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.