Knowledge Centre Archives - Green Frog Systems

Jul 23 2020

Battery Technology Explained

By Green Frog Systems Knowledge Centre

Lead Acid Batteries – AGM / VRLA

Lead acid batteries are a group of batteries that includes VRLA (Valve Regulated Lead Acid) and AGM (Absorbent Glass Matt).

The technology behind lead acid batteries was invented in the mid-1800’s and was the first rechargeable battery created that was suitable for commercial use. Today, it is still a popular choice for batteries due to its low cost and reliability, and is most commonly used in photovoltaic systems.

There are two key types of lead acid batteries, both identical in their internal chemistry. The most significant differences between the two types are the system level design considerations. The first type, flooded lead acid batteries, requires upright orientation to prevent electrolyte leakage, a ventilated environment to diffuse gases created during cycling, and routine maintenance of the electrolyte. The second type, known as a valve regulated lead acid (VRLA) battery, does not have the same requirements.

Both VRLA and flooded lead acid batteries have deep cycle and shallow cycle variations. Shallow cycle VRLA batteries are commonly used for automobiles, to deliver short, high energy pulses of power. Deep cycle batteries are best suited to stationary uses, as the batteries often discharge at a low rate over the course of multiple hours.

Lead Acid Batteries – Advantages

Lead acid batteries are a group of batteries that includes VRLA (Valve Regulated Lead Acid) and AGM (Absorbant Glass Matt) these battery types are often used in cars, boats and trucks.

When used correctly, lead acid batteries are long-lasting and reliable. They offer low self-discharge, among the lowest out of available rechargeable battery systems, but are capable of high discharge rates. The maintenance requirements for these batteries are low, with no memory or electrolyte to fill.

VRLA batteries specifically are affordable and simple to manufacture, offering the least expensive cost per watt hours. In addition to this, VRLA batteries are a mature, reliable and well understood technology.

Lead Acid Batteries – Disadvantages

Lead acid batteries cannot be stored in a discharged condition, and have a limited number of full discharge cycles. They are better suited for standby applications that only require occasional deep discharges. The poor weight-to-energy density limits lead acid battery use to stationary and wheeled applications.

There is a risk of thermal runaway occurring with improper charging, which causes the battery to rapidly generate heat internally and can eventually destroy the battery.

Lead acid batteries have a resource-intensive manufacturing process; requiring large amounts of raw material, which has a lasting effect on the environment during the mining process. The lead processing industry also generates large amounts of pollution.

Li-ion Batteries – Advantages

Lithium ion batteries are generally more reliable than other battery types such as nickel-cadmium and don’t suffer from the “memory effect” problem where batteries become harder to charge unless they are completely discharged first. Since lithium-ion batteries don’t contain cadmium (which is a a toxic, heavy metal), they are theoretically better for the environment and we are all for that! — It is worth mentioning that improper disposal of any batteries lithium or otherwise is destructive to the environment.

SEE : GREEN FROG SYSTEMS BATTERY RECYCLING SCHEME

Batteries contain metals, plastics, and a variety of other chemicals that should never find their way into landfills. Compared to lead-acid batteries and VRLA batteries used in some of our solar street lighting products, lithium-ion batteries are relatively lightweight for the amount of energy they can store making them a serious advantage for portable devices and other applications that need to remain mobile such as electric cars.

Li-ion Batteries – Disadvantages

Lithium-ion batteries biggest issue is safety: Li-ion batteries will catch fire if they’re overcharged or if they short circuit or malfunction in any way the batteries heat up in what’s called thermal runaway, which can lead to fire or explosion. This problem is mitigated through the use of a current interrupt device or CID, which kills the charging current when the voltage reaches a maximum, if the batteries get too hot, or their internal pressure rises too high. This technology is managed through Green Frog Systems’ MPPT solar charge controllers that regulate the flow of current into the battery throughout the charging cycle including active over-discharge and short circuit protection.

Lithium Iron Phosphate (LiFePO4) – Advantages

The key benefit of Lithium Iron Phosphate (LiFePO4) battery technology is that it has a high current rating and long cycle life, increasing thermal stability and enhanced tolerance if anything goes wrong. The overall safety of this battery type allows for batteries to handle full charge conditions when kept at high voltage for a prolonged time.

