The Fox Report
Barry Fox’s technology column
Turning up the heat on batteries
A
s lobbyists continually remind
us, the problem with renewable
energy is that it’s unreliable.
Solar only delivers when the sun
shines and wind only when it’s windy.
So, all eyes are on power storage. With
the high prices and limited capacity of
lithium batteries for solar storage, you
will know what’s not (yet) the answer.
Alternative solutions like pumping water
up hills is only viable on an industrial
scale. What’s needed is an affordable consumer store. I’m surprised there has been
so little talk of heat stores or heat batteries.
I first became interested when a friend
in the country, with no online gas supply
and facing ever-increasing prices for oil –
which can be stolen from external tanks
on dark nights – installed electric heating.
My country friend had already paid
a huge price for EV solar power and big
batteries but there was no way this could
provide hot water. There was no space for
large, insulated hot water tanks and no
three-phase mains available.
But the installed system, with only a
small water “tank”, can run instant hot
baths. How? The system maker, Fischer,
provided a pile of loosely-related paper
manuals as impenetrable as early computer tomes. They mainly tell how to
program and control the radiators. There
was very little on the big question: how
is the water being so rapidly heated?
Fischer’s web postings and sales publicity promise to tell “Everything About
Our Heaters And What Makes Them
Special”. But the details on offer are
very sketchy:
Aquafficient [the trade name for the
Fischer water heater] is an innovative,
Practical Electronics | November | 2024
modern and highly efficient solution to
heating water... it uses a single heating
element and patented thermal storage
technology, to provide hot water without
the need for tanks.
Instead, the hot water is produced from
stored heat energy within a unique phase
change material… known as a heat battery.
Once the battery has been fully charged,
it will pass the heat energy that has been
stored inside to the cold water coming
into the unit… the cold water comes into
a highly efficient heat exchanger that has
been embedded within the battery, and
this transfer of heat only happens when
hot water is called for.
This electric water heater provides hot
water until the battery is depleted. The
battery will recharge itself to ensure you
have access to hot water 24/7. [It has a]
Life span of 40,000 cycles, equivalent to
50 years of usage.
There is no detail given on the PCM
(phase change material) used and who
invented it. Out of curiosity, and because
I suspect our readers will be interested
in the under-discussed concept of heat
storage, I decided to do some digging.
To cut to the chase, British company
Sunamp (https://sunamp.com/en-gb/)
developed, patented and manufactures
a practical and reliable PCM heat battery
technology that other companies now
build into their heating systems.
Although I found no mention of Sunamp
in Fischer’s promotional material, and no
mention of Fischer in Sunamp’s publicity,
the University of Edinburgh, where the
key PCM research was carried out, names
Fischer as a user of Sunamp technology.
This is to be found in a detailed research
Case Study published in 2021 by Edinburgh University’s School of Chemistry,
EaStCHEM: https://pemag.au/link/abzb
The nitty gritty of that lengthy report
is that the idea of PCM storage is old, but
was until recently commercially flawed.
The heart of a heat battery is phase change
material (PCM) that absorbs heat when
melting and releases it when it freezes. It
has long been known that, in theory, salt
hydrates make ideal PCMs because of their
high energy density, plentiful supply, low
cost, safety and sustainability.
In theory, sodium acetate trihydrate
(SAT), with a melting point of 58°C, is
an ideal PCM for domestic use. But the
practical downside, which Sunamp found
in 2006, was that SATs change their chemistry in use, mainly through the formation
of solid anhydrous sodium acetate. So,
like an electric battery, the heat battery
degrades with use.
EaStCHEM Professor Colin Pulham,
who specialised in crystallisation science,
helped Sunamp crack the problem by
adding polymers. It then remained chemically stable for up to 40,000 heating and
cooling cycles. Sunamp extrapolates this
to a predicted lifetime of over 50 years,
as Fischer claims in its sales literature.
The University report cites Fischer
Future Heat as a key partner and quotes
Fischer as describing the technology as
a “must have” hot water solution. A big
plus is the option to heat the PCM with
off-peak electricity – or solar power – and
then use the heat to run hot water later.
Gluttons for technical and chemical
detail can go to the three source patents,
all readily available to read free on line.
The original patent (WO/2014/195691,
Improved Phase Change Compositions)
was filed in June 2013 by Sunamp Ltd and
three inventors: Andrew Bissell, David
Oliver and Colin Pulham, Professor of
High-Pressure Chemistry at the School
of Chemistry in Edinburgh University.
Two more patents on improved PCMs
followed, also naming Professor Colin
Putnam: WO/2015/025175 (August 2013)
described the use of Strontium Bromide
and WO/2020/074883 (October 2018) with
PE
metal nitrates added to the mix.
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