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Optare Introduces Battery-Electric Bus

The Solo EV. Click to enlarge.

UK-based Optare PLC has introduced the Solo EV, a full battery-electric bus. The Solo EV is a progression of the established Solo family of buses. The Solo EV is available in lengths of 8.1m, 8.8m and 9.5m and widths of either 2.3m or 2.5m.

Replacing the usual diesel engine is an all-new electric drive, featuring an Enova Systems P120 AC induction motor rated at 120 kW and powered by two banks of Valence Lithium Ion Phosphate batteries. The two packs work in parallel and provide 307V with a total capacity of 80 kWh. The batteries are housed in two steel crates set either side of the centrally mounted motor for excellent weight distribution.

The Solo EV power pack. Click to enlarge.

Behind the motor are the cooling radiator, electric power-assisted steering pump, motor controller unit and charger unit. On the right, above one battery crate, is the electric air compressor.

The motor controller contains the power inverter to drive the motor, two 8kW AC inverters for the power steering and air compressor drives, and a 24V DC-DC converter to charge the standard vehicle batteries. This is contained in one fully sealed and water-cooled unit.

The cooling system is non-pressurized and cools the motor, motor controller and battery charger. A single electric fan draws air from the inside of the engine bay and blows it out of the underside. The water pump is controlled so that it is used during normal driving and also during overnight charging. The pneumatic system is supplied from a rotary vane compressor which couples to a standard Solo air-dryer allowing the normal service items to be carried over.

Effective heating for the driver and passengers is achieved using an Eberspacher Hydronic M12 auxiliary heater, housed in the area normally occupied by the diesel fuel tank and connected into the standard Solo heating circuit. The heater, header tank and pump are easily accessed for servicing. The installation ensures that the front circuit is prioritized for rapid screen demisting but also has sufficient capacity to maintain the cabin at a comfortable temperature of 21 °C (70 °F).

Vehicle top speed is limited to 90 km/h (56 mph) although this can be further restricted for in service requirements.

The vehicle controls are the same as for a diesel powered Solo apart from amendments to the driver display to accommodate a battery ‘fuel’ gauge and warning lights. The familiar driving experience is retained with overrun braking set to mimic the driving characteristics of the conventional vehicle.

The vehicle has regenerative braking with the drive motor being used to slow the vehicle and recover energy to the batteries. This increases vehicle range and reduces brake component wear. This system is supplemented by the Solo’s foundation brakes.

No retarder is required as the motor is used as a generator under braking conditions to achieve retardation and provide power to the batteries. Lifting off the throttle automatically signals the motor control system to produce a small amount of regeneration to mimic normal diesel engine braking. First pressure on the brake pedal starts to increase the level of regeneration up to its maximum, just prior to the service brakes coming into play. This recovers up to 60 kW of energy back into the batteries during deceleration and gives the same retardation as the electromagnetic retarder fitted to the diesel Solo.

An on-board charger can be plugged into a standard 3 phase outlet at the depot; a full charge can be achieved in less than 8 hours. Optional boost charging can be undertaken through the day either at the depot or using a suitable power outlet. The charger is programmed to match the specific charge routine of the batteries and also equalizes the batteries at the end of the procedure. This latter phase gives improved battery life and charge utilization.

The battery charger is water cooled to improve thermal management and communicates with the motor controller unit so that the water pump and 24V DC-DC converter are switched on during charging. The unit shuts all systems down at the end of the cycle. The charging process is fully automated and the vehicle can be left connected without risk of overcharge.

Optare is investigating range extension, achieved by adding a third set of batteries under the floor or on the roof. Due to the design of the Solo this can be accommodated within the axle weight limitations, and could improve the range by nearly 150%. When introduced, this could be made available as an optional upgrade to existing vehicles.

Roy Stanley, the founder and currently chairman of the Tanfield Group Plc, parent of Smith Electric Vehicles, is a Non-Executive Director of the Optare Group. As of 15 July 2008, Stanley held 28.4% of Optare Group shares.

(A hat-tip to John!)



I hope this thing costs similar to diesel busses, or at least total cost of ownership is similar.
Seems too good to be true.
Personally, I'd love to see every smelly bus replaced by either a CNG or a battery. Hope it is viable.


