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Plunging Battery Prices Expected To Spur Renewable Energy Adoption
Lucas123 writes: Lithium-ion (Li-on) and flow battery prices are expected to drop by as much as 60% by 2020, making them far more affordable for storing power from distributed renewable energy systems, such as wind and solar, according to a recent report by Australia's Renewable Energy Agency (ARENA). The 130-page report (PDF) shows that Li-on batteries will drop from $550 per kilowatt hour (kWh) in 2014 to $200 per kWh by 2020; and flow battery prices will drop from $680 per kWh to $350 per kWh during the same time. Flow batteries and Li-ion batteries work well with intermittent energy sources such as solar panels and wind turbines because of their ability to be idle for long periods without losing a charge. Both battery technologies offer unique advantages in that they can easily be scaled to suit many applications and have high cycle efficiency, the ARENA report noted. Li-ion batteries more easily suit consumer market. Flow batteries, which are less adaptable for consumer use because they're typically too large, scale more easily because all that's needed to grow storage capacity is more electrolyte liquid; the hardware remains the same.
Lead is cheap but you get what you pay for.
First, lead-acid has a shelf life even if you do not discharge the battery - the lead plates sulfate over time, reducing capacity. It is only partially reversible by occasional special charge/discharge cycles. This shelf life is something like 3-5 years, depending on how much capacity you are willing to lose.
Second, lead-acid self-discharges. This means, unless you use the battery very close in time to when you charge it, you've wasted some of the energy you put into it. Trickle-charging only makes this worse, since you will always be dropping energy into the battery without getting most of it out.
Third, lead-acid discharge voltages are strongly impacted by the current at which you discharge them - look up the Peukert exponent for the golf cart batteries you were quoting - it will be over 1.2, and probably higher, meaning that high current discharge will drain the battery much faster than expected.
Finally, even deep cycle lead-acid batteries are slowly degraded even by the 50% discharge you quote. It only takes a few hundred cycles for capacity to be diminished by double-digit percentages. This is caused by plate erosion.
Existing lithium cells don't have a known shelf-life (they probably have one, but we don't know what it is) - it could be 10 years or more. They have expected 80% discharge cycle counts of *thousands* rather than hundreds. And their Peukert exponent is very close to 1.00 since they don't have the same variable internal resistance characteristics of lead-acid.
I have first-hand experience of this - I have used all three of deep-cycle flooded, deep-cycle sealed (AGM), and now Lithium Iron Phosphate (LiFePO4) cells in my home-built electric vehicle conversions. My lead-acid shelf lives were right along with that 3-5 year expectations. The LiFePO4 cells are going on 2 years now with no measurable decrease in capacity.