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Volvo Buses officially launches the all-new plug-in Electric Hybrid bus

Volvo 7900 Electric Hybrid with overhead conductive charging station and pantograph extended. Click to enlarge.

As previously announced (earlier post), Volvo Buses will officially launch the new plug-in 7900 Electric Hybrid bus at the International IAA Commercial Vehicles show in September. The plug-in hybrid drive reduces diesel fuel consumption and carbon dioxide emissions by up to 75%, compared to a conventional diesel bus. Total energy consumption is reduced by 60%.

The Volvo Electric Hybrid Driveline is an extension of the well-proven driveline used in the Volvo 7900 Hybrid. The difference lies in a more powerful electric motor, increased energy storage and equipment for overhead conductive opportunity charging. The bus is equipped with a 150 kW electric motor that delivers maximum torque of 1200 N·m (85 lb-ft) and is powered by a 19 kWh Li-ion battery pack as well as a 240 hp/918 N·m Volvo D5K 240, 4-cylinder, in-line Euro 6 diesel engine with common rail injection.

The battery pack uses a heater/cooler system which operates both at the ramp and when driving. The bus is rapid-charged at select bus stops via a pantograph. Recharging takes approximately 6 minutes at end stations. The bus, which can operate about 70% of the time on electricity, has an electric range of about 7 kilometers (4.3 miles).

Volvo Electric Hybrid drive system
  1. Diesel engine
  2. Electric motor/generator (I-SAM)
  3. Gearbox
  4. ESS (Electrical Storage System)
  5. Power electronics
  1. Charging interface onboard
  2. Charging interface off-board
  3. Power charger
  4. Grid
  5. Electrified auxiliaries

The bus runs primarily in electric mode. To enable full electric drive, the bus is equipped with electric power steering; an electrical air compressor ; and a DC/DC unit that converts 600 V power to 24 V power. The DC/DC unit replaces the conventional alternator. The vehicle switches between hybrid drive and full electric drive depending on the current conditions.

When additional power is required or when battery capacity reaches a pre-determined level, the bus goes into hybrid drive. The diesel engine and electric motor then propel the vehicle together. Torque is distributed between the two units depending on the ESS charge status, speed and other conditions.

During braking or retardation, kinetic energy is generated and used to charge the ESS. This regenerated energy is later used for propulsion or for auxiliary consumers such as the air compressor, DC/DC unit or air conditioning system.

Volvo has already signed contracts with several European cities for the first deliveries. Hamburg, Luxembourg and Stockholm will implement the new bus system in 2014 and 2015. Series production is scheduled to start in early 2016.

I am very proud to launch this ground-breaking bus system. Electric-hybrid buses and full-electric buses are tomorrow’s solution for urban public transport. They will allow us to reduce energy consumption, air pollution, climate impact and noise, which are some of the biggest challenges facing large cities worldwide.

—Håkan Agnevall, President Volvo Bus Corporation

Noise is a growing problem in many cities. The noise level beside an Electric Hybrid is 65 decibels, that is to say normal conversation level. The Volvo 7900 Electric Hybrid runs in electric mode on average 70% of the route, silent and emission-free.

Three Volvo Electric Hybrids have run in a field test in Gothenburg over the past year, a test that has verified the reduction in energy consumption and emissions. (Earlier post.)

As of this autumn and for two years ahead, eight Volvo Electric Hybrids will be put into regular operation in central Stockholm. This is part of ZeEUS, an EU project being conducted in six European countries.



Not bad for routes that have long (or high-speed) stretches between charging points, though CNG hybrid would be a better option IMO. With $50/kW SOFCs that could take CNG directly, it would be even better.

I think I still like the Proterra bus a bit more though, even if it requires a bit of additional infrastructure to accomodate in-transit quick charging.


