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fixed focus

 

Hello everyone interested in solar energy technology and clean energies

Welcome to fixedfocus, in this site will learn about new ways to access clean energy that I hope be taken into consideration.

For suggestions or criticisms can email me at the address  sand20251@gmail.com.

1. Modern solar water heater.

Along with solar concentrated invention in fixed focus, it can be said that a new development is provided for using "clean solar energy". The first type designed and provided by this system is new generation of solar water heater. In addition to low cost on manufacturing, it has special abilities compared to the other types in the market.  This water heater is formed by solar parabolic dish and a circular horizontal and a vertical rail and three DC motors with solar panel and solar tracker with fixed focus.

Some of its unique features are as follow:

  1. It can raise tank water temperature to boiling point even in winter; while no the other solar heater water can be such that;
  2. If its dish is bigger, it can be used as a tankless water heater; it looks like gas wall water heater without a tank;
  3.  This is a fixed focus water heater which could be changed into a desalination system and it can be used in some areas lacking drinking water;

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Typical Solar Water Heater

 

 

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Modern Solar Water heater

 

In order to analysis and get to know how modern solar water heater works with changeable dish, it is necessary to know about method of "solar concentrated invention in fixed focus". For this, we firstly consider the strategies in the world to concentrate the sun radiation in power stations.

In short, thermal solar power stations are divided as:

1. Concentrating Receiver Systems

2. Parabolic Trough

3. Parabolic dish

4. Solar chimney

5. Fresnel collector

 But only two methods, Concentrating Receiver System and parabolic Trough, have rather been successful and affordable.

It is significant to use solar power station for its affordable feature in basic investment and electricity production. Thus, it is uneconomical to apply some methods in producing and converting solar energy.

Now, the best thermal solar power station being economical rather than the others is such central receiver (solar tower). This station has a lot of big reflective mirrors called Heliostat always transferring sun radiation on a reservoir and on a small tower in power station as concentrated director in power station control center; because of many reflective mirrors so the temperature on reservoir turret is too high. Now, this fluid is getting hot by moving it from this turret.

Water, thermal oil, nitric salt can be passed over thermal tower; if we directly pass water over thermal tower, water should be changed into steam and steam turbine could be moved by the pressure and temperature of water steam. There are two basic problems about these stations:

1. Compared with other thermal solar power stations, they are complicated and made in more technologies; so, they are not installed easily in undeveloped countries in particular.

2. Since it is needed to change angle of incidence in long distance mirrors. So, this station can not develop excessive mirrors. Because the reflex of Heliostat mirrors in long distance with the least their vibration is practically ineffective and movement change of each one being far from thermal tower needs developed technology.

This is such a power station:

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Solar Tower

For more details and its application, you can see some books written about thermal solar power stations.

Another successful power station is Parabolic Trough. Parabolic Trough mirror rows are used here that they are less technical complicated than Concentrating Receiver Systems. But its productive capacity is less than for concentrating receiver systems.

Thermal solar power stations are a type of Parabolic Trough collector system including a set of long parallel and series rows that need to parabolic concentrators (solar farm); concentrator includes parabolic reflective levels made of mirrors or glasses. And receiver of this radiation includes penetrator tubes that pass over parabolic mirror focus covering with pyrexia and they are always put in the linear length of the focus. Tracker system in these systems are uniaxial and sun tracking from east to west is performed on circular uniaxial as the sun beams are concentrated on focal penetrator's tubes in whole time. A fluid transferring heat, specifically oil, is moving through focal tubes in 300-400º C and hot oil in thermal exchanger (boiler) converts water in steam and superheated steam with high pressure causes to circulate turbine and, ultimately, circulate generator and produce electricity.

Following picture shows solar farm of parabolic trough mirrors in the station:

تصاویر سایت: fix_4.jpg

Parabolic Trough

This power station has some its own specific faults such as:

1. since parabolic trough dishes move in a certain direction to follow sun in this station so, a significant loss is developed in angle of incidence .; and if these dishes move vertically and horizontally, angle of incidence loss will lead to zero.

2. Radiation intensity is as linear in parabolic trough system; that is, in order to reach appropriate heat and capacity, the surface of parabolic mirror should be wide leading to raise cost and weight of structure.

For more details, you can see some books written about parabolic trough power station.

