Phocos works with a lot of solar distributors, solar installers, and EPC’s in our day to day business. Often technical support end user questions come in about system sizing, odd projects, product features and troubleshooting. From our experience, there are some misconceptions out there when it comes to proper energy storage preparation and wiring. Often troubleshooting questions bring us to understanding if the system was set up for success on day one. During design and installation stages, details matter, so in an effort to support battery optimization for all customers, the team has put together a list of best practices for energy storage with batteries. Following these recommendations and checking with your local requirements will help assure the best outcome and best return on investment for your next energy storage project.
Important equipment considerations that are often missed or misunderstood:
- Conductor sizing: Make sure to size all wires appropriately based on local rules and regulations, to confirm they are designed to handle the expected continuous currents. Here is an example of best practices for wiring size based on ampacity rules in North America NECAmpacityWorkflow.pdf (nfpa.org), for reference only. Installers should always confirm they are following the local regulations applicable to their region.
- Terminal Crimping must be solid and executed with the right tools using a properly sized crimp die. It’s best to heat shrink the interface (see below) as it reduces the conducting area to lower the chance of unintentional short or shock. Taking care to crimp properly keeps terminals, wires, and connections securely in place, and minimizes excess heat generation at the contact area.
See below an example of two very well executed crimps. A good crimp should feel solid and stiff but should not cut through any of the copper wire.
- DC Disconnect and Breaker Sizing: It is a common misconception that breakers are included in system design to primarily protect the connected equipment, but in fact their main purpose is to protect the wires from overheating, or melting, therefore protecting against potential fires. Some local regulations require sizing a breaker to 125% of the total expected continuous current plus 100% of the non-continuous current through the conductor that it is protecting. Always check with local requirements and rules for proper breaker sizing. In general, good practice is to size your wire based on the current requirements, then size your breaker no more than the maximum breaker size allowed by local regulations for that wire size.
Best Practices: When daisy chaining batteries in parallel from the terminal posts on the batteries, always take the positive connection to the charger/load from one end of the battery bank and the negative connection from the other end of the battery bank. This assures proper balancing of all batteries for best performance and equal state of charge for all batteries.
NOT BEST PRACTICES (BELOW): If taking both positive and negative wires from the same side of the battery bank, the last battery in the chain will never reach the same charge as the other batteries in parallel. This is because as the voltage drops across the wires, there will always be voltage loss from one battery to the next in the example below. This will not optimize battery life or performance. When wiring in parallel, make sure to consider voltage drop and look to the best practices description and image above to properly charge/discharge your batteries.
Busbars: Using busbars for the positive and negative busses of your storage system can help ensure minimal loss due to difference in voltage drop. Always be sure the lengths of wire connecting different batteries or ‘strings’ to the busbars are of equal length.
Taking the time to factor in these considerations when designing a solar system with energy storage, buying equipment, and installing power systems, is easy and takes little investment of time or money. These best practices tips will help with optimization and system performance, as well as elevate safety to ensure a proper energy storage installation.