One of the most common questions I get asked by you good folks out there is "what can I do as
an individual to reduce my own carbon footprint?" It's a very good question, and nowhere is it more
relevant than in your own home. In the United States, households account for more than 21%
of the total energy mix. Here in Europe it's more than 27%, so finding ways to reduce your domestic
energy consumption is one of the most impactful actions you can take as part of your contribution
towards climate mitigation. We've looked at some of the proposed alternatives for household energy
generation in previous videos - things like solar PV, ground or air source heat pumps,
and even the possibility of hydrogen as a fuel source. All those options look set to become more
commonplace as we move towards 2030, and hopefully the more enlightened governments around the world
will put in place very healthy incentives and subsidies to help and encourage us all to make
the change. A great deal of development work is also being carried out to produce smarter,
more efficient household products and systems that can help us all achieve our carbon footprint
reduction goals, and one of the most impressive designs I've come across in recent months
is an intelligent hot water storage system from a UK company called Mixergy. I caught up with
the folks at Mixergy recently to find out how their technology can not only cut down your
energy consumption and save you money, but also contribute towards electricity grid stability as
we move towards greater reliance on renewable but intermittent forms of energy like wind and solar.
Hello and welcome to just have a think. If you've got a water storage tank in your house
you may well have experienced the frustration of coming home after being away and having to wait
ages before you get any hot water through the taps, or perhaps the other delight of stepping
into the shower only to find that someone else in the house has used up all the hot water having a
nice luxurious bath. One of the main advantages of the Mixergy system is that it only heats up what
you need. That means it produces usable hot water about five times faster than a standard tank.
Inside the mixer cylinder there's a fairly standard heating coil transferring heat,
in most cases, from a gas boiler. The difference here is that the coil is at the top instead of the
bottom. This means that initially only the top slug of water gets heated up. There's also an
electric immersion heater up there which we'll come back to in a moment. One of the thermal
properties of water is that while it's very good at moving heat from a surface via convection,
it doesn't like transferring heat downwards into a colder section of water via conduction. So,
unless there's some physical mixing or stirring of the hot and cold water in the tank, then the
warmer water tends to stay warm and the colder water stays cold. And for the technically mining
among you that junction between hot and cold is called the thermocline. So the coil heats the top
section of water to the desired temperature of say 50 degrees Celsius then a pump starts moving cold
water from the bottom of the tank up to the top at a precisely controlled flow rate so that the
energy balance of cold water going into the hot section matches the heat input, which then stops
the temperature going up any further. If that cold water was pumped straight out of a pipe
then the system wouldn't work because the water would just sink straight back down to the bottom,
taking some of the hot with it through physical churn, so the cold is transferred into the hot
via a diffuser that spreads the water out like a mist allowing it to very rapidly achieve the
same temperature as the hot water. Effectively the tank is heating from the top down instead of the
bottom up. And that clever arrangement results in reduced heat losses. Overall the Mixergy tank can
save up to 20% on energy consumption through a combination of those reduced losses and better
control of the energy source heating the tank. And as you'd probably expect there's a smart app that
allows the householder to see exactly how much hot water is available at any given time and operate
the heating controls remotely. It even works with voice control via Alexa or Google assist.
But the Mixergy software is also smart enough to learn the patterns of behaviour of the
householders, and it uses that information to work out the optimal times to pre-heat the tank,
which in most cases is best done at night time using low or even negative tariff electricity
rather than gas. Which brings us to that electric immersion heater element I mentioned earlier.
This chart shows a typical night-time heating cycle for a Mixergy tank on a
flexible energy tariff. Mixergy's cloud software is constantly talking to the energy supplier
and it can see when the electricity supply price goes negative. Normally this tank would
be receiving heat from the system gas boiler, but in this case between 2am and 2.30am the consumer
is actually being paid a small amount for every unit of electricity they consume. So instead of
using gas, the Mixergy system takes advantage of this situation and starts using that electricity
to heat the tank via the immersion heater. Same thing between 2.30am and 3am, then the electricity
price goes back into positive territory so the tank stops consuming for half an hour,
coming back on again at 3.30am when the consumer gets paid 1.34 pence for every unit consumed.
Another pause at 4am, and then a final spurt between 4.30am and 5am, by which time the water
at the top of the tank is well over 60 degrees Celsius. And because of the astonishing level
of insulation that modern materials provide, the tank stays very close to that temperature
for the rest of the day. That opportunistic use of electricity means the tank is sometimes being
paid to heat. Plus you get the benefit of switching between gas and electricity
which is something that will most likely become more and more desirable as the grid decarbonizes.
But the smart features don't stop there. Because the Mixergy software is capable of monitoring
the frequency and voltage of the electricity supply, it can make the water tank function a
bit like a battery to help stabilize the grid through a mechanism called frequency response.
We looked at that in detail in a previous video, and you can click up there somewhere
to jump back to that one. In basic terms though, the transmission system operator, which in the UK
is the National Grid, predicts national energy consumption on a half-hourly basis throughout
the day and night and prices are set accordingly to incentivize generators to either turn up or
turn down their production during each half-hour segment. Once that's set, it's pretty much fixed,
so if something unexpected happens during a half hour slot that increases or decreases demand you
need to either find extra power or dump unwanted power. Not enough power could lead to blackouts
and too much power could lead to, you know, blowing up your substation - which you don't want!
