True south

System

I know that there is a magnetic south and a true south. of course magnetic south will be excately oppensent of mag north on the compas. but what will be the readings for true north and true south on the compas if its set at mag north? I know i can guess but I've always been weird about wanting to get things perfect and if my new house is a little off i know it will bug me for years.

crewzer

Re: True south

The variation between magnetic north and true north is called "magnetic declination". Try this Google seach strng for more info:

http://www.google.com/search?hl=en&q=magnetic+declination

HTH,
Jim / crewzer

nigtomdaw

Re: True south

Have a look at this months latest Homepower Magazine it has a full article on it and a very easy way to find True Polar south using the stars ,Big Dipper/Little Dipper

mike95490

Re: True south

I've always like the Stick & Shadow method.
Mid morning, poke a stick into the ground. 3 foot is nice. Look at the shadow, and mark it in the dirt. Mark the shadow location an hour later, and again and again. (or use an existing stick, flagpole, etc...
The marks create a true West -> East line, any time of the year, when you have sun casting a shadow. A good square will give you North & South.

niel

Re: True south

in addition using a stick like mike suggests at solar noon will create a true north/south line with the shadow. solar noon is the time in the middle of sunrise and sunset times for your location.

Windsun

Re: True south

mike90045 wrote: »

I've always like the Stick & Shadow method.
Mid morning, poke a stick into the ground. 3 foot is nice. Look at the shadow, and mark it in the dirt. Mark the shadow location an hour later, and again and again. (or use an existing stick, flagpole, etc...
The marks create a true West -> East line, any time of the year, when you have sun casting a shadow. A good square will give you North & South.

Their is a variation on that if you know the times of sunrise and sunset.

Figure out what time it would be at exactly half way between - that will be solar noon.

A stick in the ground will cast a shadow that is exactly true solar north-south for your location. In summer you might need a really long stick since the sun is almost exactly overhead.

And BAH on niel for beating me to it.

niel

Re: True south

raspberries. raspberries. raspberries. gee, i didn't know you need at least 18 characters to make a post.

nigtomdaw

Re: True south

I tried the Home Power method last night locating the Ploaris star in the northern hemisphere, I aligned this with my solar array which I thought I got perfect using a compass and deviation and was surprised That I was only about 5 degress from true south. Funny enough after building my array and watching sunrise and sunset (mainly sunset) I suspected I was a little off but I was surprised that the error I had was slightly to the west when I thought I was slightly east biased. It was a two second job to find the Polaris Star *providing no clouds* and lining up two sticks with it gives u a perfect true North South bearing. Try it I was impressed

System2

Re: True south

The stick method sounds good but I use a 4 foot piece of ABS pipe. I set one end on the ground and point the other end at the sun. When the disk of sunlight showing on the ground is as full as possible I have both azimuth and angle for that time of day. I shot mine on the 21st of December at noon. Keep It Simple Smarty.

I live in South Kona, Hawaii and because of the usually bright mornings and often cloudy afternoons many installers orient an hour to the East for a greater total return.

LowGear

niel

Re: True south

welcome and yes, it is simple, but people sometimes make it more complicated than it is.

weather does factor into things and if at certain times it is better than at other times then there certainly isn't anything wrong with compensating for it.

solarvic

Re: True south

You have to find true south to get a movable satelite dish set to follow the CLARK BELT also. I heard on tv that the MAGNETIC NORTH is changing. Some airports have to change the Degree signs so the pilots don,t get confused. Not sure but I think you can get the true north compass reading from your local airport.
:Dsolarvic:D

icarus

Re: True south

The north magnetic pole (and the south for that matter) are always moving, and indeed they will reverse polarity at some point in the near (geological) future. The last time they reversed was ~ 780,000 years ago. It will be curios to see what will happen to electricity and electronics during the transition.

http://en.wikipedia.org/wiki/Geomagnetic_reversal

stephendv

Re: True south

Google maps/google earth shows true south quite easily.

niel

Re: True south

stephendv wrote: »

Google maps/google earth shows true south quite easily.

yes, they do, but the problem would be to accurately translate that to which way the pvs face as you are not seeing lines when you look out over the landscape unless the landscape was surveyed or you make the determination of these lines by following what has been said. one does not mount their pvs on a map or it would be a cakewalk.

stephendv

Re: True south

Maybe that's a problem in barren landscapes, but I would think that in most typical environments there would be some landmarks, trees, bushes, buildings that you can see both from google earth and from the position of the panels.
Even if they're not directly south, you could use the distance tool in google earth to determine how far east of west you need to go to find true south, then plant a pole in the ground and aim at it from the PV position.

