Facing panels to the west, optimal angle?

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solar_dave
solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
in General Solar Power Topics #1
As titled, assume all my reasonable south facing is consumed, if I want to put some panels up facing west as awnings for my west facing windows what would be the optimal angle?
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #2
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    Re: Facing panels to the west, optimal angle?

    Seems like it should be mid point of the angles where the sun hits you panels fully, ie where they start to put out full power to when they stop..
    make sense?
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
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  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    #3
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    Re: Facing panels to the west, optimal angle?
    solar_dave wrote: »
    As titled, assume all my reasonable south facing is consumed, if I want to put some panels up facing west as awnings for my west facing windows what would be the optimal angle?

    I am going to do the same thing, except I have east and west facing slopes I can put more panels on. I don't think it will work all that great in the winter here, but I think it will work good in the summer to get more constant output all day. I think the roof pitch on our house is 23° (5/12 pitch). I plan on putting some IronRidge rails on there, purchased from our host, and mount the panels on the roof at the same angle as the roof slope, with equal panels facing east and west - probably 1 kW of capacity (with 250 watt panels) on each slope.
    --
    Chris
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  • jaggedben
    jaggedben Solar Expert Posts: 230 ✭✭
    #4
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    Re: Facing panels to the west, optimal angle?

    The way I would answer this question would be to go to PVWatts, put in the azimuth, and then try different tilts until I found the highest annual production. The answer may vary slightly depending on the precise azimuth.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #5
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    Re: Facing panels to the west, optimal angle?
    jaggedben wrote: »
    The way I would answer this question would be to go to PVWatts, put in the azimuth, and then try different tilts until I found the highest annual production. The answer may vary slightly depending on the precise azimuth.

    Of course they will be in full shade until just before noon, unclear how to get pvwatts to take that into account unless you take the hourly data and drop all the morning hours.
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  • Eric L
    Eric L Solar Expert Posts: 262 ✭✭
    #6
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    Re: Facing panels to the west, optimal angle?

    Whether you want more, less, or an equal amount of winter vs. summer sun may be a bigger variable than optimizing the azimuth angle for maximum annual harvest. A starting point might be to aim them where the sun sets at the equinoxes at your location (I mean in terms of azimuth angle). That should make (I think) the summer and winter angle of incidence "equal" at the solstices. If you wanted a little more winter sun, then aim them a bit more to the south; more summer to the north.

    Edit to add; the angle of incidence at the solstices will also vary with latitude, so what I said above isn't right. Still, the equinox sun position gives a good starting point, I think.
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #7
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    Re: Facing panels to the west, optimal angle?

    I read the Jagged response and thought it out, since the sun would be essentially off the Panels till noon or later all you would get is afternoon sun...???
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #8
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    Re: Facing panels to the west, optimal angle?

    PV Watts does have an "hour by hour" output--So you could pick (for example) the solstice and look for maximum on those days. Or you can get real fancy and do a macro/conditional where it only adds up numbers past Noon.

    If you have time of use billing (higher summer power costs/reimbursement), then you might want to go a month or so past solstice to maximum your day time/afternoon power when it is "worth more".

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #9
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    Re: Facing panels to the west, optimal angle?
    solar_dave wrote: »
    Of course they will be in full shade until just before noon, unclear how to get pvwatts to take that into account unless you take the hourly data and drop all the morning hours.

    Seems pretty simple (if the shading is because of the angle of the panels and not something like trees or other structures). PVWatts knows that if the light is coming from the back of the panel (based on the elevation and azimuth you entered) the panel will produce no power.
    SMA SB 3000, old BP panels.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #10
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    Re: Facing panels to the west, optimal angle?

    If they're facing due west then I would think that they should be at a very steep angle, almost vertical for the setting sun?

    If you have enough space I'd also consider tandem junction amorphous panels, or CIS or CIGS panels as they tend to do better on less than optimal angles and diffuse radiation, so you wouldn't lose as much power while they're shaded. There was a study done at Oxford some years ago on how the different PV technologies performed in the UK climate (lots of high cloud): http://www.eci.ox.ac.uk/research/energy/downloads/pv-inthe-uk.pdf

    Attachment not found.
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  • jaggedben
    jaggedben Solar Expert Posts: 230 ✭✭
    #11
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    Re: Facing panels to the west, optimal angle?

