The Ultimate Guide for Solar Energy Battery

The energy industry is one of the major contributors to global greenhouse gas emissions. Energy sources such as coal, oil, and natural gas, have their own fair share of negative environmental implications. According to the United States’ Environmental Protection Agency or EPA, the sector of electricity production is the second-largest contributor to greenhouse gases. Encompassing all aspects from generation to transmission, and the distribution of electricity, significant amounts of mostly Carbon Dioxide is unceasingly emitted day and night. As people nowadays become more self-aware of its detrimental impact, we had in such a way became more proactive as well in executing countermeasures to resolve the pressing issues of climate change. Driven by the urgency to decarbonize the energy system, alternative solutions such as the utilization of renewable resources instead of traditional fossil fuels in energy production are quickly turning into a viable option for companies and individual consumers to actively take part in. 

Renewable sources such as wind, solar, hydropower, and biomass are some of the most sustainable and cleanest means to generate electricity from. Considering its abundance, inexhaustibility, and affordability, its production causes far less harm to our environment thus making it a brilliant alternative to fossil fuels. Nevertheless, such resources are bound to be highly dependent on certain environmental conditions as well. Like for example, solar power can only be harnessed when the panels are exposed out in an open, unshaded and sunny location. Thus, it cannot be helped that there would really be circumstances when the supply of renewable energy becomes limited or, at times, unavailable. Here is where the vital role of battery storage comes into play. The information below will help you gain a deeper understanding of what battery storage is all about, how it works, and its specifications in order to help you make a better and wiser decision when buying.

What is solar battery storage?

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Today, the growing demand for cleaner and greener energy becomes more apparent. In fact, according to the industry research data of the Solar Energy Industries Association, it was evident that solar had garnered an average annual growth rate of 50% in the last decade in the U.S. alone. Along with this trend, the call for an efficient storage solution technology has also intensified in order to address the intermittent nature of solar power. Needless to say, the battery is an essential component of sustainability in the energy industry. It mainly serves as a temporary storage device to help extend the availability of generated renewable electricity until such time its usage is deemed required. 

How does solar battery work?

Technically, batteries are devices made up of a series of electrochemical cells that when comes into contact with an electrolyte solution creates a chemical reaction that produces a flow of current. So basically the electrochemical cells convert the chemical energy into an electric energy per se. Solar power systems today typically use rechargeable deep cycle batteries. This can be repeatedly discharged down to at least 50% to 80%.

On a bigger picture though, batteries simply work by storing the solar energy produced by the panels for later use. So when a battery is installed in addition to your solar panel system, this enables you to store the excess solar power into the batteries instead of sending it back to the grid. Nonetheless, if in case the total amount generated is greater than your actual energy needs, then the spare is used for charging the batteries itself. During nighttime or on days when sunlight is limited, or even during power outages, the energy you previously stored can be alternatively utilized to power your home. 

It is also possible for you to send off the oversupply of solar energy back to the grid and consequently earn extra credits. Nevertheless, it is only applicable once your battery becomes fully charged. On the other hand, you will only be drawing electricity from the grid to your home once the battery becomes depleted. 

What are the benefits of using battery storage?

benefits of using battery storage

Energy Availability

One of the major downsides of using renewable energy such as solar power is its intermittence which is beyond human’s control. Hence, the batteries offer solution to compensate on behalf of this mishap. It provides the user the energy it needs on certain times when sunlight is limited or unavailable, such as during the night time or in the event of a power outage.

Energy Security 

Having an efficient solar power system allows the users to become more resilient and less dependent on the grid. This is particularly helpful especially to those users residing in areas where the grid is occasionally unstable. Thus, power interruptions can oftentimes be experienced. The solar batteries, in return, will enable you to become more self-sufficient and be in control in terms of energy supply.

Carbon Footprint Reduction

Choosing to patronize renewable electricity is a conscious effort to help diminish carbon dioxide emissions in the industry of energy production. Solar power systems undeniably produce far less pollution than fossil fuels such as coal, oil, and natural gases. Furthermore, it also allows the users to consume fewer resources throughout the years with the risk of leaving an only minimal impact on the environment. 

