Solar power systems have gained popularity as a clean, renewable energy solution. However, the challenge of energy intermittency due to reliance on sunlight can be addressed by integrating batteries. Adding batteries to a solar system enhances energy storage and reliability by allowing surplus electricity to be stored and used during low sunlight periods.

This article explores the benefits of adding batteries to solar systems, including improved energy storage capabilities and increased sustainability. By optimizing solar power investments, this integration empowers individuals and businesses to thrive in an energy-conscious world and pave the way for a greener future.

Why Add Batteries to Your Solar System?

In the pursuit of energy independence and sustainability, adding batteries to a solar system has emerged as a game-changing solution. By incorporating battery storage, solar system owners can overcome the challenges of intermittency and maximize the benefits of their renewable energy investment.

One of the key advantages of battery storage is its role in achieving energy independence. While solar panels generate electricity during daylight hours, without a means of storing excess energy, reliance on the grid during periods of low sunlight or at night is inevitable. However, by integrating batteries, surplus electricity can be stored and utilized when needed, reducing dependence on the grid and providing a reliable source of power round the clock.

Moreover, having stored energy becomes crucial during power outages or when solar energy production fluctuates. In regions prone to natural disasters or grid failures, having a dependable backup power source is paramount. With batteries in the mix, solar system owners can experience uninterrupted power supply, maintaining essential appliances and services even when the grid goes down. This can bring peace of mind, especially in critical situations where power is indispensable for medical devices, refrigeration, or communication.

Fluctuating solar energy production is another concern that batteries effectively address. Weather patterns, shading, or other environmental factors can impact the intensity of sunlight and consequently the amount of electricity generated by solar panels. By storing excess energy during peak production periods, batteries provide a reservoir of power that can be tapped into when solar energy production is low. This ensures a steady supply of electricity and mitigates the impact of intermittent solar generation, optimizing the efficiency of the solar system.

Additionally, the integration of batteries also facilitates load shifting. During times when electricity demand is low, typically at night, batteries can store surplus energy that can be used during peak demand hours. This allows solar system owners to avoid purchasing expensive electricity from the grid during peak periods and instead utilize their stored energy, effectively reducing their overall energy costs.

How Do Solar Batteries Work

The working principle of solar batteries is to store and provide electricity when needed. They act as reservoirs for power, similar to how pressure tanks and water heaters store water. When batteries are used to draw energy, their stored power is depleted, but in a properly wired system, they can be automatically replenished by capturing any excess electricity flowing through the system from sources such as solar panels or the grid. The installation of batteries can vary depending on the objective of the system:

1. Connected solely to solar panels: Batteries connected only to solar panels are charged with sunlight and discharged when electricity is being used and there is no sunlight or when it is obscured by clouds. This is an option if you are off-grid and far from power facilities.
2. Connected to both solar panels and the grid: If you have a solar inverter that can temporarily disconnect from the grid, then you have what is called a hybrid solar system. In such a system, you can charge the battery either from the solar panels or the grid, and use the stored energy in your home or send it back to the grid, saving some money through rate arbitrage (if you have time-of-use rates). Hybrid systems can also provide power to your home during a blackout.

1. Connected only to the grid: While they are not referred to as solar batteries, you can install batteries without solar panels. They will charge from the grid and can be used as a backup power source or contribute to a virtual power plant.

Advantages and disadvantages of solar batteries

Advantages

• Can reduce energy costs
• Becomes more affordable and qualifies for tax credits and incentives
• Stores electricity when the grid fails
• Storing and releasing energy during peak usage times can alleviate grid stress
• Cleaner backup power source compared to generators
• Latest battery chemistries like Li-PO4 are very safe and easy to maintain
• Improves energy independence

Disdvantages

• Savings depend on local utility rates and net metering rules
• Expensive
• Large battery systems require ample storage space
• Not all utility companies encourage or reward this practice
• Generators may be more useful in major emergencies
• Some batteries can pose health and fire risks and require management and maintenance

The excess solar power stored in the batteries can replace the power you would normally have to buy from or sell back to the utility company, saving you some money and alleviating stress on the grid during peak demand (whether this is a viable money-saving option for you depends on the net metering rules of your utility company).

Some companies are starting to allow people to register their batteries into virtual power plants, a collection of batteries, smart thermostats, and other home appliances that work together to reduce the demand from the grid. Virtual power plants can provide additional benefits for battery owners where feasible.

Additionally, you can use the battery system if the grid fails due to outages, natural disasters, or even solar flares. Backup generators can also help maintain power during emergencies (and charge batteries), but they require burning fossil fuels, typically natural gas or propane.

Batteries do add a significant cost to your home energy system, but federal tax credits and other incentive programs can often be applied to offset storage costs.

Different Types of Solar Batteries

There are various types of batteries used in solar backup systems, including lithium-ion batteries and lead-acid batteries. Here is a quick overview.

Lithium-ion Batteries

There are different lithium chemistries available in the market, including nickel-manganese-cobalt, lithium polymer, and lithium iron phosphate (LiFePO4). The fire risks of the latest lithium technologies are smaller than what the sensational headlines might lead you to believe. They are capable of deeper discharges compared to lead-acid batteries (up to 90% of capacity per cycle without significant damage) and are easier to maintain with a longer lifespan. However, they come at a higher price and are temperature-sensitive. Nonetheless, they are gradually becoming the standard for residential solar applications.

