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Solar Power Energy

Solar power energy refers to the way sunlight is converted into usable electricity, through photovoltaic systems or concentrated solar power equipments.

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Photovoltaic solar power energy

The term 'photovoltaics' refers to a method of producing direct electrical current from sun radiation, using some semiconductors that work based on the principle called photovoltaic effect.

This effect defines the creation of an electrical current inside a certain material that is exposed to any type of light. As a consequence of this exposure, electrons that are generated inside the material are transferred from their valence band to a conduction one, resulting in a voltage between the semiconductors electrodes.

Commonly, these photovoltaic cells are made of materials like silicon (mono-crystalline, poly-crystalline or amorphous), cadmium telluride or different combinations of cooper, indium, selenium, gallium and other similar elements that are able to capture and transform solar power energy.

Each solar cell is able to generate a specific amount of energy, usually around 2 or 3 watts of electricity, depending on its size. Typically, these photovoltaic cells vary from 10 x 10 mm to 100 x 100 mm, so they're quite small. This makes it clear that in order to obtain enough electricity for a building or appliance with this technology, more photovoltaic cells are needed.

When more solar cells are connected into a single structure, they form a photovoltaic module and two or more interconnected modules form an array. Usually these modules contain 25 to 40 cells therefore they produce 50 to 120 watts of electricity, while photovoltaic arrays may include as many modules as necessary for fulfilling the energetic requirements of a building.

So these solar panels are used for converting the light captured from sun into direct current (DC). But this form of electricity is rarely used by household appliances therefore another element needs to be added to the photovoltaic system, and that is the inverter.

A solar power energy inverter is a device that converts the direct current generated by the photovoltaic cells into alternating current, the form of electricity required by most electronic equipments and devices.

Now let's assume the solar power system would be made only of these two components - the panels and the inverter; it would be perfect for powering any device during daytime, of course, but what would happen with all the equipments run by this system during nighttime?

Well the answer is very clear: with no sunlight available, the photovoltaic system wouldn't be able to produce any more electricity and as a consequence, it would only be useful until dusk.

This is why producers involved in this field of technology came with the idea of including a rechargeable battery in these photovoltaic systems, a battery that would store a percent of the produced electricity for later use.

So the built-in batteries of solar power energy systems are able to store a limited amount of electricity. But limited doesn't necessary mean little! In fact, highly qualitative rechargeable solar batteries are able to store so much electricity that they can run electronic devices during nighttime for up to 8 hours.

In most photovoltaic equipments, these batteries have some charge controllers attached, in order to prevent overcharging and complete discharge. Although a little more expensive than regular ones, rechargeable batteries are more efficient and more recommended for solar powered systems.

Concentrated Solar Power Energy Systems

Just like photovoltaic devices, CSP (concentrating solar power) systems are used for generating electricity, only that the structure and working principle are different in this case.

A CSP system is made of some lenses or mirrors placed at a specific angle, in order to focus the captured sun rays into a smaller and more powerful beam. This beam is used as a regular solar heater, which runs a turbine or an engine.

This engine or turbine is the part of the system which actually generates solar power energy. However, the electricity obtained is not usually used in household appliances but delivered to the national grid.

CSP produce electricity, just like PV systems, from a renewable source of energy which is sunlight. Just like solar cells and panels, concentrating solar power systems are environmentally friendly and they produce no toxic liquids or gases.

The engines or turbines run by CSP systems may be considered a little noisy by some people, although they are generally pretty quite. But this is not the most important drawback of concentrating solar power energy devices.

As mentioned before, these equipments use some lenses or mirrors, which aren't able to actually store the energy they generate. With no batteries included, these systems are more or less useless during nighttime!

In order for CSP systems to work, it is critical for the sun to be present, so we can affirm that this type of equipment can only generate enough electricity during daytime. Now this doesn't mean they are totally inactive after dusk.

Some models of concentrating solar power devices have some oil or molten salts which are used for storing the heat produced by the system in the presence of sunlight. And yes, these materials are way cheaper than solar rechargeable batteries, but their storage capacity is also smaller.

The most common types of concentrating solar power energy systems are power towers, dish/engine devices and parabolic equipments. Although these are all CSP systems, their structure and functionality may vary a little.

The first ones use large mirrors named heliostats to concentrate the captured sunlight onto a receiver which is usually placed centrally, at the top of the power tower. Filled with a heat-transfer fluid, the receiver creates steam which runs a conventional generator that produces the needed electricity.

Dish/Engine power systems use parabolic reflectors to focus the sunrays onto a receiver which is placed, this time, into the so called 'focal point' of the system. Similar to the previously presented system, the receiver in this device is filled with gas or fluid, which is heated and used to run an engine.

Last, the parabolic concentrating solar power energy system uses reflectors shaped as parabolas and focus sunlight onto a tube which contains a heat-transfer fluid. And this is the part of the system which generates steam to power a conventional electricity generator.

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