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This seems like a common configuration: connecting solar panels + MPPT charger to lead-acid batteries which are also connected in parallel to an inverter.

Assume that, momentarily, the battery has been charged fully (as per the charger's logic), the solar panels are supplying their peak power, and the inverter is drawing current. I would like to know what is happening inside the battery in the following cases:

  • Both the battery and solar panel are capable of supplying the power requirement.
  • The solar panel is not able to satisfy the power requirement, so the battery has to provide it.

Does the battery undergo chemical changes which count towards cycles of the battery? How to count these cycles which I assume are not complete cycles?

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  • \$\begingroup\$ The battery is either being charged or discharged (ignoring the float state). The length of time it is being charged or discharged is all that counts. A complete cycle is fully charged to fully discharged and back to fully charged (or vice-versa), everything else counts towards a partial cycle. . \$\endgroup\$ – Jack Creasey Jan 5 at 6:19
  • \$\begingroup\$ @JackCreasey Do I need to worry about partial cycles of the battery during the time that solar power is sufficient to drive the load and battery is full? \$\endgroup\$ – HRJ Jan 5 at 6:25
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    \$\begingroup\$ If the battery is full, you need to worry about over-charging the battery. However, the MPPT charger usually worries about that for you, and doesn't overcharge the battery, as long as you told it the correct battery chemistry, voltage, capacity etc at setup. You generally don't have control over when battery cycles occur, the timings of your load demand and solar input control that. So don't worry, be happy, and replace the battery when its capacity falls too low to meet your needs. \$\endgroup\$ – Neil_UK Jan 5 at 6:57
  • \$\begingroup\$ @Neil_UK and Jack, I am mainly concerned about the environmental impact, as my motivation to invest in solar power is to reduce my environmental footprint. Hence, I want to know what exactly is happening inside the battery. If connecting the solar panel reduces the battery life, then it adversely affects the net benefit of switching to solar power. Thanks for your responses! \$\endgroup\$ – HRJ Jan 6 at 7:07
  • \$\begingroup\$ @HRJ you reduce your footprint by not stepping on the earth. There is no warm, cuddly way to consume electricity. Batteries cost resources to make. Solar panels cost resources to make. It's true that using panels and batteries are less bad than burning fossil fuels, and some of that is simply giving you less to use, so weaning you off the drug. You could ditch the battery, and do something else in the hours of dark. You could manually disconnect and reconnect the battery to reduce cycling, but that's inconvenient. Your inconvenience, or the planet? Tough one. \$\endgroup\$ – Neil_UK Jan 6 at 10:19

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