How to Choose the Best Solar Batteries & Panels for your System

There are different types and brands of solar batteries and panels in the market. Some brands are of better quality and more efficient than others. Also, some types of batteries last longer and can withstand heavy duty and deep cycle. But there are some tips you need to know, which will help you choose the best solar batteries and solar panels, based on both quality and budget. All these tips are revealed in this article.

Differences between PV Cells, Modules, Panels, Arrays & Solar Generators

PV (Photovoltaic) cells, modules, panels and arrays are most times used interchangeably when discussing about solar systems. Although they are related, but they have some distinct features.

PV cells or solar cells are the building blocks of solar panels, made of semiconductor materials that convert energy from sunlight into direct current (DC) electricity. The output current or power of a PV cell depends on factors like its efficiency and surface area, which is proportional to the sunlight intensity incident on the surface of the cell. A typical silicon PV cell generates about 0.5 to 0.6 DC voltage (open circuit). But under peak sunlight condition a typical PV cell having a surface area of 160cm² can generate about 2 watts peak power.

PV modules consist of PV cells laminated with an environmentally protective seal.

When one or more PV modules are pre-wired and assembled into a field-installable unit, it is called a PV panel or solar panel.

A complete power-generating unit, consisting of any number of PV modules or panels is called a PV array.

A set of solar PV system components that can generate electricity from sunlight is called a solar generator.

Comparison: PV cell, module, panel, array and solar generator

Different Types of Solar Module Technology & Recommendations

For most residential solar installations, the two most commonly used solar module technologies are:

Mono-crystalline Silicon Cell Solar Modules
Poly-crystalline Silicon Cell Solar Modules

Some of the factors that determine the choice of solar module technology to use include: your budget, required PV array capacity, mounting methods, etc.

Mono-crystalline Silicon Cell Solar Module Technology

Mono-crystalline silicon cell wafers are cut from single-crystal ingots. Due to the beveled corners of these cells, they have an octal appearance. The mono-cell modules have a distinctive “white diamond on black” appearance once they are assembled into typical multi-cell configurations with a white back-sheets and aluminum frames.

Mono-cell solar panels have higher efficiency than poly-cell solar panels, even under low sun intensity. As a result, the mono-cell module types are more expensive.

The mono-cell module technology has other types like:

Mono-crystalline Cell, All-Black Modules: Here, a black back-sheet is used instead of a white one. This gives the module an “all-black appearance”. Note that at higher temperature, the all-black module type has a slightly lesser efficiency than the normal, mono-cell type that has a white back-sheet.

Mono-crystalline Cell, Bi-facial Modules: Here, a clear class back-sheet and a second layer of solar cells are used in manufacturing this type of solar module. Thus this special type of mono-cell module can capture solar energy from sunlight incident on both front and rear surfaces, unlike other types of solar modules that can only capture solar energy from sunlight incident on the front surface.

Bi-facial solar modules are usually used on outdoor shelters, such as pergolas or as railings in buildings, especially tall buildings.

Poly-crystalline Silicon Cell Solar Module Technology

Poly-crystalline silicon cell wafers are cut from multi-crystal ingots that are formed from molten silicon. This gives the cells a characteristic square-corners. Also, the poly-cell modules have a distinctive blue colour once they are assembled into a typical module with a white back-sheet and aluminum frames.

Poly-crystalline solar panels are generally less expensive than the mono-crystalline solar panels. But also note that the poly-cell type of solar panels are also less efficient than the mono-cell type.

Building Integrated Photovoltaic (BIPV) Products

BIPV solar cell technology is one of the latest and promising solar technologies where photovoltaic cells are integrated into conventional roofing materials. BIVP technology has been fully developed, therefore is available in few countries marketplace.

In summary, if you really want a solar system, with improved efficiency, especially during seasons of low sun intensity, then go for mono-cell solar panels. Poly-cell solar panels are only recommended to those who have very low budget.

Things to Consider when Choosing the Best Panels for your Solar System

First thing you should check is the efficiency of the panel, which is usually between 15% to 20%. Go for the panel brands that have higher efficiency. Generally, mono-crystalline solar panels usually have higher efficiency and better performance than poly-crystalline solar panels.
You might also consider the number of years of warranty for the panel. It should be between 20 to 25 years.
Also go for solar panels of higher ratings, say 300W and above, especially if your solar system require a high solar array rating.
You should also check how resistant the solar panels are to PID, especially if you are installing the panels for commercial use, and on roof tops. PID is a phenomenon whereby the solar panels installed on rooftops begin to degrade as a result of the movement of unwanted charge carriers, and also due to the high potential difference between the solar cells and the grounded aluminum frame. A good solar panel should exhibit less than 5% power degradation when tested at high temperature (say 85 degree C) and voltage (say 1000V).
Also consider the ease of maintenance of the solar panels, especially when the panels are to be mounted on rooftops. Make sure the panels have smooth surface and does not have spaces around the edges, to avoid the accumulation of dirt. You can also reduce the rate at which dirt accumulate on the panel edges by mounting the solar panels at a moderate tilt angle, say between 15 to 25 degrees. This will ensure that the surface of the panels are automatically washed by rainfall.
The manufacturing country of the panel might also be considered. Most people say that the best solar panels are made in Germany, while the worst panels are made in China. There might be some atom of truth in this, but that does not imply that all German solar panel companies are better than all Chinese solar panel companies. For example, in 2013, some Chinese solar panel companies like Sopray, Risen and ET are topped the list of the best solar panel companies. Also note that some solar panel companies are fully made in Germany, while some were only engineered in Germany before the company was bought by other countries like Korea and China. Some top solar panel companies include: SunPower, Sunrun, Tesla, LG, Panasonic, Vivint, Auxin Solar, Certainteed Solar, etc.
Finally, always check the solar panel name plate, where all the necessary specifications of the panel, such as temperature coefficient, power tolerance, maximum power, maximum and open circuit voltage, maximum and short circuit current, dimensions, etc. are stated.

