New Parallel Hybrid System

Readers of this forum might be interested to know of a new retro fittable Hybrid system that has been developed and is just going to market in the UK. Designed to be a cost effective and versatile Hybrid solution the system addresses many of the critisms often levelled at Hybrid systems as applied to boats.

The system itself has been developed and tested over five years by a company called Hybrid Marine www.hybrid-marine.co.uk.

In simple terms Hybrid Marine's parallel Hybrid follows the model of the Toyota Prius car in that as well as providing electric drive for slow to medium speed the combustion engine is retained to drive at higher speeds. This is the same as the Toyota where the car drives around town at slow speeds under electrical power but on the open freeway uses the combustion engine. Key advantages in using this approach in a boat include those of cost and weight. To try and match top end high speed hull loads to an electric system simply does not work, the size of the motor(s) required are cost prohibitive and heavy. It is far better and actually more efficient to allow a combustion engine to meet the high speed requirements. However for the low to medium speed requirements in average conditions relatively small lightweight and cheap electric motors can do the job very nicely. For example in calm waters a 17 ton Malo 46 needs in excess of 50hp to achieve hull speed of 8.5 kts BUT will achieve an acceptable 6kts quite easily with a 12hp electric drive.

Sports Fishing boats suit the parallel hybrid concept whereby they can use the powerful diesels engines to get out to the fishing grounds quickly and can then switch to quiet clean electric drive whilst trolling at slower speeds.

Other key advantages of the parallel approach is that of efficiency, as soon as the diesel engine is switched on the 10kW electric motor becomes a 5kW generator able to recharge the batteries quickly and efficently but also of course able to support on board domestic services including air conditioning through an inverter. The additional generating load on the shaft when the boat is using diesel propulsion assists in "forcing" the engine to operate at a higher point in its efficiency curve - a win win situation.

The parallel system also offers redundancy in that if the combustion engine (or its fuel) fails then the electric drive will get you home and visa versa.

In a sailboat the system can also regenerate up to about 1kW of electricity under sail - very useful in offshore passages - this will introduce some drag (about 1kt at 1kW) but in Hybrid Marine's system you can cleverly tweak how much power you regenerate v how much drag you wish to accept or you can simply turn it off.

At about $8,000 (not dissimilar to the cost of a generator) the system can be retrofitted to any engine on any boat and would seem to be a good solution particularly if you are considering buying a heavy bulky and expensive generator!

 

A semi diesel electric system with a batterypackage.

Similar systems are widely used, but with engines instead of batterys.
I think there is a cruise ship using a system like that with fixed pitch proppelers. instead of having a reverse gear or a engine that can run both ways they clutch out the main engine and clutch in a electric engine controlled by a frequensyconverter and powered by the aux's

quite similar to your system just that you use battery.
If you recharge the battery from solar panels I can say it's clever, but from shaft generators is a waste. You have to pull around on a heavy battery package and controls. The diesels have a 30% efficensy, generator 98% efficensy and then the batterys develop heat while charging/discharging and then again a 98%loss when you use the generator as motor. You probartly nead to go up one size on the engine when wanting it to run shaft generators witch cost both money and weight.

 

Parallel Hybrid

Hi StianM

You are correct in that similar technologies have been used (for some years in fact) by large ships the difference being of course that here is a system available at a cost effective price to the leisure market.

On your technical points I should have said that this system is actually a power management system and can accept inputs from solar and wind generators and thus provides the boat owner with a system that is as energy efficient as possible.

Regarding the shaft generator functionality you do not need to go up a size in engine to run the shaft generator in fact this is the exact reason it is so efficient. A diesel engine as you point out is very inefficient when it is pushing a boat - there is actually a lot of wasted energy. For example in the UK there are narrowboats (barges) on the canals which are typically fitted with a 40 or 50 hp diesel engine - in the old days these boats would have been pulled by one horse (1hp) and actually it only takes about 5hp to move the boats at the canal speed limit therefore there is a lot of wasted energy from a 40hp diesel. Hybrid Marine's system captures this wasted energy, puts it into the battery bank allowing the owner to turn the diesel off and drive electrically once the batteries are charged. This is therefore a very efficient system as you are reducing the running hours of the inefficient diesel. Also diesel engines are even more inefficient at light loads and actually become more efficient at higher loads and so you can see this system (by increasing shaft load) again improves efficiency.

