More and more solar customers are looking into the benefits of home batteries, but designing and installing a retrofitted storage system comes with a host of potential challenges, writes Selectronic’s Rod Scott.
In part one of this article, we looked at some of the key design issues you need to consider in a battery retrofit. Here we check off some of the critical installation issues that every installer should bear in mind.
DC wiring
When retrofitting batteries, DC power adds a whole new set of challenges. It’s really important that you check the installation of DC terminations, battery links and fuses. Be sure to use the correct cable sizes and battery fuses. Undersized cabling can result in unacceptable power losses and voltage drop, premature failure and thermal issues. Using pre-charge cabling between the battery bank and the inverter allows these losses to be measured. Any issues with the DC side will be reported by a good-quality inverter charger.
Even new battery cells can fail, so you need to measure across all cabling and under different load/charging conditions. There was an example of a call to our support department where the installer couldn’t track the cause of a DC fault. Finally they found that one of the DC cables had been nicked by a tradesperson drilling into the wall.
Battery monitoring
Lithium batteries usually come with their own BMS, which usually allows for cell-level monitoring. Lead-acid batteries can be monitored using both pre-charge cabling and temperature sensor. This will allow for mid-point monitoring – indicating whether the battery bank voltage is different between the two halves and equalisation is required.
Temperature compensation also allows the charge voltage to be adjusted based on the battery manufacturer’s requirements. Make sure the temperature sensor is located around the middle of the bank and mid-cell to give a representative reading.
AC-coupled solar
AC coupling, where the grid-tie inverter is connected to the load side of the inverter charger, is now common. DC coupling is still used, but less frequently. One mistake that can be made with AC-coupled solar is to install it on the AC source side. This means that when the grid fails, the solar generation also stops. This may be a legitimate design in some circumstances.
Commissioning checks
Any commissioning checklists should be followed completely to avoid the end user having to “˜test’ the system after you have left. Running the loads up and down, pulling the power to ensure a smooth transition to island mode and checking any voltage variations on the load and source is essential. You don’t want to wait for the first blackout to reveal any issues. Avoiding a return visit not only saves money but also produces a satisfied customer.
Future
If the needs of the customer change down the track, then being able to change parameters of the system to accommodate future requirements is important. Future developments of the product should also be upgradeable through firmware updates. If the customer has different load/generation requirements at different times of year, these should be programmed to automatically change during those periods. Peace of mind for both the customer and the installer means not only having the right products but also the right company to support them.
Keep in mind that the liability for any warranties starts with the installer. Risk management 101 would emphasise the importance for due diligence on any supplier.