Check:

Solar Batteries

Solar batteries serve as backup storage for solar systems, especially in times of inadequate sunlight or AC power from the grid or mains. There are special types of batteries made for solar systems. They come in different forms and designs, depending on use and manufacturer. Basically all solar batteries must be able to frequent charging, while delivering the required voltage or power needed by the loads connected to the solar system. A good solar battery does not fail within a short space of time, especially when properly used.

PV Storage batteries perform the following key functions:

It stores electrical energy in form of direct current (DC) produced by the PV array and the inverter charger (for self-use, grid-connected PV systems).
A PV storage battery also supplies energy to electrical loads connected to the PV system, when needed.
PV storage batteries also perform voltage and current stabilization functions by suppressing or smoothing out transients that may occur in PV systems.
Most electrical appliances draw surge or peak current immediately they are turned on. So the PV storage battery also supplies this surge current to the electrical load that needs it.

Why you should Not Use Car Batteries for your PV System

Most people ask, Can I use a car battery for my inverter system? Yes, you can. But it is not recommended for the following reasons:

Car batteries have very small capacity that is not suitable for continuous charging. So they won’t last long.
Although they are cheaper in price than PV solar batteries, but on the long run, you need to replace them with new set frequently (probably monthly or bi-monthly). So, using car batteries in solar PV systems is not cost-effective.
Car type batteries discharge too quickly. Also, they don’t have deep-cycle feature, which means that after they discharge to a certain level, they don’t work well again, no matter how well you try to recharge them.

Different Types of Solar Batteries & Recommendations

Deep cycle batteries are the recommended batteries for use in solar PV system. They fall into 2 major categories: wet or tubular (flooded or liquid vented) and sealed (valve-regulated) deep cycle batteries.

There are 4 main types of deep cycle batteries suitable for use in solar systems:

Flooded Type Deep Cycle PV Batteries

These batteries are good batteries, but they require periodic maintenance in which you need to refill them with distilled water (which evaporates during their charging process), through their vents. Flooded batteries last long and can serve as heavy-duty backup storage if well maintained. Also, tubular batteries need to be placed outside your room or in a well-ventilated area, as they emit gas, which can be dangerous if placed in a place with poor ventilation.

A popular type of flooded batteries is the Lead-Acid tubular battery. Here, the lead plates are submerged in its electrolyte (fluid type, usually sulphuric acid).

Flooded or tubular type deep cycle PV batteries

Gel Type Deep Cycle PV Batteries

Gel batteries don’t have vents and they don’t emit gas. They are one of the examples of sealed deep cycle batteries and are safe to use indoors. A special type of Silica gel is used to hold the electrolyte, making the electrolyte to be in a semi-solid state. Gel batteries also have freeze-resistance feature, making them a good option to use in excessively cold regions, though they perform best at constant temperature.

Generally, gel batteries are not the most recommended deep cycle batteries because they charge slowly and overcharging can easily damage them. But with a good charge controller and making sure they don’t discharge below 50%, gel batteries can last up to 5 years.

Absorbed Glass Mat (AGM) Type Deep Cycle PV Batteries

AGM batteries are another example of sealed PV batteries. They are seal-proof and don’t emit gases, which makes them the safest and easiest to maintain. The electrolyte solution is contained in a special fiberglass mat between the battery plates. The woven glass mat is placed in between the cell plates of this type of batteries helps them to retain charges for a longer period. Most solar users consider AGM batteries as the best type of solar PV batteries because of their ability to hold charges for a longer period and also the tendency to last longer if properly used. As a result, they are usually more expensive than the flooded and gel types. AGM batteries meet the industry standard, and are used in grid-tied PV systems, where batteries are kept at a full charge state. Also, they are used in hospitals, airplanes and remote communication centers.

Lithium-Ion Deep Cycle Batteries

They are one of the latest deep cycle battery technologies. This type of battery is made up a cathode (Lithium Iron Phosphate), anode (graphite carbon) and a special lithium salt solution as electrolyte. They are the most rugged of all deep cycle batteries because they can be used until they are completely discharged without causing any damage to the battery. Also, they recharge very fast, even faster than AGM batteries, and also have longer lifespan. They can also withstand any weather condition.