Parabolic dish

This power station is less as well as no considered. It includes solar dishes that a specific system is inevitably used to produce electricity in their focus; one of them is application of sterling motor. This system has not been considered for its efficiency rather its high cost. In the following, you can see such a station:

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A schematic of a parabolic dish with sterling motor

It is clear that these dishes are not able to produce electricity because in order to use these dishes, we depend on applying a system that could be put in dish focus and it follows sun in vertical and horizontal axis with dish and produce electricity. In the most cases, sterling motor is used to do this. But there are two significant faults in sterling system:

  1. Low efficiency in sterling motor with generator in dish focus (maximum 29%)
  2. High cost in making and maintaining sterling motor

 

Also, there are other methods except of using sterling motor; for instance, applying Rankin & Brayton motors which causes to this Dish inefficiency. It should be noted that thermal concentration in this dish focus is so great; for example, we can easily reach to high temperature by a dish less than parabolic trough dish, and transferring solar radiation energy in such dishes on its focus is more than 98%. But there is no high temperature in parabolic trough dishes because the reflex is concentrated on longitudinal focuses; finally, it can be said that focal thermal degree of a parabolic dish is higher than parabolic trough dishes in its same level.

If we want to use these parabolic trough dishes, we can consider a trick as follow:

The problem could be solved if we circulate a fluid in dish focus. But it is not possible to do because dish moves horizontally and vertically to follow the sun and it makes trouble in fluid joints which are too hot. However, this has already been done in the Shenandoah, US, but has not been very successful.

Following figure shows this system with the connectors connected to focus. You can see equipment weight obviously; So that a 907-kilogram weight is used to balance it so it is not efficient and does not have enough productivity.

 تصاویر سایت: fix_6.jpg

Therefore, we should find better strategy.

The best way is a fixed focus dish and it does not move with dish. For this, we raise this problem.

Problem: you should design a system with a concave mirror that the focus of a point is fixed and the mirror is able to circulate in 360º and 90º horizontally and vertically, respectively.

This problem is solved by "solar concentrator with fixed focus" invention; therefore, parabolic dishes are appeared in solar power station field. The following figure shows a kind of dish with fixed focus:

تصاویر سایت: fix_7.jpg

Solar conductor with fixed focus

 

  • So, using these parabolic dishes is developing and parabolic dishes with fixed focus are a modern method in solar energy industry. The advantage for this system is considered as solving and removing whole problems of the dishes with movable focus. Some advantages of these fixed-focus dishes are as follow:

 

  1. Structure of the system loses its weight significantly; because it does not need to carry heavy focus.
  2. Thermal transfer fluid is easily able to move in fixed-focus tubes.
  3. Since its low weight, the dish moves horizontally and vertically with less energy.
  4. System is economical due to less equipment applied in the system.
  5. The system is much less complicated than the old ones.
  6. This system can be applied in a big power station (a wide solar farm) as unlimited.
  7. There are some problems in solar tower in terms of their need to change angle of incidence of long distance mirror. But it is not seen any problem in these dishes; therefore, there is no limitation to install them.
  8. It can be made a new generation of roof solar power system for their fixed focus. For instance, a solar dish with a 5-m2 surface of its mirror can approximately transfer 10-12 KWH energy to center in different parts of Iran. If we produce electricity with coefficient 40% of focus energy and produced steam by micro turbine, we can obtain electricity in 4-10KWh.
  9. Since this system has 98% energy reflected to focus, it could be developed modern solar water heater with its certain advantages and 90%.

10. By this system, it is possible to perform certain actions that they have not been able to do; Such as solar desalination, solar package, solar heater, modern solar cooker (with temperatures ranging from zero to 400 ° C) and we all thank to solar dish with fixed focus.

Now, it can be said that a method has been added to thermal solar power water method; that is fixed-focus parabolic dish.

Note: Because the focus length is low in this type of dish (1 - 3 m) so, focal concentration and radiation error are significantly decreased. Thus, heavy structure is not needed to fix the focus; it is only need to resist in front of the environment wind velocity and possibly heavy snowfall.

Here, it is practically described the function of modern solar water heater:

  1. Solar trackers turn on in sunrise, dish is put in radiation direction by circulating vertical and horizontal axis, and dish focus is getting hot fast.
  2. There is hot oil in metal tubes that they are directed into water reservoir by an oil pump; then, the oil heating water turns out to fixed focus again.
  3. Two solar panels are always directed in the sun radiation, they produce the electricity of DC motors, and they cause to charge the battery as well.
  4. If it was cloudy during system operation, its solar tracker turns off and it will be off till sunshine.
  5. When operating the machine, the temperature of tank water could be adjusted to a desired value.

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It is suggested to notice the following plan to learn more:

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It is hoped that each home uses a solar concentrator with fixed focus on the roof to supply its needed energy.

In future, it will be considered domestic electricity power plant using fixed focus.

I appreciate your attention; and please send me any suggestion or critic

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ism to me by  sand20251@gmail.com
Thanks
E.Hashemi