CaptTurbo

Re: True south

30 some years ago when I was in Sea School preparing for my Ocean Operator's exam I was taught about magnetic variation. That was back before GPS was an option so we had to navigate the honest way. The magnetic variation for my area (SW Florida) is slight so it was simple to calibrate the compass to negate it.

Not saying that all the ideas posted here aren't good ones but in truth you can find true South using a compensated compass. Then again any hand held GPS would work for the new kids that have never heard of a compass. LOL

bmet

Re: True south

Google Earth intentionally has a % of error, and barren landscapes aren't given the same resolution as a square block of Metropolis. I have a well-known landmark on my ranch, an abandoned oval track which has been in place 40 years. Google Earth shows a 1/8 mile difference from my off-roading GPS program. In fact, I used a Google Earth jpg of my property to import into map-maker, and needed to use a minimum of 6 points for scaling.

stephendv wrote: »

Maybe that's a problem in barren landscapes, but I would think that in most typical environments there would be some landmarks, trees, bushes, buildings that you can see both from google earth and from the position of the panels.
Even if they're not directly south, you could use the distance tool in google earth to determine how far east of west you need to go to find true south, then plant a pole in the ground and aim at it from the PV position.

solarix

Re: True south

Try a google earth view of your property. They are aligned true north. Or even better, many local counties have an online free GIS information system that can provide aerial photos of your property that is often very clear (I use to it to measure roofs) an is also lined up to true north.

russ

Re: True south

Google Earth is updated in the states I guess but here the picture is at least 6 years old.

I checked a site where I worked in India for many years and they have updated it once in the past 5 years.

ggunn

Re: True south

LowGear wrote: »

The stick method sounds good but I use a 4 foot piece of ABS pipe. I set one end on the ground and point the other end at the sun. When the disk of sunlight showing on the ground is as full as possible I have both azimuth and angle for that time of day. I shot mine on the 21st of December at noon. Keep It Simple Smarty.

That could be quite a bit off depending on where you are in your time zone and daylight savings time. The reading has to be taken at local solar noon which could be as much as 1 1/2 hours displaced from what your watch says.

BilljustBill

Re: True south

LowGear wrote: »

The stick method sounds good but I use a 4 foot piece of ABS pipe. I set one end on the ground and point the other end at the sun. When the disk of sunlight showing on the ground is as full as possible I have both azimuth and angle for that time of day. I shot mine on the 21st of December at noon. Keep It Simple Smarty.

I live in South Kona, Hawaii and because of the usually bright mornings and often cloudy afternoons many installers orient an hour to the East for a greater total return.

LowGear

LowGear,

With your post from Hawaii, I thought I'd get it "Straight from the horse's mouth", if I may...

1. I have heard that it costs about .40-.45 cents a KWH in the Islands. Is that about right these days?

2. From a metal detecting site, I read that if copper is sold as scrap anywhere in Hawaii, that you must have the original receipt showing the what items the scrap is coming from before a metal recycling business can buy the old copper?

Thanks for helping clarify,
Bill

Peter_V

Re: True south

Wow, it sounds like folks are over thinking this.

If you're off from true south by say 10 degrees, you'll only loss about 1% of your potential power. 10 degrees is a fair bit off.

However, if you're really picky about getting it right there are two easy ways to do this.
Find out the magnetic declination for your area and use a compass. Magnetic declination will tell you how far off from magnetic north is true north.
http://www.ngdc.noaa.gov/geomagmodels/Declination.jsp

Or you can use the pipe trick posted by lowgear, but instead of using 12 noon local time, look up "Solar Noon" for your area to find the time the Sun will be at it's zenith. Try one of these.
http://www.solar-noon.com/
http://www.srrb.noaa.gov/highlights/sunrise/sunrise.html

BB.

Re: True south

It is a "zombie thread"

Original question was asked about 3 1/2 years ago.

Of course we over think it.

-Bill

kadesmith

Re: True south

bmet wrote: »

Google Earth intentionally has a % of error, and barren landscapes aren't given the same resolution as a square block of Metropolis. I have a well-known landmark on my ranch, an abandoned oval track which has been in place 40 years. Google Earth shows a 1/8 mile difference from my off-roading GPS program. In fact, I used a Google Earth jpg of my property to import into map-maker, and needed to use a minimum of 6 points for scaling.

