Home page -> Renewable Energy basics -> Photoelectricity
pages in this folder
Photoelectricity Irradiation Photovoltaic effect Photovoltaic modules Photovoltaic cells PV Longevity & Degradation	Photovoltaic systems Solar Charge controller Orientation Tilt Angle Batteries Inverters

Эта страница на русском | Printable version

Photovoltaic panels

Solar panels consist of solar cells. As one single solar cell does not produce sufficient energy for most purposes, solar cells are put together in solar panels so that they produce more electricity jointly.

Solar panels (also called Photo Voltaic or PV modules) are produced in many types and sizes. The most common ones are 50 Wp (Watt peak, producing a maximum of 50 Watts of solar electricity in bright sunlight) and consist of Silicon solar cells. Such panels are about 0,5 m2. However, a wide range of smaller and larger panels is commercially available. Solar panels can be interconnected to generate more solar electricity (two interconnected 50 Wp solar panels equal one 100 Wp panel).

The efficiency of the solar panels that are commercially available varies from 5-15%. This means that 5-15% of the energy of all sunlight that reaches the cell will actually be transformed into electricity. Research laboratories all over the world are developing new materials with higher efficiencies (up to 30%). Production costs are evenly important. Some new technologies (such as thin film) allow labour extensive large scale production which would decrease the cost significantly.

Solar panels mounted on a tilted roof.	Multicrystalline solar cell.

How long will PV last?

PV modules have been tested in controlled settings and in the field, with results showing module lifetimes in excess of 20 years. Other system components have varied lifetimes (batteries can last 2-15 years, and power electronics are the most sensitive components).

The Electric Characteristics of PV Modules: The Current-Voltage (I-V) Curve

Amperage & Voltage:

1. Solar panel current (amps) output increases nearly linearly with increases in light intensity.
2. Solar panel voltage, however, is not linear with light intensity. At 10% of full sun intensity, panel operating voltage is about 95% of its rated capacity. Example- if the panel has a Typical Power Voltage of 17.0V, at 10% lighting it will read about 16V.

Panel Specifications

Solar panels will have the following specifications:

• Typical Power – The average (advertised) wattage rating of the panel.
• Minimum Power – The minimum wattage allowed for the panels in that series.
• Nominal Battery Voltage – The nominal voltage of the battery & system the panel is designed to operate with – i.e. 12VDC, 24VDC, 36VDC, or 48VDC.
• Open Circuit Voltage – The full light voltage of the panel with no loads connected and no circuit between the positive and negative terminals.

Solar panels have a “maximum power point” (MPP). For all solar panels, this is the combination of voltage and amperage (current) that produce the maximum amount of power (watt).The MPP voltage is roughly 75% of the Open Circuit Voltage and is designated in the Photowatt Specifications as the Voltage at Typical Power. The Typical Power rating divided by the Voltage at Typical Power gives the Current at Typical Powerspecification. Hence, the panels have both a maximum wattage specification (Typical Power) and a maximum amperage specification (Current at Typical Power). Restricting the panel to a voltage lower than the Voltage at Typical Power results in a correspondingly lowered maximum amperage and less efficient panel operation.

The PV module can be operated at any combination of current and voltage found on its "I-V curve." But in reality it operates at only one combination at a given time. This favoured combination is chosen not by the modules, but rather by the electric characteristics of the circuit that is connected to the modules.

Important points that characterize a PV module.

The voltage that occurs when current is zero is known as the open-circuit voltage (V_oc). On the other hand, the current when the voltage is zero is referred to as the short-circuit current (I_sc). While current and voltage are at their highest under short-circuit and open-circuit conditions, respectively, the power at these points is zero. In practice, a system operates at a combination of current and voltage at which a reasonable amount of power is produced. The best point is the maximum power point (MPP). Corresponding voltage and current are called V_p (nominal voltage) and I_p (nominal current), respectively. This point of operation (MPP) is used to define the nominal rating and efficiency of a module.

Typical information found on a PV module label.

You should find all of these electric characteristics (V_oc, I_sc, MPP, V_p, I_p) on the label of a good-quality PV module (note that the V_p and I_p values are also called nominal or rated voltage and current). Do not expect to get the rated power from your installed system – it is impossible for a fixed system to operate at the highest power point at all times. Temperature variations alone will change the amount of power your system generates.

Information from http://www.mysolar.com and other sources were used, hardly edited by our engineers.

:: menu

:: Search

:: TEXT_ICQ

379315905

:: banners

Текущие посетители