One of the big experiments with the new #BoatingEurope lifeboat is to see how far we can move towards electric cooking and propulsion using solar power. The aim isn’t to build a high-speed electric boat, this is a slow, down-river cruising boat, where we can take advantage of the river current, travel at relatively low speeds and use solar energy for much of the everyday electrical demand.
The basic idea is simple – lots of solar + a decent battery bank + efficient electric pod motors = slow cruising without running the diesel engine most of the time. It is an experiment, and we are trying to do it without spending ridiculous amounts of money.
Two solar systems
The boat currently has two separate solar systems.
800W solar at 48V for the main propulsion and high-power kitchen electrical system
600W solar at 24V for the house electrical system
The 48V system is the interesting one because it will eventually feed the electric propulsion system as well as the 48V 6.5K inverter.
We are deliberately keeping the systems separated rather than trying to make one enormous electrical system do everything. The 24V bank will continue to look after the more conventional boat systems and most of the domestic electrical loads.
48V propulsion system
The main battery bank is currently 10kWh at 48V, with 400A of BMS. There is physical space to increase this to 20kWh or more when we find that the extra capacity is useful. That is important because battery capacity matters more than peak motor power for the sort of cruising we are planning. We aren’t expecting to run the motors flat out, the plan is to run them at roughly half power for normal cruising, with full power available for short periods when manoeuvring, getting off a mooring or dealing with stronger water. That should make the available battery capacity go considerably further.
The motors
We are looking at relatively inexpensive Chinese electric pod motors rather than an expensive western purpose-built marine electric propulsion system. The current candidate is the TH60 48V 5600W brushless IP68 pod motor, rated at around 60kg of thrust each. The proposed setup is two motors.
The quoted package is:
2 × TH60 motors
1 × 200A ESC with built-in BEC
1 × remote control and receiver
DDP shipping/tax included
The quoted total is $1,408.90
That is the sort of price that makes the experiment interesting. Obviously there are questions around longevity, efficiency, spares and how well these motors actually perform in a real boat. That’s part of the experiment, we are not pretending that buying cheap motors from China magically solves electric propulsion.
Charging
We are also trying not to make the system dependent on one charging source. Initially we will have a limited 200w charge from the existing boat alternator into the 48V system. There will also be 800W of mains charging when the boat is connected to shore power. That gives us option for longer electric cruising. For example, if we spend a night in a marina, we can put a decent amount of energy back into the batterys before setting off again, the interesting part is what happens when we leave the marina.
The solar path
Most of the time we expect to be traveling slowly in sunny weather. That means the solar system doesn’t necessarily have to replace everything we use every day. It just needs to put a useful amount of energy back into the batteries while we are cruising and sitting around during the day. With 800W of solar feeding the 48V system, we should be able to generate a useful amount of energy over a day’s cruising, particularly when the boat is moving slowly and the motors aren’t being pushed hard.
The 7.2KW 24V system provides a separate source for the house loads. So rather than thinking of solar as an emergency backup, we are trying to make it part of the normal energy cycle of the boat.
Sun → solar → batteries → motors → movement.
The other battery bank
There is also a completely separate 24V house battery bank of around 7.2kWh. This means that laptops, cameras, lighting, electronics, pumps and the other domestic loads don’t have to compete with propulsion for battery capacity. That’s quite important, one of the mistakes with electric boats can be thinking only about the motors. In reality, the boat itself consumes energy all the time. Keeping the house and propulsion systems separated gives us a much clearer picture of where the energy reserve is.
The 6.5kW inverter
The 48V system will also feed a 6.5kW inverter, which gives us 240V AC for the kitchen and other high-power tools and equipment. We are currently working through the cable runs and bus-bar arrangement.
The minimalist cable plan is
3m of 70mm² cable from bilge battery bank to the cabin main bus bar at the inverter and out towards the motors.
short 35mm² cable to the inverter, then 240V AC onward to the kitchen
around 4m of 50mm² cable from the main system to the rear boat bus bar
around 2m of 16mm² cable from the rear bus bar to each pod mounted on the back platform
This is maybe a little under speck, still being worked through rather than treated as a finished design. High-current 48V systems need careful attention to voltage drop, fusing, isolation, connections and cable heating, particularly when there are long cable runs and several kilowatts involved.
Why 48V DC power?
At these power levels, 48V makes a lot more sense than trying to run the propulsion system at 12V or 24V. The higher voltage means substantially lower current for the same amount of power. That’s particularly useful on a boat because copper cable gets expensive and heavy very quickly once you start pushing hundreds of amps around. Even so, 6kW at 48V is still a lot of current, which is why the battery, BMS, bus bars, fuses, cables and connectors all need to be designed as one system.
How far can we actually go?
That’s the big question. We have already done a five-year journey through 13 European countries using conventional diesel propulsion. This next stage is partly about seeing whether the same sort of slow, river-based traveling can be done with a much larger proportion of our energy coming directly from the sun.
The boat isn’t going to become a solar-powered speedboat, that’s not the point, the idea is to use the characteristics of down-river cruising to our advantage. If we travel slowly, use the river current, avoid unnecessary acceleration and don’t expect to run the motors at full power all day, then our energy requirements become much more manageable.
And when we do need more energy, we have several options:
solar → battery → electric motors
shore power → battery → electric motors
and, at least initially trickle charging
diesel alternator → battery
The diesel engine therefore becomes more of a sea crossing and range extender rather than the thing that has to run continuously.
A real-world experiment
This is very much a #BoatingEurope experiment rather than a finished commercial system. We are using what we already have, adding relatively inexpensive components where they make sense, and leaving ourselves room to expand the battery capacity and solar generation when the experience shows that we need it.
The eventual target is around 20kWh of 48V battery capacity, backed by the existing 7.2kWh 24V house bank, with around 2KW of solar across the two systems. Whether that is enough remains to be seen, the interesting bit is finding out in the real world. A slow boat moving down European rivers, powered partly by the sun, with the river doing some of the work as well. That feels like a rather good experiment for the next chapter of #BoatingEurope.
Sun on the roof.
Electric pods in the water.
A river underneath us.
And hopefully a lot less diesel.
