RE: SP Angel BMN9 Mar 2020 11:13
power loss is a poorly defined term in this context - they mean efficiency which is the energy loss of what you get out compared with what you put in. Actually if you leave a Li-ion battery charged up at 100% then it loses charge over time, at a much faster rate than a VRFB would so round trip efficiency is usually quoted on the basis of the energy you get out on a discharge immediately after you have charged it up - so no waiting around.
The real world round trip efficiency depends on the situation you are using the battery system in - i.e. whether you include the inverters for converting between AC and DC and whether you also include any of the ancillary equipment for running the battery - eg pumps in the cases of a VRFB or aircon system in the case of a lithium-ion battery. The lithium-ion boys can play tricks on you by leaving all this stuff out and only quoting figures at 20 deg C and keeping the aircon turned off- it is harder for the VRFB boys to be economical with the actualite as you can't get a VRFB to run without the pumps etc.
Also power availability is a confusing term - it is not to be confused with the availability factor of a power station, which is the amount of time it is actually not broken or under repair. If he means the switch on time then a VRFB can switch on in under cycle, as demonstrated over years by Sumitomo. This requires the stacks to be always full of electrolyte (though the pumps do not have to be on) - some batteries allow the electrolyte to drain back out of the battery when the pumps are not on, in order to reduce the effects of self-discharge, as alluded to in the first paragraph.
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