PV panels in shade « Alternative Technology Assn Forums

Alternative Technology Assn Forums » Energy

PV panels in shade

(17 posts) (13 voices)

Started 11 years ago by eggman
Latest reply from solarexpert

Tags:

No tags yet.

eggman
Member

I am contemplating installing a PV system consisting of 8 panels. However the bottom 4 panels will be in shade for a few months of the year. I am wondering if anyone has any ideas about panels that will be in shade for a few months of the year. I don't have enough roof space for thin panels. I am wondering if anyone has any ideas about panels that might be more shade resistant? Or perhaps panels that can be connected with bypass diodes or the like in order to isolate the shaded panels when they are not producing any output.

Many thanks.

Posted Thursday 16 Sep 2010 @ 11:17:24 pm from IP #
franks
Member

Your suggestion of 8 PV strings with bypass diodes (normally set up) would be ok, assuming the inverter can handle a MPPT voltage range 130 to 280 volts. 4 or 8 panel aprox MPPT voltage
Need to speak to your installer for advice.

Posted Friday 17 Sep 2010 @ 1:12:25 am from IP #
Michael L.
Member

Don't forget that even when shaded they are producing, maybe not as much but you are still getting an output. Mine are still producing even when the sun has gone behind a house on the other side of the road to me, maybe only 50 or so watts, but they are still prductive.

Posted Friday 17 Sep 2010 @ 1:42:29 am from IP #
eggman
Member

Thanks franks. My next challenge is to find an installer that knows what a bypass diode is:) Some of them even seem to struggle with the concept of meeting the minimum startup voltage for the inverter.

Does anyone know of a particular brand of panel that has buil it bypass diodes?

A lot of people are telling me that the shaded panels would reduce the currently flow to a point that there is no output. So I am happy wiht a reduced output. However I don't want the whole string to shutdown.

Posted Friday 17 Sep 2010 @ 2:55:29 am from IP #
rsigmund
Member

Solar panels are made of individual cells and modern panels have inbuilt bypass doides as far as I know...

Which months of the year?

One problem (which frank touched on) to over come will be the voltage supplied to the inverters input... If when shaded, the string voltage falls out of range or into a lower effeciency section of the output curve your system performance will suffer even more than just the effects of the shading...

Posted Friday 17 Sep 2010 @ 4:12:38 am from IP #
Benny
Member

Theres a good discussion of the effects of shading here eggman ...
http://forums.energymatters.com.au/solar-wind-gear/topic1215.html

Perhaps you should try to have your 8 panels as 2 strings of 4, so that the top string is completely in the sun and independent of the shaded bottom string. This might still need a dual MPPT inverter though.

Posted Friday 17 Sep 2010 @ 6:39:24 am from IP #
PV2010
Member

The new Aurora >3.6kW had dual MPPT,suitable for two strings. It also has a large voltage operating window. The dealer told me it was only $400 more than a 2kW.
http://www.solarinverters.com.au/files/products/datasheet-qberab.pdf

Also consider panels that have efficiency in lower light/diffuse light conditions. However, thin film take up alot of room so probably not suitable if its a squeeze.

There are also panels/add-ons that have individual MPPT, I am not aware there are any available in Australia at reasonable cost.Worth a search though.

The new Sunpower panels maximise your solar real estate, with a whopping 19.5% efficiency, meaning smaller area.
http://us.pv-contractor.com/us_store/panels/sunpower-e19-series-318-solar-panel.html
however I have been advised they are not compatible with transformerless inverters

Posted Friday 17 Sep 2010 @ 10:29:52 am from IP #
dymonite69
Member

And your payback period might end exceed the life time of the panels themselves

Posted Friday 17 Sep 2010 @ 11:12:12 am from IP #
amun-ra
Member

Solco Choice Electric Solar Edge SE3300 270-450 3300 Yes Yes SAA100597 SAA Approvals 3-Aug-10
Solco Choice Electric Solar Edge SE4000 270-450 4000 Yes Yes SAA100597 SAA Approvals 3-Aug-10
Solco Choice Electric Solar Edge SE5000 270-450 5000 Yes Yes SAA100597 SAA Approvals 3-Aug-10
Solco Choice Electric Solar Edge SE6000 270-450 6000 Yes Yes SAA100597 SAA Approvals 3-Aug-10

Posted Friday 17 Sep 2010 @ 10:35:02 pm from IP #
undy
Member

There are solar maximizers available in Australia which may be useful (I'm thinking about buying some). Solco apparently import both the Tigo Energy unit and the over-priced (IMHO) National Semi-conductor SolarMagic units.

