Monocrystalline solar panels and polycrystalline solar panels: it’s all about the cells

Both monocrystalline and polycrystalline solar panels serve the same function in the overall solar PV system: they capture energy from the sun and turn it into electricity. They are also both made from silicon, which is used for solar panels because it is an abundant, very durable element. Many solar panel manufacturers produce both monocrystalline and polycrystalline panels.

Both monocrystalline and polycrystalline solar panels can be good choices for your home, but there are key differences between the two types of technology that you should understand before making your final solar purchase decision. The main difference between the two technologies is the type of silicon solar cell they use: monocrystalline solar panels have solar cells made from a single crystal of silicon, while polycrystalline solar panels have solar cells made from many silicon fragments melted together.

Monocrystalline solar panels

Monocrystalline solar panels are generally thought of as a premium solar product. The main advantages of moncrystalline panels are higher efficiencies and sleeker aesthetics.

To make solar cells for monocrystalline solar panels, silicon is formed into bars and cut into wafers. These types of panels are called “monocrystalline” to indicate that the silicon used is single-crystal silicon. Because the cell is composed of a single crystal, the electrons that generate a flow of electricity have more room to move. As a result, monocrystalline panels are more efficient than their polycrystalline counterparts.

Polycrystalline solar panels

Polycrystalline solar panels generally have lower efficiencies than monocrystalline options, but their advantage is a lower price point. In addition, polycrystalline solar panels tend to have a blue hue instead of the black hue of monocrystalline panels.

Polycrystalline solar panels are also made from silicon. However, instead of using a single crystal of silicon, manufacturers melt many fragments of silicon together to form the wafers for the panel. Polycrystalline solar panels are also referred to as “multi-crystalline,” or many-crystal silicon. Because there are many crystals in each cell, there is less freedom for the electrons to move. As a result, polycrystalline solar panels have lower efficiency ratings than monocrystalline panels.

Ecco Solar Charge Controller

The technology for Ecco Solar Charge Controller has advanced dramatically over the past five years. The most exciting new technology, Pulse Width Modulation (PWM, has become very popular. The solar charge controller is needed in all solar power systems that charge batteries. The job of the solar charge controller is to regulate the power going from the solar panels to the batteries. More modern charge controllers use Pulse Width Modulation (PWM) to slowly lower the amount of power applied to the batteries as the batteries get closer and closer to fully charged.

A 12v battery charge controllers voltage from the solar panel to the charge controller is around 18v. Using an MPPT controller allows much higher voltages from the panels to the solar charge controller. The MPPT controller converts the excess voltage into additional amps. Higher voltage from the solar panels to the charge controller is reduced power loss.

The final function of modern solar charge controllers is preventing reverse-current flow. You’ve worked hard all day using solar power to charge the batteries; you don’t want to waste all that power!

Major functions of the Ecco Solar Charge Controller 50A 12/24 Volt Ecco solar controller

  • Ecco solar controller is for off-grid solar systems and control the charging and discharging of the battery.
  • Humanized LCD displaying and double button operation of man-machine interface.
  • High efficiency intelligent PWM 3 stage charging.
  • Reliable over voltage protection: short circuit protection, over load protection, overcharge protection, over-discharge protection.
  • Accurate temperature compensation, correcting the charging and discharging voltage automatically, improving the battery lifetime.
  • Roundly reverse connected protection.
  • Solar panels, battery, solar charge controller positive poles are all connected together, adopting negative MOSFET in series control circuit.
  • Size: 168 x 92 x 41.5 mm

Solar Inverters

All solar powered systems require a solar inverter to operate AC powered equipment and appliances. A solar inverter is a device that converts direct current (DC) generated by solar panels or other alternative sources, into alternating current (AC) for use in industrial, commercial and residential use. Remember too that you need to differentiate between pure and modified Sinewave Inverters – Anything that has a screen e.g. TV, PC etc. needs to be run on a pure Sinewave inverter; modified inverters are simply used for lights, kitchen appliances etc.


Types of solar inverters

There are two types of solar inverters: pure sine wave inverters and modified sine wave inverters.


