Last week one of our 125Ah 12 volt batteries on our off grid solar system failed after only 20 months use since we purchased the battery.
For the past two years we have been monitoring the utilisation of the solar panels and the output power we are using from the storage system (3 x 125Ah batteries) and we found that the current used during the evenings and overnight was being recharged back into the battery bank within a few hours each morning and for the rest of the day during the peak sunlight hours the solar PV output wasn’t being used apart from charging mobile phones and tablets which is a waste of the 400 watts of PV power we have on the roof.
Rather than spend more money on a replacement battery which isn’t being used to its full potential and with a limited lifespan we took the decision to change the off-grid hybrid system with the mains inverter which drives the lighting system in the house and 12 volt system which runs mobile / tablet chargers and low power lighting (including bedside reading lights) to be two separate systems with an off-grid solar PV setup which uses a new single 100 watt panel to charge the two 125Ah batteries to maintain the low voltage system and the other remaining panels will be using a Soladin 600 feed-in inverter to convert the previously unused PV energy into mains 240v power for us to use in the house.
The 600w maximum output on the inverter isn’t enough to run many appliances in the house but it will reduce our external load from the mains grid when only one or two computers are running in the house.
The Soladin 600 also has a serial output to log data from the inverter and we are planning to include this in a new version of our home energy data logger.
If we find that the feed-in inverter is giving us a good conversion of the PV energy we will look into the possibility of adding an additional 2-3Kw of PV panels to the roof and buying a much larger feed-in inverter system.
In the cupboard which houses the solar 12 volt system we removed all the previous hardware from the wall and started again with a simpler layout and added two large high current isolation switches so we can now completely isolate the batteries and the PV panels from the rest of the circuit.
We are still using the same Raspbery Pi data logger as before but it no longer has the mains inverter connected and logged.