    Okay folks, I put it into PV Watts for a randomly picked location (Topeka KS), and at azimuth 270 the max annual production is at 2-4 degrees tilt.

    If you do the shading analysis it would higher, but my guess is not by much.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #12
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    Re: Facing panels to the west, optimal angle?

    Probably want 5 degree minimum tilt or the panels many not be as self cleaning (if leaves and trees are around).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    #13
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    Re: Facing panels to the west, optimal angle?

    Well, for my east and west facing "booster" panels I've decided to go with 23 degrees of tilt (same as the roof slope). The panels' output don't change much up to 15 degrees off from the sun being directly on them, according to experimenting I've done. In the summer the sun goes directly overhead here. So at solar noon I'll only get slight drop from maximum output because each bank of panels will be 23 degrees off ideal. But on each side of solar noon I'll get a "boost" with one of the arrays being at ideal tilt angle so I get a "flatter" energy production curve all day as compared to having them all facing south azimuth.

    On overcast days it won't make any difference because they work off refracted ambient light off the cloud deck anyway.

    Solar panels have gotten cheap enough that I question the economics of trackers. Just bolt on several arrays at different azimuth settings. That's my latest theory.
    --
    Chris
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #14
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    Re: Facing panels to the west, optimal angle?

    that 2, 3, and 5 degree tilt better be off of vertical as a flat pv will not perform better than a vertical one facing east or west. the sun sits lower to the horizon.
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #15
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    Re: Facing panels to the west, optimal angle?
    niel wrote: »
    that 2, 3, and 5 degree tilt better be off of vertical as a flat pv will not perform better than a vertical one facing east or west. the sun sits lower to the horizon.

    I think they mean flat. The software chooses flat because it catches sun from all directions. Flat panel facing west is the same as flat panel facing south.

    But flat panels will look really silly on the roof :D
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #16
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    Re: Facing panels to the west, optimal angle?
    NorthGuy wrote: »
    I think they mean flat. The software chooses flat because it catches sun from all directions. Flat panel facing west is the same as flat panel facing south.

    But flat panels will look really silly on the roof :D

    really, i didn't know that pvs when catching the sun's rays near 90 degrees off to the side because the pv is nearly flat on the ground will still produce during sunset. the pv must be nearly vertical so that the sun can hit it as nearly straight on as possible. in the winter the sun won't set optimally for a west facing pv so very little will be produced no matter what angle the pv gets tilted to. in the summer it's a different story as the sun will set in the northwest.

    btw northguy, if you've ever caught the discovery channel show bearing sea gold they have shown a building there a few times in nome alaska that has pvs on the front side of it hanging vertically because the sun is coming in optimally from the horizon. same deal. now in this case it should be a few degrees off of vertical because he isn't as far up as nome, but he won't see production like he would from a pv at an angle of latitude aimed south.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #17
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    Re: Facing panels to the west, optimal angle?
    niel wrote: »
    that 2, 3, and 5 degree tilt better be off of vertical as a flat pv will not perform better than a vertical one facing east or west. the sun sits lower to the horizon.

    I think this is one of those grid-tie vs. off-grid choices. If you're grid tie, then you want the most kWh per year, doesn't matter when it's generated so an almost flat panel facing west would produce more because it's optimally inclined for the midday summer sun. If it were vertical, it would be optimal for the weak setting sun which doesn't have as much power in it.

    But if you're off-grid then harvesting more power at sunset is probably better because you can lengthen the time you're not running off batts. As Chris said, it gives a flatter but longer production.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #18
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    Re: Facing panels to the west, optimal angle?

    i'll go along with the flat argument if there are no obstructions that would shade it during other times of the day such as the building's roof, chimneys, vents, etc. if there are then the pv must sit just off of vertical as the westerly sun would be the only sun there. if there isn't any obstructions then he could leave them flat and could also theoretically still tilt the pvs toward the south as per normal due to no shading issues, but it would not look right as far as aesthetics go.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #19
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    Re: Facing panels to the west, optimal angle?

    Well my intent is to use them in a dual purpose, to shade my AC units and my West facing windows as awnings. With that in mind, I hacked around in PVWatts and sort of came up with a compromise of 45 degrees. For shading the best I think horizontal makes the most sense but for solar production more vertical makes the most sense.