I've been unsuccessful in finding out from Solco the names of anyone who actually sells or installs these to Joe Public, so good luck.

Posted Tuesday 21 Sep 2010 @ 10:13:11 pm from IP #
Russell Moore
Member

eggman, I would do all that is humanly possible to try to get those bottom panels out of the shade. Have you thought of extending the panels above your ridge line, say by about 300mm, and/or extending them over the edges? Not only may this allow you to rearrange the panels, it can also increase airflow (wind) under the panels for better summer production.

Is there any way you can remove the object/s that will be causing the shade?

Have you thought about using panels such as Sunpower, Suntech Plutos or Sanyo HITS?, you can use less panels to get similar outputs that you can from standard panels, of cause they do cost more.

Shade sucks.....

Russell.

Posted Tuesday 21 Sep 2010 @ 10:36:20 pm from IP #
rockabye
Member

From a purely technical point of view putting solar PV modules in a location with significant shading is a silly idea. You can save more energy with less money spent by replacing inefficient appliances, insulating the house and better energy management. You could buy a more efficient car or an electric bike for example and save far more CO2. Save your money and spend it in those areas for a much better outcome.

Posted Tuesday 21 Sep 2010 @ 11:05:13 pm from IP #
swanning_it
Member

To follow on from Russell, I've been looking at overhanging panels (for sun alignment not shade) at my place. The upside I can see is benefits from better rear cooling and the panels then form summer shading for windows beneath. Downside is that so far, I've not yet been able to get someone to attest that the panels will handle the wind loads. Any suggestions?

A bit more on undies solar maximisers is here at this link.
http://www.dcpower-systems.com/uploads/productcategories/760_1.pdf
Interesting reading and at only about US$60 each, affordable.

Posted Wednesday 22 Sep 2010 @ 12:09:11 am from IP #
Russell Moore
Member

swanning_it, I can't believe that small overhangs would be a liability in strong winds.

johnpao has his panels on south facing roofs, on tilt adjustable frames, and they have withstood some very strong winds of late with no problems. He has a photo link on his thread at 'New 5.2kW solar system'.

If you extend them over a ridge line, they should pick up any southerly component breeze as it compresses up the south sloped roof, and you can get more space on your roof to rearrange the panels as well.

I quite agree about having panels in shade, not all roofs are suitable for panels, and they shouldn't be placed on them, yet I see quite a few placed to the south of tall trees etc....

Posted Wednesday 22 Sep 2010 @ 9:28:21 am from IP #
swanning_it
Member

Hi Russel, I'd like to think that too. But what's a "small" overhang? My new roof will be curved (east/west or very close to it) and quite long (north/south) so to fit the most panels in the flatest section (on slightly elevated brackets) along the ridge line, I was contemplating an overhang of about 400mm. I can overhang the whole roof, but was thinking I could save materials (and cost) if I only overhung the panels. But strong winds would then act directly on the two bits of aluminium frame sides. If they gave way, the panels would break........expensive lesson to learn!

Posted Wednesday 22 Sep 2010 @ 10:39:39 pm from IP #
eggman
Member

Thank you all for your comments. I must admit that I put this issue to bed late last year as it was all getting a bit hard. However I would like to revive it.

My next question is, can I install 2 strings of 4 panels without an inverter that has a MPPT input. I was looking at getting a SMA SB-1700 inverter taht doesn't have MPPT.

Does anyone know of installers in teh Melbourne area who have experience with this sort of installation, i.e. somone who knows what a bypass diode is?

Posted Tuesday 19 Apr 2011 @ 12:48:05 am from IP #
solarexpert
Member

Solar panels obviously produce less power when they are shaded and should idealy be situated where there wil never be any shadows on them. There may be situations where this cannot be avoided, and the effects of partial shading should be considered.

A shadow falling on a small part of a panel can have a surprisingly large effect on output. Not only will the cells that are shaded be producing less power, but as the cells within a panel are normally all wired in series, the shaded cells afffect the current flow of the whole panel.

If the affected panel is wired in series (in a string) with other panels, then the output of all those panels will be affected by the partial shading of one panel. Therefore in a situation where partial shading cannot be avoided, there may be a case for not having the panels wired in series to produce the higher voltages that can be used with some inverters.

Posted Friday 29 Apr 2011 @ 9:06:36 am from IP #

RSS feed for this topic