Noiseless Solution 

Unlike the traditional generators that run fossil fuels, solar power systems and battery storage do not create any noise. Thus, it is highly advantageous to use especially in locations where a residential neighborhood is within close proximity. 

Reduced Electricity Cost

One of the most valuable perks of having a solar power system is the ability to cut down the cost on the electricity bills. Generating your own power, plus storing the excess load of energy in the battery allows you to become more self-sufficient and less dependent on the grid. Thus, minimizing the need to consume the power provided by electric utility companies. Moreover, you may also have the chance to earn extra credits by selling off your extra solar power back to the grid hence further lowering the total cost of your bill.

What you should look for in a solar battery?


This is defined as the total amount of electrical charge the solar battery is capable of storing. The more electrode material the cells in the battery contains, the greater the capacity will be. It is measured in either watt-hours (Wh), kilowatt-hours (kWh), or ampere-hours (Ah). Though the latter is the one most commonly used in the battery system. The Ah capacity represents the number of hours the battery is able to deliver a current equal to that of the discharge rate at a nominal voltage.

Depth of Discharge (DoD)

In general, the battery’s maximum amount of stored energy cannot be fully discharged. Otherwise, it may cause serious and irreparable damage to the unit itself. The Depth of Discharge, or in short, DoD, refers to the fraction of power than can be safely withdrawn from the battery. Take, for example, a 10 kWh-battery has a DoD of 80%. That means the user is allowed to discharge up to 8 kWh before recharging, and nothing more than that to prevent shortening its lifespan. The DoDs are specified by the manufacturers themselves.

Charging & Discharging Rates

The charging and discharging rates contribute a significant impact on the rated battery capacity. In principle, when the battery is discharged expeditiously at very high current, this results in the reduction in the potential amount of energy that can be extracted, and at the same time, it lowers the battery capacity too. That is mainly because the essential components were not given sufficient time to create an effective reaction. On the contrary, when the battery is discharged at a very slow rate in low current, it increases the total amount of energy can be feasibly drawn out and as well as enhances the battery capacity.


Batteries basically operate in a chemical process. Thus, environmental considerations such as the temperature present a relative effect on its overall performance and lifespan. Generally, solar batteries function best at room temperature, 68°F or 20°C to be precise. However, exposing the unit under extreme temperatures can be quite damaging. 

Cold temperature affects the battery in two ways. First, it increases the internal resistance with which the heat generation within the battery is altered during the charging process. Second, it lowers the battery capacity. As the coolness causes the chemical reaction within to slow down, the capacity to charge and discharge also becomes less efficient. At a temperature of 15°F or 8.3°C, the battery life in lead-acid batteries is typically reduced by half or more. Meanwhile, extreme cold weather conditions reaching as low as -4°F or -20°C, is enough to cease the battery from functioning.

On the other hand, exposing the unit to higher temperatures can in some way increase the battery capacity. However, it can also shorten its lifespan. At a temperature of 77°F or 25°C, the battery life of a lead-acid battery can be cut down by 50% or more. Continued use of the battery in high temps not only causes damage to the unit but also poses a potential fire hazard due to extreme heat.

Age & History of Battery

Despite following the DoD as specified by the manufacturer, the battery capacity will hold up equal to or as close as its rated capacity for a limited number of charge/discharge cycles only. The history also contributes a big impact on the lifespan of the battery. Exceeding beyond the suggested maximum DoD prematurely decreases the capacity and disrupts the rated number of charge/discharge cycles way below than what is originally expected.

What are the best batteries for solar?

  1. Lead Acid  

Batteries consisting of lead acids have long been a tested technology suitable for off-grid energy systems. Compared to other battery types, Lead Acid batteries are cheaper in cost. However, it is also known to have a shorter lifespan, lower depth of discharge or DoD, and may require periodic maintenance. 

Types of Lead Acid Battery

  1. Flooded Lead-Acid Battery (FLA)

It is also known as “wet cell” since the battery is mainly filled with an excessive volume of electrolyte fluid. The electrolyte fluid basically acts as a catalyst to enable the electrical conductivity of the battery. In this case, it is definitely essential to maintain the plate tops completely submerged at all times to prevent causing any damage. Moreover, FLA batteries have a tendency to decompose water from the electrolyte during periods of charging. Thus, regular maintenance and inspection are absolute requirements to ensure that there are sufficient levels of electrolyte and water in the unit.