Google earth is probably more accurate than your offroading GPS even if the aerial photo is a 2 meter aerial. You're GPS is typically accurate to within 15 meters. I don't know where you got the idea that they put an intentional % of error in Google. It's kind of hard to put an intentional error in an aerial photo. However, there is an intentional % of error in your off-road GPS that the gov't puts in satellites and varies from time to time so that recreational GPS units cannot be used for much more than that, recreation.

kadesmith

Re: True south

solarix wrote: »

Try a google earth view of your property. They are aligned true north. Or even better, many local counties have an online free GIS information system that can provide aerial photos of your property that is often very clear (I use to it to measure roofs) an is also lined up to true north.

Depends on where you are within the aerial and how large of an area the aerial covers. If you are at the edge of the aerial and it is a large aerial, you're not going to be lined up to true north. Although for most people it's probably going to be closer than they can get, especially if they are like me and grew up in the digital age when a compass is a novelty item you only used in Scouts to get a merit badge.

Peter_V

Re: True south

kadesmith wrote: »

Google earth is probably more accurate than your offroading GPS even if the aerial photo is a 2 meter aerial. You're GPS is typically accurate to within 15 meters. I don't know where you got the idea that they put an intentional % of error in Google. It's kind of hard to put an intentional error in an aerial photo. However, there is an intentional % of error in your off-road GPS that the gov't puts in satellites and varies from time to time so that recreational GPS units cannot be used for much more than that, recreation.

Actually the government stopped adding the error signal years ago, there were several ways of getting around it so it wasn't really working anymore and no longer served any real purpose.

FWIW flat Maps and arial photos have an inherent error in them because they don't accurately portray a globe. Think about it, try to cover a ball with a piece of paper without getting any wrinkles in the paper.

The error gets worse as you approach the corners of a map or photo. I.e. if you make the position of the center of the photo accurate there will be a position error toward the corners.

Google maps is made of many small photos stitched together. When you are zoomed in the errors are too small to even measure, but when you are zoomed out they are small but measurable. However, they generally don't have much effect directly north or south of the center.

russ

Re: True south

Google Earth - the free version - is a toy and a publicity gimmick but not too much more. Accuracy would be somewhat incidental.

Maybe better in the US but I doubt it.

niel

Re: True south

russ wrote: »

Google Earth - the free version - is a toy and a publicity gimmick but not too much more. Accuracy would be somewhat incidental.

Maybe better in the US but I doubt it.

russ,
google earth has its uses and is better where higher resolution pics were taken. with the higher resolution one may roughly see landmarks to judge the general southerly direction, but this is in no way accurate by any stretch of the imagination as i'm sure you'll agree.

kadesmith,
all methods have a small amount of error to them, but transposing maps and google earth imo are too far gone to do for solar work. better ways are compensated compass readings and the solar noon shadow i mentioned.

peter v,
i liked you analogy of the paper around a ball. many do think that a straight line is what connects 2 points on a map and that is totally false as in reality it is an arc.

ggunn

Re: True south

russ wrote: »

Google Earth - the free version - is a toy and a publicity gimmick but not too much more. Accuracy would be somewhat incidental.

Maybe better in the US but I doubt it.

Google Earth can be quite useful as long as you don't expect too much out of it. Recently we did a preassessment of a potential rooftop system using Google Earth. We took measurements of roof dimensions and orientation from Google Earth to rough out the system. When we did the site visit, we found that the actual orientation was within 5 degrees of what we could measure on the computer screen, and the roof dimensions were correct to within a foot or two on a 150 X 60 foot roof. For a first approximation, that's not too bad.

jagec

Re: True south

Peter_V wrote: »

Actually the government stopped adding the error signal years ago, there were several ways of getting around it so it wasn't really working anymore and no longer served any real purpose.

I heard that part of the problem was that the military really didn't have enough military-grade receivers for their troops, and the civilian models had gotten so good that they decided to save the taxpayers some money and just let everyone enjoy high accuracy. May or may not be true.

Surveying GPS receivers on fixed stations can achieve accuracies within 5 millimeters (but not real-time). Considering that this implies one could measure the distance between two points on different sides of the earth within 10 millimeters, that just blows my mind.

niel

Re: True south

there's plenty of military receivers, but they are at a premium cost due not just to specs, but due to abuses seen while pressed into combat service. most commercial radios wouldn't last long under the same circumstances, but i can see the government or even the military itself stooping to cutting corners by going this route of commercial stuff.