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The author's calculations for the capacity of the battery are very wrong and the battery will not last many years the way he's using it. Deep cycle lead-acid b

The author's calculations for the capacity of the battery are very wrong and the battery will not last many years the way he's using it. Deep cycle lead-acid batteries should not be discharged below 50% (known as Depth of Discharge, or DoD) unless you really want to kill them quickly. The author's calculations assume he can drain the battery 100% (35Ah), which while technically correct, will kill his battery very quickly. Unfortunately the manufacturer doesn't provide any data on the capacity over discharge cycles at different DoD's [0], but I can guarantee the author will significantly shorten the battery's lifespan by discharging it so deeply. If you want some idea of the effect of DoD on battery health, Hoppecke have a very good chart in their datasheet on page 43. [1] At 50% DoD, the battery will last for approximately 3000 cycles, or 8 years. At 90% DoD, the battery will only last for 1500 cycles or 4 years. If you want to go for 100% DoD in solar, you're looking at Redox flow or Lithium battery technologies, both of which are more expensive than Lead-Acid. There are other problems with this setup as well. At $17, the charge controller is very unlikely to support an equalization charge mode, which is required to periodically balance the cells within the battery to ensure a long lifespan. The author would be better off skipping AC entirely and charging their MacBook/iPad from a car charger which operates on 12V. DC lights can also be purchased quite inexpensively. The AC inverter is likely putting out something closer to a square wave than a sine wave, and the low voltage cut-off is far too low to avoid damaging the battery. This is really a case of "you get what you pay for" and for such cheap components, the system will not perform well or last for very long. If this sounds really negative, I'm sorry. I want more people to become energy independent, but if you follow the author's example, you're going to have a very bad time. If you are seriously interested in going off grid, you should invest in quality components like Victron, Outback, Studer, Hoppecke, etc. Something like the Victron EcoMulti would be a good choice for someone who wants an easy to use system that's been designed for longevity. [2] [0] http://www.expertpower.us/exp12350 http://www.expertpower.us/exp12350 [1] https://www.hoppecke.com/fileadmin/Redakteur/Hoppecke-Main/Products/Downloads/Montagehandbuch_verschl_EN_final.pdf https://www.hoppecke.com/fileadmin/Redakteur/Hoppecke-Main/P... [2] https://www.victronenergy.com/solar-pv-inverters/ecomulti https://www.victronenergy.com/solar-pv-inverters/ecomulti

mindslight 9y ago
To be fair, the DoD vs cycle numbers aren't as dire as they first look. Even an ideal deep-discharge battery would have a 1/x curve, as the real metric is total energy stored, which is proportional to DoD*ncycles vs DoD. For instance, for the two datapoints you gave. At 50% DoD, the battery will have stored 1500 times its capacity over its life. At 90% DoD, the battery will have stored 1350 times its capacity over its life. This is only a 10% degradation.

mindslight 9y ago

To be fair, the DoD vs cycle numbers aren't as dire as they first look. Even an ideal deep-discharge battery would have a 1/x curve, as the real metric is total energy stored, which is proportional to DoD*ncycles vs DoD. For instance, for the two datapoints you gave. At 50% DoD, the battery will have stored 1500 times its capacity over its life. At 90% DoD, the battery will have stored 1350 times its capacity over its life. This is only a 10% degradation.