Solar Installation
One of solar energy facts that the position of the sun in the sky changes from hour to hour, day to day, and year by year. While this might be interesting, it is not very helpful to prospective solar energy users— where exactly do we point our solar device?
How the position of the sun changes over the day
If you dig a stick into the ground, you will see that as the sun moves through the sky, so the shadow will change Figure below.In the morning the shadow will be long and thin; however, toward the middle of the day, the position of the shadow not only changes, but the shadow shortens. Then at the end of the day, the shadow again becomes long.
Of course, this effect is caused by the earth spinning on its axis, which causes the position of the sun in the sky to change relative to our position on the ground.
How the position of the sun changes over the year
The earth is slightly tilted on its axis; as the earth rotates about the sun on its 3651⁄4 -day cycle, different parts of the earth will be exposed to the sun for a longer or shorter period. This is why our days are short in the winter and long in the summer.
The seasons in the northern hemisphere will be exactly the opposite to that in the southern hemisphere at any one time.
We can see in Figure below that because of this tilt, at certain times of year, depending on your latitude you will receive more or less sunlight per day. Also if you look at your latitude relative to the sun, you can see that as the earth rotates your angle to the sun will be different at any given time of day, depending on the season.
We can see in Figure below an example house in the southern hemisphere we can see that the sun shines from the north rather than the south . . . obviously if your house is in the northern hemisphere, the sun will be in the south!
This graphically demonstrates how the sun’s path in the sky changes relative to your plot at different times of year, as well as illustrating how our rules for solar positioning are radically different depending on what hemisphere we are in.
What does this mean for us?
Essentially, it means that we need to change the position of our solar devices if we are to harness the most solar energy all year round.
Which direction should my solar device face?
Regardless of where you are on the planet and regardless of the time of year, the sun will of course always rise in the east and set in the west. Let’s say that you live in the northern hemisphere therefore, the sun is above the equator, your solar panels will work best if they are south facing. This is because they will be facing the sun all day long. North facing panels will be facing away from the sun and will be inefficient.
What is the best angle for my solar device?
Whilst everyone can easily agree upon the optimum direction for solar panels, the question of angle of tilt is less straightforward. On the equator it is simple – horizontal is best as the sun will be directly above. At the poles the sun will always be near to the horizon so vertical is best. At other latitudes, such as Egypt, the sun will appear at a different angle relative to the Earth at different times of year (i.e. it will be lower in the sky in winter and higher in summer). This means that if you point your device at where the sun will be at midday on the summer solstice (midsummer) then you may maximize summer efficiency but you’ll lose out in winter when your array will be pointing “over” the sun.
For the Northern hemisphere, your device should be facing as close to south as possible.
In the Southern hemisphere, you want to orientate your solar device to the North.
The best angle for your solar panels to be at is the angle of your latitude.
You can also set your solar device for optimum performance in summer and winter. In summertime, the solar panel should be at a lower angle. This is because the sun is higher over head.
In wintertime, the sun moves across the sky at a lower angle. So by angling your solar panels higher, you will catch more sun rays.
If you plan to adjust your solar array tilt angle seasonally, a good rule of thumb is:
Cairo Egypt : 30.04449
New York USA :40.7143528
London UK : 51.5112139
Keeping your solar panels out of the Shade
Shade is the thing that will have the biggest negative effect on the efficiency of solar device, and it can even cause damage. Before deciding how to position them therefore you should assess the area to see whether there are any surrounding structures or trees as well as moving throughout the day, shadows will be in different positions throughout the year due to changes in the angle of the sun, so if you are in doubt you may need to make an assessment over a six month period in order to see the full range of shadows. You’ll also need to check at different times of the day.
There are computer models available that will give a virtual picture, which would avoid the need to measure over an extended period.
Solar tracking devices
The best way to ensure that you get maximum efficiency from your solar panels is to use a solar tracking device. A dual axis system (one that tracks the sun across the sky and adjust the angle of the panels according to the height of the sun in the sky) could increase efficiency by 30% – 40%. Such systems are expensive however and it may be more cost effective to either purchase additional panels or simply accept the lesser efficiency of a fixed array.
As well as the initial expense, solar tracking devices tend to need more maintenance than fixed arrays because they have more moving parts.
As you saw making our world a big solar city isn’t very difficult; Just little knowledge, little experience and a lot of work then it could be done .
