What is a Solar Furnace? How does it work?

A solar furnace is one of the extraordinary uses of solar energy that have emerged in recent years.   

It works on a simple principle of reflecting the sun’s rays and their concentration onto a point to raise its temperature, which belongs to the solar concentrator energy generation family. 

Utilising the solar furnace principle, many affordable products such as solar cookers, solar water pasteurisation, solar-powered barbecues, and even solar crematorium have been created. 

All the aforementioned products are strong contenders that can displace human dependence on non-renewable energy sources. 

Read on to discover how a solar furnace works, its price, advantages, and disadvantages.

How Does a Solar Furnace Work? 

A solar furnace employs an array of heliostats to reflect the sun’s rays and concentrate them onto a focal point of the parabolic mirror. The mirror, in turn, focuses the rays onto a furnace. 

This furnace reaches a very high temperature, typically more than 800 degrees Celsius.

Furnaces are of two types: direct and heliostat solar furnaces. The operation principle of both these types is quite simple. It employs two mirrors for heat collection and temperature rise. The two mirrors are as follows:

• Plane Mirror: It is also called heliostat. It is angled to direct parallel beams of light to the parabolic mirror. 
• Parabolic Mirror: It brings the light beam to focus on a single point.

Increasing the number of mirrors increases the temperature and makes it possible to generate a large amount of energy. 

The energy and heat levels obtained from solar furnaces can be used for a wide range of purposes like boiling water, cooking food, and even melting metals. 

The efficiency and amount of energy produced by these furnaces rely on the accuracy of mirrors to concentrate the rays, i.e., their ability to focus rays at a point.  

How Does a Solar Furnace Produce Electricity? 

A solar furnace is used to produce electricity. The process involves molten salt being pumped into the furnace to raise its temperature. 

• The hot molten salt gets delivered to a storage tank. 
• It leaves the storage tank, passing through a steam generator where it heats water until it turns to steam. 
• The generated steam moves to the steam turbine. 
• The cold molten salt is transferred back to the storage tank.
• Steam reaches the steam turbine and makes it rotate while passing through the blades. 

An alternator is usually connected to the steam turbine via a gearbox. A condenser then condenses the steam, and the generator generates electricity. It gets pumped back to the steam generator and converted back to steam.

The major components for power generation are as follows:

• Heliostats
• Parabolic Mirrors
• Tower
• Furnace
• Salt Storage Tanks
• Steam Turbine
• Tower
• Electrical Transformer
• Steam Generator
• Pumps

Solar Furnace Price

The costs are usually high, ranging from ₹10 lakhs to ₹15 lakhs. However, the investment cost is easily recovered within a year or slightly more than a year. 

Hybrid furnaces are used to manage the time when sunlight isn’t available. These furnaces are fitted with automatic gas burners. So, when solar energy is reduced, gas heating begins. A hybrid solar furnace can cost up to ₹5 lakhs.  

Uses of Solar Furnaces 

These furnaces concentrate the sun’s radiation at a focal point in such a way that the temperatures rise to 3600-4000 °C. 

Here are some examples of the use of different types of solar furnaces:

• Electricity generation: They can supply heat energy, and thermal power plants can transform that heat into electricity. These furnaces can also be used in combination with water turbines for electricity generation. Such power plants usually acquire temperatures between 300-1000 °C.
• Material heating: They are used to test the resistance of materials that will be used in extreme heat conditions.
• Engine heat source: It helps convert solar energy into mechanical energy.
• Food cooking: These furnaces can help replace conventional ovens on a smaller scale.

Certain other alternate uses of solar furnaces are:

• For creating hydrogen fuel from water
• To carry out research tasks that require high temperatures without causing pollution 
• For testing the age of plastic and paint 
• For agricultural purposes such as drying farm products or incubation of chicken 
• For Industrial purposes such as welding metal

Pros and Cons of Solar Furnace 

The primary advantages are as follows:

• Huge heat capability: These furnaces can produce very high temperatures ranging from 600-4000°C.
• Ease of use: Dependence on the sun, a renewable energy source, makes these furnaces readily available options. 
• Green energy source: Unlike fossil fuels that emit large amounts of poisonous gases and cause deforestation, solar furnaces cause minimal environmental damage. 

The cons are as follows:

• Dependence on sunshine: The reliance of solar furnaces on sunny weather is a limiting factor. However, their tie-up with the thermal energy storage system for energy production helps combat this limitation.
• High cost: Creating and installing these furnaces involves high costs. 
• Space constraint: These furnaces occupy a large amount of space.

Conclusion

Solar furnaces have existed for decades but need to be explored for widespread commercial purposes. 

They are promising options, and it is believed that they can be used in premium sectors such as aerospace, defence, and electronics. 

Researchers are working on exploring even more applications of solar furnaces that could help eliminate dependence on non-renewable energy sources like fossil fuels. 

FAQs

Q1. How hot can a solar furnace get?

It can concentrate solar radiation up to 10 kilowatts in a 10 cm diameter. It can attain temperatures of 1800°C, and with specialised secondary optics, the temperatures can rise to 3000°C.

Q2. Which mirror is used in a solar furnace?

These furnaces involve concave mirrors as they converge the parallel sun rays at a point. 

They capture all the incident solar radiation and reflect it to a single focal point. Thus, concentrating all the thermal energy obtained from a big area to a focal point. 

Q3. Which is the largest solar furnace in the world?

The largest solar furnace is situated at Odeillo in the Pyrénées-Orientales, France. It was established in 1970 and up to 63 heliostats were employed to gather the sun’s rays and reflect them onto a larger curved mirror.