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.