How the position of the sun changes over the day
If you dig a stick into the ground, you will see that as the sun moves through the sky, so the shadow will change Figure below.In the morning the shadow will be long and thin; however, toward the middle of the day, the position of the shadow not only changes, but the shadow shortens. Then at the end of the day, the shadow again becomes long.
Of course, this effect is caused by the earth spinning on its axis, which causes the position of the sun in the sky to change relative to our position on the ground.
How the position of the sun changes over the year
The earth is slightly tilted on its axis; as the earth rotates about the sun on its 3651⁄4 -day cycle, different parts of the earth will be exposed to the sun for a longer or shorter period. This is why our days are short in the winter and long in the summer.
The seasons in the northern hemisphere will be exactly the opposite to that in the southern hemisphere at any one time.
We can see in Figure below that because of this tilt, at certain times of year, depending on your latitude you will receive more or less sunlight per day. Also if you look at your latitude relative to the sun, you can see that as the earth rotates your angle to the sun will be different at any given time of day, depending on the season.
We can see in Figure below an example house in the southern hemisphere we can see that the sun shines from the north rather than the south . . . obviously if your house is in the northern hemisphere, the sun will be in the south!
This graphically demonstrates how the sun’s path in the sky changes relative to your plot at different times of year, as well as illustrating how our rules for solar positioning are radically different depending on what hemisphere we are in.
What does this mean for us? Essentially, it means that we need to change the position of our solar devices if we are to harness the most solar energy all year round.
Which direction should my solar device face?
Regardless of where you are on the planet and regardless of the time of year, the sun will of course always rise in the east and set in the west. Let’s say that you live in the northern hemisphere therefore, the sun is above the equator, your solar panels will work best if they are south facing. This is because they will be facing the sun all day long. North facing panels will be facing away from the sun and will be inefficient.
What is the best angle for my solar device?
Whilst everyone can easily agree upon the optimum direction for solar panels, the question of angle of tilt is less straightforward. On the equator it is simple – horizontal is best as the sun will be directly above. At the poles the sun will always be near to the horizon so vertical is best. At other latitudes, such as Egypt, the sun will appear at a different angle relative to the Earth at different times of year (i.e. it will be lower in the sky in winter and higher in summer). This means that if you point your device at where the sun will be at midday on the summer solstice (midsummer) then you may maximize summer efficiency but you’ll lose out in winter when your array will be pointing “over” the sun.
For the Northern hemisphere, your device should be facing as close to south as possible.
In the Southern hemisphere, you want to orientate your solar device to the North.
The best angle for your solar panels to be at is the angle of your latitude.
You can also set your solar device for optimum performance in summer and winter. In summertime, the solar panel should be at a lower angle. This is because the sun is higher over head.
In wintertime, the sun moves across the sky at a lower angle. So by angling your solar panels higher, you will catch more sun rays.
If you plan to adjust your solar array tilt angle seasonally, a good rule of thumb is:
- latitude minus 15° in the summer
- latitude in the spring/fall
- latitude plus 15° in the winter
Cairo Egypt : 30.04449
New York USA :40.7143528
London UK : 51.5112139
Keeping your solar panels out of the Shade
Shade is the thing that will have the biggest negative effect on the efficiency of solar device, and it can even cause damage. Before deciding how to position them therefore you should assess the area to see whether there are any surrounding structures or trees as well as moving throughout the day, shadows will be in different positions throughout the year due to changes in the angle of the sun, so if you are in doubt you may need to make an assessment over a six month period in order to see the full range of shadows. You’ll also need to check at different times of the day.
There are computer models available that will give a virtual picture, which would avoid the need to measure over an extended period.
Solar tracking devices
The best way to ensure that you get maximum efficiency from your solar panels is to use a solar tracking device. A dual axis system (one that tracks the sun across the sky and adjust the angle of the panels according to the height of the sun in the sky) could increase efficiency by 30% – 40%. Such systems are expensive however and it may be more cost effective to either purchase additional panels or simply accept the lesser efficiency of a fixed array.
As well as the initial expense, solar tracking devices tend to need more maintenance than fixed arrays because they have more moving parts.
As you saw making our world a big solar city isn’t very difficult; Just little knowledge, little experience and a lot of work then it could be done .
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