Ultra Safe LFP’s high thermal runaway temperature and optimum energy density make them the safest and most popular lithium-Ion battery system. Green Frog Systems integrated BMS removes the possibility of incorrect connection or installation that can be associated with independent BMS systems. Finally, lithium iron phosphate produces no explosive gasses during charge or discharge, unlike lead-acid systems.

Fast Charging Compared to AGM and lead-acid batteries, lithium-ion batteries not only charge faster with a full recharge typically taking just 2.5 hours in a 100Ah battery at the optimum rate of charge.

Highly Efficient When it comes to the efficiency of lead batteries versus lithium iron, the choice is clear. Lead acid batteries typically store around 70-80% of the energy provided in a whole charge cycle. However, when operating in the top 20% state of charge and in hotter climates, this can drop to below 60% of the charge energy provided being stored during the absorption phase. This leads to slow charge cycles and wasted solar energy. On the other hand, lithium iron phosphate batteries store more than 95-97% of charge energy supplied and have no absorption phase leading to ultra-efficient use of the available energy and faster recharge times.

Longer Lifespan Lithium Iron Phosphate batteries last up to 15 times longer than budget flooded lead-acid batteries. With a 50% depth of discharge, more than 6000 cycles can be achieved. For most people, the investment in lithium will save time and money in the long run, delaying the need for a battery replacement in their solar lighting assets.

Lightweight They are up to 60% lighter than equivalent lead-acid batteries, making them a lightweight option. Their ultra-compact size allows you to increase capacity and maximise space. Bulky batteries can, therefore, be a thing of the past! This is vital in modern, sleeker designed solar lighting systems with in-pole battery storage such as the GFS-ASPIRE solar light range.

DID YOU KNOW ? : A 300Ah Lithium battery weighs about 27kg, but provides the SAME USABLE ENERGY as a 480Ah flooded lead-acid system that would weigh around 120kg!

Environmental Impact and Sustainability

We can all do our bit to reduce our carbon footprint and dispose of waste in the safest way possible. Another positive characteristic of LiFePO4 batteries is that they contains non-toxic and biodegradable materials. Additionally Iron and phosphate do not produce toxic gases when operating and do not contain any heavy metal materials that can contaminate if they come into contact with nature upon disposal.

Lithium Iron Phosphate (LiFePO4) – Disadvantages

Similar to most batteries, cold temperature reduces the performance of Lithium Iron Phosphate (LiFePO4) batteries and high temperature shortens the service life. LiFePO4 has a higher self-discharge than other Li-ion batteries, which can cause cell balancing issues as they age.

This is only avoided by using high quality cells and sophisticated battery management control systems. All our LiFePO4 batteries come with a battery management system (BMS) to protect the battery. These battery management circuits ensure the longest possible lifespan from this battery type with more recent product releases such as the DEFENDER-55 solar light making use of passive cell balancing technology to further extend battery life and reliability.

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Jul 15 2020

Solar Panels Explained

By Green Frog Systems Knowledge Centre

How Do Solar Panels Work?

Solar panels work by harnessing the natural power of the sun; allowing photons (or particles of light) to knock electrons free from atoms which generates electricity. Solar panels are made up of photovoltaic or solar cells that convert sunlight into a direct electrical current which can then be used to power electronic systems.

Photo-voltaic cells are created by using two pieces of semiconducting materials such as silicon, one piece of which is given a positive electrical charge and other, a negative charge, which then creates an electric field. Excess electricity generated during periods of sunlight can then be channeled to a battery storage system, and retained for use at night.

For the photo-voltaic cells to function, they need to create an electric field. This is similar to creating a magnetic field, where polar opposites create a reaction. Opposite charges need to be separated in order to make an electric field between the two slices of silicon. To do this, one half of the materials has to have a positive electrical charge and the other negative to conduct electricity.

To explain the concept further, manufacturers of solar panels will add phosphorus to the silicon on top of the cell. This gives the top layer a negative charge caused by having extra electrons.

