UK Narrowboat Electrical System

 

Traditional System

Generation of energy comes from a 12V alternator, perhaps pumping out 150 amps.

Storage comes from 2, 3 or 4 Lead Acid batteries, perhaps storing 100 Ampere hours each.

A typical boating electrical energy useage is 80 Ampere hours, of which half of that goes on running a Fridge.

Right, first things first. Let us use more modern units of measurement.

The 12V Alternator can produce around 2kW of electrical energy.

The batteries can store around 4kW of electrical energy, with half of that being available to use.

80 Ampere hours is 1kW

Modern System

This does not just add solar and intermittent use of an inverter. Not in my opinion.

Energy generation could be upgraded with effort to an AC alternator of perhaps 4kVA with twin ‘V’ belt drive. An inverter capable of accepting a generator input would be required. This turns the boats ICE engine into a generator.

Ideally, storage of electrical energy could be LiFEPO4 at 48V. Narrowboat owners with existing systems may simply choose to add a 12V LiFEPO4 battery. I will discuss reasons for this later.

With carefully chosen hardware, we now have a modern system capable of storing and releasing enough energy to run modern household appliances. Standard domestic washing machines, coffee machines and kettles can be run without any issues.

Energy Generation

An alternator providing 2kW of energy will also be producing 2kW of waste heat energy. A combined load of 4kW on the engine. Might as well get a 4kVA AC alternator.

Solar panels with a MPPT controller would be very beneficial for three of the four UK seasons. Try for 1.2kW minimum up to 1.8kW at the upper end. Bearing in mind there is only a limited amount of roof on a narrowboat.

1.2kW of panels ought to provide 2.5kW hours of energy at a minimum, except in winter where 0.5kW hour is likely. 0.5kW hour will keep the inverter alive but nothing else.

Energy Storage

LiFEPO4 are happy to charge or discharge at 50% of their kW rating. Lead Acid batteries prefer 5%.

So, to run a standard house kettle of 2kW from an inverter requires a 4KW hour LiFEPO4 battery bank or a 40kW hour bank of Lead Acid batteries. (This is 3,200 Ampere hours or 32 standard Lead Acid batteries.)

For those adding a 12V LiFEPO4 battery to their existing set up. I would get a battery and kettle with matching kW ratings. You will lose a couple of years from 15 years the LiFEPO4 will likely last but you buy 50% less batteries.

Let me be clear here, whatever the highest load is that you wish to apply, get the battery to suit. Many narrowboat owners will not see the need for a domestic kettle and that is a perfectly acceptable attitude to hold. Those who like the idea of a 1kW coffee machine need only buy a 1 or 1.2kW 12V LiFEPO4 battery. Modern narrow boaters call this mix of Lead Acid and LiFEPO4 a hybrid system.

With a new system I would consider 48V as the battery will be far cheaper and so will the cabling costs.

Basic Modern System

4kVA AC alternator professionally fitted

2 * 2.2kW / hr 48V LiFEPO4 battery

3kW Victron MultiPlus II

1.5kW of solar with a MPPT

With this system you get 4 times the daily energy budget of a standard narrowboater. You can use normal household appliances. You can have a normal fridge. A normal freezer. A coffee machine. A washing machine. Best of all, you can use any of them without the need to run the engine or be hooked up to a landline.

In summer this all runs from the solar panels. Autumn and spring will require running the engine at a specific speed for a while. Winter will require a set engine speed for 2 hours each day for the full 4kW / hours of energy replenishment. Traditional narrowboat users will be doing that anyway.

Advanced Modern System

6.5kVA AC alternator professionally fitted

1 or 2 * 5kW / hr 48V LiFEPO4 battery

5kW Victron MultiPlus II

1.5kW of solar with a MPPT

With this system you get 7 times the daily energy budget of a standard narrowboater. You could consider going gas free with an electric oven and induction hobs.

In summer this all runs from the solar panels. Autumn and spring will require running the engine at a specific speed for a while. Winter will require a set engine speed for 2 hours each day for the full 7kW / hours of energy replenishment. Traditional narrowboat users will be doing that anyway.

Disadvantages

Brand new narrowboaters ought to go for 48V from the start. It will be cheaper and better, which is a rare combination. Those with 12V systems will need to think hard about the cost of replacing existing equipment. A hybrid system would be my recommendation.

Connecting a 12V LiFEPO4 battery to an existing bank of 12V Lead Acid batteries requires a competent person who knows what they are doing.

Fitting an AC alternator requires someone who can make physical changes to swap from a standard belt drive to either a V belt, twin V belts or something even more robust.

The main problem for narrowboaters is that standard cruising will not charge the house batteries as the AC alternator output varies greatly with engine rpm. The Inverter will require a very specific engine speed which will likely mean that this isn’t feasible whilst cruising.

Traditional narrowboaters will scoff at this ‘preposterous’ idea but it means next to nothing in terms of being a disadvantage. It is really more of something to be aware of.

Additional Information

You can use more batteries if you want more capacity. You can use more solar if you have space.

Cost

Well, five times more daily energy useage needn’t cost five times more for your system.

3 large solar panels will cost more than the one a traditional boater has but the MPPT will be of similar cost if 48V is chosen for the house / leisure battery. A traditional boater does not have a large inverter and you needn’t unless you want to run power hungry AC devices.

Comparing 48V LiFEPO4 with 12V lead Acid batteries

A 2.2 kW/hr LiFEPO4 is about equal to 4 Lead Acid batteries, in terms of useable capacity.

The LiFEPO4 will be double the cost with double the lifetime. (More or less.)

In this like for like comparison, the LiFEPO4 can comfortably power a 1,000W piece of equipment and charge at 1000W too. The Lead Acids will be happier operating at 100W. In my opinion, 100W is not good enough. The LiFEPO4 could go to 2,000W and only ‘age’ 20% faster. A very beneficial trade off, again in my opinion.