"Personally, I'd love to see every smelly bus replaced by either a CNG or a battery."

Personally, I'd love to see every smelly bus replaced by a streetcar. Steel wheels on steel rails give the passengers a smoother ride.

Justin VP

What's the range on this?

Range seems to be the hurdle for electric bus use. A typical diesel bus on a city route can run for 16 hours with one quick fillup. Having to take an electric bus out of service after the battery is used up seems like a major hurdle to widespread adoption since you'd need twice as many vehicles.

I too really would like to see pure electric busses in our cities. Noise polution bugs me just as much as the particulate from diesel.


They are a bit coy on the range.
They have 80 KWh of energy so that wouldn't be very many miles - I am not sure how many miles you get / KWh in a bus like this - 1? 2?
They talk about applications where there is a lot of ideling (which isn't such a good sign).

Sounds like they need a range extender, preferably natural gas to maintain the low pollution characteristics.

For most applications, a natual gas hybrid (of whatever type) would seem to be optimal (in terms of economy of use and pollution).

Unless someone invents a pantograph style charger for intermittant charging.


In the 80s, engineering became "market driven" meaning that you actually talked to potential customers about a product concept and actually pre sold the product to buyers under contract before putting pencil to paper.

It still looks like there is a "build it and they will come" mentality to some of the innovators. If they can get funding on a wing and a prayer, more power to them. If investors want less risk, they will demand a better marketing position.

Bob Uppendown

Electric buses have been in use for more than ten years in parts of Italy, and a few in France. Checkout this Tecnobus website for examples

Account Deleted

With only 80kWh for a bus the range will be less than 100 miles. Thunder sky are going to market a couple of full size pure EV city buses (32000lb) later this year together with FAW a leading Chinese automaker with an annual production of 25000 buses. The buses have a battery pack of 300 kWh and a range of about 300 km with air-conditioning on. Se for example

I have found out that Thunder-sky charges about 312 USD per kWh and with a battery life of 1500 cycles these city buses are economical compared to diesel buses if diesel cost 3 USD a gallon. At 2 USD a gallon a diesel bus is cheaper but not much (total life cycle costs). These calculations are based on a number of other assumptions such as 10 cents per kWh, diesel bus 5mpg, EV bus 1.6 kWh per mile, 50 USD sales price per kWh for used lithium batteries (after 1500 cycles they still have much life back that utilities will pay for).

City buses are the first kind of EV applications that will become economical because the frequent stop and start of a city bus makes it impossible to get a good mpg with a diesel bus since it is operating far from its peak efficiency. However, we need 300 USD per kWh of battery or less and diesel at 3 USD a gallon or more for this to be clearly economical. Batteries will come down in price. The preferred LiFePO4 battery only needs about 10 USD worth of lithium carbonate for the production of a 1 kWh unit and probably less than 10 USD worth of the other necessary raw materials. The rest is cost of energy, machinery and work input all of which can go down in mass production and with new process technology.


I look at the battery market something like the solar cell market. As long as the market is small and people are willing to pay a premium, then that is where it is.

As soon as someone can come up with a better and/or cheaper product, suddenly demand increases and production volume rises. When a battery supplier is willing to take a smaller profit per unit on a larger volume of units, then things could take off.

The potential market is there, but must be proven to attract the capital for investment in facilities. We may be on that threshold, if the customer is convinced this is the product they want.
I am not convinced that they are sold on electric buses nor cars yet.


My god that sucks. A half ton of batteries and all its got is the range of a fat man chasing a snickers bar.


We are still missing out on a lot of Regen capacity. Ideally a peak somewhere around 2 - 5 times engine max will minimise those losses. That being likely impractical, the full 2 peak should be sought. Capacitor buffer with voltage converter can offer high braking Regen independent of battery capacity and high burst current while reducing battery demand through a suitable management.

The low resistance power devices and engine management systems alongside concerted chassis weight reductions can improve ev,s beyond sight.
These technologies are understood and possible but cost as investment is undervalued at this stage.

AC induction motor rated at 120 kW but only 60 kW of deceleration energy back into the batteries.


