Getting quotes for solar pv - but what panels are decent

[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.

 

[Tabraz Khan]

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.


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

Clicking on this picture should take you to 8 snapshots i've taken from google earth.



here is the direct link : http://imageupper.com/g/?galID=S020001007O13773508651996751&n=1

I was concerned the the neighbour house (Dr Surgery) being taller than mine would cause shading in early hours - whilst this might be true looking at different images on google earth (from different years and months) it seems to be ok - however the sun path feature on google earth shows a different picture.

Space wise seems i have 5.1 metre diameter upto chimney (got more space on lower rows) and approx 4.6 metre in height from front to ridge.

I also have a the possibility of the dorma which is 2.6*1.8m.

So seems I can have a 2.75 system if i fit 11 250 panel on front - possibly 3.25kw if dorma is used (can 2 panels go there?) or 12 panel 4kw without using dorma if i opt for sunpower 327 panel which are smaller size - what kind of premium would that be ?

 

[Earthstore]

Hi, I think you need to get some help from a decent company, personally I would not use the dormer for a few reasons, as to Sunpower, which are the best on the market you really have to do your sums on that to see if the extra outlay can be justified in the return, which can get very complex due to your energy usage.

Why not just get someone from here to quote for you, there are some very good companies here??

 

[Tabraz Khan]

Hi, I think you need to get some help from a decent company, personally I would not use the dormer for a few reasons, as to Sunpower, which are the best on the market you really have to do your sums on that to see if the extra outlay can be justified in the return, which can get very complex due to your energy usage.

Why not just get someone from here to quote for you, there are some very good companies here??

I have approached a couple of people via the forum to quote me. If anyone else is local to Birmingham and/or wishes to quote please private message me and I shall give you my details.

Tabraz

 

[FB.]

The panels will be free from shading at peak generation time from late-morning to mid-afternoon. That's a good thing, and your problems will be relatively minor.

The height difference between your house and the slightly taller building next door won't cause much of a problem - probably no more than 5% loss of output and no losses at peak generation time (lunchtime) nor on cloudy days when it is just light reflecting off the clouds above that powers the panels.

The chimney is slightly more of a concern, with it casting a "hard shadow". There will be no shading from the chimney until 1pm in summer (2pm in winter due to clock change, but by then the sun will be close to setting and weak by the time the chimney causes a problem).
In summer, from 2pm onwards the upper row of panels will suffer gradually more shading as the sun moves round. By about 5pm you could have two or three panels dropping-out of the string due to shading. The chimney might well knock 10-15% off the annual total generation by confusing the inverter from mid-afternoon, but won't affect the ability to reach peak output of 2.5kW around mid-day.
Panels on the upper row near the chimney might benefit from being in portrait layout, which will knock out less of the panel from shading than in landscape layout, due to the way the bypass diodes are arranged. A few panels - such as Panasonic/Sanyo have a different layout of the cells relative to the bypass diodes.

Some inverters have a setting which helps to more regularly scan a wider optimum voltage range than older or lower-tech inverters. This can overcome panels dropping-out of the string due to hard shading, and with a suitable inverter you'd probably be under 5% losses from the chimney.

If the roof was larger (or the panels smaller), it might have been possible to fit the panels as two strings - say 6 or 7 in each row, operated by two independent processors in the inverter so that at least the lower panels aren't impaired by shading on the upper panels. But smaller strings of about five panels often don't have enough voltage to meet an inverter's startup requirement.

Putting panels on the rear roof extension might cause more problems than it's worth because of the flat roof presenting a very different angle to the sun compared to the sloped roof on the front of the house. It'd be similar to partially shading some panels in the string, and is an example of where, sometimes, "less is more".

 

[series530]

As a consumer there is also another way to consider this purchase: we've taken the micro inverter route as we suffer from shading at certain times of the day. I'm not, for one moment, suggesting that this is the route that you should take as this adds tremendously to the cost and complexity. We took the micro inverter route because we saw the installation as a longer term investment rather than a short term money earner. We bought when the FIT was paying the most but, conversely, the cost of the systems were highest. Each year, the return we get we see as a kind of annuity payment as opposed to anything else. Averaged out over 25 years, even poor performing panels will, hopefully, pay for themselves and a lot more besides. Thus, having some shading may not be an issue as it simply means that the shaded panels take longer to pay the investment costs.

This approach, however, requires extremely careful up front system design. You cannot simply wack a load of panels on a roof which suffers from shading for all of the very good reasons outlined in previous posts because you need to bear in mind that any shading will affect overall performance: a small amount of dappled shading may be handled successfully by a decent inverter. A modest amount of heavy shading could kill a badly installed system output. Careful system design, thus, is vital.

One other consideration is aesthetics: how many times have you driven along a road and comment how ugly an installation looks? I've done it many times. While a badly installed system may give a return through the FIT it could knock twice as much off the value of the property and is, thus, a very unsound investment unless the owner has no intention of ever selling the property.

We found that the cheapest system are cheap for a reason: they often use inferior components which, as pointed out, won't drastically affect you ROI but, if those components are simply thrown up on the roof without careful thought to system design (efficiency working together, quality of cable runs, remote monitoring, shading analysis, load bearing analysis, functionality of the roof in conditions of high wind and rain) and if the system comes without an insurance backed guarantee, it could be a false economy in the long run.