Then bottom layer then has boron added, giving it a positive charge and fewer electrons. When the two layers are together and a photon from the sunlight hits an electron, the energy between the two layers forces the electron out of the photovoltaic cell.

Once the charged electrons are forced out of the cell, they are transferred along a set of wires after being collected by the bordering metal conductive plates. At the end of the process you have electrons that resemble regular electricity and can be used to power any number of devices and electronic items including lighting systems.

Monocrystalline vs. Polycrystalline vs. Thin-Film Solar Panels

Solar panels are made up of photovoltaic or solar cells that convert sunlight into a direct electrical current which can then be used to power electronic systems.

Solar cells are created by using two pieces of semiconducting materials such as silicon, which is then shaped into evenly sized cells.

Solar cells can either be monocrystalline, where the solar cell is made from a single crystal of silicon, or polycrystalline, where solar cells are made from multiple different silicon fragments melted together. Below we explain in detail the difference between these two types of solar panels, as well as the benefits and drawbacks to both.

Monocrystalline Solar Panels

Monocrystalline solar panel cells are made from a single crystalline silicon ingot, which is essentially a bar of silicon in its raw form. These cells are slightly more efficient compared to polycrystalline panels due to cells being made from a purer silicone source.

They also perform better in high heat and lower light environments, which means they will produce closer to their rated output in less than ideal conditions. However, they are more expensive to produce, and that cost is reflected in the retail price.

The manufacturing process for mono panels also results in more silicon waste than poly panels. Mono panels are cut from square silicon wafers with the corners shaved off, which creates a white rhombus shape between all-black cells.

Polycrystalline Solar Panels

Polycrystalline solar cells are created by blending multiple pieces of silicon together.

They are molded into shape and treated to create the solar cell. Very minimal amounts of raw materials are discarded in this process, making it more efficient to manufacture.

But when it comes to power capacity and performance, they are slightly less efficient at generating electricity. This is due to the imperfections created in the surface of the solar cells, through blending different bits of silicon together.

However, the manufacturing process is cheaper compared to mono panels, which means they cost less to purchase retail.

The blended silicon is what creates the easily recognizable dark blue cell colour. Upon closer inspection, texture and colour imperfections in the cells are able to be seen.

Thin Film Solar Panels

Most solar panels that are manufactured and used today utilise either monocrystalline or polycrystalline solar cells. However, there is a third type of solar panelling, known as thin film panels. Due to the way the panels are created, it is a far less efficient but much more affordable option suited to large scale projects.

This type of solar panelling is rarely used in domestic installations, as residential roof space often has a small surface area. In this instance, mono or poly panels are the better option to maximise energy production with limited available space. In situations without any space restrictions, thin film solar panelling becomes a more cost-effective option to roll out on a larger scale.

Thin film panels are created by meshing a thin layer of silicon on to a backing plate made of glass or plastic, the latter creating flexible solar panels. This is ideal for mounting to a curved surface.

N-Type vs. P-Type Solar Cells

In order for a solar cell to function and generate an electrical current, two pieces of semiconducting materials such as silicon are needed. One piece is given a positive electrical charge and other, a negative charge, which then creates an electric field. There are two types of solar cells that utilise either a positive or negative charge, which are explained below.

What are P-Type Solar Cells?

P-type cells are usually made with a silicon wafer coated with boron. Since boron has one less electron than silicon, it produces a positively charged cell, which attracts negatively charged electrons to it.

P-type cells are cheaper to manufacture and as a result, more widely used for solar panels. The downside of this type of solar cell is that it is affected by light-induced degradation (LID), which causes an initial 2-4% drop in cell efficiencies.

What are N-Type Solar Cells?

N-type cells are coated with phosphorus, which has one more electron than silicon, making the cell negatively charged. The benefit of using this treatment is that N-type cells are not affected by light-induced degradation (LID).

As a result, these are considered a more premium option because they degrade less over the life of the panel.

An example of a Green Frog Systems solar light that utilises N-Type solar cells is the GFS-STEALTH solar light

Majority of Green Frog Systems solar lighting products use P-type sells, which degrade marginally faster than N-type cell technology, but can still perform well for over 30 years. Most customers prefer to compromise a small reduction in efficiency for a more affordable module.

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