Best roof angle for solar panel

Anthonyk2010

I'm building a garage and I want to move my solar panel to the garage room.
The problem I have that in the original application the garage roof is the same as the house 45 degrees, but the county council want me to build no higher than 5m, which will reduce my angle to around 30 degrees.

What I would like to know is there any documents out there stating that panels are more efficient at 40 or 45 degrees then 30 degrees.

I'm going to contact them and see if we can compromise on the height and I want something to put in front of them.

Poor Uncle Tom

Can't you ask the manufacturers of your chosen system for a report on the optimum pitch required for best results, I'm sure they would be happy to oblige.

Anthonyk2010

Poor Uncle Tom wrote: »

Can't you ask the manufacturers of your chosen system for a report on the optimum pitch required for best results, I'm sure they would be happy to oblige.

Ya good idea tom i'll give it a go.
Never crossed my mind, must be the cold weather.
Any other ideas are welcome.

Blisterman

The maximum gain on average all year round is to have the angle from the horizontal the same as the latitude. So about 53 degrees for Dublin.

However if you want to maximise the solar collection for winter, then increase the angle to 63 degrees.

To maximise it for summer, decrease it to 43 degrees.

That being said, the difference between 30 degrees and 53 degrees is only a matter of a couple of percent efficiency. So it's not a major problem. There's many cases where photovoltaics have even been installed flat.

Source for the optimal pitch was a book called Ecohouse by Sue Roaf. Although there's plenty of websites out there with the same info if you google them.

caesarthechimp

Appendix H2 of the DEAP manual gives a table with some angles (might be available on SEAI website).
In contrast to that other advice re latitude; it gives 30 degrees as being better than 45 degrees.

holdfast

Agree with blisterman. Deap has just got the reading for those angles. It would a bigger table for all the relevant angles. The angle of lat is the best because it is a happy medium between the summer sun and winter sun angle.

caesarthechimp

holdfast wrote: »

Agree with blisterman. Deap has just got the reading for those angles. It would a bigger table for all the relevant angles. The angle of lat is the best because it is a happy medium between the summer sun and winter sun angle.

Are you saying Deap is wrong?
30 degrees as advised by Deap is even shallower than the summer angle, so it is completely outside the range 43-63 advocated by blisterman and co.

caesarthechimp

http://www.wattsun.com/misc/photovoltaic_tilt.html
This gives the optimum angle for 53 latitude as 30 degrees in midsummer and 76 degrees in midwinter.
I assume the Deap figures are skewed towards the summer angle because that's when most solar radiation is received.

Blisterman

Funny how the figures vary so much. I suppose it depends what you're looking for.

The panels will be most efficient when the sun's rays are closest to 90 degrees to the panel.

An angle of 30 Degrees will mean the rays will be close to 90 degrees when the sun is most powerful. This means around midday in the summer. So potentially, it may recieve the most energy in total at this angle, but it will be concentrated at a single time, not ideal as you'll want hot water all year round.

At a higher angle like 63 degrees, you're optimising it for winter when the suns rays aren't as strong, and the hours of daylight are less. If you think you'll need a lot more hot water during winter, it'd be worth going for.

53 degrees would be a good compromise if the water needs are going to be relatively stable all year round.

caesarthechimp

Agreed, also in midsummer some of the energy will be wasted, being surplus to requirements. In midwinter any energy is more valuable, but there may be none available. Optimizing for spring/autumn @ 53 degrees seems the most sensible.

quentingargan

Blisterman wrote: »

The panels will be most efficient when the sun's rays are closest to 90 degrees to the panel.

Your post is spot on, but there is a quirk in that many vacuum systems are actually at their optimimum output when the sun is 50 or 60 degrees off due south. This effect is known as Incidence Angle Modifier (IAM).

For that reason, I should imagine that they would work a bit better at a steeper pitch than flatplate. You really need simulation software such as T-Sol which takes in IAM.

However, flatplates would behave the same as photovoltaic per the chart, and I agree that you are going to have heaps of hot water for most of the summer so on a well insulated house with the heating off, you are optimising for spring and autumn.

Q