Pure Sine Wave Inverters

Pure sine wave solar inverters provide a purer form of power than modified sine wave inverters. The power from a pure sine wave solar inverter is similar to that supplied by Eskom and enables devices such as microwave ovens, game consoles, fans, fluorescent lights and answering machines to run quietly without distortion or disturbance. Pure sine wave solar inverters also ensure that computers run smoothly and without overheating.

 

They are also safe and stable and operate in a number of unfavourable conditions, such as excessively high or low temperatures and over and under-voltage.


Modified Sine Wave Inverters

Modified sine wave solar inverters have higher efficiencies at lower cost per watt, but do not necessarily work for all applications. For instance, laser printers and certain types of fluorescent lights don’t function as well as they would with pure sine wave inverters, as do certain power tools and battery chargers for cordless power tools.

 

Modified sine wave solar inverters can also interfere with the proper functioning of televisions sets and digital clock radios, as well as important medical equipment. In addition, a modified sine wave solar inverter isn’t as robust as a pure sine wave solar inverter and so doesn’t guarantee uninterrupted power.

 

For the best performance across a wide range of applications and devices, pure sine wave solar inverters are best and teamed with quality solar panels from Sustainable.co.za will see you well on your way to sustainable living. View our product range of solar inverters or contact us if you have any queries or require more information about which solar inverter is best for you.

What Types of Batteries are Used in Solar Electric Systems?

A brief overview of the different types of batteries that may be used in solar electric and backup power systems.

LEAD ACID

The common automobile batteries in which the electrodes are grids of metallic lead-containing lead oxides that change in composition during charging and discharging. The electrolyte is diluted sulfuric acid.

The new AGM Battery technology has made a huge impact on lead-acid batteries, making it one of the best batteries to use in solar electric systems. Learn more about AGM batteries here

Industrial-type batteries can last as long as 20 years with moderate care, and even standard deep cycle batteries, such as the golf car type, should last 3-5 years. Intermediate batteries, such as the S460 and other batteries made by Surrette should last 7 to 12 years.

LITHIUM 

Lithium batteries have many advantages over traditional battery types. They have an extremely long cycle life and high discharge and recharge rates. Learn more about Lithium batteries here

NICAD (NICKEL CADMIUM)

Alkaline storage batteries in which the positive active material is nickel oxide and the negative contains cadmium.

Downsides:
  1. Very expensive
  2. Very expensive to dispose of – Cadmium is considered VERY hazardous.
  3. Low efficiency (65-80%)
  4. Non-standard voltage and charging curves may make it difficult to use some equipment, such as standard inverters and chargers.

My impression of traditional pocket plate NiCads–this is a turn of the century technology–is that they have many good points–low self-discharge, non-freezing, and so on–but their CYCLE LIFE IS NO BETTER THAN, IF AS GOOD AS properly chosen lead-acids. To put it another way, they have a long life in *chronological terms,* but not in *cycle* terms. This makes them good for emergency/standby systems, but not for systems with a daily cycle. Not recommended for most solar or backup power systems.

NIFE (NICKEL IRON)

Energy storage density = 55 watts per kilogram

Alkaline-type electric cells using potassium hydroxide as the electrolyte and anodes of steel wool substrate with active iron material and cathodes of nickel plated steel wool substrate with active nickel material. This is the original “Edison Cell”. Very long life.

…”Our experience with customers using alkaline batteries in stand-alone AE systems suggests that they may have as many drawbacks as advantages when compared to lead-acid type batteries. We suggest that potential alkaline users evaluate the economics and performance claims carefully to determine the suitability of any battery being considered…”

Christopher Freitas Xantrex

Downsides:
  1. Low efficiency – may be as low as 50%, typically 60-65%. Very high rate of self-discharge
  2. high gassing/water consumption
  3. high internal resistance means you can get large voltage drops across series cells.
  4. high specific weight/volume
  5. can reduce the overall efficiency of the solar system as much as 25%

This also means that the output voltage varies with load and charge much more than other batteries. If you are using an inverter, the inverter needs to be designed with these voltage swings in mind. You may not be able to use NiFe’s if your system depends on a stable voltage, for example, if you are running certain common DC appliances such as a refrigerator directly off the batteries. Also when using NiFe’s to power DC lighting, you will notice the light intensity fluctuates. One could always use a voltage regulator to feed those appliances that need it, but that would decrease the efficiency even more.

