Charging Infrastructure
SPR vehicles are powered by battery systems. These can be permanently installed or swappable. Our preference is for permanent batteries as explained below.
Battery systems have a large number of advantages including proven reliability, safety and flexibility. The main limitation is energy density (comparative to mass). Therefore external power supply options were originally considered for the SPR project, including ground based DC systems (‘Third Rail’), overhead power supply and induction systems, even including maglev. It should be clear that in the SPR system these would be to augment the internal battery systems, not to replace them, as battery operation has great advantages in stations and terminuses such as Euston. External power supply would also require accurate tracking, whereas the autonomous SPR shuttles have some flexibility of manoeuvre. Any external power system would be designed to ‘top up’ battery systems whilst travelling, not directly drive the motors.
As the SPR system requires some battery installation, the one disadvantage of a battery system (ie Mass of vehicle due to energy density limitations) would only be partially alleviated. It is important to note also that although low mass is always desirable, mass is not a critical element as the vehicle is travelling in a straight line at constant speed. Also even with the battery system in the 64 seat shuttle currently proposed, the weight would be comparable to a conventional railway carriage or a commercial road coach.
Advantages of Battery Systems over external power systems
No capital needed for installation of power lines and associated sub stations. This is an important aspect for HS2 given the projected cost of construction. (Battery Banks have similar needs but they can be located more conveniently). We suggest the saved amount in this area be directed to constructing a overhead canopy as described in Roadway page
Batteries have a ‘round trip’ efficiency of 90%-95% comparable or better than energy losses over length of power line for either AC or DC systems. Obviously the figure for power lines vary but realistically for a 120 mile line (as for HS2) at least 10% loss should be assumed..(even more when taking into account the inefficiencies of the pantograph connection and the continuous energising required. Batteries on the other hand use most of their energy in useful work. Transmission is supply led not demand led.
No rectification or transformer systems needed on board Shuttles to convert AC to DC power suitable for batteries and motors.
Far lower maintenance costs for battery systems. Transport and battery changing systems are mechanically simple and autonomous requiring less human interaction.
No electric power is required for vehicles in stations increasing safety and reducing construction and OEM costs.
No drag penalty for contact wheels or shoes, or aerodynamic losses from pantographs
No weather issues such as ice formation, debris and winds ( to be fair the proposed canopy element of the SPR system will provide protection for both types of system)
Allows a variety of formats to be adopted (Robocars, Single Shuttles, entrained Shuttles).
If an external supply were to be adopted for the SPR system, it would have the following characteristics:
Be an overhead system with pantographs that can handle sideways movement of vehicle up 1m either side of centre
Operate as a DC system (because it is a ‘top up’ system long distance continual transmission is not required, and can be separated. Lower power is also required, although voltage can be set higher than ground based third rail systems as the trackway is enclosed from humans and animals
As SPR is conceived with a canopy system, there is already an infrastructure available to hold wires. If a future development (e.g. superconductive lines or longer distance beyond battery capacity is required), a canopy system is already in place, allowing future development. of an external power line system.
Battery Cells and Packs
With current developments in battery density (as shown in our White Paper), we have concluded that augmented power systems add to complexity and construction cost for little gain and are therefore not required. We therefore propose that the system would run as a battery only system. Whilst permanently installed battery systems are possible and maybe inevitable, with current battery tech, we propose a battery swap system that is operationally simple and straightforward to operate, offers flexibility and operational convenience and the opportunity for ‘future proofing’
For example we currently propose the use of the current generation 4680 cell format as adopted by Tesla for their CyberTruck and Semi vehicles. However other battery formats can be utilised. These would be assembled into battery modules or packs that are either permanently installed or swappable.
Permanent Battery Systems vs Swappable Batteries
Earlier iterations of the SPR system supported the idea of battery swapping because it was thought that there would not be enough range to allow vehicles to make multiple journeys. A “Battery Bank” system was concieved with a robust simple and large capacity system to allow fast autonomous swapping. This retains some advantages over permanent battery installations, as it allows fewer shuttles to be in use. However following the dictum that “the best part is no part” we have now removed this concept from our project If you would like to find out more about this system. please contract us.
However with the increase in charging speed and performance we now believe that shuttles including the 1.6MWh SPR64 can be charged quickly and efficiently, within 1 hour and be in service within 90 minutes or less. Whilst more vehicles would need to be manufactured, the simplification of the system and removal of many moving parts would have great financial and operational benefits.
Permanent batteries installed in the floorpan of the vehicles would reduce the centre of gravity and distribute load more evenly. Also this would permit liquid cooling systems to be adopting allowing for a greater cell density than for air cooled swappable battery packs.
Whilst there may be many ways to package battery systems we conceive of the system as follows:
Battery cells (2170 or 4680 cells) are installed in battery packs (1.2m x 1.8m), with a capacity of 90kWh or more
These packs are installed in groups of four beneath each vehicle section. They all have separate charging systems but these are grouped together so they can be accessed by one charging point.
These charging points are situated in the bottom centre line of the vehicle at 4m intervials
An SPR64 would have 4 groups of 4 making 16 individual packs
When charging the vehicles would simply align with static charging points in the roadway and using their air suspension lower themselves onto these points
A full charge should take one hour. However the packs may be generally only half discharged and this will oftern require less time.
Vehicles can be charged at times of low demand (e.g at night) and queued for peak times. This will allow less draw on the power grid at peak times which could not be avoided by HS2 trains in their projected density of 36 trains an hour (or even 10 trains for Birmingham and Manchester only,
Battery cooling systems
Installation of permanent batteries in the Shuttles will have the advantage of both better aerodynamic performance and higher energy density as cells can be more tightly packed. We envisage that a smooth highly conductive cooling plate is located underneath each battery pack using the airflow underneath to cool with additional oil cooling pipes. Additional radiator systems might be placed in the tractor units.
Charging Structure in the Roadway
No moving parts are required for charging structures All movement is undertaken by the vehicle. This reduces maintenence and construction requirements
The charging points would be approximately 120mm above ground level and would have a larger collar that would bear the weight of the vehicle . This would also allow tyres to be ‘rested’ to avoid flat spots
The charging points would be symmetrical thus allowing charging in either direction
A soil removal and water replenishment connector would operate in a similar way and could be located either within the charging areas or separately (given that it can complete its task within seconds)
Cleaning services can be undertaken whilst vehicles are being charged. We have allowed for safe access in our designs for charging areas.
We have envisioned either a dedicated charging area to be located within a couple of kilometres of major stations or alternatively charging can be undertaken above the main trackway.
We calculate that the largest 64 seat Shuttle, which would have at least 1.15 MWh of Energy. This is enough energy to allow the shuttle to undertake a 155mph return trip between Birmingham and London without recharging.