Solar and energy storage – using solar batteries to maximise your solar power system

Solar with energy storage is the best way to use solar power around the clock and to utilise the excess supply generated by a solar power system. In our last blog, we talked about the entry-level option - using a solar diverter (if interested in viewing, please click here to read the blog). Now, we want to cover more about the most popular option - solar energy with batteries.

How solar batteries work

Solar batteries work by taking the excess electricity produced by your solar power system and storing it for later use. When the solar panels produce more electricity than you are using, the excess generation is used to charge the battery. In a time when your solar energy system isn’t producing enough electricity to meet your demand, or when solar is not functional at night, you will draw stored electricity from the battery to supply your needs.

With solar batteries included in your solar power system, you will only send excess generation back to the grid once the battery is fully charged. Additionally, you will only draw electricity from the grid once the state of charge in the battery drops to its lower set limit. The amount of electricity that can be stored depends on the capacity of your battery, with the greater capacity allowing greater levels of storage.

Things to look at when considering a solar battery

When considering a solar battery option, you will likely come across a lot of complicated product specifications. The most important ones to use during your evaluation are the Capacity & Power, Depth of Discharge (DoD), Round-trip Efficiency, and Battery Life & Warranty.

Capacity and power

Capacity is the amount of electrical energy that a battery can store, measured in kilowatt-hours (kWh), while the Power is the amount of power draw that a battery can deliver at one point in time and is measured in kilowatts (kW).  A battery with a higher capacity can store more electrical energy, and a battery with a higher power-rating can supply a greater level of power at any point in time. A simple analogy is to think of Energy as the volume of water in a water reservoir and Power as the thickness of the hose used to move the water from one location to another - the thicker the hose, the greater the volume.

When considering solar battery options, you should think of the total amount of Energy (kWh) you want the battery to be able to store and supply, as well as how much Power (kW) you will need the battery to be able to supply at the same time. Some solar batteries are designed to be modular, which means that you can include a different number of battery configurations with your solar energy system to get the right capacity and power needed.

Depth of Discharge (DoD)

The DoD of a battery refers to the amount of a battery’s total capacity that has been or is able to be used. In order to maintain a healthy, useful life, solar batteries should retain some charge at all times and not use 100% of total available energy. Most manufacturers will specify a maximum DoD for optimal performance and, generally speaking, a higher DoD means you will be able to utilise more of your battery’s capacity. Some manufacturers will state that their batteries have a 100% DoD, meaning all energy within the battery can be used. However, there will always be a residual level of energy available to ensure the battery remains operational and its health is not adversely effected.

Round-trip efficiency

When a solar battery stores the energy itself, a certain level of the energy will be lost. A battery’s round-trip efficiency represents the ratio of power you draw to the battery vs. the level of power that is actually fed to the battery when charging. Generally speaking, a higher round-trip efficiency means you will get a greater proportion of energy destined for your battery actually make it there.

Battery life and warranty

The majority of solar batteries are designed for daily "cycling" (charge and discharge) and, although they may have different chemical properties and operational characteristics, should provide the system owner with reliable, long-term energy storage.

Your solar battery will have a warranty that guarantees a certain number of cycles and/or years of useful life. Most manufacturers will also guarantee that the battery keeps a certain amount of its capacity over the course of the warranty. Generally speaking, the longer the battery life and warranty, the better the protection you will have.

Not ready for solar batteries yet? You have a ‘Battery Ready’ option

A solar power system with batteries is the ultimate in being able to use your solar energy around the clock. However, depending on your situation and level of energy consumption, it may still involve considerable investment at this stage. Therefore, a battery ready system is something that many people consider when weighing up their options.

Having said that, every solar power system can theoretically be ‘battery ready’, as you can always add a battery onto pretty much any system. However, there are some major differences between the types of systems.

Off-grid capable

Adding a battery to your solar power system doesn't mean you can use your system completely off-grid. In fact, most of the battery systems currently in the market still need grid support. If you really want a battery ready system that will perform an off-grid function in the future, you will need to make sure your system has the ability to operate in a pure off-grid manner.

‘Hybrid’ battery-ready system

A ‘Hybrid’ battery-ready system, or what we called a ‘Plug and Play’ system, has a solar inverter that converts DC power from the solar panels into AC power for usage in your home. Without a battery it operates in the same manner as a normal grid-tied solar inverter but also contains the hardware to charge and control the battery, and convert DC power from the battery to AC power for delivery in to the home. With this function available, you can add batteries to your system at any stage without any further hardware being needed. This is a true example of a battery ready system. The majority of quality hybrid inverters should also have an inbuilt 'back-up' function, providing power to the essential loads within the home in case of a grid power outage.

With batteries in place, the hybrid inverter only converts the amount of power being consumed in the home to AC, allowing the rest of the solar generation to travel through to the battery in DC form. This provides greater utilisation of solar generation from the system and improves conversion efficiencies.

‘AC-coupled’ battery-ready system

An ‘AC-coupled’ battery-ready system, or a battery ‘Up-gradable’ system, will need a further inverter for the battery in addition to the solar inverter within the existing solar power system. In this type of system, the solar inverter converts all solar generation from DC to AC and delivers it to the house switchboard for distribution throughout the property. From there, the battery inverter will convert the excess solar energy not used in the home from AC back to DC, in order for it to be stored in the battery. The majority of AC coupled systems will need additional hardware to allow the system to operate in a back-up capacity and provide power to essential loads in the case of a grid power outage.

The initial cost of a Hybrid battery-ready system is higher than a straight grid-tied system, but it should provide total system savings when installing a battery at the same time or a later stage. Additionally, the inbuilt function of Hybrid inverters should provide better control over the complete solar power system when the battery is added to it.

With an AC-coupled battery-ready system, you will pay less for the solar power system but will likely need to invest more when adding a comparable battery to it. Depending on which type of battery you want, there may be flexibility in selection based on the battery being separate from the solar power system itself. However, you would need to ensure that the battery is designed for an AC-coupled installation.

Think about what you want to achieve, take experienced advice and choose the system that best suits your needs

Solar batteries do add an increased level of function to solar power systems, but at ZEN we recommend you consider your power consumption levels and patterns, any necessary future expansion capability, and obviously your budget. Our experience shows that the majority of our customers focus on the function they are looking for and the budget they are wanting to allocate to achieve this.

If you are not sure what the best option is for you, you can always call on ZEN's experience to handle the job for you. At ZEN Energy Systems, we have a different range of solar and battery systems, including Hybrid, AC-coupled and Off-grid. Simply tell us what you are looking to achieve and we will help to design the system that best suits you.

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