Lithium-ion batteries are leak-proof and therefore fall into the sealed battery category. The only drawback of this type of batteries is that they are very expensive, but they worth it. Lithium-ion batteries are also used in mobile phones, automobiles, golf carts, marine, etc.

Lithium-ion type deep cycle PV batteries

Things to Consider when Choosing a Solar Battery

Rated Storage Capacity

This is the amount of energy a battery can store, usually measured in Ampere-hours (Ah). The battery capacity tells you the amount of energy that a battery can supply when fully charged before discharging completely. For example, a 200Ah battery can supply 200A for 1 hour, or 100A for 2 hours.

Note that there are some factors that determine the actual storage capacity of a battery of a battery at any given time. Some of these factors are age of the battery and the rate at which power is drawn from it. The actual capacity of a battery reduces with age. Also, if high current is drawn from a battery of low rated capacity, the actual capacity of the battery will reduce. If you want to use more appliances simultaneously, then go for a higher capacity battery.

Volt Rating

Most solar PV batteries have 12V as their rated voltage or nominal voltage. If the battery will power heavy machines or appliances, then choose batteries with higher volt rating, or you combine them in a way that will yield a higher effective voltage.

Charge Time

Some battery types charge faster than others. For example, gel types allow small charging current, therefore will take more time to charge.

Depth of Discharge (DoD)

This tells you the discharge level a battery can withstand without affecting its performance (efficiency) when it is recharged. Although it is not advisable to allow your battery discharge below 50%, but always go for batteries whose depth of discharge is up to 80%.

Discharge Cycle

This talks about the number of times a battery can charge or discharge before its efficiency starts to reduce.

Tolerance

Go for batteries that can withstand high and low temperatures, shock and vibration. But it all depends on the battery mounting location.

Shelf Life and Self-Discharge

The shelf life of a battery is determined mainly by its cell chemicals, its idle time and storage temperature.

Self-discharge is as a result of the reactions that occur within the cell when left idle or uncharged. The rate of self-discharge depends on the temperature (weather), age and presence of impurities or dirt at both the terminals and the electrolyte.

Always go for batteries with very low self-discharge and high shelf life, say 10 years.

Height of Placement

Normally it is not advisable to place batteries at extreme heights like ward robes. But if you must place or install your batteries at extreme heights, then go for AGM or Gel batteries. Do not install tubular batteries at extreme heights.

Tips to Help your Solar PV Batteries Last Longer

If you want your deep cycle battery to last longer, then you must take note of these tips.

Most deep cycle batteries are rated 12V. This is just a nominal value or term used to distinguish some categories of batteries from the other. A fully-charged 12V battery, when allowed to rest for a few hours (or days), with no load connected to it, will balance out its charge and measure about 12.6 volts between its 2 terminals.

What this means is that when a 12V battery reads exactly 12V under the above conditions, then note that it is almost fully depleted. In fact, if a 12V battery reads about 12.0 to 12.1 between its terminals, it means only that only 20 to 25% of its useful energy is available. This simply implies that the battery has been overused or it has been deep-cycled, which reduces the efficiency of the battery. Note that a battery can only be deep-cycled for only a limited number of times, after which it becomes “dead”.

So, always ensure that your deep cycle solar batteries don’t regularly discharge below 50% on usage before you recharge it. Adhering to this will ensure that your deep cycle batteries serve you for years (up to 5 years), before their efficiency drop to a noticeable level.

For more detailed battery maintenance tips, check out this article on how to maintain batteries.

One of the best ways to avoid regular deep-cycling of your batteries is by ensuring that the total capacity of your batteries bank is high enough to power the connected loads for a long period of time, without much stress on the batteries. Another tip is to ensure that the total wattage of your solar panels is high enough (at least 200% of the total capacity in Ah of your batteries bank) to properly charge your battery banks. For example, to properly charge a battery bank of 400Ah as total capacity, you will need at least a solar array of at least 800W to 1000W total wattage.

If the total wattage of your solar panels of your solar panels is not high enough to properly charge your solar batteries, then make sure you use MMPT charge controller of adequate rating.

Some Recommended PV Deep Cycle Battery Brands

For Lithium-Ion Batteries: LifePo4, PowerPlus Energy, Blue Energy, Sterling, Mastervolt, Relion and Victron Smart.
For Tubular/Flooded Batteries: Trojan, Surrette, Deka, Luminous, Amaron and V-Guard.
For AGM Batteries: Sun Xtender, the Concorde, Renogy, Universal Power, Pure Energy and Lifeline.
For Gel Batteries: Forgo, Renogy, CsPower, Gem, Z-Power and Microtex.

See:

Conclusion

You have learnt the things to consider when choosing the best deep cycle batteries and panels for your solar PV system. In summary, if you want the best battery in terms of performance, then go for either Lithium-ion or AGM batteries. But if you have a tight budget, then you can go for either Gel or flooded batteries. If your home is located in remote area or the battery storage space will not suit regular battery maintenance service, then choose a sealed battery.

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