The motor generator unit they use is actually 92% efficient as a motor and so your suggestion of a 98% loss is incorrect.

You are correct in that there is often a need to increase the size of the battery bank but if the correct battery technology is used this is not usually a problem and certainly the weight (and size) is less than that of a separate diesel generator

 

Let me ask a question regarding a boat I'm designing right now that it has been suggested I look into a hybrid / electric system.

The boat is a small (27') displacement hull boat (6kts only), at present a 10hp diesel running at 80% capacity will push the boat to (and maintain) hull speed in adverse conditions and 60% capacity is used for normal conditions. The diesel's alternator is keeping a set of house batteries charged for general use, but an aux. generator will be needed for electrical needs while on the hook for multiple days (or the main engine will have to be run at low efficiency).

Is this a good example for a hybrid electric system?

 

I would say that as long as the cost of the Hybrid system can be justified in relation to the overall cost of the boat then yes it is. The parallel hybrid described in my earlier posts runs a 10kW (12hp) motor so like your diesel it will be able to push the boat to hull speed but in near silence and of course its clean. It is also far easier to manouvere a boat with electric drive as you have instant torque availalbe and can run the motor down to 1rpm giving slow speed manouverbility you cannot get with a diesel.

You mention that you will need a generator to cover domestic demands whilst at anchor, the parallel Hybrid scores well here because there is a second clutch which allows you to disconnect the prop when the boat is stopped - you can now run your propulsion engine as a 5kW generator at anchor - this saves you the cost of a generator, finding the space for it, the weight of it and also of course saves on maintenance costs. The only down side of this solution is the fact that most generators come in an insulated cocoon wheresas with the hybrid your noise intrusion levels are dictated by the quality of the insulation of the engine compartment but then I guess you could design in some additional insulation if you thought it necessary

 

Just to introduce an alternative for a fair comparative publicity - Steyr has won the IBEX Innovation Award with his Hybrid Drive, which is a 7 kW (9.4 HP) electric drive which can be attached at a diesel engine's output shaft flange. It does all the things you have desribed in the opening post and is very compact:
http://www.steyr-motors.com/products/pdf/hybrid.pdf

 

Yes the Steyr system is very well engineered however it is only a 7kW system and Hybrid Marines is 10kW and probably more importantly to buy the Steyr system you have to buy their engines - it does not fit to any other brand whereas Hybrid Marines fits to any manufacturers engine even in existing boats. There is no doubt that the Steyr engines are superb engines but it has to be said they are at the higher end of price range

 

If you only nead 5hp, but got 30-40 hp your ebgine choice is really bad.

You should have a engine that run on 90-95% load and therefore adding a shaft generator to a engine that is correctly matched to a hull would require you to go up one or two sizes in engine witch means added cost, added weight and probably a more expensive maintenance. I would newer use a diesel to charge battery's.
I had a incident with a UPS a few months ago with battery acid leaking out causing DC current to flow out on earth witch went the earth guard go crazy.
We (it was two of us) carried a new 6000VA UPS dow to the switchboard room and claiming down I was sure my coworker would droop it in the stairs and I would die under it. It was extremely heavy.

 

"Is this a good example for a hybrid electric system?"

What on earth would you expect to actually GAIN?

What you propose would be state of the art efficient with one modification.

You would need to purchase AGM or some other battery type that will absorb at a huge rate. That would allow you to run the engine at anchor , and not underload the engine. A bus or truck alternator of 150A DC is not very heavy or expensive , and quite reliable , although if the bat set is acomidating enough a 250A 24V alt from a bigger truck, or bus could be found used.

A 3 stage regulator WITH a temperature sensor will allow the fastest recharges.

Sure you cant slink silently around the harbor for 20 min at slow battery speeds , to kill off that big expensive batt set , but is that really worth an extra $5 or $10K?

FF