Getting quotes for solar pv - but what panels are decent

[Tabraz Khan]

Good Morning Chaps,

Came across this forum when I was looking for reviews on the the perlight 250+ panels.

Now I know this might not be the right place but what should i look for in a panel a couple of companies have quoted me £5k and 4.5k for a 2.5kw system (one company was thorough and said they would use perlight and a samil power 3000 inverter, whereas the other company who rang said we use good stuff but when pressed said will use what ever they had to hand :goofy: ) whereas a third company who is yet to quote me (but quoted a relative £15k for a 4kw system) told me you get what you pay for and said something about the thin glass shattering due to hail etc - any truth to this ?

So to summarise, which panels are decent, what should I look for, what questions should i ask the person who comes to quote me ?

(Also what does this mean (taken from perlight brochure) High efficiency crystalline solar cell (up to18.48% - I understand the higher the percentage the more efficient it is, but what are the figures so low (below 20%) - is that saying 20% of the light is converted to electricity ?



Any advice would be greatly appreciated, Also as you can tell i'm in the markets for a system - do you have an ad board ? (in birmingham)

 

[Somecamel]

I'm sure one of the guys that covers Birmingham will be along soon

 

[telectrix]

as above. some good solar installers on this forum that install to give you the best system for you, not the one that makes the best profit.

 

[FB.]

System design is just as important as the components used. You can't just cobble together a dozen panels and an inverter and expect it to give good performance. You can't just stick panels on a roof without considering shading issues or optimising the number of panels per string to suit the input ranges of the inverter.

From what I've seen, there isn't much difference between different brands of panels. I'd be much more interested in the proposed system layout and design, and how much I'm being charged for it.
More efficient mostly just means they are smaller for the same peak power output.
I'd quite happily have a bunch of large, bulky, low-efficiency old-technology polycrystalline panels if the price was right (probably half as efficient per square metre of area as a modern Sanyo/Panasonic, but probably a quarter of the price per panel).

I just called up a comparison of my array of Kinve (Chinese) panels facing East-South-East near Cambridge with an array of Sanyo 240W hybrid/high-efficiency panels facing South-West near Norwich.
The difference in performance is minimal.
Compare Cambs S P 3.750kW vs Norwich Power UK 3.840kW

Comparison of mine with South-East-facing Suntech in a nearby village - minimal difference, probably attributable to my panels being slightly more East than South:
Compare Cambs S P 3.750kW vs CambourneSunTrap 4.000kW

But compared to ideal-South-facing Sanyo/Panasonic in North Cambridge - I'm not surprisingly lagging due to the off-South facing of my panels (but although I'm 14% behind, if I'd wanted Sanyo/Panasonic panels I would have had to pay 35% more for my system before even considering my disadvantaged panel facing of ESE):
Compare Cambs S P 3.750kW vs Woodland Road 2.940kW

 

[SolarCity]

Nothing wrong with the Perlight 250w panels. But as has already been said, there really isn't a huge amount of difference between the panels. There is some difference, however, and it can be a case of getting the right balance between performance and expense. Some panels can slightly outperform others, but they may well be disproportionately expensive for the improvement they offer.

By far the most important aspect of a job is the layout and a decent shade analysis. A setup needs a bit of thought to get a good match with an inverter. This is far more important than picking the right panel.

Hail breaking panels? Maybe if you get big enough hail. But we're talking golf ball size hail. If you get that sort of stuff then everything is in danger of getting damaged. I've not heard of a panel being broken in Britain under such circumstances.

 

[All Eco]

Hi There.

Perlight are great panels... but Solar City is right - proper design is key. There are lots of good installers, and there are some that aren't as knowledgeable as well. Some information on them here:Perlight Panels, as we sell to trade and actually helped Perlight get MCS accreditation (so we can share more detailed test reports if required which includes hail impact tests etc).

You do get what you pay for, but there are many companies out there that either cut things out to increase their margins, or will charge extra when other installers include it. I'm sure by speaking to the sales guys or installers that you're speaking with then you'll find an excellent system. And, if you've got any queries then you can always drop us an email where we'd be happy to answer any queries for you.

With regards your point on efficiency... you're right. That quoted figure is the % of Solar energy converted to DC energy. Many people get hung up on the figure being so low... but it's actually a high figure compared with a few years ago. The key thing is what's the performance over a year in real world conditions, what energy are you going to generate and what are you going to make. Just remember, 15-20% of Sunlight falling on your panels is worth a lot more to you and the environment than the same amount of Sunlight falling on clay tiles or slates...

 

[Tabraz Khan]

Thanks guys - I really appreciate the help and input - didn't expect so much advice

FB: System design is just as important as the components used....... You can't just stick panels on a roof without considering shading issues or optimising the number of panels per string to suit the input ranges of the inverter.

