FixAMess Posted January 16, 2020 Share Posted January 16, 2020 What does it mean to have a balanced system? Is there a relationship between Panels, Inverter and batteries that one should try maintain? What is that relationship? Quote Link to comment Share on other sites More sharing options...
___ Posted January 16, 2020 Share Posted January 16, 2020 1 minute ago, FixAMess said: What does it mean to have a balanced system? Perhaps the easiest way to explain is by using examples of unbalanced systems. One example is when you have too much PV compared to the battery capacity. If you put 4 x 100Ah batteries into a 48V system, it has a total capacity of 4.8kWh. If you have low load or no load during the day, it would be silly to install more than about 1kWp of PV (maybe a bit more), because most of it will go to waste. 1kWp is sufficient to generate up to 5kWh a day. The batteries also want to charge at no more than 20A (about 20% of the Ah capacity... and technically I'm pushing it, 15A is better), so going over 1kWp increases the danger of overcharging your (lead acid) batteries. Similarly, a 5kW inverter on that same 4.8kWh bank is also not balanced. The battery will not like more than a 0.2C discharge rage (again, 20A), so 1kW is about the maximum continuous power available to you, maybe 2kW for a few seconds. Sometimes people will buy the oversized inverter with the plan to upgrade the batteries later. That is fine, it is an imbalance you can manage. Many so-called solar installers may however sell you a system that is underbatteried without telling you such things. 11 minutes ago, FixAMess said: Is there a relationship between Panels, Inverter and batteries that one should try maintain? There isn't a fixed ratio, but as I explained above, you can do some simple math to see if a system is completely ridiculous or not. In my experience, people tend to under-battery their setups (cause batteries are expensive). Also note that Lithium Iron Phosphate batteries have higher charge and discharge rates (typically 0.5C or even 1C), which does allow a higher ratio of PV or inverter to battery capacity. And just in case you haven't picked up on the C notation, 0.5C means half the Ah capacity, so if I discharge a 100Ah battery at 50A, that is a 0.5C discharge rate, and the same when I recharge it. What that means is that I can charge and discharge a LiFePO4 battery at least twice as fast as lead-acid (and often even more), which means I can have twice the PV and double the inverter size without getting out of balance. FixAMess and dvdwalt 2 Quote Link to comment Share on other sites More sharing options...
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