example, PVGIS is saying that I would generate ~350kwh in December with such an array (it would be somewhere between 11-12kwp). In April through August it states between 1150 to 1350 kwh, September is over 1050kw before the cliff then happens.

I use electricity to power "everything" in the house except a gas hob, and a gas combi boiler. So domestic hot water and heating are still gas, plus two diesel cars. Main difference from a normal household is that I run 4 refridgeration devices (I have to store food for multiple households each week), but still somewhere between 8-11kwh/day. The hob could be changed to induction but I reckon that would be a negligible increase in power use.

This potential is in excess of my usual usage which varies between 240-300kwh/month, to an absurd degree, but it's not an unrealistic scenario for some people to still need that

For example, I checked my "heating" gas costs, and in May 2022 this were over 500kwh. Now yes, with an ASHP this would drop dramtically, but the decision to remove a functioning gas boiler is a tough one to manage financially when it's still working and in warranty, but then there is also the need for the unvented cylinder and sudenly costs, which are already high for the full solar PV installation, look to jump again. And the running costs would still increase (OK, this is debatable in the current climate) suggesting that it would be prudent to install extra solar pergola array before progressing.

But if I install that amount of solar, before I can use the power generated, I really could do with the option to sell it to start subsidising the cost, and if I'm hiding 5kwp behind a battery and need the inverter to sell it, then I (and others in my position) would want a greater DNO signed off export limit so we can sell it at a more "profitable" time, as that is when the use of FF derived power is required.

Which actually brings me to the other point about this greater efficiency panel type: I have the opportunity to make this work, the land available, and the financial resources to pull it off, but a lot of other people don't. As panel efficiency increases, yes I could use less land, but is there not a moral dimension to this, that those who are able should try to produce more so that other people who can't, can reduce their reliance on fossil fuels? So even though I will benefit long term, there is a significant gap (potentially measured in years) where if I can produce and sell usuable RE, I should do so to reduce societies reliance, as a personal contribution to managing the current energy crisis?

(The other point is: I have the timber for the pergola and will build it myself. If the rooftop array, inverter and battery are considered sunk costs, the cheapest part of the next expansion is just buying one or two MPPT and 12 solar panels and yet this is where the real benefit lies to society)