CheapLonger deep-cycle life than VRLA batteriesHigh discharge rate capabilityTolerance to low temperature (>90°F)Can perform equalization chargesReadily available worldwidePeriodic maintenance is requiredRequires proper ventilationMust be in an upright position onlyCan emit acid spray if frequently overchargedProduces oxygen and hydrogen when charged thus likely causing corrosion of wiring and other parts
  1. Sealed Lead-Acid Battery (SLA)

This kind is also referred to as “Valve-Regulated Lead-Acid” or the “Maintenance-free” batteries. What it basically does is that it prevents the movement of electrolytes within the container unit thus trapping the hydrogen close to the plates to enable a more efficient recharging process. In this manner, the water loss during the discharge/recharge cycle is greatly reduced, hence, considered as “maintenance-free”. Primarily, VRLA batteries are further divided into two types:

B.1. Gel Cell 

As the name suggests, the electrolyte is transformed into a jelly-like mass. This happens when the sulfuric acid is mixed with fumed silica causing it to become immobile and more resistant to shock and vibrations. Furthermore, it minimizes the evaporation and spillage of electrolytes, and as well as the issue of corrosion, which happens to be the common problems encountered with FLA or wet cell batteries. However, because of its viscosity, the recombination of the gases while in a charging state transpires at a much slower rate. Hence, the charge rate is lower with Gel Cell as compared to an FLA or AGM batteries. If it is charged hastily, gas pockets may be inclined to form and prevents effective contact with the lead plates. Thus, reducing the capacity of the gel to recombine and then absorb renewable energy.

No maintenance requiredNo risk of acid sprayCan be easily transportedMore expensiveSlower charge rateStill emits gases though minimal

B.2. Absorbent Glass Mat (AGM)

In AGM batteries, the electrolytes are contained in a very thin boron silicate fiberglass mat to somehow act like a sponge holding the acid solution. This mat is suspended in close proximity with the lead plate to allow for effective contact. The manner it is constructed enhances the discharge/recharge efficiency of the battery by encouraging the recombination of hydrogen and oxygen gases. The plates in AGM batteries are very flexible thus it is highly suitable for it to be mounted in any position without the risk of leaking the electrolytes. In addition, it has a low internal electrical resistance and quicker acid reaction between the plates and the fiberglass mat. In effect, it is feasible for the batteries to accommodate both receiving and giving of electricity in higher amperage.

No maintenance requiredNo risk of acid sprayAllows flexible placementCan be easily transportedDoes not emit gasesMore expensiveSensitive to overchargingLimited amp hour (AH) capacity

II.  Lithium Ion Battery

Lithium Ion or Lithium Iron Phosphate, or shortened to as LiFePO4 or LFP batteries, are found by many as the most efficient type of battery storage. This new technology can often be found in the latest models of energy storage systems. Opposite to Lead-Acid batteries, LFPs costs more expensive. Although, given the efficiency it offers, it can conceivably make you spend less for every kilowatt-hour of its capacity throughout the years. Furthermore, it has a longer lifespan and higher charge/discharge rates, and requires minimal to no maintenance hence highly convenient to use for off-grid energy storage. 

III. Salt Water Battery

Practically a newbie in the market, the Salt Water batteries are said to be safe, non-toxic, and non-flammable. Unlike the two types of batteries discussed previously, Salt Water batteries do not contain hazardous heavy metals. Instead, it basically relies on a concentrated saline solution to act as its electrolyte. In addition, it is found to be more environmentally friendly as it can be easily recycled without the requirement of any special disposal procedure contrary to that of lead-acid and lithium ion battery types.

Battery Comparison Summary

BatteryCostLifespanDepth of Discharge
Lithium Ion★★★★★★★★
Salt Water★★★★★★★

What are the stages of battery charging?


By the word itself, Bulk charging covers the majority of the recharge process. On this initial stage, a current is delivered into the battery at a maximum safe rate it is capable to accept until such time the voltage is raised to as much as 80% to 90% charged level.


