Off-grid Solar System Battery Installation

Batteries are what makes a solar energy system an off-grid solar system. Without adequate storage, the energy generated is fed into the house and used or not used and wasted. Batteries enable you to take generated energy and store it for later use.

Aside from the solar panels, batteries require the most thought and the most planning. How much storage do you need? Do you want a 12v, 24v or 48v system? Will you be feeding excess energy into the grid?

All these questions will need to be answered to be able to design and build your solar system.

Today let’s talk about solar system batteries and their installation.

Solar system batteries

There are two primary types of solar system batteries, lithium and lead acid. Lead acid comes either flooded or sealed. Both types have strengths and weaknesses and will be suitable for one type of solar system over another.

Lithium batteries – Lower weight and smaller than lead acid. Ideal for indoor installations or where battery storage is insulated from the cold. Lithium has a good cycle life and can be depleted up to 80%. They also offer excellent life expectancy.

The downsides of lithium batteries are that they don’t work well at temperatures under 14°C, they have low current tolerance, up to 50A or 70A and require regular recharging.

Lead acid batteries – Lead acid batteries include AGM batteries. These are reliable batteries that have been around for years and are easy to manufacture and relatively cheap to buy. They can cope with larger currents than lithium and can be depleted to around 70% charge.

The downside is that they are larger and heavier, lose energy in the cold and require longer charging cycles than lithium.

Battery room setup

While the common term is ‘battery room’, it’s often a cupboard or purpose-built enclosure on smaller solar systems. Essentially it means somewhere set away where your batteries can be installed and won’t be disturbed.

You can store your batteries anywhere as long as they can be installed and kept secure. The area must have adequate ventilation and be cool enough to allow the batteries to not overheat and to cool adequately.

Batteries lose efficiency at higher temperatures so the cooler the room is, the better. But don’t let it get too cold, especially if you’re using lithium batteries!

In an ideal scenario, your batteries would be placed next to each other with a 2cm space between each of them.

Wiring should be kept short and straight wherever possible. Consider using bus bars to connect batteries instead of wires. Most battery manufacturers make them for their respective brands. Bus bars look tidy and are harder to dislodge during maintenance.

Flooded lead acid battery considerations

Flooded lead acid batteries have specific requirements when it comes to installation.

• Ensure adequate ventilation to vent any gas emitted by an overcharged or overheated battery.
• Consider using a battery enclosure if the situation allows.
• Ensure adequate insulation and ventilation to keep temperature around 20-25°C.
• Use spill containment trays underneath batteries just in case of leaks.
• Install a hydrogen gas monitor to watch for any emissions from the battery.
• Avoid using any other electrical items in the battery house aside from what’s required for your solar system.
• Keep baking soda around and use on any acid spills or leaks.
• Secure a whiteboard to the wall to track maintenance and charging.

Lead acid batteries can vent hydrogen gas, so ventilation is key. Try to ensure there is adequate venting above the batteries and it vents into the atmosphere and not the property.

Once installed, you may need to refill them regularly with distilled water. How much and how often depends on the size of the battery, the manufacturer and how often the charge cycle happens.

Plan on topping up at least once per month, more if you’re building an off-grid solar system for your home.

Don’t be tempted to use tap water. While clean, tap water contains contaminants that can shorten the operating life of the battery. We suggest only using distilled water unless the manufacturer recommends otherwise.

Sealed lead acid battery considerations

Sealed lead acid batteries have slightly different requirements in their installation.

• Ensure adequate ventilation to cool an overcharged or overheated battery.
• Ensure adequate insulation and ventilation to keep temperature around 20-25°C.
• Keep baking soda around and use on any acid spills or leaks.
• Secure a whiteboard to the wall to track maintenance and charging.

Sealed lead acid batteries require less maintenance than flooded batteries. Just use a multimeter regularly to check the state of charge according to the battery operating instructions.

Lithium-ion battery considerations

Lithium-ion batteries have their own set of considerations for installation but fewer than lead acid.

• Ensure adequate insulation and ventilation to keep temperature around 20-25°C.
• Secure a whiteboard to the wall to track maintenance and charging.

Lithium-ion batteries require very little maintenance. Set up a routine to check the state of charge with a multimeter and perform visual checks on battery and wire condition.

All solar system batteries should be installed on a flat surface adequate for the weight. All batteries should have a minimum of 2cm gap on all sides for cooling.

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Solar system battery wiring

Just like your solar panels, off-grid solar system batteries can be wired in series or parallel.

• Connect the batteries in series and you increase the voltage of the system. 2x 12v batteries creates a 24v system.
• Connect the batteries in parallel and you double the capacity of the system without increasing the voltage.
• You can also combine the two systems to provide a higher capacity 24v or 48v system. Choose whatever works for your needs.

If combining series and parallel, we recommend connecting your battery banks in parallel first and then in series. The output will be the same as the other way round but wiring should be much simpler!

Keep battery banks even. If you have 8 batteries, use two banks of four with identical length and size wiring between them. If you’re using 16 batteries, use 2×8 or 4×4 batteries with the same wiring length and thickness across the array.

General wiring guidelines for solar system batteries

Here are some general tips for wiring your solar system batteries.

• Keep all connecting wires the same size and length wherever possible.
• Try to avoid shorting batteries and be very careful when connecting them up.
• Use a torque wrench when connecting wires and check them during maintenance.
• Always maintain a gap between batteries to ensure adequate cooling.
• Minimize dirt and debris around the battery house to avoid shorting and damage to batteries.
• Place the battery bank and the inverter as close as practicable to keep things efficient.
• Route your wires carefully to keep them as straight as possible and easily visible.
• Use cable ties to secure wires regularly to maintain capacity and minimise electromagnetic interference.

Everything on this page is for general guidance. Always read the manufacturer’s operating instructions before connecting the batteries to the system and before charging.

Solar system battery balancing

Even the tidiest off-grid solar system battery bank may fall out of balance occasionally. This is where some batteries are drained faster or more than others, bringing the entire battery bank out of balance.

It isn’t terminal but should be addressed to prevent some batteries wearing faster than others.

Checking each battery regularly with a multimeter will soon tell you if your battery bank is out of balance. If some batteries show lower voltage than others, you should balance the system.

1. Discharge the batteries to their minimum
2. Disconnect the battery bank from the solar system
3. Connect all batteries in parallel and leave them for 24 hours
4. Reconned the system back to its original configuration and allow to charge

Battery balancing is a simple but time-consuming task but will preserve the operating life of your batteries and ensure all the energy storage potential is utilised.

If you need help, advice or would prefer to have your off-grid solar system installed by experts, contact Sunstore at [email protected] or call us on 01903 213141.