5 Keys to Choosing Solar Energy Storage

Written by Tony Chang

November 11, 2020

5 Keys to Choosing Solar Energy Storage

Solar energy storage systems work by storing excess energy from the solar panels and help your home become energy independent from the power grid.

To make a good storage system work, you will need to look carefully at a few key metrics in the datasheets to choose the right battery for you.

What Is the Benefit of Solar Energy Storage?

PV systems without storage produce electricity that needs to be used right away, while the excess energy shall be fed back to the grid to earn an FiT.

When the energy consumption is higher than the solar energy, for example at night, the balance needs to be supplied by the grid to keep the lights on.

A solar installation without energy storage cannot truly be free from the grid.

With a battery system, the excess solar energy generated during the day can be stored for use during the evenings, making off-grid and complete energy independence possible.

To get the best solar energy storage that fit your needs, here are a few key metrics to help you choose the best batteries for your rooftop installation.

Capacity Defines How Much Energy You Can Store

The solar battery capacity is how much electric energy it can store when fully charged.

It is measured in the same way your energy bill measures your electricity usage, kWh.

By choosing an energy storage system with a large capacity, you can keep your home appliances running off stored energy for many nights and cloudy days.

Power Indicates How Much Energy Your Batteries Can Supply at One Time

The power rating of a battery is the amount of electricity your system can deliver at a given moment, measured in kW.

The higher the power rating your battery has the more home appliances you can operate at the same time.

But higher power means the stored energy in the battery will deplete faster.

The key takeaway is to choose a power rating that satisfies your home consumption while scaling the capacity with enough batteries to keep the appliances running long enough.

Round Trip Efficiency Defines How Much Energy Is Lost During Operation

round trip efficiency
90% round trip efficiency.

Round trip efficiency is the ratio of energy recovered from the battery over the energy charged into it.

Since a small amount of energy would be dissipated as heat losses, typical round trip efficiency of batteries can range between 70%-90%.

Choose a storage system with high round trip efficiency to get more out of the stored solar energy.

Depth of Discharge (DoD) Defines the Maximum Amount of Charge a Battery Can Draw

Depth of discharge (DoD) is the maximum level you can deplete your battery capacity without damaging it.

The chemical properties of a battery mean a minimum level of charge is stored at all times.

You would choose a battery capacity that is large enough while maintaining a manageable depth of discharge to keep your home appliances on.

solar battery depth of discharge
DoD is how much energy you can use.

Energy Retention at the End of the Warranty Shows How Much Battery Performance Degrades Over the Lifetime

While the warranty protects you from product defects during the battery’s expected lifetime, usually 5-10 years, it also defines the residual capacity leftover in the battery when the warranty is up.

This can help you understand the slope of degradation over the battery’s lifetime, and help you plan future upgrades as you solidify your independence from the electric grid.

Now you know all the key metrics that matter for a battery, the next time you choose a solar energy storage system, you can balance the capacity with power output and DoD to make sure the batteries can supply your home appliances when the sun is out.

By understanding the round trip efficiency and energy retention you can choose a battery system that will operate as expected throughout its lifetime.

To learn more about how WINAICO solar technologies can help with your rooftop energy production, please get in touch with us,

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