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Discuss True south or magnetic south?? in the Solar PV Forum area at ElectriciansForums.net

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hanky-pankysex

Active EF Member
After leaving a compass with our ground worker for any ground mount installations I always tell him use the compass to find south, Am I right in saying there is a magnetic and a true south because there is a true and magnetic North??
 

telectrix

Scouser and Proud of It
Respected Member
i suppose that a 180deg. reciprocal bearing from magnetic north would give a false bearing for true south, but the difference will not change the world of solar power, IMO.
 

SolarCity

Electrician's Arms
Realistically it should be true south. Magnetic south actually moves about.

However, it's not really going to make a fat lot of difference. If you really want to be accurate then you could try sticking a pole in the ground and finding which way the shadow is cast at midday. Were interesting in where the sun is at it's peak in the sky, not magnetic south.
 

telectrix

Scouser and Proud of It
Respected Member
and having done all the calculations, you discover that the optimum time for generation is ten past 12., not exactly noon.
 

balbecdaze

Electrician's Arms
Cross posted with Solar City, his method is much more straightforward and relevant! Don't forget to allow for BST!
 

JulianC

Electrician's Arms
Your compass reading is typically up to a few degrees out due to what's known as magnetic declination (the difference between magnetic and true north). For the UK Midlands, declination is currently around -2 degrees. Negative indicates mag. north is currently west of true north. Therefore, what you are measuring as 180 degrees (south) is actually 178 degrees from true north.

magnetic-declination.com
 
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FB.

Electrician's Arms
Point the hour hand of your watch in the direction of the sun.
The mid-way point between the hour hand and the number 12 will be South.
 

FB.

Electrician's Arms
Remember to take an hour off the displayed time when we switch from GMT to BST.
 

supasparxs

Electrician's Arms
i suppose that a 180deg. reciprocal bearing from magnetic north would give a false bearing for true south, but the difference will not change the world of solar power, IMO.

the difference between Map north (or South) and Magnetic South is printed on the bottom of an OS map. the too do vary across the country,
 

FB.

Electrician's Arms
Point the hour hand of your watch in the direction of the sun.
The mid-way point between the hour hand and the number 12 will be South.
Oh....and if you want to verify that it works before you head to work tomorrow morning: try it out from your house by imagining where the sun came up this morning (probably shortly after 7am if you have a nice open view to the SouthEast), then imagine where the mid-day (South) sun is in your garden at this time of year, then imagine where the sun sets (around 5pm today if you have an open aspect to the SouthWest).

In reality, the earth and its orbit is not perfectly circular, so the peak of the sun varies slightly at different times of the year, although the difference in timing of the sun's peak only amounts to a matter of, at most, several minutes either side of 12.00/noon (although remember the hour difference when we switch to BST, with peak sun around 1pm).
 

danesol

Regular EF Member
and having done all the calculations, you discover that the optimum time for generation is ten past 12., not exactly noon.

surely that depends on your latitude ??? ( if in the same time zone, relative speaking )
 
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TedM

Electrician's Arms
For maximum production (assuming no shading) you would want panels pointing towards the local 'solar noon'. This is the term for the direction where the sun reaches the highest point in the sky for a particular location and its GMT time will vary depending on longitude. i.e. 4 minutes for each degree.

Solar noon for Kent and Cornwall will be different by about 28 minutes. Longs: Margate = 1.4 and Penzance = -5.6 so 7 degrees difference.

You can find the exact longitude of a location easily using this map Map Channels Simple Geocoder
 
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