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Heliostats Can Direct or Focus Sunlight
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Heliostats and Solar Trackers Increase the Yield of You Solar Panels Up to 30%
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We also design custom made solar tracking and actuator systems.
A heliostat keeps the sun in one place (helios=sun, static=constant). If they are used for PV they are also called solar trackers. You can keep the heliostat at a constant orientation to the sun, or keep the reflectioon off the heliostat at a constant location. Heliostats are used both to optimize the yield of PV panels and to concentrate sunlight for lighting and thermal energy.
We have a number of them listed here
Learn more about light sensing here
Light up your home for free
If your house is North facing but there is room for a Heliostat you can get light and warmth inside and enjoy more daylight hours. Heliostats allow you to do is create light tunnels down from the roof into a building. They can reflect from the edge of the roof, down into the middle of a boulding block. You can also use glass fiber conduits and bring sunlight deep inside.
Harness the incredible power
A simpler calculation can be made as follows: Average insolation (clear sky) of one square meter is about 800 Watts. With mirrors of 90% reflectivity you have 720 Watts. Simply multipy this by the number of mirrors you have fixed in one spot say 6, then you create a spot recieving 4320 Watt. That is more than twice the power of the average residential heater (1500 Watt). If you circulate this heat into your existing central heating system you can heat your home even in winter.
Optimize your PV panel output
Using a DIY single axis solar tracker you can make your PV panel produce up to 20 % more electricity. This is a much better investment than more panels, and it can mean an upgrade of existing installations.
"Analysis of data and comparison to the performance of the tracking system to the stationary system is underway. A preliminary analysis showed that tracking could yield up to 67% higher output between spring and autumn, and could operate at higher efficiency. This implies that in order to produce a certain amount of electric energy, up to 40% less roof area would be needed for a tracking system (source)."
Cool your Office or Home with the sun
The heat you generate with a heliostat can be used to cool. There are several types of cooling that run on heat, most spectacularly is steam jet cooling. Simple absorption chillers have used heat (gas generated) as a power source for years.
Usher in the Solar Steam Era
Last but not least is pos system power generation. Steam generated can be used to drive a turbine or other type of steam driven device. The heat can be used directly with a Stirling engine. PV panels are 15% efficient while a steam turbine driven by solar thermal steam can reach an efficiency of 30%. Steam can also be used to drive engines directly.
Tracking the sun
There are two basic ways to track the sun:
1. You look for it
2. You calculate where it is
3. You use a clock
You can find plans and schematics om our solar tracking page
1. Looking for it
Sun tracking can use sets of leds or ldrs sensors or even a camera to cause a signal to the tracking motors and keep the relative brightness of two sensors equal. There are several designs of this using different types of microcontrollers and electronics. To get 2 axis tracking one can use two sets of diodes etc. More info on our solar tracking page
2. Knowing where it is
Because the mathematics of our planets movements relative to the sun are known we can calculate exacly ehre the sun is at a certain time, lattitude and longitude. This information can then be used by correctly calibrated (stepper) motors. Any system that can verify its orientation will do.
3. Using a Clock
As you know tha sun revolves around the earth in 24 hours each day. A mirror that turns at exactly the same speed (in the opposite direction) will always be aligned with the sun. This tipe of control is rarely used.
Moving the heliostat
Two Axis tracking
Regardless as to how you determine the orientation of the heliostat, you can use two motors to move it as necessary. This is the 2 axis type heliostat, with horizontal and azimutha (up and down) freedom of movement. You can use stepper motors, servo's and regular dc motors with appropriate control, or manual tracking.
One Axis tracking
You can simplify the design by making one axis align with the earth axis (at the angle of the latitude). This gives you a one degree of freedom movement that needs to be adjusted seasonaly (because the earth wobbles, so the tilt related to the lattitude changes slightly).
Target Aligned Tracking
Another way to look at targeting the mirror is by aligning one of the axis with the line of sight to the target. This has the advantage that one can orient the mirror so it can tilt in the same plane with the sun and the target. The mirror axle needs to turn with the time of day, the mirror tilt needs to be halfway the target angle and the sun.
Steam and other means
One can use other means then light and electricity to move the heliostat, f.i. steam, which can also drive gears and switches. Think about it..
Controling the heliostat
Based on these three approaches you can then have two tasks
1. To point at the sun
2. To point somewhere else
Pointing at the sun
If you point at the sun, or at a fixed angle away from the sun the motor control is easy. You probably have a light sensor that you give the desired orientation relative to the sun and of you go.
Pointing the reflection at a constant location
If you want to refelct sunlight to a specific place you will find you can not have a constant angle to the sun, because the solar incident angle's is doubled my the mirror. This means you have to either use a target sensor to make sure the heliostat is aligned, or use some calculation to determine the right angle.
Simplified for one axis in the above image light comes in at an incident angle of 0 degrees (relative to the normal). This means that angle b + angle a is 90 degrees. Because of the rules of mirrors the angles relative to the mirror normal are a and c, and the angle at which the light leaves the mirror is b+a+ 2 x c.
If the incident angle is positive (to the right of the 0 degrees incident line) the a will be a bit larger, therfore c a bit smaller, therefore b + a + 2 x c a bit smaller (the light reflects more towards the mirror normal).
If you are pointing the light at something this means for every positive X degrees of incident angle you need to tilt the mirror 1/2 X degrees to retain the same overal angle of reflection.
A real life model
Regardless of the position of the mirror along the horizontal the reflecting angle remains the same for all mirrors by moving them the same amount with the sun. This simplifies the control and is one of the reasons for horizontal fresnel mirror installations. These however have the drawback of losing reflectance due to considerable dust gathering.
An example of the solar trajectories in Holland. It is cilindrical with a maximum span of 260 degrees (right to left)
Opensun Project
Nice example
tracking
new type of heliostat PATH
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