Thanks FB, From a consumer point of view I would have just thought good inverter + good panels = good system so thanks for pointing out it more complex than that.

As for design element what should I look for/ask about when looking at quotes. As most just will say panel in this formation is best. I'm lucky as I have a 20-25m2 (depending on if you use measurements with tape from ground level or use google earth) south (slightly SE) facing roof plus a dorma on the opposite side which can be used (have other roof space but not ideal) but looking at various pictures on google earth from different years there appears to be slight shading at times from the neighbours slightly elevated building - would it be better to not put any panels on that area ? (as i've read 6% shading can cut out 33% of system.)

Solarcity:
Some panels can slightly outperform others, but they may well be disproportionately expensive for the improvement they offer.

By far the most important aspect of a job is the layout and a decent shade analysis. A setup needs a bit of thought to get a good match with an inverter. This is far more important than picking the right panel.
Thanks - when you say layout are you referring to placing of panels ?
AllEco:

You do get what you pay for, but there are many companies out there that either cut things out to increase their margins, or will charge extra when other installers include it.

What should I look for in a quote ? The company who quoted for perlight seem to assume a 1% drop in efficiency of system per year is this standard (meaning does it happen, therefore assuming a 75% efficient system after 25 years?) or is the company being cautious ?

I've been told inverters typically need replacing after 10 years and can cost £1000, is their warranty around to extend this to 25 year to match the panels ?

Are maintenance checks common and generally carried out by installer - or can I simply tell the system is not performing well by looking at the attached meter ?


PS: Is a 2.5 Kw system sufficient to power a 4 bed house ? My annual usage last year was 7000 units. What does a 2.5 KW system run /power ??

 

[SolarCity]

Yes, by layout I mean the layout of the panels.

Some firms offer a 3D shading analysis of your roof. This means that the shading from a dormer window or chimney can be calculated and system design can accurately take this into account. There are ways of negating the affects of shading but it a good analysis is required first of all.

Regarding panel degradation, solar panels performance will degrade over the life of the system. However, it is likely to be far less than a drop of 1% a year.

Inverter life/warranty - Most inverters are guaranteed for 5/10 years. From manufacturers that we have spoken to, it seems that 20 years is the expected life of a unit. If it is likely to malfunction, this is likely to happen in the first 12 months; get past this and it should last the whole 20. Personally, I wouldn't recommend extending the warranty. By the time the warranty runs out, in the unlikely event that your inverter does fail, the price of inverters will more than likely have dropped significantly - perhaps less than the price you paid for the extended warranty. And the new, cheaper units will more than likely be better.

 

[FB.]

As for design element what should I look for/ask about when looking at quotes. As most just will say panel in this formation is best. I'm lucky as I have a 20-25m2 (depending on if you use measurements with tape from ground level or use google earth) south (slightly SE) facing roof plus a dorma on the opposite side which can be used (have other roof space but not ideal) but looking at various pictures on google earth from different years there appears to be slight shading at times from the neighbours slightly elevated building - would it be better to not put any panels on that area ? (as i've read 6% shading can cut out 33% of system.)

Shading can cause complex problems. Some people insist on a system of the largest size that can be squeezed on a roof, when, in fact, reducing the number of panels by one or two might make it work so much better. With shading, it can only take one or two panels to be affected for it to knock-on to all the others.

Reasons for poor performance due to shading vary, but the most significant is usually the inverter running the array at a sub-optimal voltage after one or more panels go from sun to shade or from shade to sun. In other words: the shaded panel drops out, but the inverter doesn't notice and doesn't adjust the voltage to compensate for the dropping-out of a shaded panel, thus running the other panels at too high voltage. The result can be a loss of as much as three-quarters of the output if the inverter spends hours each day running the panels at the wrong voltage.

Can you use google maps to get a zoomed-in aerial view of your roof plus the nearby buildings, and post the picture here?

 

[FB.]

Are maintenance checks common and generally carried out by installer - or can I simply tell the system is not performing well by looking at the attached meter ?

You can usually do some simple checks yourself using the inverter's screen or Bluetooth widget to see what's going on. You can also compare your daily generation with similar systems in your area using the PVOutput site I linked to in my earlier post (although on PVOutput some people are uploading fantasy numbers because their measuring equipment with automatic data uploading has a calibration error; I manually enter the reading of my generation meter each evening).
I also contribute readings to the Sheffield University Solar team (my system is URN 774, just North of Cambridge). They only want generation meter readings because they are aware of major errors in the readings from some makes of add-on measuring devices.

 

[All Eco]

Tabraz

A couple of things to note here:-

Degradation:- Warranted output is going to be 90% at year 10, and 80% at year 25. The 1% reduction is an estimate that many make. Some panels will experience degradation worse than this, but something good like Perlight will be better than this.

