How is Solar Energy Stored? – Solar Storage Methods in 2020

How to store solar energy
How to store solar energy

Solar technologies have grown since they first made their beginning in the 1960s. 

Also, people’s interest in solar power has been growing extremely over time.

And why not? 

Solar is providing us sustainable solutions to our energy problems.

According to IRENA (International Renewable Energy Agency),

Cumulative installed capacity of solar PV would rise to 8519 Giga Watts by 2050 becoming the second prominent source (after wind) by 2050.

Solar power will clearly continue to be an essential renewables option in the coming decades.

Using specific methods, we can use solar energy by converting it into various usable forms such as electricity, heat, and chemical energy fuels.

However, At night time or on cloudy days , we get reduced or eliminated sunlight. So, we need an option to capture solar energy for later use.

In this post, I am going to share various solar storage methods that we can use to store solar energy.

Let’s dive right in!

Methods of Storing Solar Energy

The method to store solar energy depends on the application whether we are using it.

Here are two ways in which we can store solar energy:

  • Solar heating applications for thermal storage
  • Solar PV system for electricity storage

Let’s have a look at each of them.

1. Solar Thermal Storage

Thermal energy storage is a technology that allows storage of thermal energy by heating or cooling a storage medium for a later use.

I have shared two main types of solar thermal storage methods below:

Molten Salt Tank

Molten salt storage is a utility-scale system.

In this system, a large array of parabolic mirrors or sun-tracking mirrors are used to concentrate sunlight to melt a special salt.

A refractory tank is used to store this melted salt.

The salt is so hot that it can vaporize water into steam to drive a steam turbine. 

This hot salt is stored in an insulating container during off-peak hours. 

When energy is needed, the salt is pumped into a steam generator that boils water, spins a turbine, and generates electricity.
To illustrate, Below image from Wikipedia clearly depicts the working of molten salt tanks.

Molten Salt Reactor
Molten Salt Reactor

According to Stanford University, molten salt can function as a large-scale thermal storage method that would allow other energy sources, such as nuclear and solar, to become more feasible by smoothing out the fluctuations in demand and weather. 

Solar Water Heater

If you need to store energy for water heating, an option is to heat water with sunlight and store it directly in an insulated tank.

I have tried to explain the concept of solar water heater by the below image.

Solar Water Heater Diagram
Solar Water Heater Diagram

Solar thermal water heaters are capable of heating water during the day and storing the heated water for evening use.

There are two types of solar water heating systems:

i ) Direct circulation Systems
  • Having circulating pumps and controls
  • These systems circulate water through solar collectors which is heated by the sun.
  • Work better in an environment where it rarely freezes.
  • Eg. water that you’ll use for bathing or for heating your home.
ii) Indirect Circulation Systems
  • The sun’s thermal energy heats the fluid in the solar collectors. Then, this fluid passes through a heat exchanger in the storage tank, transferring the heat to the water. The non-freezing fluid then cycles back to the collectors. 
  • These systems are good for climates prone to freezing temperatures.

2. Solar PV System (for Electricity Storage)

In order to store solar energy in the form of electricity, we use the below methods:

Batteries

Solar panels produce DC energy and batteries save this DC energy by converting it into AC energy for later use.

Below illustration can help you understand the working of the solar system in a better way.

Working of Solar PV System
Working of Solar PV System

To overcome the drawback that sun cannot provide sunlight at night or on cloudy days, batteries let you use more of your PV System’s output.

This will reduce the amount of grid electricity you need to buy, saving you money on your electricity bill.

The most commonly used batteries are:

  • Lithium Ion Batteries 
  • Lead Acid batteries
Lithium Ion Batteries 

These batteries have longer expected lifespan.

Some examples of Lithium ion batteries include electronic devices like laptops, and mobile phones.

Lead Acid batteries

On the other hand, Lead Acid batteries are generally used in off-grid properties where we need large storage like in cars.

Also, these batteries have a shorter expected life span in comparison to the lithium ion batteries.

There are 4 major solar battery systems:

  • DC coupled systems
  • AC coupled systems
  • AC Battery Systems
  • Hybrid Inverter Systems

The term coupling refers to “point to point connection”.

However, in off grid solar installations, only DC or AC coupled systems are generally used.

Whereas, AC coupled systems have higher efficiency when they are used to power AC appliances during the day such as air-conditioning, pool pumps, and hot water systems.

AC Battery systems are designed for grid connected systems. 

These consist of lithium battery cells, a battery management system and inverter/charger all in one compact unit. 

A most popular example of such a system is the Tesla Powerwall 2.

Moreover, these provide the economical way to add battery storage .

But hybrid Inverter systems have a disadvantage that they do not have back-up power capability or the backup power is very limited.

Net-Metering

Before I explain net metering, let me share a basic overview of how grid-connected Solar PV systems work

Grid Connected Solar PV System
Grid Connected Solar PV System
Step-by-step guide on how grid connected solar PV system work

At First, the solar panels convert energy from the sun into DC. Then, the inverter converts this DC output into AC.

Switchboard is used to distribute electricity between electrical sources. 

In order to find your electricity production and consumption, the digital meter is used.

Finally, a power grid or electric grid delivers electricity from producer to consumer.

And, Net metering is the method by which we can store energy in the electric grid.

Understand Net-Metering

Let’s understand it with an example, that I have taken from SEIA.

If a residential customer has a PV system on their roof, it may generate more electricity than the home uses during daylight hours.

If the home is net-metered, the electricity meter will run backwards to provide a credit against what electricity is consumed at night or other periods when the home’s electricity use exceeds the system’s output.

Customers are only billed for their “net” energy use. 

On average, only 20-40% of a solar energy system’s output ever goes into the grid, and this exported solar electricity serves nearby customers’ loads.

At the time of bill payment, you would pay for the electricity you use, minus excess electricity that your solar panels generated.

Net Metering not only helps you to reduce your energy bills, but you can also earn according to your electricity generation.

Conclusion

Advancements in solar technology present the potential of power in our lives if we just leave it to the sun.

I have covered major types of solar energy storage. Each storage method does have advantages and disadvantages.

Also, future challenges include improving the efficiency of different storage methods.

I will be covering each storage method individually in detail in my next posts.

Stay tuned with SolarFunda and #GoSolar!

Keerti Bhatnagar

Keerti is a tech geek with a vision to save the environment. She is from Uttarakhand, India. And, She is currently pursuing her MCA from G.B. Pant University of Agriculture and Technology, Pantnagar.

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