SOLAR ENERGY SYSTEM

Solar energy as renewable energy (RE)

Solar energy is renewable energy in which energy are generated from natural resources that can continually be replenished. It is clean, and it doesn’t contribute to global warming either through pollution or green gas omissions. Thus, it is environmental-safe. Not only that, RE gets significantly cheaper as time and technologies progress too.

Literally, solar energy is the radiation energy being produced by the sun.

Figure 1: Solar energy is the radiation energy from sun (Source: ZME Science)

Usage projection & current solar energy consumption

The International Energy Agency projected in 2014 that under its ‘high renewables’ scenario, by 2050, solar photovoltaic (PV) and concentrated solar power (CSP) would contribute to about 16% to 11% respectively of the worldwide electricity consumption. The following is the ranking of countries with their current solar energy consumption.

Ranking	Country	Installed PV [MW]
1	Germany	32,411
2	Italy	16,361
3	China	8,300
4	USA	7,777
5	Japan	6,914
6	Spain	5166
7	France	4,003
8	Belgium	2,650
9	Australia	2,650

Figure 2: Statistics shown by Renewable Energy Policy Network for 21st century (REN21) (Source: Renewables 2014 Global Status Report)

Advantages of solar energy

• Renewable energy source: Among all the benefits of solar panels, the most important thing is that solar energy is a truly renewable energy source.
• Reduce electricity bills: Since you will be meeting some of your energy needs with the electricity your solar system has generated, your energy bills will drop
• Low maintenance cost: Solar energy systems generally don’t require a lot of maintenance. You only need to keep them relatively clean, so cleaning them a couple of times per year will do the job
• Environment safety
•  No noise and no moving part

Figure 3: Green solar energy save electricity (Source: Pixabay)

Disadvantages of solar energy

•  Cost: The initial cost of purchasing a solar system is fairly high:
• Large area needed to gain more energy: The more electricity you want to produce, the more solar panels you will need because you want to collect as much sunlight as possible
• Solar energy storage is expensive: Solar energy has to be used right away, or it can be stored in large batteries. These batteries, used in off-the-grid solar systems, can be charged during the day so that the energy is used at night.
• Weather dependent: Although solar energy can still be collected during cloudy and rainy days, the efficiency of the solar system drops. Solar panels are dependent on sunlight to effectively gather solar energy

Figure 4: Initial cost of installation is rather high (Source: Vector Stock)

Solar energy can be used in two ways: -

A. Passive solar:

Passive solar energy is the direct use of the heat and light energy absorbed for heating, lighting, drying, ventilation purposes etc. It is used in both architectural and urban planning by applying the green house concept, but also used in agriculture and horticulture, where techniques such as timed planting cycles, tailored row orientation, staggered row heights, mixing of plant vegetation, fruit walls, ad drying chicken manure are used.

      1. Direct gain:

Figure 5: Indirect gain passive solar system (Source: Tech-addict)

The presence of large and south facing exterior windows allows the sunlight to enter the building. In order to absorb radiation, thermal mass is used. The overhang also perfectly protects the large panel of window from higher angle summer sun but give access to lower angle winter sun, allowing it to absorb more heat during winter season. The sunlight is absorbed by the concrete flooring in the morning and the heat is reradiated back to the living space at night, providing warmth and next cutting down expenses required for HVAC system.

2. Indirect gain:

Figure 6: Passive indirect solar system (Source: Reseach Gate)

Collect and stories the solar energy in one part of the house (thermal mass) and use natural heat transfer to distribute heat to the rest of the house. The thermal mass most commonly used is the Trombe Wall which is a massive masonry that acts as the solar collector.

3. Attached Sunspaces:

Figure 7: Attached sunspaces passive solar system (Source: premies.com)

Uses a combination of direct and indirect-Gain systems that use water arums and a masonry floor as heat storage in the attached greenhouse. This conservatory can’t be overpopulated with vegetation as the foliage might cover and shade the floor or wall as heat absorber and collector.

B. Active solar:

Active solar convert the power from the sun and amplifies it using some special equipment. The solar panel is basically made up of the low iron tempered glass covers with a dark metal plates to absorb heat at the bottom of it, and also an insulated aluminium large flat box. It can provide 50 – 80% of household hot water required on a daily basis. The technologies used in generating electricity from active solar system include photovoltaic method (PV) and concentrated solar power (CSP).

Figure 8: Active solar using solar panel (Source: MIT Intiative)

1. Photovoltaic Cell (PV)

When sunlight strikes the surface of solar panel, the photons from the light hits the electrons in the negative plate (N- type semiconductor), where the energy is transferred from photons from the electrons. The electrons then flow to the equipment, and the flow of these electrons create current. The semiconductors that are commonly used are phosphorus, boron and silicon.

Figure 9: Photovoltaic cell (Source: Alternative Energy Tutorials)

2. Concentrated Solar Power (CSP)

Lenses or mirrors plus tracking system is used to focus a large area of sunlight into a small beam of transmitting the energy to the applications. It is contrary to PV in which PV converts light directly into electricity, but CSP makes use of the radiation energy from sun to generate electricity from the conventional steam driven turbine system. Technologies in tracking and focus sunlight include parabolic trough, compact linear Fresnel reflectors, parabolic dish and solar power tower.

Parabolic Trough

It consists of aa linear parabolic trough that concentrates the sunlight into a receiver filled with working fluid which is located on the reflector’s focal line. The working fluid then will pass to various heat exchanger and enter condenser to be discharged to turn the turbines, generating electricity. This system provides the best land-use factor of any of the solar technology.  

Figure 10: Parabolic Troughs (Source: Cleanleap)

Compact Linear Fresnel Reflectors

It uses many linear thin mirror strips to concentrate the sunlight into two tubes (linear absorber) with working fluid. The working fluid then undergoes the same process as the one in parabolic trough. This system is relatively cheaper, and a larger amount of reflectors can be placed in the same area of space, indirectly minimising the space consumed.

Figure 11: Compact linear Fresnel reflectors (Source: Shaikh Mohasin)

Parabolic Dish

It combines a parabolic concentrating dish with a Stirling engine which normally drives an electric generator. Stirling solar is of higher efficiency in converting sunlight into electricity. And also, it has a longer lifetime.

Figure 12: Parabolic sterling dish (Source: Department of Energy)

Solar Power Tower

It comprises a central receiver and a field of heliostats where the array of tracking reflectors (heliostats) will focusing the light onto the central receiver with air. The air then enter an air circuit and electricity generating system consisting of several steam generators and thermal storage and turbines. This is the most cost- effective technology among all, yet it offers higher efficiency. Better energy storage capability is achieved by this solar power tower too.

Figure 13: Heliostats type (Source: Alibaba)

NOT ALL ENERGY IS CONVERTED

However, not all energy strike on the surface is converted. Only when the photons hit the electrons, and the energy of the photons equals to that of the electron, absorption occurs.

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