With a remaining charging level of approximately 20% or less, the voltage has already peaked and stabilized and the current starts to gradually decline as the internal resistance within begins to elevate. At this point, the charge controller cuts off the maximum voltage.


The third stage is also referred to as “Trickle Charging” or “Maintenance Charge” since essentially the function of this phase is to maintain the battery’s charge level at a more controlled manner. Through the process called Pulse Width Modulation (PWM), the charger delivers shots of electrical pulses or small, short charging cycles as soon as it detects a decline in the voltage. The float stage is attained when the battery charge level is at 100% already.


This fourth step is done only in a periodic basis, from once a month to once or twice a year. The equalization charge is the intentional overcharging of the battery by increasing the voltage at 2.50V/cell, or a 10% elevation from the recommended charge voltage. Doing such helps to prevent or remove the sulfation that builds up in the plates. Furthermore, equalization also reverses the occurrence of Acid Stratification, a condition wherein there is sulfuric acid accumulation especially at the bottom of the battery. Hence, unevenly increasing the electrolyte concentration at the bottom as compared to that of the upper half.

What is the life expectancy of a battery?

Batteries, such as Deep Cycle Batteries, used in renewable energy storage applications are designed to last between 5 to 15 years of efficient and dependable performance if duly given appropriate handling and maintenance. How you take care of your battery directly correlates to its actual longevity. Few among the many factors affecting the premature reduction in its lifespan include low electrolyte levels, over and undercharging, excessive vibration, exposure to extremely high and low temperatures, incorrect charging levels and settings, using tap water to replenish fluids, degradation or corrosion of internal components, and others.

How to properly care and maintain the batteries?

Batteries is an important element in achieving energy sustainability. Nevertheless, in order to ensure you’ll get the most out of your investment in the solar power system, both in the efficiency and financial aspect, proper handling and regular maintenance must be observed. According to reports, about 80% of battery failures are associated with Sulfonation. It is a process wherein crystals form on the lead plates thus hindering the chemical reaction to take place. This occurs because of two main reasons: low charge and electrolyte levels. To avoid experiencing such a problem, the following measures are best followed periodically:

Check the charge level

Some batteries nowadays come with a charge indicator, however, this only indicates that the battery voltage is relatively high but does not necessarily mean that the state of charge or SOC itself have reached 100% already. One definitive way to check the actual charge level of batteries especially in FLA type is through the use of a Hydrometer. This device fundamentally measures the specific gravity of the battery’s electrolyte to determine the SOC or the DOD. Use the table below as reference:

State of ChargeSpecific GravityVoltage
6 Volts12 Volts24 Volts

On the other hand, the definitive way to check the charge level for the Sealed Lead-Acid (SLA) batteries is through an Amp-Hour Meter. It is a solid-state measuring device hence more informative and user-friendly. It works by calculating the total amount of used electric charge by simply multiplying the flow rate of the electron against the amount of time it took the electrons to travel through the wires. 

Check the fluid level

This is particularly applicable in the case unsealed batteries, or better known as the Flooded Lead-Acid (FLA) or “wet cell” batteries. Given the circumstances of FLA batteries with which excessive amounts of electrolytes are required for it to essentially function, checking the fluid level regularly is a-must. To do this, you simply have to open the battery cap and take a peek inside. Additional fluids in the form of Distilled Water may be added right into the cells every 6 to 12 months. Most of the batteries come with a fluid level indicator to avoid overfilling and cause spillage of the electrolytes. Typically, the maximum level is approximately half an inch to a full inch below the cap.

Prevent Corrosion

This is one of the most common problems that need to be addressed the soonest possible, especially in the case of FLA battery installations, because once corrosion starts to set in it is already difficult to halt the progression. Notwithstanding, it is quite easy to prevent the issue way before it develops. All you need is to apply thin coats of non-hardening sealant to all the metal parts involved including the battery terminals, wire lugs, nuts, and bolts. There are a lot of special compounds available in the market today, though a good-old petroleum jelly or Vaseline would do just fine as well. Also, remember to apply the sealant before assembly to ensure thorough coverage and refrain from neglecting a spot. 