Disappointing design relying too much on large ICE. It is a mild hybrid?:

1. e-motor is too (2X) small.
2. battery pack is way (4X to 8X) too small.
3. diesel ICE is (2X to 4X) too large

Nick Lyons

Looks pretty good to me--good balance of cost and efficiency. 75% CO2 reduction is impressive.


The pantograph concept might really pay for itself if postal/parcel vans, taxis,bakery delivery trucks, street sweepers etc. utilized it too. This might even form the basis of an emergency generator concept. All enough to justify the costs to cut and cover new electrical lines ( I note that only the pantograph is above ground).


Proterra had a video about their bus being recharged, it just went under an awning then the bus was charged. There was NO visible anything, the overhead covering kept people dry in the rain.

Thomas Pedersen

Baby steps, I guess - regarding the hybrid driveline.

Nice job of making the pantograph look more attractive! However, it looks like the bus needs to be aligned very accurately. I hope the bus has an 'automatic parking' program to handle that.

It seems to me that this bus begs for a serial hybrid, perhaps with higher power output from the motor for high speed cruising. But something like a 2.0 TDI engine chugging along in its most efficient mode, producing 40-50 kW, would be more than enough to keep the battery topped of. It would also be much more efficient. And save supposedly hundreds of kg of engine weight.

I do realize that the constant drone of a serial hybrid can be 'weird' to some people. But the noise level can and will be much, much lower. And the ICE could easily be turned off at bus stops.

I suppose we will see a serial hybrid bus from Volvo at some point. I my memory serves me, the hybrid buses in London are serial..?

william g irwin

I think this is an excellent first step to convince the conservative transport systems to start the fleet conversion.
The ICE can satisfy the non-believers that it will keep running in those odd circumstances that they worry about - like breakdowns or traffic jams between charges.
Bigger, better, longer, stronger will come as they gain support.


Proterra's awning charger had automatic X/Y movement of the charge pad. The driver gets close then the computer on the charger does the rest. Nothing magic, no need to have a computer park the bus.


This seems to be an EASY first generation city bus hybridisation effort using existing ICE version and adding a small battery pack + e-motor.

The next generation will probably move further away from conventional ICE-Diesel version and make more room for electrification with much large battery pack and a second e-motor and smaller more efficient ICE?

Bob Wallace

There's major competition from the BYD battery powered bus.

No need for along the route charging infrastructure. Just recharge at night and drive the route.

The BYD's 150+ mile range meets about 80% of urban needs. And battery capacity will improve.


The battery capacity that can be recharged at the end stations will be fully used each journey. Any extra capacity will only be utilized once per shift. So there will be a big difference in benefit and pay-back per day between these two parts of the battery capacity. So I expect that the battery is sized to what can be recharged at the end stations, that is I'd guess the buses typically stop for about 6 minutes at the end stations.


It is fantastic what they're getting out of a 19 kWh battery pack.  If battery manufacturing capacity is one of the limiting resources (and it is), far more vehicles can be electrified than with all-electric buses.

The BYD bus has, if a quick search can be trusted, 324 kWh of battery.  That's enough for 17 Volvo buses.


It does seem like more good is done with limited resources by using hybrids instead of EVs. 1 Kwh for HEV versus 6kWh for PHEV or 16 kWh for an EREV or 24 kWh for an EV should be evaluated on the basis of how much fossil fuel and CO2 they offset.

It seems like 24 HEVs do a lot more good than one LEAF. I like the LEAF but 24 HEVs getting 50% better mileage is like taking 12 cars off the road, not just one.


A hybrid bus carrying 20 people at 10 MPG beats with 5 SUVs carrying 20 people at 10 MPG each by a factor of 5. THIS is why public transit makes sense in the city and not so much sense in the suburbs. You need ridership to make it pay off.

I favor more smaller buses, a 20 passenger hybrid bus getting 20 MPG would allow more routes and less waiting. However some have a bias against "fat union drivers" so this is a non starter. Just make the buses autonomous.

