Best angle for solar panels

[FB.]

I guess what I'm saying is that steep-angled panels are more dependent on direct sun at a complementary angle than shallow-angled panels which can better gather diffuse light from the cloudy sky.

 

[Worcester]

Because of the angle of the sun in summer (53 degrees plus 26 degrees = 79 degrees) the math shows that a 15 degree North Facing Roof produces MORE TOTAL kWh output that a VERTICAL South facing Wall ......... Just run it through PV*Sol

15 Degrees North give an angle of incidence from panel to the Sun of 64 degrees
Vertical South facing gives an angle of incidence from panelof 21 degrees

 

[FB.]

Because of the angle of the sun in summer (53 degrees plus 26 degrees = 79 degrees) the math shows that a 15 degree North Facing Roof produces MORE TOTAL kWh output that a VERTICAL South facing Wall ......... Just run it through PV*Sol

15 Degrees North give an angle of incidence from panel to the Sun of 64 degrees
Vertical South facing gives an angle of incidence from panelof 21 degrees

One of the ten commandmens of solar, apparently, is "Thou shalt not ever install solar panels on any roof with a Northerly aspect anywhere in the UK".

Back on-topic:
My panels produce more on cloudy afternoons than on sunny ones - because often cloud is brighter than clear blue sky if the sun is too far behind the panels to shine on them.

Just as panels oriented towards the sun will tend to gather more, panels oriented towards the sky will tend to gather more when the whole sky is light cloud but no sun.

 

[Vegelen]

Just as panels oriented towards the sun will tend to gather more, panels oriented towards the sky will tend to gather more when the whole sky is light cloud but no sun.

But diffuse light adds a fraction of the generation output of direct light output, long term.

 

[Worcester]

[MENTION=52061]Vegelen[/MENTION], it depends upon wether, as FB has been saying, you want maximum output / generation or maximum SELF useable output/generation. With 4kWp systems most people will be exporting during the summer, so there is the argument (ignoring Feed In Tariff payments) that to get the maximum self useable output, it should be optimised for winter....... when we reach grid parity, then optimising for winter may become more interesting. Having said all that, getting paid 43p to generate and 3.2p for 50% export, more than makes up for buying at 10p... AT THE MOMENT..

 

[SolarCity]

FB is suggesting a 20 degree mounting angle which would get more benefit in the summer than the winter, regardless of diffused light.

 

[Vegelen]

In winter the sun is very low in the sky.

Buildings and obstructions become important in affecting the amount of solar power generated.

Solar panels with very low orientations, don't generate much mid winter from diffuse light.

If these panels were inclined steeply, they would increase their generation potential, but it

also depends on where these systems are located, how high up are they, how affected are they by obstructions from nearby buildings etc.

People focus on how much their solar system generates, what angle is best to generate the highest or most consistent yearly output, but few consider what their properties background power consumption is during the night when they are asleep.

Night time power consumption makes up an important percentage of everyone's power bills.

Inefficient appliances on standby grab power relentlessly in the night when no one is looking.

 

[FB.]

Having said all that, getting paid 43p to generate and 3.2p for 50% export, more than makes up for buying at 10p... AT THE MOMENT..

At the old 40-odd pence FiT which some of us are fortunate enough to have, yes, it's worth going for maximum generation and not worry about in-house usage.

But if the FiT is 14.5p, electricity prices 12.5p and export tariff 0.5x4.5p (2.25p) the amount of in-house usage becomes a very significant factor.

 

[FB.]

FB is suggesting a 20 degree mounting angle which would get more benefit in the summer than the winter, regardless of diffused light.

I'm suggesting that maybe, given the predominance of cloud in the UK, that those who want a good "baseline" on the majority of days which are cloudy, then perhaps shallower angles would be better.
As FiT rates are now only slightly above retail electricity costs, it's becoming important to make use of it in-house.

Looking at my stats for the least year, by weather type:

8% Sunshine all day.

51% Partial cloud cover but generally a bit more sun than cloud.

31% Mostly cloud cover but occasional sunny spells.

