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Solar Panel Specifications: The Basics

Solar power technologies are some of the greatest inventions. They can harness the power of the sun, which will remain in existence for as long as humankind does (provided we don’t discover a way to travel to another solar system).

One day, it may become our main source of energy. However, for now, solar power works best for an RV, Van, Cabin, tiny houses, or even full-sized homes.  

If you want to get off the grid with solar power, you need to know what solar panels are, the different features you need to consider, and how best to employ them.

Solar Panel Specifications and the Science Behind Solar Panels

What exactly are solar panels?

Solar panels are made of solar cells. Solar cells convert light energy from the sun into electricity through a mechanism known as the photovoltaic effect. The power can supply a small cabin, a big boat, or even a large house. Solar panels are even used to power factories.

But not all solar cells are created equal. The performance of the solar panels depends on the type of solar cells, in addition to wiring type and the space in which they are installed. Understanding the specifications of solar panels is essential to being an informed buyer.

Specifications of Solar Panels

Here are some of the basics of solar panels:

  • A solar cell is a silicon wafer. The typical size range is 125mm x 125mm or 156mm x 156mm.
  • A solar module typically has 60, 72, or 96 solar cells.
  • Solar cells can be monocrystalline or polycrystalline.

Monocrystalline vs. Polycrystalline

Both these types of solar panels meet residential requirements. 

Monocrystalline Solar Panels

Usually referred to as mono, these photovoltaic cells are a piece of silicon that is cut from a slab of ingot or an unbroken, single silicon crystal. They are considered the purest but are also more difficult to manufacture versus their polycrystalline counterparts.

They are also more efficient. In addition to saving energy, they have better heat endurance and superior performance in low light. These qualities make them ideal for hot, sunny deserts and cloudy, rainy climates alike.

Many people also like their black color, which is aesthetically pleasing. Monocrystalline solar panels have many pros, but there are also some cons. 

Check out this pros/cons list:

Pros

  • Very effective and efficient
  • Great performance in heat and low light
  • Uniform black appearance most people like

Cons

  • Expensive versus polycrystalline
  • Less variety versus polycrystalline

Polycrystalline Solar Panels

If you are on a tight budget, you might want to consider polycrystalline solar panels. Most often referred to as poly, these solar panels also feature silicon, but there are still major differences.

The photovoltaic cells for polycrystalline solar panels are manufactured silicon blocks made with tiny grains of silicon. Because of this, the poly cells have a flaky appearance and a blue tinge. 

They are also less efficient versus their monocrystalline counterparts, do not tolerate heat as well, and perform poorly in low light. But if you are willing to accept these tradeoffs, they are a whole lot less expensive. The lower cost is due to a less complex production process.

So what are the pros and cons of polycrystalline solar panels?

Check out this list:

Pros

  • Still efficient (though less than mono)
  • Broad selection (though less than mono)
  • Comparatively less expensive versus mono

Cons

  • Polycrystalline perform poorly under varied conditions, such as high temperatures and low light
  • Some people find the blue tint unappealing

Standard Test Conditions (STC)

Standard test conditions (STC) are a battery of tests used to rate solar panel performance under various conditions. Solar panels must meet the criteria of all the regular test conditions. 

Why are STCs applied?

To create a standard of comparison amongst all solar panels. All solar panels undergo these test conditions, which feature a mutually agreed upon scale. Based on these tests, the performance of solar panels are rated.

These standard test conditions include:

  • The solar temperature of cells of 25℃ (77℉)
  • The straight, incident light intensity =1000 watts per square meter
  • Air mass of 1.5

(The angle of the sun straight and vertical to the solar unit at about 500 ft. above the sea level)

However, these conditions do not accurately represent real world conditions. For that reason, normal operating cell temperature tests are employed.

Normal Operating Cell Temperature (NOCT)

Normal Operating Cell Temperature (NOCT) tests provide a further assessment of solar panels through more authentic physical conditions found in different Earth environments. We need to know how the solar cells react to different temperatures, and the NOCT tests provide this data.

Cell temperatures have a direct correlation to voltage.

NOCT practices the test settings as follows:

  • The light intensity = 800 watts per square meter
  • 20°C of current air temperature
  • Wind speed of 1m/s (meter per second) while the solar panel is mounted at an angle of 45°

Other tests:

  • PTC as PVUSA Test Calculation
  • CEC as in California Energy Commission Test Conditions

Rated Output Specifications

After solar panels are tested using the STC and NOTC methods, they are rated for performance. These ratings are found on the back of the solar panel or in the panel’s data sheet. 

The ratings show you the output specs of the solar panel. By comparing the ratings, we can decide which solar panel best fits our needs.

Here are the output specifications you need to know:

Open Circuit Voltage (OCV)

Open Circuit Voltage (OCV) rates the maximum level of power a module can produce when no connection exists between it and an electrical system or circuit. In other words, it shows the output of the solar panel when there is no load placed upon it.

OCV is measured with a voltmeter. The voltmeter is either placed directly on a module’s terminals or its disengaged cable.

OCV ratings are key because they show the optimum yield of a solar panel’s voltage under standard test conditions. This rating allows you to determine how many solar boards you need per charge controller or inverter. The higher the rating, the less you need and vice versa. Without accurate OCV ratings, you could not figure out how many solar panels you need to keep up with demand. 

Short Circuit Current (ISC)

Short Circuit Current (ISC) shows the amount of current (in amperes) the solar modules yield when they take no load. ISC readings are taken by applying an ammeter, which measures positive and negative leads.

ISC rates the highest current solar panels can yield under standard conditions.

Maximum Power Point Voltage (VMPP or VMP)

The Maximum Power Point Voltage (VMPP) rates the maximal voltage. Maximal voltage occurs when full power becomes available from the photovoltaic unit.

Most solar panel manufacturers specify the maximum power voltage (VMPP) of their panels. The voltage generally ranges from 70 – 80% of the panels’ open-circuit voltage (Voc).

Maximum Power Current (IMPP or IMP)

Maximum Power Current (IMPP) shows the maximum power point current. The value is shown in amperes when the power output is full.

IMPP is the output at the time of the solar panel’s connection to the solar gear under standard test conditions.

Maximum Power Point (PMAX)

The Maximum Power Point (PMAX) is the point where you get the highest and optimum value, as the volts and amps combine.

Nominal Voltage

Nominal voltage is the power or voltage of the battery that is most compatible with the unit, thus the best choice.

The term nominal voltage has gone out of style. It was primarily used when solar panels needed their batteries recharged.

Nowadays, nominal voltage helps explain that two different products with the same nominal voltage are compatible.

For example, you can use a 24V solar panel with a 24V charge controller, a 24V battery bank, and a 24V inverter.

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Final Thoughts

There are many things to learn about solar panels. By becoming educated, you can buy the right type of panels for your needs and use them efficiently.

With the current era’s energy prices and increasing utility bills, more and more people are forced to search for alternative energy sources. If you are one of those people, solar power may be the best option.

Now that you’ve gained knowledge of the basics of solar panel specifications, you are ready to make comparisons between the different options. The first consideration is monocrystalline or polycrystalline panels.

This depends on your needs. If you require heat tolerance or low light capabilities, the mono variety is your best option. Otherwise, you can save money with a poly panel, provided you are okay with the blue tint.

Beyond the choice between mono and poly, you need to compare the ratings of each panel option according to standard test conditions and electrical specifications.

You need to pick a panel that suits your power needs and is compatible with your equipment. With a bit of comparison shopping, you can select the ideal panel for your off-the-grid paradise.

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