Inverters are electronic items and may need replacing after a few years, or may go on forever... If you were an investor in many systems you'd be assuming a replacement in year 10. You can extend the warranties on inverters but you'd have to ask if it was worth it... Will the manufacturer be there in 25 years time to replace the inverter for you?

Maintenance checks - Get a feel of what your system can do on bright days, dull days and then check from time to time to see if the system is still performing acceptably. Ask your installer for details of the readings that should be displayed on the inverter, and check that the meter light flashes by day and is constantly on by night. Performance may dip slightly with dirt accumulation, but the reduction in peformance may be less than the cost of a clean. It's all about understanding and getting to know your system. No doubt your installer could come back to check the system over, but they may ask for something in return, which would be quite reasonable as a well installed system should have no reason for an installer revisit.

2.5kW won't "power" a decent kettle. But what it will do is power the majority of your house throughout the day on a bright day, and make a decent contribution on a dull day with the balance being made up from the grid. If you've got people in the house throughout the day you'll find that you get a great benefit from the system, and that's true of a system of any size.

 

[FB.]

PS: Is a 2.5 Kw system sufficient to power a 4 bed house ? My annual usage last year was 7000 units. What does a 2.5 KW system run /power ??

Definitely not.
A well-designed, well-positioned 2.5kW system would probably not generate much more than 2500 units per year.

A 2.5kW system means that it can produce around 2.5kW per hour in good conditions (sun directly opposite the panels, high in the sky, on a day with cool air or a good breeze to chill the panels). It might manage a little more, perhaps 2.75kW per hour in perfect conditions.
Unfortunately, the peak output of 2.5-2.75kW per hour will only be for a few hours on good days.

A big problem with solar is that it is often "feast or famine". In summer I have far too much power and can't use it all. In winter I don't have enough power. After dark the solar can't help. When I'm out or on holiday the house isn't using much power so any sunshine goes to waste.
My household electricity usage is 3000-3500kWh per year and my solar array produces about the same amount, but I only manage to use between one-third and one-half of the power.

Here are a couple of snapshots from my inverter's screen.
The top of the scale is 3.6-3.7kW output.
The first picture is the output on a day which was mostly sunny with a few clouds. You can see the gradual pickup in output as the sun got stronger, peaking at 3.6kW from mid-morning to early afternoon, then a gradual tailing-off for the rest of the day. The output occasionally plummets below 1kW when a cloud covers the sun. The whole chart is slightly skewed to the left because my system is ESE-facing and faces into the sun mid-morning.

The second picture shows a day with a cloud and showers in the morning (power generation not exceeding 0.5kW) then the sun comes out in the afternoon. Unfortunately, the sun is off to the side orbehind my panels in the afternoon, so I didn't produce much power that day.

 

[FB.]

Tabraz

A couple of things to note here:-

Degradation:- Warranted output is going to be 90% at year 10, and 80% at year 25. The 1% reduction is an estimate that many make. Some panels will experience degradation worse than this, but something good like Perlight will be better than this.

Real-world figures from old solar arrays suggest the actual degradation averages much less than 1% per year over two decades, with most of the degradation happening in the first year or two as the panels "settled". I think it was something like 5% drop in the first two years, then 0.25% drop each year after that unless a panel has a total failure (perhaps due to perished seals allowing water in, or a junction box burnout perhaps as a result of pushing the bypass diodes too hard due to complex shading issues).
Most panels have a "plus" tolerance of up to about 5W (e.g. a 240W panel is usually 240.0 to 244.9W when flash-tested at the factory) so even after "settling" the panel will still be close to its nominal output.

I can't say I've noticed much change in my array's performance over time and with variable weather from year to year it would not be easy to prove.

 

[SolarCity]

Degradation:- Warranted output is going to be 90% at year 10, and 80% at year 25. The 1% reduction is an estimate that many make. Some panels will experience degradation worse than this, but something good like Perlight will be better than this.

I strongly doubt that any of them will experience degradation anywhere near that and I don't see any reason or evidence to suggest why Perlight should suffer less degradation than any other panel.

- - - Updated - - -

Degradation:- Warranted output is going to be 90% at year 10, and 80% at year 25. The 1% reduction is an estimate that many make. Some panels will experience degradation worse than this, but something good like Perlight will be better than this.

I strongly doubt that any of them will experience degradation anywhere near that and I don't see any reason or evidence to suggest why Perlight should suffer less degradation than any other panel.

 

[All Eco]

Here's a study on nearly 2000 panels...
http://www.nrel.gov/docs/fy12osti/51664.pdf

Going for a quality product, of which there are indeed many, should indicate that you'd be less than the median figure of 0.5%/year degradation. There are of course likely to be many factors affecting performance... so I'll add that also going with a quality installer may have an impact.