Full Electric With Range Extender
Full electric with range extending generators is a hybrid design that only has electric motors attached to the shaft. This is the greenest option as the operator can operate without the use of any fossil fuels. A large solar array will provide sufficient power for house needs as well as deliver excess power to the high voltage batteries. In practicle use, our yachts are sized so the owner can operate on electric alone for 1 day. While this may sound limiting, 85% of yacht trips are day trips. We understand the need for additional range which is what one or two generators will provide. Fuel tanks are sized to allow the owner similar range (~1 week) of runtime as an original diesel cat. At Nova Luxe we build superior cats to diesel and do not view electric yachts with limited range as viable products.
Additional information on this type of hybrid design can be found on the manufacturer Torqeedo's website. The key points are summarized in the image below.
Only electric motors propel the yacht. The power for these motors is stored in high voltage batteries built by BMW. In a pinch, if an issue occurs with the battery, it will act as a pass through system allowing the generator to power the motors directly. This is one form of redundancy.
Power can enter the high voltage batteries from a variety of sources. Most commonly, shore power can re-fill the batteries in one night unlike Tesla's road charging infrastructure challenge. Marinas that service yachts of this size have 50a, 220 power available. Second, "always on" source of power are the solar panels. Solar panels provide power to the 24 volt house battery bank. The first use of solar is to cover all house needs. Next, when the house battery bank is full, a DC/DC multi-directional converter will send power to the high voltage batteries. Finally, the DC genset can provide power while underway giving our yachts the same functionality of the original diesel model.
A large inverter provides AC power to the yacht and pulls from the house load as normal. Some of the house load is dedicated to navigation equipment for safety. If the house load runs low on power, then the bi-direction DC/DC convert will pull power from the high voltage batteries. At a minimum our yachts will have 80kW of power. A typical house in America uses 25kW of power in a day. In short this will provide ample power and prevent the need to run a generator at night. A few cloudy days can be ridden out and eventually the solar array will re-power the yacht.
Fully Redundant Blue Water Hybrid
In this configuration we leave a diesel engine in one of the two hulls. We then modify the alternator on that engine for a significant increase in power generations. We expect this version of hybrid yacht to be more popular as it combines the old and known diesel technology with the newer electric motors. This design also allows for a higher top speed. A catamaran will run straight or with very little rudder adjustment on a single engine. Some catamarans, such as Aspen, are even designed to only have one engine. This model also allows for zero emission operation by using the electric motor. Again, it is sized so typical single day use can be all electric. Extended cruising can be done by using a combination of the electric and diesel motors. While it is possible to integrate the diesel and electric motor controls we choose to keep them separate for a fully redundant blue water system.
The hybrid design above has two major changes. One electric motor and both generators are removed from the system. The diesel engine has a larger alternator attached and that alternator acts as the generator for the high voltage batteries. It will automatically power the high voltage batteries if low and the diesel is operating. Conversion costs for this model are lower as one engine compartment remains in a large part, unchanged.
An independent analysis on the merits of both hybrid designs was performed the DMS Naval Architects. For purposes of the analysis, both designs used a Leopard 51 PC as the model yacht. The full report is available for download below.
Hybrid On The Same Shaft
One hybrid design worth mentioning is placing both an electric motor and diesel engine on the same shaft. This is the method Green Line uses and we think it is necessary to electrify monohulls at this point in time. The typical configuration uses a smaller electric motor, usually 20kW for electric propulsion at low speeds. Near docks and in 5 mile an hour zones passengers enjoy the silence and cleanliness of electric. For higher speed operation the diesel kicks in and users have the best of both worlds.
We do not use this hybrid method for a couple reasons. First, we only re-power catamarans which require much less power to propel. In this market, we feel larger electric motors can achieve the necessary performance for a great yacht. Also, our goal is to be fully electric and while the two hybrid designs above are not fully electric they can be. Parts can be changed as other technologies mature but the overall design does not change. Especially in configuration 1 with duel electric motors, we believe future products will allow us to remove the diesel generator in favor of a carbon neutral hydrogen generator. If our design included a large diesel and small electric motor then it would need to be completely replaced for future 100% electric designs. Since product development for batteries and electric is moving so quickly, our modular approach will allow for modifications in the future without a complete overhaul.
We do believe this hybrid model to superiour to only diesel and if your interested in learing more, you can visit the webpage for Greenline.