    BTW my contractor buddy is coming by to quote a "trellis" over my walk way to add ~12-16 panels facing south. If under 120 Sq Ft no permit is required for the construction, I am sure the electrical will need one however. Then the remainder of the pallet of 24 panels will be used to shade as described above. I will construct steel frames out of 1 inch sq tubing for the awning applications.
    A permit is also required for a storage shed, playhouse or gazebo if it has over 120 square feet of floor area, or if it is attached to the house.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #20
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    Re: Facing panels to the west, optimal angle?

    Or if there is electrical involved (permit)--At least in my city.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #21
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    Re: Facing panels to the west, optimal angle?

    S-Dave, don't forget to show us some pics of the end product... sounds interesting, multi-purpose structure
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #22
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    Re: Facing panels to the west, optimal angle?
    BB. wrote: »
    Or if there is electrical involved (permit)--At least in my city.

    -Bill

    Yeah here they usually require both a structural and an electrical but it looks like my structural is a pass according to the local permitting site.
    http://www.glendaleaz.com/buildingsafety/DevelopmentServicesCenter.cfm
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #23
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    Re: Facing panels to the west, optimal angle?

    i'll 2nd westbranch's request of pics and i'll ask for good detail on the mounts.
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  • jaggedben
    jaggedben Solar Expert Posts: 230 ✭✭
    #24
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    Re: Facing panels to the west, optimal angle?
    niel wrote: »
    i'll go along with the flat argument if there are no obstructions that would shade it during other times of the day such as the building's roof, chimneys, vents, etc. if there are then the pv must sit just off of vertical as the westerly sun would be the only sun there.

    This statement makes no sense. It would only make sense if the shading obstructions were covering over the entire space of the panels. If shading happens until noon, as has been described, then the panels will be getting sun from when the sun is at 90 degrees vertical to when it is at 0 deg on the horizon, and the most sensible angle would be around 45 degrees.

    Leaving aside questions of off-grid charging times as stephen raised, it will pretty much never makes sense to place panels with their plane near vertically unless you are really in the polar regions. In a west facing situation, you will reach peak production just as the sun sets, getting only half the potential bell curve.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #25
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    Re: Facing panels to the west, optimal angle?

    jaggedben,
    it makes sense because it is to cover a window area and would be below eaves and or roof areas with a flat pv. these could shade the pvs unless raised up almost as high as the eaves or roof are sitting. remember, he is going to use them as awnings and awnings sit just above a window and this is not usually at roof level. add in any vents, chimneys, etc and it could shade at times even if the eaves and roof does not shade it. now if said pv is able to see light just past noon then it could also be tilted to optimize the angle, but that takes away from the symmetrical aesthetics one would want in an awning that faces west. i am in agreement with flat if there's no obstructions. any obstruction would necessitate a nearer to vertical mounting as production would be tunnel visioned due to shading issues.

    i think we are on the same page, but looking at it from a different angle confuses i suppose, pun intended.
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  • jaggedben
    jaggedben Solar Expert Posts: 230 ✭✭
    #26
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    Re: Facing panels to the west, optimal angle?
    niel wrote: »
    jaggedben,
    it makes sense because it is to cover a window area and would be below eaves and or roof areas with a flat pv...

    Maybe you have some knowledge of Dave's site that I don't have. If true that the panels would be underneath an eave, then perhaps an angle near vertical does make sense. However I have to say that placing panels underneath eaves doesn't seem like a very wise thing to do in the first place.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #27
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    Re: Facing panels to the west, optimal angle?
    jaggedben wrote: »
    However I have to say that placing panels underneath eaves doesn't seem like a very wise thing to do in the first place.

    i would agree with you that it is something to try and avoid, but to use pvs as an awning would mean right there above the window to the wall.

    i am not familiar with dave's place, but i had to throw out the possibilities.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #28
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    Re: Facing panels to the west, optimal angle?
    niel wrote: »
    i would agree with you that it is something to try and avoid, but to use pvs as an awning would mean right there above the window to the wall.

    i am not familiar with dave's place, but i had to throw out the possibilities.

    The eves are really shallow, about 1.5 ft. and about 15-20 ft above the window tops. Minimal impact.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #29
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    Re: Facing panels to the west, optimal angle?

    BTW the person that must be obeyed may have put the kibosh on the whole plan.
    "It won't be very pretty", says she.
    Just remember, Happy wife, happy life.

    PS as I grumble under my breath.
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