If you’re looking at installing a battery supported solar system, or you’ve recently had one installed, you may be wondering how the system works in different situations. 

Although your system would’ve been designed to meet your current requirements, you may be wondering what will happen in cases where you use more or less than expected and how your family, the weather, or other variables may impact on your solar system over time. 

 

How are off grid solar installations designed?

Your solar installer will look at your current usage, or in cases of installations on new properties, will calculate usage based on industry standard usage of the appliances you’re planning to use. 

An important part of designing an off grid solar installation is ensuring the solar panels, inverter, and batteries cover all your needs, while still having spare capacity for night time and a rainy day. 

While off grid batteries once offered enough storage for up to seven days of power, many systems now only include 24 hours of backup storage. One of the reasons for this is that older lead acid battery systems couldn’t have additional batteries added after installation; with modern lithium batteries, additional batteries can be added whenever a property owner either needs them, or feels it’s a financially viable option. 

Another reason is, in the past, seven days of power would be running one fridge and two small lights, so seven days of power was not a big ask. Modern off grid systems are often expected to run the entire load of a modern home. 

 

What happens when off grid solar batteries are full?

In most normal usage cases, your batteries will often become full, or 100% charged. A well designed system will recharge the battery to capacity in less than a day. 

In older style lead acid batteries, overcharging could be dangerous, as the batteries produce hydrogen gas, which can lead to an explosion if in a badly installed or maintained system. 

Modern lithium batteries are much lower risk as they don’t vent hydrogen gas in normal operation. They also have a built in computerised battery management system to ensure the system stays safe. 

Thermal runaway is a potential issue with lithium batteries. This is when the battery’s many failsafes fail and the chemical reaction in the cells gets out of hand, causing a fire. This is why battery safety is our #1 selection criteria. 

Should the battery bank become full, it will stop absorbing power from the solar system. The solar panels will continue to generate voltage, but that voltage will not be used or stored until there is available energy demand, or battery space. 

 

What happens when grid connected solar batteries are full?

 If you have a grid connected solar system with battery backup, the good news is that excess energy earns you money from your solar retailer’s Feed in Tariff (FiT). Any excess energy produced once the battery reaches capacity is returned to the grid, and you’ll see a reduction or credit on your next power bill. 

 

What should you do if your batteries regularly become full? 

Many modern systems have smart metering installed, either at the battery or inverter level. Smart metering allows for tracking of production in real time, as well as battery levels. 

If you notice that your batteries are regularly reaching capacity, then happy days. The less you discharge the cells each day, then the longer the service life of the battery. 

 

Peter Sutrin
Written by Peter Sutrin

Peter is a Licensed Electrician and the Director of Proven Energy, a Clean Energy Council Approved Solar Retailer. After working in the industry, Peter’s interest in renewable energy lead him to found the company in 2012, offering honest and reliable solar system supply and installation for residential, commercial, off-grid and agricultural properties. Peter is a CEC Accredited Installer. Electrical Contractors Lic No. 74650