Best angle for solar panels

[Allan Hogg]

I am trying to find the best angle (from the horizontal) at which to fit solar panels. Checking with installers is useless as they suggest every angle from horizontal to vertical. They will not be mounted on the house but on a 4M high retaining wall on the north side of the house and will point due south. Is the latitude I am at - 57.5 degrees best?

 

[Ian-LS]

I am trying to find the best angle (from the horizontal) at which to fit solar panels. Checking with installers is useless as they suggest every angle from horizontal to vertical. They will not be mounted on the house but on a 4M high retaining wall on the north side of the house and will point due south. Is the latitude I am at - 57.5 degrees best?

A 35 degree angle will generate the most energy throughout the year and is the standard angle used for ground mounted mounting kit such as schuco etc.

 

[SolarCity]

At 57.5 degrees you may find that a slightly steeper angle would work better. I'll do some checks on PV Sol and come back to you.

 

[SolarCity]

Okay, from PV Sol calculations I get an optimum angle of 40 degrees at your latitute.

 

[Vegelen]

I am trying to find the best angle (from the horizontal) at which to fit solar panels. Checking with installers is useless as they suggest every angle from horizontal to vertical. They will not be mounted on the house but on a 4M high retaining wall on the north side of the house and will point due south. Is the latitude I am at - 57.5 degrees best?

h**p://www.suncalc.net is a 2D website that will help give you an impression of the track of the sun, for your locality at different times of the year.

You wont be able to see the height of the sun at different times of the year -as it isn't in 3D
but you can get a good idea how the suns behaviour changes over time.

In winter it is lower in the sky and less intense, in summer it gets progressively higher and brighter.

Use this website along with frequent observations of your locality and you'll be able to build up a picture of the suns behaviour in your locality.

November to Early February are dead solar months in the northern hemisphere.

Mid spring to late summer is when the lions share of energy is generated.

Your panels need to be installed at an angle to optimise generation in these months when the sun is more intense and higher in the sky.

Solar City may be able to explain why 40 degrees is your optimum installation angle if you ask him nicely.

 

[SolarCity]

If you're based at the equator or presumably within the tropics then the sun is going to be directly above you at certain parts of the year - when this happens, the panels would produce most on a horizontal plane. In practice, the further north/south you are based especially as you pass the tropics you will need to increase the angle of the mounting. The north tips of Scotland will benefit from 40 degrees due to the fact that the sun will spend most of the year lower in the sky than it would in the south of England where an angle of 36 degrees would be better.

I hope this makes sense. I'm bloody awful at explaining things.

 

[jason121]

At the summer solstice in June, the sun reaches an angle of 61.9 degrees at solar noon, in London. That's as high as it ever gets. At the winter solstice in December, it reaches its lowest angle, of 15.1 degrees.

 

[FB.]

Okay, from PV Sol calculations I get an optimum angle of 40 degrees at your latitute.

Sometimes I wonder whether maximum generation isn't the whole story, since I'd gladly accept 5-10% less generation per year if I could double the amount I can use in-house to trim my bills.

I've often thought about optimum angle and it depends on whether:

1. Maximum generation for maximum Feed-in-Tariff.

2. Maximum ability to make use in-house, with a bias towards more generation on cloudy days (when it's easy to use it all) and less on sunny days (when it's difficult to use it all).

3. Optimised for good generation in the all-too-dull winter when the low sun means peak power is only about 50% of potential, for about an hour a day.

#1 is around 35 degrees in my area - a little more "up north".
#2 would be shallower - perhaps around 20 degrees - in order to have the panels closer to facing a white sky when it's cloudy.
#3 would be steeper - perhaps around 60 degrees.

 

[The Solar King]

40 deg sounds good. I am sure it is 38deg where we are, but it wouldn't alter by 2 deg in 150 miles. Any where around that will be fine. 40 makes it easy for who ever builds the framework.

 

[liquidity]

And I thought is was simply 90 minus your latitude for the optimal value for a fixed system?

 

[Worcester]

Rememerthe earth moves 'up and down' +- 23° 26′ 16″ it's only at the two equinoxes that your get the 90 degree angle at your latitude (if that makes sense) (that's why at 90-53 = 37 degrees elevation)

So to maiximise summer output it would be 'shallower' and to maximise winter output 'steeper' as FB has pointed out above.

As for the maths.... longer days, shorter days, plus that angle is at midday, as the sun rises at 0 degrees in the East and sets at 0 degrees inthe West

 

[balbecdaze]

We're talking about quite small differences in output here, 35-ish degrees is fine. Mind you it's been so cloudy recently that the 3-8 degree inclination of the panels on my "solar pergola" has been performing well on pv ouput - my link here - you have to gamble on your assumptions (e.g. cloudiness) but remember that there are more important things to consider:

is your inverter well matched to your panels?
have you minimised shading?
given that the export tariff is "deemed" etc, are you better off producing enough to cover your households baseline energy at low generation times, rather than maximising your generation on an assumedly perfect summers day?

I like FB's post, maybe your best angle delivers less energy overall but delivers more useful energy all year round. (i.e. a shallower angle)

 

[SolarCity]

2. Maximum ability to make use in-house, with a bias towards more generation on cloudy days (when it's easy to use it all) and less on sunny days (when it's difficult to use it all).

I don't really understand this point. Why do you think that angling at 20 degrees will give more generation on cloudy days? This isn't something I've noticed when I carry out light readings.

 

[FB.]

I don't really understand this point. Why do you think that angling at 20 degrees will give more generation on cloudy days? This isn't something I've noticed when I carry out light readings.

When there is cloud cover, diffuse light is coming from the whole sky.
The more the panels have a direct facing to the light sky the better they can generate.
I've also noticed that my array's best days of generation are sunny mornings and white cloud or partly cloudy afternoons. The white cloud being slightly luminous and much brighter than a blue sky - somewhat reflecting the light around and benefitting my panels if the sun is too far round to shine directly on the panels.

I know someone with a peculiar arrangement of 2kW North and 2kW South (they've even had a solar installer come round and say "you've been mis-sold because you've got 'em on the wrong roof!") but their array is performing ridiculously above expectations due to about a 30 degree roof slope (maybe a little shallower - perhaps 25'), allowing those North-facing panels to point much more up to the sky on cloudy days which make up the majority of British weather.
Last I heard from them, about a week ago, they had gone through 2100kWh between mid-May and late-November (both the generation meter and inverter logs confirm this).
That's 2100kWh from a part-month of May &November, and full months of June to October, with a 2kW North + 2kW South array at 30deg. Their huge outperformance so far relative to expectations appears as if they'll get to around 3100-3200kWh total generation in their first year.
Performance has matched my 3.75kWp ESE array with 40degree slope.
Their inverter and panels same as mine.

Furthermore, they never have a really bad day, and never have a massive day (my panels are much more extreme from one day to another - tenfold variation from one day to the next can be seen sometimes from my array) - partly due to their split array, but partly due to those shallow panels pointing at the light sky even on days when there is no direct sun.
In summer, for example, I could get mid to high 20's kWh per day, but they never got above low-20's. However, on the many dull days they performed much better than me, with far fewer low generation days.
Also shallower angles tend to be better at catching some sun at any time it may appear, whereas my 40-degree angled panels give almost-unusably huge generation on sunny spring/summer mornings but very little in sunny afternoons nor on cloudy days as the panels face almost as much towards the dark landscape of the horizon rather than the sky.

 

[John Allen]

Allan
Why not look at using an adjustable mounting system so that you can vary the angles of the panels as you desire?