Electricity, Solar

Chapter 6: Solar Panel Basics

Solar photovaltaic (PV) Panels, commonly known as Solar Panels, come in Poly-crystalline and Mono-crystalline. The two are immediately distinguishable by their appearance.

The main difference between the panels you’ll find, is the purity of the silicone in the panels wafers. Purity is important, because it is one of the largest variables in the panels efficiency. Lets take a look at some other differences:

Monocrystalline solar panels, also called single-crystalline cells are manufactured from the purest silicon. A crystal of this type of silicon is grown in a complex process to produce a long rod. The rod is then cut into wafers that will make the solar cells. Monocrystalline solar panels are known to deliver the highest efficiency in standard test conditions when compared to the other 2 types of solar cells. The current delivered monocrystalline solar panel efficiency stands at 22-27%. You can recognise a monocrystalline panel by the rounded edge and the dark colour.

Polycrystalline solar panels, also called multi crystalline cells are slightly less efficient than those made up of monocrystalline solar cells. This is due to the nature of production. The silicon is not grown as a single cell but as a block of crystals. These blocks are then cut into wafers to produce individual solar cells. The current delivered polycrystalline solar panel efficiency stands at 15-22%.You can recognize a polycrystalline solar panel by the square cut and blue speckled color.

Thin film solar panels are made by covering a substrate of glass, plastic or metal with one or more thin-layers of photovoltaic material. Thin film solar panels are usually flexible and low in weight. It is known that thin film solar panels degrade somewhat faster than mono and polycrystalline solar panels. Production of this kind of panels is less complex, thus their output is 5% less than monocrystalline solar panel efficiency. Normally, thin film cells deliver between 15-22% solar panel efficiency.

Reading Solar Panel Data Sheets

Physical, Electrical, and Thermal Specifications can be found in the manufacturer provided data sheet for whichever panels you choose.

Optimum Operating Voltage (Vmp) 18.9V
Most solar panel manufacturers will specify the panel voltage at maximum power (VMP). This voltage is typically around 70 – 80% of the panel’s open circuit voltage (VOC)

Optimum Operating Current (Imp) 5.29A

Open Circuit Voltage (Vcc) 22.5V

Short Circuit Current (Isc) 5.75A

Module Efficiency 15.47%
To determine solar panel efficiency, panels are tested at Standard Test Conditions (STC). STC specifies a temperature of 25°C and an irradiance of 1,000 W/m2. This is the equivalent of a sunny day with the incident light hitting a sun-facing 37°-tilted surface. Under these test conditions, a solar panel efficiency of 15% with a 1 m2 surface area would produce 150 Watts.

This Renogy 100w Solar Panel has a claimed efficiency of 15.47%. We can tell that the Renogy panel has an average panel efficiency. The current highest-efficiency monocrystalline solar panel stands at 22-27%.

Maximum System Voltage – 600VDC
This specification is used to determine the maximum size of your array, or the strings within your array. The Maximum System Voltage for the Renogy 100w Panels is 600VDC. The reason that solar panels have a maximum system voltage is because the blocking/bypass diodes on each panel can only work up to a certain voltage. Over that voltage you can “push past” them and damage a panel. Remember how voltage is like water pressure? Too much pressure and power could “leak” through a closed valve.

Maximum Series Fuse Rating 15A
This specification is used to determine the maximum size of your array, or the strings within your array. For the Renogy 100w Solar Panels, the max. fuse rating is 15 amps. Generally, the internal wires to the solar panel have a maximum current that can flow through them. The max fuse size it to make sure you never go above that.

Since these panels have a maximum Isc of only 5.75A, an individual panel should never be, on its own, the cause of an over-amperage situation. However, when wired in parallel, it seems that as few as 3 panels would be enough to over-amp the 15A fuse rating.
3 Panels in Parallel x 5.75A = 17.25A

When these panels are wired in series though, the amps don’t increase for each string.

Operating Module Temperature 

Nominal Operating Cell Temperature

Temperature Coefficient 
on the manufacturer’s data sheet for your solar panels. The temperature coefficient tells you, in a percentage per degree Celsius, how much power a solar panel will lose when the temperature increases by 1 degree over 25°C (77°F). Solar panels are generally tested at about 77°F and are rated to perform at peak efficiency between 59°F and 95°F. However, solar panels may get as hot as 149°F during the summer. When the surface temperature of your solar panels gets this high, solar panel efficiency can decline.

Temperature Coefficient of Voc 
-0.44% per °C

Temperature Coefficient of Isc
0.04% per °C

Full Datasheet for Renogy 100w Solar Panel

Next: Chapter 7: Sizing Your Solar Array

2 thoughts on “Chapter 6: Solar Panel Basics”

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