"fat man chasing a snickers bar"

Ha! That's great.

Why not make the chasis out of carbon fiber? From what I could obatain at Optare's website, this thing weighs a minimum of 16,000lbs. CF could pull this down to 6,000lbs.


"A half ton of batteries"

About the same as the weight of a diesel engine for one of these then.

Incidentally, in city service buses such as these rarely go further than 100 miles in one day.


Actualy in the h2 fuel cell bus trials they state that the average city bus needed to go 218 miles per day and work 18 hours a day or something.


The recent real-life city hybrid bus trials showed they went about 75 miles per day in New York.


Prolly why we will wind up with different kinds of busses in different areas.

Account Deleted

For EV city buses range is not an issue. They can charge at their home base and at the end stations where the chauffeurs are changed or have eating brakes. The busses that Thunder sky is selling can charge at 360kW. So if a city bus is operated 18 hours a day it implies 6 hours of possible charging time enough to charge 2160 kWh per day or drive 1350 miles per day. Hydrogen has no important advantages over EV city buses but they cost about five times more or so than an EV bus.


and use about 5 times as much primary energy


Um you do know 5x as much would be a nearly 7 million buck fuel cell??? They are less then 100 grand now so.. try again...

And on energy cost.. they now require less then 2x the power. But none of that matters realy what matters is the transit companies need and want BOTH in large numbers before fossil fuel prices go up again.

Louis Jennings

I have been working or the design and development of EV's now for the last year and find it very possible - I agree that the cost must come down and believe that it will as the cost of black gold (Crude oil) goes up. The supply of oil is very limited, and drilling is not the answer. We need other sources of energy like solar, wind and water to produce electricity. In so far as the electric vehicle (EV) goes, we need to developed high amp hour batteries (100 to 200 AH) and light weight aluminum 3 phase motors ACV motors that will produce high Kw (50 to 400 HP) and high torque that will operate off of 250 to 350 volts. They currently require 350 to 460 volts. I think the motors ideally would have duel drive shafts with roller bearings that have lubrication ports and that are replaceable. Another plus would be to have the motor water cooled. The cooling could also be used with the motor controller/Inverter and the DC to DC Converter. The weight could be further reduced by having the motor shaft hollowed out. (Similar to high performance race car crank shafts) In so far at the Concept1 conversion goes we want to be able to convert any make or model automobile (Car, truck, van, bus or motor cycle) from it internal combustion engine (ICE) over to battery powered electric communally referred to as EV. Our goal is to be able to use the existing transmission and especially the automatic transmission. Big buses and motor homes are ideally suited to immediately be converted as they can easily handle the weight of the batteries and present motors. They may or may not need transmissions depending on they desired speeds. Soon the average income person with the average vehicle will also be able to afford the conversion. It is presently very expensive and cost $30,000 to $50,000. I would like to see manufacturing of these components done here in the United States. I believe that big business manufacturing will need tax breaks from Congress to make it profitable to keep the jobs here in America. I also believe that tax credits or other incentives to the owners of the EV need to me made by congress to help the transition from ICE to EV affordable. I welcome your comments and look forward to yours. I did not mention it, but I also thought of the onboard ICE generator that many of the automakers are coming out with. This make the conversion a hybrid, but it greatly extends the range of the vehicle without the need for extra battery packs. Another thing that the buses can use is a plug in charging station at each stop to top off the batteries. I assume that the busses stop for a few minutes every now and then. These plug in adaptors could be universalized so that one type fits all, and they could be located at hotels, highway rest stops, truck stops, fuels stations, etc. My web site is and I think I will try to implement a comment section like this. I like it a lot.
Louis Jennings, Orlando Florida


Welcome Louis, you have a good looking site and have done some nice work on conversions. How many vehicles have you done so far?


Well I found more on this thing.

Its only got a 60 mile range and even in its largest config it only seats 33.. 21 extra can stand;/

In other words its totaly silly.


Of course it's totally silly. I wonder why would they spend so much money on developing it?

Perhaps they know their (potential) customers better than you do, wintermane.


The problem is you could do a better job 30 years ago just taking an OLD mid sized bus and converting it to lead acid batteries.

Its pathetic.

Account Deleted

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