Benefits of Lithium-ion Batteries

Lighter Weight and Maintenance-Free

 One advantage of switching to lithium marine batteries is their significantly lighter weight compared to traditional lead-acid batteries. While a 12V 100Ah lead-acid battery weighs about 60-70lbs, a LiTime 12V 100Ah mini lithium battery weighs only 19 lbs. Additionally, lithium batteries do not leak and require no maintenance, allowing for a hassle-free boating experience.

100% Depth of Discharge: 

Lithium batteries offer a 100% depth of discharge (DOD) rate, meaning they can be discharged fully without causing any harm. This provides more flexibility in utilizing the battery's capacity without worrying about reducing its lifespan. In contrast, lead-acid batteries should not be discharged below 50% to maintain optimal performance.

10 Year Lifespan:

 On average, lead-acid batteries last around 3 to 5 years, with their lifespan being decreased if frequently discharged deeply or exposed to harsh conditions. However, LiFePO4 batteries have a lifespan of approximately 10 years or more, depending on proper care and maintenance. They are designed to handle a greater number of charge and discharge cycles without significantly degrading their capacity, making them durable and suitable for marine deep cycle battery applications.

Lead-acid Batteries

The basic foundation of this technology has remained largely unchanged for over a century. They are still inexpensive and widely used. For solar systems, more expensive sealed batteries are typically used, which require less maintenance and eliminate the risks of potential acid leaks and hydrogen gas escape. For a time, sealed lead-acid seemed to be the future of solar batteries.

However, compared to lithium-ion batteries, all lead-acid batteries require more careful monitoring of the charging levels and cannot compete in terms of efficiency, energy, and lifespan, but they are a good and adequate budget alternative.

Flow Batteries
Flow batteries (or redox flow batteries) are not as common in residential systems as they are primarily designed for commercial purposes. However, this technology seems promising and may have wider applications in residential battery backup systems in the near future.

Nickel-cadmium Batteries
Nickel-cadmium batteries have high energy density, twice that of lead-acid batteries. They are very durable, expensive, and can operate in extreme temperatures, making them a good choice for large commercial and industrial projects. However, cadmium is toxic and generally not suitable for residential use.

Financial Considerations about Adding Batteries for Solar System

1.  Initial Cost Analysis

The upfront investment required for battery installation can vary depending on the chosen method. DC coupling typically requires more equipment, such as a separate charge controller and inverter, making it potentially more expensive compared to AC coupling or replacing the grid-tie inverter.

It is important to consider any applicable government incentives or rebates when assessing the initial cost. These incentives can help offset the upfront investment and make the battery installation more financially feasible.

2.  Cost Savings in the Long Run

One of the significant cost savings achieved through battery installation is self-consumption. With a battery backup system, excess solar energy produced during the day can be stored and used during the night or when the solar panels are not generating electricity. This reduces reliance on electricity from the grid, leading to lower electricity bills.

Additionally, battery backup systems allow for peak shaving. During times of high electricity demand, such as evenings when many households are using electricity simultaneously, batteries can be utilized to supply power, reducing the need to draw electricity from the grid. This further helps in reducing peak demand charges.

Another financial benefit of battery backup systems is the avoidance of grid electricity costs during blackouts. When the grid goes down, battery backup systems automatically provide power to essential appliances or the entire household, depending on the capacity of the battery. This eliminates the need to rely on expensive and potentially unreliable backup generators or purchasing electricity from the grid during an outage.

Other Tips To Maintain Your Solar System

Maintaining the battery backup system

For all batteries, follow the manufacturer's instructions for monitoring discharge depth. As a general rule, for lead-acid batteries, this means keeping them at least half charged whenever possible. Many lithium-ion batteries can safely be discharged down to just 10% capacity. Flooded lead-acid batteries also require occasional topping up with distilled water.

Lifespan and warranty considerations

After a few years of installation, you may notice that your battery backup system does not hold a charge as well as before. This is because, like any other type of battery, backup batteries lose storage capacity over time.

With this in mind, the backup batteries come with a warranty that indicates how the battery's efficiency should be at the end of the warranty period. Many top-tier solar batteries offer a 10-year, 70% usable life warranty, meaning the battery should still operate at 70% of its original performance at the end of the 10-year warranty period. Lead-acid batteries typically have warranties ranging from two to five years.

Inverters and batteries

Inverters play a crucial role in storing and converting solar energy. While solar panels produce direct current (DC), the grid and households typically use alternating current (AC). Inverters can convert AC to DC and vice versa. Most solar batteries include an inverter that stores energy in DC form and an inverter that converts it back to AC for use by the grid or the home. It’s recommended to use pure sine wave inverter.

As power inversion is not completely efficient, battery manufacturers have been working to minimize inversion frequency and improve battery efficiency. As a result, certain battery systems may not come with inverters for both input and output. Discuss with your solar installer the battery system you are considering to ensure you have all the necessary external inverters.

Beware of cheap inverters that are readily available. Pure sine wave inverters are essential to power modern household appliances; otherwise, you may end up damaging some more sensitive electronic circuits in your home.