Photovoltaic cell and panel

Direct conversion of solar energy into electrical energy. The amazing invention known throughout the world, which we find on the roof of the most modern buildings of the world, even in remote indigenous village in the middle of the jungle. How to understand it?

What is photovoltaic cell

The solid state component, which is the impact of solar radiation on the surface of the cell changing part of the solar spectrum into electrical energy. It's about the direct conversion of solar energy into electrical energy. The entire ultraviolet spectrum, the entire visible spectrum and part of the ultraviolet solar spectrum is involved in the conversion into electrical energy. For detailed information I recommend to visit for example: the conversion of solar energy in electrical energy

The effectiveness of the first cell was 6%, and this efficiency increases from year to year up to the theoretical limit. slightly over 30 percent of today's single-layer articles already reach. The theoretical efficiency is 34%. The remaining energy from the Sun is largely converted into heat warming article. High temperature articles do not help. This applies to articles and panels with silicon basis. 

With the turn of the millennium, there was a lot of new experimental photovoltaic cells and other still counting. Once again embarking a journey from expensive laboratory prototype to practical applications. Slowly cheaper, or are dying for lack of interest, too costly production, the lack of primary raw materials... we Can read about perovskite cells, hybrid, plastic, bifaciálních...

Difference between cell and panel

Photovoltaic cell is a basic semiconductor device (photovoltaic diode) and connecting more cells into one circuit creates a photovoltaic panel.

More at the link: photovoltaics – what is a photovoltaic panel

I'd hate to have latched onto the list of possible technologies, therefore, to briefly focus on a group of easily available, cheap, and virtually applicable to cells and panels.

Monocrystalline, polycrystalline and amorphous panels

Into practice are the most worn over the three types of silicon panels. Their great advantage is the availability of the basic raw materials, historically handled production, low and constantly decreasing price.

Types of panels: from left to monocrystalline / polycrystalline / amorphous
panel type
drag the monocrystal silicon from the melt
pressing the crushed silicon
deposition of amorphous silicon on the board glass, plastic...
how to know
black, or blue continuous surface
blue with irregular patterns
black color
16 to 24%
13 to 18%
7 to 11%
working temperature
to 25°C, at higher temperatures decreases the efficiency of the
works better at higher temperatures
less sensitive to shade, high temperature resistant
ideal environment
for sunny and warmer areas
areas with large fluctuations in temperature, less sunny
the greatest efficiency = the most effective use of area
cheaper, works better at higher temperatures
the cheapest, flexible, lighter, works in shading, cloud, diffuse light
the decreasing effectiveness at temperatures above 25°C
they take up a larger area than monocrystalline for the same performance
at least the executive, shorter service life

The two most commonly used types are still monocrystalline and polycrystalline.

Today, the price of monocrystalline and polycrystalline are nearly equalled, if by converting the price for 1Wp. Polycrystalline take about 15 – 20% more surface area compared to mono-crystalline at the same power.

Therefore, in the present, it is recommended to choose the type of the panel in terms of the temperature conditions at the installation site. If I have a house in the mountains, in the Polabska plain, or on the hotter Moravia.

And according to the predominant period of the use of energy. For the predominantly winter operation, use monocrystalline (family house), for the summer operation of the I'm voting for polycrystalline (cabin?).

What is 1 Wp?

Watt-peak is given for each panel and if to speak about the installed performance such as 320Wp on one panel, it's this value. Watt-peak is literally the point of maximum power in ideal laboratory conditions. 

It is theoretically attainable value. The actual performance of that panel show, will be lower and over time will fall within the wear of the panel. 

How are we doing with the Sun in the CZECH republic

On the territory of the CZECH republic hits per 1 m2 of approximately 950 to 1340 kWh of solar energy per year, of which about 75 percent of the hits in the summer. These values mean, how much energy falls on 1 m2 of the earth's surface, not on the surface pro panel. 

the energy of the Sun falling per year on the territory of the CZECH republic

Table of the incident solar energy per day.

solar energy
8 kWh/ m2/ day
spring and autumn
5 kWh/ m2/ day
3 kWh/ m2/ day

How is it with the ideal placement of the panels?

The perfect tilt of the panels for the territory of the CZECH republic, therefore, for the 50° parallel of latitude north of the length is from 34° to 45°. While 34° apply for the summer months and 45°for the winter.

If there is a possibility to choose, it is used most often angle of 35°C. Panels must often respect the inclination of the substrate, the roof, the walls. How the performance changes well shown in the following chart and orientation in space.

A graph of the percentage of exposure depending on the angle of tilt of the panel and orientation in space. Valid for the CZECH republic.

If we have a good access to the panels, for example if they are accessible on the flat roof, or available on the property, it is often convenient during the year reconfigure the angle of the panels. It is possible to produce a structure with a variable angle of tilt relative to the Sun. 

Then, roughly, for summer operation, set at 35°, and for winter operation 45°. Alternatively, we can manually change the settings gradually during the year by the required angle.

the percentage of the presentation of the exposure areas on a simplified model of a house for the territory of the CZECH republic

Examples of performance areas:

  • horizontal surface 1045 kWh/m2 per year
  • slippery slope facing to the south of 40° 1203 kWh/m2 per year
  • perpendicular surface oriented to the south 900 kWh/m2 per year

(source: Renewable sources of energy, Diamonds, Adamovský, 1993)

Wandering in the Sun - trackers

The most ideal is definitely a stable vertical desktop settings panel to the current position of the Sun. That can be achieved by the so-called trackers, however, for larger surfaces of the panels of the price of acquisition of the tracker does not match the price of the electricity produced. For smaller areas of the panels is a fairly simple make your own tracker.

Instructables – how to make a tracker for photovoltaic panels (english)

The following link is an interactive Geographic information system for pv (English). After entering the localities orientation, inclination, performance and the type of the considered panels will tell you what will be the performance of the pv industry and what benefits it will bring. Furthermore, here you will find the typical development of the weather throughout the year in the locality: PHOTOVOLTAIC GEOGRAPHICAL INFORMATION SYSTEM (english) 

Cooling panel

The problem of the panels is the heating of the surface, which is not good for them. Therefore, the emerging ideas on the cooling surfaces of the cell. Witness, for example, water cooling circulating water, which forms on the surface of the photovoltaic panel water filter for part of the thermal energy from the desktop panel.


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