Temperature Regulation

We have already established how extreme temperatures affect the capacity and performance of the batteries. Hence, measures involving its storage must be well considered to protect the unit from deterioration or untoward damages. In cases where a thermally-stable structure is not accessible, then an earth-sheltered dwelling can be a possible alternative. Moreover, avoid locations with direct radiant heat sources in proximity as this may induce more warmth to other batteries.

Other than strategic placement, it is also well worth to acknowledge temperature compensation. In most types of battery chargers, the voltage setpoint is fixed at room temperature, 25°C or 77°F to be precise. Deviation from the said setpoint may cause the battery to overcharge if the temperature is too warm, or may become undercharged if the temperature is too low. Hence, charging the battery without proper adjustment of charge voltages to accommodate the thermal changes may adversely impact and shorten the lifespan of the unit. Some battery chargers come with a fixed temperature compensation voltage, like for example, -5mV/°C/cell. Meanwhile, other chargers have an adjustable setpoint which is more favorable since the recommended temperature compensation values of various battery manufacturers may differ from one another. 

Periodic full State of Charge (SOC)

Even though the battery naturally achieves a full state-of-charge during the course of a year, it is still advisable to run a full SOC at least once every 3 weeks. The main purpose of this is to prevent internal degradation and to help maintain equalization. Through this process, we can ensure that the weakened cells will not continue to fall even weaker than what it is already. 

Cleaning the batteries

Another way to help prolong battery life is by regularly cleaning the terminals in particular. The most common cleaning solution used is a simple mixture of baking soda and distilled water.  Before proceeding, make sure to remove the clamps, negative first. Use the baking soda mixture and a brush cleaner to gently scrub off the surface of the terminals. Afterward, thoroughly rinse the battery with water. Then, coat all the metal parts with a commercial sealant or a high-temperature grease to prevent corrosion. Finally, reattach all the necessary connections and ensure it is done securely

Battery Replacement

In replacing your batteries, always follow this simple rule: Do not mix old from new batteries. Using both simultaneously will adversely cause faster degeneration in the performance and lifespan of the newer units. Thus, consequently lowering the quality and, of course, the value for money.

What are the safety hazards in using batteries?


Mostly, cases of misuse or malfunction are the primary culprits of a battery explosion. Typically, recharging of batteries tends to give off a highly explosive combination of hydrogen and oxygen gases. Nevertheless, when it is charged at an excessive rate, the production of the said gas mixture is faster than the amount released from the built-in vent. Thus, the pressure from within rises significantly that eventually leads to an explosion. The bursting of the unit may induce violent acid sprays that cause irritation or chemical burns when comes into direct contact with the skin, and respiratory tract problems when accidentally inhaled. 


The majority of the chemicals contained within the battery unit is either or both corrosive and poisonous. Hence, when an incidence of leakage happens, it is safer to generally conclude that it is hazardous. With utmost precaution, you may rinse off the acid leak from the battery with a baking soda and water mixture to help neutralize the chemical. When in contact with the skin, it is likely to cause irritation or burns. Immediately wash the area and seek professional treatment to properly address the injury.

Toxic Materials

The battery is one form of electronic waste, or also referred to as e-waste. It contains numerous toxic chemicals and components that pose a high risk for environmental damage when it is not recycled or disposed of properly. Potential problems such as ecotoxicity and water pollution may develop if the waste batteries are improperly handled. Its corrosive acids and dissolved metals release toxic substances that are unsafe and unhealthy for humans, and as well as for the animals and plants too. Furthermore, it also has the possibility to sip into the groundwater which may prompt disturbances in the aquatic system.

Overall, the usage of solar batteries to maximize the efficiency and sustainability of renewable energy is undeniably an essential component to success. Hence, thorough knowledge and assessment must be given equal importance to ensure that you will be able to get the utmost performance and value from the batteries. From learning how it technically works up to understanding the nature of its active chemicals, differences in terms of its types, and the awareness of its proper maintenance will help you determine which solar battery is the most appropriate and sufficient for your energy requirements. Moreover, getting the right kind of battery will ensure that you will receive the expected benefits for a long time at the most efficient value for money.