Solar Panels for Dummies

wiggers

Martyn1981 said:

Did you perhaps enter the wrong orientation? ESE has an azimuth of about -70.

I entered the whole circle bearing of 113deg from North. Is that wrong?

Martyn1981

wiggers said:

Martyn1981 said:

Did you perhaps enter the wrong orientation? ESE has an azimuth of about -70.

I entered the whole circle bearing of 113deg from North. Is that wrong?

PVGIS uses azimuth, with the sun (south for us) being the point of interest. Try -67deg?

Just had a play with the EST calculator, and for an approx ESE 4.5kWp system for me (in Cardiff) it suggests 3,050kWh pa. Whereas PVGIS suggests 3,960kWh. I went with 4.5kWp purely as a rough guess against your 3,800kWh figure.

wiggers

I have a background in surveying and astronomy, azimuth is always measured from North! And since we're dealing with the sun...

Better results now thanks.

https://www.timeanddate.com/astronomy/horizontal-coordinate-system.html

Martyn1981

wiggers said:

I have a background in surveying and astronomy, azimuth is always measured from North! And since we're dealing with the sun...

Better results now thanks.

https://www.timeanddate.com/astronomy/horizontal-coordinate-system.html

That's interesting, I always thought that azimuth was 'most commonly' measured from North, not always.

In the case of PV calculations, with the sun being our point of interest, they seem to use south (for the Northern hemisphere) as zero, and north as zero for the Southern hemisphere.

But my knowledge is very limited, coming from a PV friend over a decade ago on here explaining the term, who was a military helicopter pilot. He explained about setting the destination as an azimuth, so that you could measure your deviation as you travelled, in degrees above or below that point of interest.

That would seem to fit in with the link you provided where the azimuth depends on your reference choice, and for PV I can understand why the sun or should I say equator(?) would make sense.

• Azimuth: The object's cardinal direction, such as north, east, south, or west. It is specified as the horizontal angle the object makes with a reference direction, such as true north (see illustration 3). Imagine a vertical line connecting the object with the horizon. The azimuth is the angle between the spot where that line crosses the horizon and the reference direction. If true north is used as reference, it is represented by an azimuth of 0°, and angle values increase towards the east. This means, for example, that an azimuth of 180° means due south.

wiggers

The advantage of whole circle bearings from north is that it avoids the use of signs to denote east and west. So 90 is east and 270 is west. I guess the solar industry adopted south as zero to save lots of adding and subtracting 180 degrees!

Heedtheadvice

Ah yes variation of standards....

That is why things need defining, documenting and promulgating.

Now North...is that true North, magnetic  North, grid North  or.....  

wiggers

Heedtheadvice said:

Now North...is that true North, magnetic  North, grid North  or.....  

Grid North can be anything you want. I worked on one project where it was due East! But you have to define it carefully and obviously to avoid errors. PVGIS doesn't appear to define Azimuth as being measured from South, nor which is the positive direction, although it probably doesn't make a lot of difference for solar unless you're shaded from a particular direction. In the Cartesian coordinate system, angles are measured anticlockwise from the X-axis.

Martyn1981

wiggers said:

Heedtheadvice said:

Now North...is that true North, magnetic  North, grid North  or.....  

Grid North can be anything you want. I worked on one project where it was due East! But you have to define it carefully and obviously to avoid errors. PVGIS doesn't appear to define Azimuth as being measured from South, nor which is the positive direction, although it probably doesn't make a lot of difference for solar unless you're shaded from a particular direction. In the Cartesian coordinate system, angles are measured anticlockwise from the X-axis.

Hiya, here's the PVGIS definition for you. Don't worry, you're not the first to struggle with azimuth, and you certainly won't be the last. As mentioned previously, I got a lesson from a pilot, as my 'by mail' Astrology degree let me down. [Typical Pisces.]

The azimuth, or orientation, is the angle of the PV modules relative to the direction due South. -90° is East, 0° is South and 90° is West.
For some applications the slope and azimuth angles will already be known, for instance if the PV modules are to be built into an existing roof. However, if you have the possibility to choose the inclination and/or orientation, this application can also calculate for you the optimal values for inclination and orientation (assuming fixed angles for the entire year).

Blue_Doggy

Wow! That took off unexpectedly and developed a life of its own! Very interesting discussion, people, but rather than wait for the government to introduce some, probably short-lived, scheme with eligibility criteria I probably wouldn’t meet, I’d prefer to make my own arrangements.
 

As far as pay-back times are concerned, since I’m now in my mid-70s, I’d rather live for the moment now, and spend what I’ve spent my earlier years saving. I can’t live entirely off-grid, which the Romantic in me would like to do, but installing my own partial power supply will be a step towards it.

wiggers

"I’d rather live for the moment now, and spend what I’ve spent my earlier years saving."

Spend it on a good holiday, or a decent case of your favourite tipple!