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.

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