7% Full cloud cover all day and often some light rain/showers at times.

4% Full dark cloud cover and usually considerable rain.

 

[balbecdaze]

I just took an irradiance reading of 66.7 W/m2 (=dull and overcast), and my 4kW of panels are producing in the region of 335W. This easily covers my baseline power use. My panels and inverter are basic Suntellite/EverSolar, the inclination of my panels goes from around 3 to 8 degrees (I know but I'd never built a pergola before, and my garden is uneven!).

It's hard to be sure from PVOutput but live readings close to me at the time for a 40degree system with a slightly better orientation were ~250W.

Over time, a very well performing system near me compares like this:



which I think demonstrates the arguments made above.

Is it better? Well my overall performance is 92% of this better oriented system and I don't have a very big roof anyway, and I can't simply tell how much electricity I would be buying because my meter's still going backwards.

Just thought I'd add some real world data.

 

[FB.]

Hi balbecdaze

It is clear to see that although "Solar Pergola" is 8% inferior in total generation, it is also less variable; more dependable.

KillaWatt is feast and famine by comparison. My own system is feast and famine and it annoys me as I either have way too little or far too much. Immersun attempts to address this, but if solar is to be a long-term "planet saver" then we need to start thinking about a more reliable daily generation, even if a lower total yield.

If the FiT rate was still 43p (45p) then KillaWatt would be desirable because FiT is so much higher than the cost of buying electricity.
However, with FiT rates around 14.5p and the cost of buying electricity around 12.5p, then a higher baseline might be more useful.

 

[immerse]

If you go to the EU website at PV potential estimation utility you can put in the roof inclination and orientation and find monthly outputs for systems of different size and technology, and of course annual outputs. The beauty of this free software is that it is computed based on a vast database of European weather gathered at great expense using several technologies, both ground and satellite based, and includes all important cloud cover statistics and the effects of scattered radiation ('skylight'). All kinds of optimisations are possible by varying the inclination angles in the program. You can even import a self surveyed horizon file to allow for obscuration.

 

[solarfred]

This is the sky I tested panels horizontal and angled.
http://i1145.photobucket.com/albums/o517/freddyuk1/IMG_0551_zpsd09f32d3.jpg

Here are the current readings
http://i1145.photobucket.com/albums/o517/freddyuk1/IMG_0553_zpsa5d7b42c.jpg
http://i1145.photobucket.com/albums/o517/freddyuk1/IMG_0552_zpsf8884d3a.jpg
http://i1145.photobucket.com/albums/o517/freddyuk1/IMG_0559_zps10e8aa6a.jpg

A 100wp panel gives 0.6amps angled and 0.8 amps flat.

 

[FB.]

FB is suggesting a 20 degree mounting angle which would get more benefit in the summer than the winter, regardless of diffused light.

I happened to visit the 2kW North + 2kW South array's owner on a cloudy afternoon (about 1.30pm) over the Christmas period; I looked at the inverter screen and saw that the North panels ("array2") were generating 0.83x that of the South panels ("array1").
Only on the rare sunny days do North panels lose out. However, for base/background load on dull days the North panels really help boost the usable amount of power. On bright days it's hard to use all the power and it goes into the grid, but on dull days there never seems to be enough power, so it really helps to have extra North panels at 0.83x that of South, when we're close to the shortest day and lowest sun.

I should add that the owner had three choices for solar:

1.
2.0kWp South-facing array (~30 degrees).
Cost would have been about £5k, annual output estimated 1800kWh by SAP-2009 = 0.36kWh per year, per £1000 spent.

2.
2.5kWp South-facing array, but one or two panels would be partially "hard-shaded" in the mornings due to a gable.
Cost would have been about £6k, annual output estimated 2300kWh by SAP-2009 = 0.38kWh per year, per £1000 spent.

3.
4.0kWp split equally North-South (~30 degrees, with no shading).
Cost about £7k, annual output estimated 2800kWh by SAP-2009 = 0.4kWh per year, per £1000 spent.

Option 3 would therefore have given the same or slightly higher ROI as option 2, but without the risk of shading.