Bob Wallace

Battery plants can be built quickly. Certainly within two years. And battery prices will come down considerably as manufacturing volumes increase.

Whether the cost of the infrastructure for frequent charging hybrids (Volvo) or larger battery packs (BYD) turn out to be the least expensive alternative will be decided over time.


"...battery prices will come down considerably as manufacturing volumes increase."

What does the curve look like? If you double the output does that reduce the price 50%? LG and Panasonic certainly produce in high quantity, I don't see those prices dropping rapidly.


Let's see:

You have 17 buses.  You have 324 kWh of batteries.  You put them in 1 BYD bus and take one ICE bus out of service.  Savings:  6%.

You have 17 buses.  You have 324 kWh of batteries.  You put 19 kWh each into 17 Volvo buses and remove all 17 ICE buses out of service (maybe you use the extra 1 kWh for commemorative flashlights).  Savings:  70%.

I'm not sure it matters how much batteries cost; if you need less than 20 kWh per unit the cost isn't going to be very much.  That's one way to get lots of volume and push the production up so that possible economies of scale really are achieved.


Ad Tesla coud use 2 kWh battery in 42.5 Tesla S-2 and recharge every 2 miles or so.

That argument does not make sense in a country with plentity of unused human and material resources.

Who wants charging stations at most every bus stops to compensate for overly small battery pack.

It would make more sense to put more batteries (at least 5X the Volt) on board (to use less charging stations) and use smaller ICE on board diesel engine.

Roger Pham


A 2-kWh solid-state Lithium battery can put out 80 kW, weighing about 20 lbs and take up 5 liter of volume, or comparable to the lead-acid car battery. A car the size of the Model S with 1300 lbs of battery remove will weigh only 3,000 lbs when considering lighter suspension, wheel, tires and chassis. Sporty performance will need about 170 kW or 228 hp of power, so, in addition to a 80-kW motor, it will need 90-kW engine, preferably a 1-liter-3-cylinder turbocharged engine like the Ford 1-liter Ecoboost engine. A minimal 3-speed automated manual transmission is all that's needed to add to the engine because the motor provides a lot of torque at low speeds, 1/2 the size and weight of a 6-speed dual-clutch transmission now in vogue.

The engine and the minimal transmission can go on the front axle, while the 80-kW motor can go on the rear axle, instantly offering 4-wheel drive capability that is very desirable in higher-end models. The electric motor and inverter are downsized from 300 kW down to 80 kW with a lot of weight and cost savings that will offset a lot of the weight and cost of the engine and minimal transmission.

2 kWh will provide electric range of about 6 miles highway or even 8 miles city driving, enough to drive thru downtown in ZEV mode. Its high C rate allows it to be charged using 12-kW public charger in minutes, thus extending this 6-8 mile range many folds, to 12-24 miles a day with enough public chargers in place. When mass produced at 100,000 units yearly, it may be sold profitably at 30,000 USD.

A 4-kWh battery version can deliver 160 kW of power, and this battery will add only 20 lbs and 5 liter of volume more, while raising electric range to 12 miles highway and 16 mile city. It can be charged 2-3x daily using public chargers in minutes to double or triple this range. Total power in this up-scaled version will be 160 + 90 = 250 kW, or 336 hp, enough to rival the acceleration of the Model S 85-kWh, due to lighter weight. This high-end version can be marked-up to $40,000-$45,000 USD and people will flock to buy it, while the $30,000 lower power version will serve to draw-in young and first-time buyers.

MPG on engine power is estimated at 60 mpg at hwy cruise, so a 6-gallon fuel tank will be needed to realize 360-mile range. This 6-gallon fuel tank will cost a few hundred dollars to achieve 100-mile more range than $46,000's worth of battery, while save 1,500 lbs from the curb weight of the vehicle.

