Correct Battery Configurations on a Renewable Energy System
A human’s guide to battery configuration, set up and installation.
If you are reading this, then no doubt you have scoured google seeking an answer to some fairly basic questions regarding batteries. In some cases, your questions are pretty basic, ‘how to set up in series or parallel or both’, in some cases they can be a little more complex.
For my part, I have grown tired of being called out to hundreds of sites across the country only to diagnose the same problems over and over and over. In general, these basic ‘solar battery’ problems are limited to sites where the installation was done by an electrician, auto mechanic or DIY installs but in some cases even RE (Renewable Energy) installers have created the mess.
So, in a way, my hope is that after reading this doc, maybe, just maybe, I can assist you out there by getting the most out of your solar/wind/hydro/load shed/black out kit, and hopefully reduce the number of call outs that good renewable companies are experiencing.
Parallel – Okay. When you connect batteries in parallel you grow the amperage but keep the voltage, by connecting 4 x 100Ah 12v batteries in parallel, you will effectively have 400Ah @ 12v, below is a diagram of connections, note positive to positive and negative to negative connections.
Series – Connecting batteries in series, grows the voltage but keeps the amperage constant. If you connect 4x 100Ah 12v batteries in series, you will effectively have 100Ah @ 48v, below is a diagram, note the positive to negative connections.
Series Parallel – Connecting in a series and parallel configuration grows both the amperage and the voltage. The batteries must always be balanced (i.e. – you cannot put 2 x 100Ah 12v in series and then add 1 x 100Ah 12v). If you were to use our same example of 4 x 100Ah 12v batteries, you would only be able to make a 200Ah x 24v bank, see diagram and note the combinations of series and parallel. I have done two diagrams below to 24v and 48v as they are the most common configurations.
Connecting to Battery Bank
Now that you have the basic configurations, and also the primary reason for me writing this article is the positioning of the inverter uptake and charge cables. This is the most common mistake in most RE systems so please pay attention.
The diagram below is the INCORRECT way of connecting:
The reason this is incorrect, is that the battery closest to the uptake and charge points are overworked (copper resistance), the MPPT cannot sense the far batteries properly (copper resistance), the equalization charge will never be accurate and most importantly, the system is ridiculously inefficient. In a short space of time, your battery will need replacing, you will complain to your supplier that your battery keeps cutting out when you should have plenty space. So below is a diagram of the correct method for 12v, 24v series and parallel, 48v series parallel. The rule is always the same no matter the voltage or how many batteries (hopefully not more than 12 per bank) and applying this rule will see you get longer lifespans, better usage and more even charging.
As someone who has been in a room where a giant 1050Ah 2v cell has exploded (luckily the ringing ears has healed and the installer jumped into the pool to neutralize the acid) I can tell you first-hand what you should and what you shouldn’t do when working on a bank, we sometimes take things for granted even as experienced professionals.
- NEVER have any charge or any load (inverter) on any battery bank when working on it. Disconnect absolutely everything that may cause a current movement through the bank. This does not mean merely isolating it or removing the fuses from the fuse holders, do a complete disconnect.
- Once the batteries are configured and if you are using a solar charger, you ALWAYS first connect the charger to the batteries BEFORE connecting the solar panels to the charger. ALWAYS.
- After connecting the outputs and BEFORE switching on the inverter, you ensure the inverter is off, then connect the inverter. Once connected, then you can switch on the breaker (hopefully installed) or the inverter itself.
- If you need to check for the health of a battery bank, you cannot do it by recording voltages of batteries in a connection, you need to break the bank apart and check each individual cell.
- Small sparks can occur when connecting batteries, generally this is loose connections, make sure the connections are tight. Don’t panic about it too much, it happens.
- Always install the charger output on the same node that you put the inverter uptake. In this way, should the batteries be full the output from the PV/Wind etc will go over the top of the bank and directly into the house/load.
- Enclosed rooms need extractors.
That’s it. I hope I have been helpful with this, if you need to know anything further or would like me to clarify on any point please contact me below.
**UPDATE** – Have added a solar battery calculator to our system, check it out here: Solar Battery Calculator