Currently, it appears that the only source for new NiFe batteries is from Hungary, and we have heard mixed reports on them. In short, we do not recommend them unless they are nearly free. The high losses in charging and discharging will add an extra 25-40% to the size of the solar panels you will need for the same energy usage.

In short, despite some hype about long life and thousands of cycles, we feel that overall these batteries are a very poor choice for all solar applications.

What DC Wire Sizes to use for your Solar PV System?

 

Choosing the right DC wire sizes in your Solar PV system is essential for both performance and safety reasons. The wires need to be correctly sized for the current and voltages used in your system. Before you install your system, make sure you are up to date with the South African National Standard (SANS) 10142, also known as the “Code of Practice for the Wiring of Premises”. Use SANS 10142-1 for cable sizing and derating factors.

The wires must meet the following characteristics:

 

 1. The voltage rating must be equal or greater than the voltage rating of the system;

2. The current carrying capacity must be equal to, or greater than, the current to be carried;

3. Must be able to withstand the environmental conditions;

4. Special attention to be paid to voltage drop.

 

It is important to use the correct wire size in a system. The correct cable can only be selected once you know the current in a system. Just like it is easier for water to flow through a thicker pipe, the thicker the wire is – the easier it will be for large electrical currents to flow through it. The same for shorter hoses and wires, they have a better flow than longer hoses and wires, with more resistance.

 

Generally, cable core thickness is indicated in mm2. This indicates the surface area of the cable core. Common wire sizes used for solar PV installations are: 2.5 – 4 – 6  – 10 – 16 – 25 –  35 – 50 mm2. Sometimes other sizing measurement units are used like AWG (American Wire gauge). The following categories of wires exist:

 

1. between batteries and to inverter, 50, 35 or 25 mm2

2. from solar panels to charge controller to batteries 10, 6 and 4 mm2

3. from the inverter to the grid, 4 and 2.5 mm2

 

For each category you will have to use the appropriate amperage, cable length, and accepted voltage (and power) loss. To find out the core diameter of a stranded core cable, look at the cable insulation. There will be markings on the cable that indicate cable core thickness. Be aware that some cables can have very thick insulation and they may appear thicker than they are.

In a solid cable you can calculate the surface area if you measure the diameter of the core, but in a stranded cable this method is not that precise. Please note, however, that solid core cables are not recommended for these connections.

If you know your system’s amperage and maximum voltage drop that you will accept, you can determine the most appropriate wire sizes. The below picture is an example of what cable size belongs to which current, providing that the cable distance is less than 5 meters.

If you cannot find a thick enough cable, double up. Use two cables per connection, rather than one very thick one. But if you do, always make sure that the combined surface area of both cables is equal to the recommended surface area. For example, 2 x 35 mm2 cables equal one 70 mmcable. Larger Victron inverter/chargers are equipped with 2 positive and 2 negative battery connections especially for this purpose.

 

Voltage and wire sizes

In order to avoid very thick cables, the first thing you should consider is to increase the system voltage.
A system with a large inverter will cause large DC currents. If the DC system voltage is increased, the DC current will drop, and the cables can be thinner.

 

Increase in voltage – cable can be thinner

 

The preferred upper inverter power limits per system voltage are:

 

– 12 V: up to 3 kVA
– 24 V: up to 5 kVA
– 48 V: 5kVA and up

 

If you want to increase the system voltage, but there are DC loads or DC charge sources that only can deal with 12V, you could consider using DC/DC converters, rather than to choose a low voltage for the entire system.

 

Current ratings

Wire manufacturers publish tables of current ratings applicable to the size and type, so check these ratings before you use them. If the wires are undersized, there will be a significant voltage drop in the wires resulting in substantial power loss. Also, if the wires are undersized, there is a risk that the wires may heat up to the point in which a fire may result. Note that wires have different amperage ratings, based on whether they are e.g. positioned in air or in a duct.

 

How long?

Usually, the longest wire is from the solar panels to the charge controller. Since all PV power runs through this, it is crucial to choose the size correctly to maximize performance and to assure safety. In general, try to stay below 2 – 3% Voltage drop on this run.

 

The length of the solar wire is essential, use this as a very rough rule of thumb for cables up to 5 metres, and go up to the nearest available cable size:

 

Current / 3 = cable size in mm2

Close Menu