The engine and transmission can be purchased from Ford, Toyota, Honda, GM, VW, MB, etc for a few thousands USD a piece. The solid-state battery will be available from Panasonic in a few years perhaps for $500/kWh or less. Panasonic also supplies HEV battery for Toyota as well as BEV battery for Tesla.

Many millions of these HEV-PHEV's sold yearly will do wonder to really cut down on GHG while consuming minimum of resources. The consumers should be allowed to choose the battery capacity that would fit with his/her commuting distances, while keeping cost and weight down to minimum.


I'm not sure about your numbers, Roger, but I like the vision.


"The engine and the minimal transmission can go on the front axle, while the 80-kW motor can go on the rear axle..."

You describe a "through the ground" hybrid, a design I have advocated for years. It can be a retrofit to many front wheel drive cars.



Your proposed PHEV sounds too good and too low cost to be true bu could become a reality in the post 2020 era?.

A few more Plug-in (**) 350+ wh/kg battery modules, similar to those used in the Airbus e-plane, together with an ultra light 660 cc range extender, ultra light seats, ultra light Narrow tires, ultra light Windows and printed high efficincy solar panels on roof, booth and Hood could help to make it possible in 2020+ or so?

(**) Underr floor plug-in modules could be added as required to meet user requirements and Pocket book. With battery energy density evolution, this PHEV would get more and more e-range, until it becomes a BEV again?

Roger Pham

Thank you for sharing the vision. Now that Tesla has gained market attention, PHEV versions of the Model S and X, with 10-15-20 kWh battery packs, will guarantee sales success and rapid growth for Tesla. The Giga Battery factory may be scaled down, while development of Model III can be postponed (indefinitely?), in order to give funding to develop the Model S and X PHEV versions. People would prefer the full-size Model S and X, instead of the scaled down Model III, and would be willing to pay more, hence higher profit margins.

Grid Electricity is equivalent to $1/gallon gasoline, so why the downsizing?
Let's live it up, using sustainable energy souces and resource-sparing practices! The complete downsizing of engine, motor, inverter, AND battery pack in a BIG and roomy car is a great example of Green Eco practice WITHOUT COMPROMISE ON LIVING STANDARD nor on acceleration nor speed etc!

4-Wheel-Drive hybrid will fetch higher sale value and is desirable when a lot of power and torque is present, to distribute the torque evenly in order to prevent wheel spin and transmission breakage.

However, for low-end and lower-powered model, front wheel drive is more economical and both the e-motor and the engine and transmission can share one axle. The e-motor can replace the torque converter in automatic transmission, or the dry clutch in manual transmission. As such, the car is always started using e-motor and the engine only comes on after certain speed. The engine rpm will be synchronized and then connected via torque lock-up clutch.

Roger Pham

The Chevy Volt PHEV with 16-kWh battery pack and much bigger e-motor and engine now is listed for $34,000 USD. It was developed from scratch with over $1 B USD, and with annual sale figures in the low 20k's and declining.

My proposed HEV-PHEV's with 2-kWh battery pack with smaller 3-cyl engine and smaller motor of 80 kW should have no problem being profitable at $30,000 with annual sale figure at around 100,000 units, especially when based on the already developed Model S, with sheet metal, interior, amenities etc all figured out. Much less investment cost will be needed to just change out the power plants and reduce weight on the chassis and suspension, tires and wheels.

Your economical and ultra-light car will be uber ecological, yet, may have difficult time to appeal to upper middle class people who are looking for something bigger and more substantial. Remember the good old days when gasoline was $0.25 a gallon and all cars in the street were full-sized vehicles with two long bench seats that can seat 8 people? Why don't we bring back that golden age, now that grid electricity is the equivalent of $1/gallon gasoline?


One detail about your scheme, Roger:  the front wheels do most of the braking, so you'd need a motor up front to have good regeneration.  Also, a 3-speed means the engine will be operating well off its optimum most of the time (note the 8-speeds going into new vehicles).

There are mechanical designs that address some of these issues.

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