Battery-based System Electrical Integration
Integrating the electronics for battery-based solar systems is the final step before installation. It can be very easy or tough, depending on the products you selected, and the nature of the install. When possible, I recommend sticking to one or two manufacturers max for each install. Some even have pre-wired system, such as Outback's Flexpowers and Systemedges. Harsh weather conditions and difficult layout considerations that create distance between the solar PV, batteries and inverters will require special wire sizing, enclosures and over-current protections. Let's break the process down into stages.
DC System Grounding (earthing) - Battery-based systems are either ungrounded (floating), positively grounded or negatively grounded.
- Equipment grounding (EGC) is always required, the type is determined by local practices and equipment specifications.
- Positive and negative grounding is determined by manufacturer and installer preference, read the manuals! For example, most telecommunications equipment must be positively grounded.
Breakers vs. Fuses - We typically see breakers in low voltage (<150VDC) combiner boxes, disconnects and general over-current protection (OCPD). Fuses on each PV series string will protect parallel circuits from fault currents, refer to NEC 690.9(B)(1) for sizing.
Equipment Disconnects - Anything besides direct DC-only systems will require 3-4 disconnects at a minimum.
- Disconnects can be breakers, switches, or contact combiners (breakers plus a switch). Make sure to select the right type for your system grounding method.
- Batteries should be disconnected with an OCPD breaker at the source of potential fault current, which is the battery bank itself. This is actually required by the NEC if the batteries and inverter are more than 5 feet apart. This breaker counts as an inverter disconnect as well if it within sight. Remember fuses cannot be used as disconnects!
Voltage Drop - Same rules apply as for standard PV systems, but they are more critical because PV voltage MUST be higher than battery voltage to charge them. High temperature consideration is key.
Layout Considerations - Make sure to plan this out in advance of installation!
- Equipment space - physical size, wall or floor mounting
- Working clearance - width, depth and headroom, refer to NEC and manufacturer install manual
- Proximity of battery and inverter - within sight and less than 5 feet is ideal
- Requirements for batteries - Access for inspection, maintenance and watering; ventilation and distance from flame sources; equal cable lengths
You are one step closer to a professional and clean installation! Before you start, please read Battery-based System Commissioning so you will be ready to turn the system on.
To read the Full Battery Series: