Tweed <usenet.tweed@gmail.com> wrote:
> Recliner <recliner.usenet@gmail.com> wrote:
>> Tweed <usenet.tweed@gmail.com> wrote:
>>> Certes <none@nowhere.net> wrote:
>>>> On 15/04/2022 15:13, Tweed wrote:
>>>>> Certes <none@nowhere.net> wrote:
>>>>>> On 15/04/2022 14:55, Tweed wrote:
>>>>>>> Certes <none@nowhere.net> wrote:
>>>>>>>> On 15/04/2022 13:59, Tweed wrote:
>>>>>>>>> <martin.coffee@round-midnight.org.uk> wrote:
>>>>>>>>>> On 15/04/2022 11:35, Muttley@dastardlyhq.com wrote:
>>>>>>>>>>> On Fri, 15 Apr 2022 10:33:22 -0000 (UTC)
>>>>>>>>>>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>>>>>>>>>>> Recliner <recliner.usenet@gmail.com> wrote:
>>>>>>>>>>>>> Isn't the engine running all the time?
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> Yes, but it very definitely is used to spin the flywheel up to speed before
>>>>>>>>>>>> departure. You can hear it, feel it and IIRC see it on the desk gauges.
>>>>>>>>>>>
>>>>>>>>>>> Sounds like a solution looking for a problem. Why don't they just bin the
>>>>>>>>>>> flywheel and use the engine directly with a small battery and motor for some
>>>>>>>>>>> regen and mild hybrid assistance.
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> They might do that today but battery technology has moved a long way
>>>>>>>>>> since they were designed and built.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> You can add super capacitors into the mix now as well as batteries. I
>>>>>>>>> believe some of the Birmingham trams are so fitted.
>>>>>>>>>
>>>>>>>>> https://www.polisnetwork.eu/wp-content/uploads/2019/06/hybrid-electric-and-rapid-accumulator-systems-2-finalpolis.pdf
>>>>>>>>>
>>>>>>>>> Super-capacitors and super-capacitor/battery hybrid trams are a relatively
>>>>>>>>> new addition to catenary-free tram technologies. These trams have evolved
>>>>>>>>> from battery-powered or -assisted trams as an alternative method of energy
>>>>>>>>> storage and capture. Generally, super-capacitor trams have short
>>>>>>>>> operational ranges and charge quickly at stations or points of rest. Most
>>>>>>>>> super-capacitor systems are paired with traction batteries to provide both
>>>>>>>>> high outputs during acceleration and to extend ranges during regular
>>>>>>>>> operation and cruising. Bombardier, Siemens, and CAF are all currently
>>>>>>>>> developing and offering super- capacitor/battery hybrid trams with varying
>>>>>>>>> systems. Chinese light rail manufacturer CSR has also developed a solely
>>>>>>>>> super-capacitor tram at its facilities in Guangzhou with plans to enter
>>>>>>>>> operation before 2020
>>>>>>>>>
>>>>>>>>> Super-capacitors have much lower energy capacities compared to batteries
>>>>>>>>> but offer greater charge densities. These densities can be 10 to 100 times
>>>>>>>>> greater than those of batteries and offer significant output during
>>>>>>>>> acceleration or climbing gradients and are achieved through the ‘physical
>>>>>>>>> rather than chemical’ storage of the energy. The structure of
>>>>>>>>> super-capacitors, namely the method by which they store their charge,
>>>>>>>>> allows them to be charged and discharged over 100,000 times - far exceeding
>>>>>>>>> the number of cycles capable by traditional batteries which average 2,000
>>>>>>>>> to 40,000 cycles. Super-capacitors are also able to capture power from
>>>>>>>>> braking sections of track through regenerative breaking, providing further
>>>>>>>>> charging and power generation capacities.
>>>>>>>>> With the exception of the Guangzhou super-capacitor-only tram, all trams
>>>>>>>>> using the technology to date are super-capacitor/battery hybrids. The
>>>>>>>>> batteries help to provide power through maintaining speeds on level
>>>>>>>>> segments of track while the super-capacitors help to provide additional
>>>>>>>>> high-current power during acceleration and climbing gradients. These trams
>>>>>>>>> average top operational speeds of anywhere between 45 to 70 km/h and
>>>>>>>>> average catenary-free operational distances of between 800m and 2.5 km
>>>>>>>>> before recharging. There are a number of super-capacitor-enabled systems
>>>>>>>>> available on market with CAF’s ‘Rapid Charge Accumulator’ (ACR),
>>>>>>>>> Bombardier’s ‘Mitrac Energy Saver’ (MES), and Siemens’ ‘Hybrid Energy
>>>>>>>>> Storage’ (HES) the most popular.
>>>>>>>>>
>>>>>>>>> Attractiveness
>>>>>>>>> • Offer greater energy densities and outputs than traction batteries.
>>>>>>>>> • Significantly greater number of life cycles than traction batteries.
>>>>>>>>> • Extremely short recharge times of 10-30 seconds, allowing for near-full
>>>>>>>>> recharges at stations.
>>>>>>>>> • Do not use fossil fuels and improve air quality along lines.
>>>>>>>>> • Do not require expensive third rail technologies such as electrified
>>>>>>>>> ground rails.
>>>>>>>>> • Can be installed on tradition tram carriages and integrated into
>>>>>>>>> propulsion systems.
>>>>>>>>> • Technology supported and in development by many high-end engineering
>>>>>>>>> companies, promising
>>>>>>>>> significant improvements and upgrades in next decade.
>>>>>>>>>
>>>>>>>>> Risks
>>>>>>>>> • Currently one of the most expensive tram technologies.
>>>>>>>>> • Very low energy capacities, generally requiring auxiliary or assistant
>>>>>>>>> systems to fully operate
>>>>>>>>> catenary-free.
>>>>>>>>> • High maintenance and replacement costs, although greater life expectancy
>>>>>>>>> than traction batteries.
>>>>>>>>
>>>>>>>> "Super-capacitors have much lower energy capacities compared to
>>>>>>>> batteries but ... greater energy densities". Does that mean that
>>>>>>>> capacitors with similar capacity to batteries would be smaller and/or
>>>>>>>> lighter and are not feasible only because of their very high cost?
>>>>>>>>
>>>>>>>
>>>>>>> I read that bit several times and it doesn’t make sense. What I think they
>>>>>>> might be trying to say is they can have much greater peak discharge and
>>>>>>> charge currents. Very useful for rapid charge and assisting batteries for
>>>>>>> acceleration.
>>>>>>
>>>>>> What you wrote makes more sense than what they wrote. It sounds like a
>>>>>> perfect ingredient of a hybrid system: charge the capacitor as you stop,
>>>>>> discharge it quickly as you start, use the battery for long-range power.
>>>>>>
>>>>>
>>>>> Seems the Chinese have dispensed with the battery and just use super
>>>>> capacitors:
>>>>>
>>>>> https://goexplorer.org/supercapacitor-techno-logy-leading-the-charge-for-public-transport/
>>>>>
>>>>> State-of-the-art battery technology enables electric trams to fully
>>>>> recharge in just 30 seconds. With a 20 km long route, Huai’an has
>>>>> introduced the longest running electric tram using supercapacitors in the
>>>>> world.
>>>>>
>>>>> Huai’an has implemented one of the first electric trams powered by
>>>>> supercapacitors to run on a 20 km route, servicing 23 stops in the busiest
>>>>> area of the city. Supercapacitor technology has a number of advantages over
>>>>> regular batteries, with a 30 second recharging time and long lifetimes.
>>>>> This means, that Huai’an’s trams can run all day every day for up to ten
>>>>> years, recharging at each stop on the line. The trams also use energy
>>>>> recovery technology to salvage 85% of the energy generated from braking.
>>>>>
>>>>> With no need for overhead cables to power the trams, infrastructure and
>>>>> maintenance costs are significantly reduced, and the system is less
>>>>> vulnerable to adverse weather conditions. The CNY 3.7 billion project
>>>>> carried 7 million passengers in 2016, with about 30% of journeys replacing
>>>>> private car trips, avoiding roughly 4,900 tons of CO2 emissions annually.
>>>>> While many cities are using electric trams and buses, this is one of the
>>>>> first in the world to use supercapacitors for energy storage, and plans are
>>>>> afoot to expand the service even further.
>>>>
>>>> A tram with 23 stops in just 20 km, recharging at each, won't need to
>>>> store much energy. It's a perfect niche market for supercapacitors and
>>>> doesn't need a battery. I was thinking about recharging en route and
>>>> the concern about live rails. A short third rail that's only live when
>>>> it's concealed beneath a stationary tram could be an ideal solution.
>>>>
>>>
>>> From what I’ve read, supercapacitors store about a quarter of the energy of
>>> lithium batteries per kg.
>>>
>>>
>>
>> It's the other way round. Supercapacitors store around three times as much
>> energy per kg as batteries. They're also much more efficient, about 95% vs
>> 60-80%. They also recharge very fast without over-heating, and last much
>> longer, measured both in cycles and time.
>>
>> There are two big snags, however: the voltage drops much more as the charge
>> falls, and they can be ten times as expensive.
>>
>>
>
> I disagree
>
> https://en.wikipedia.org/wiki/Supercapacitor
>
> See the table in section 2.6, Wh/kg entry
> Other sources back this up
>
> Not to be confused with Watts/kg, where supercapacitors win, hence the high
> charge and discharge current characteristics. In simple terms a
> supercapacitor has a much lower internal resistance than a battery.

Yes, you're right, supercapacitors have a high power density but a low
energy density.

> Dropping voltage isn’t too much of a problem with modern switched mode
> power supplies, they can take a wide range of input voltages.
>

Yes, less of a problem than it once would have been.