That mechanism corrects any imbalances between supply and demand on a half hourly basis, but
other totally unpredictable events can also happen from one minute to the next. Things like a power
station breaking down or a large surge in wind power that wasn't forecasted. During those brief
events the grid frequency rises or falls depending on whether there's a surplus or deficit of power.
Because Mixergy tanks can measure that frequency they can respond to those momentary fluctuations,
and one of the great benefits of that is that they can help the grid accommodate more renewables
on the system. Mixergy's early field trials demonstrated that the vast majority of consumers
rarely use more than fifty percent of their water tank's capacity when measured.
That means there's an opportunity for the grid operators to dump excess energy into Mixergy's
water tanks, very similar to the way that utility scale battery systems are now being used.
Mixergy now have just over a thousand of their tanks installed across the UK providing about
one megawatt of frequency response capability. If all the existing water tanks in the UK were
converted to this smart technology then they could provide about a hundred gigawatt hours of storage
capacity. That's more than 10 times as much as the UK's largest pumped hydro facility at Dinorwig
in North Wales. And, unlike batteries, these tanks don't care about the number of cycles they're
put through either. There's no degradation in the heating system capacity over time,
and in the unlikely event that an element fails then it can simply be swapped out without having
to replace the tank or any of the other hardware. Mixergy provide a 25-year warranty on their tanks
but they expect them to last way longer than that. The tanks can fully heat and discharge
up to three times a day, so over a 25 year period that's potentially tens of thousands of cycles.
To future proof the technology as we move towards a net zero carbon world in 2050 the
tanks have been made compatible with any kind of power source including rooftop solar PV systems,
which can divert excess solar power into the tank instead of exporting it back into the grid,
and of course the heat pumps that the UK government are extremely keen for households
to adopt over the coming years. The target is for 600,000 heat pumps to be installed in UK
homes by 2028. Quite how the government intends to subsidise this mass transition away from gas
is probably the subject for a future video, but if they succeed, and hopefully they will, then
the Mixergy tank is ready. It's got a pre-fitted port that can accept a little plate heat exchanger
to allow the system to work seamlessly with this new technology even if they've
initially been installed with a gas boiler or electric immersion as their main heat source.
Now a question that you might reasonably ask is how these tanks compare to combi boilers in terms
of efficiency for hot water supply, especially as the world moves to greater urbanization and people
transition to smaller living spaces in apartment blocks. Combi boilers don't use storage tanks,
they take water from the mains and pass it across a heating element, in theory to provide instant
hot water whenever it's required. And it works perfectly well, especially for smaller dwellings.
But in 2019, Mixergy worked with a research team at Oxford university to conduct a study comparing
the working efficiency of a market-leading combi boiler and a market-leading storage tank from
one of their competitors. That study found that the combi boiler was only 73 percent efficient
compared to just over 84% for the storage tank. And in fact the smarter system in the Mixergy
tank actually achieves an efficiency of just over 95%. The reason for that discrepancy between tanks
and combis is the fact that a lot of the time we consumers turn on the hot tap very briefly
just to wash our hands or rinse a plate or something. When we do that the combi boiler
clicks on and takes a bit of time to get the water flow up to temperature. In fact sometimes the tap
is on so briefly that the boiler doesn't have enough time to get the water up to full heat,
so a lot of energy has been invested just getting the heat exchanger up to temperature, and once
the tap is switched off again all that energy just goes up the boiler's flue and out to fresh
air. Other smart technologies are now coming to market too, like heat recovery systems that divert
hot shower drainage water back into the heat exchange pipes to pre-warm the cold water supply
going into the mixer tap. That means much less hot water is needed from the tank in the first place,
which of course means the tanks can be made more compact to fit into smaller spaces in those urban
apartments. Mixergy have also experimented with the other option for providing hot water
for apartment blocks which is to have large communal water tanks for the entire building.
They recently supplied two10,000 litre tanks to London's Southbank University as part of a project
exploring the potential of harvesting geothermal energy from an existing aquifer in Central London.
And the performance results of that project will be analyzed very thoroughly to help inform any
future development work. Mixergy aren't confining themselves to the UK either. They're working with
a very large manufacturer in France to provide systems for the French market, and in July 2021
they'll be shipping a hundred of their tanks to a holiday resort in Sochi in Russia.
Theoretically there's no reason why this technology couldn't be employed anywhere in
the world, providing household consumers with the benefits of greater efficiency
and control over their hot water supply. And that all-important frequency response facility
has the potential to play a vital role in helping to accelerate the integration of renewable energy
sources into the distributed smart grids of the future. If you're one of the thousand or
so customers who already have one of these cylinders installed in your home, or if you
work in the industry and you have some experience of these technologies, then I'd love to hear your
feedback in the comments section below. That's it for this week though. A big thank you, as always,
to the people who make these videos possible by supporting my work via Patreon. They allow me to
remain completely independent and they enable me to keep all these videos totally ad free.
You can join the team at Patreon and get the opportunity to exchange ideas and information
with like-minded folks, plus watch exclusive monthly news updates from me,
and have your say on future programs in monthly content polls,
by visiting www.patreon.com/justhaveathink . And you can hugely support the channel
absolutely for free by subscribing and hitting that like button and notification bell. Dead
easy to do all that. You just need to click down there or on that icon there. As always, thanks
very much for watching, have a great week and remember to just have a think. See you next week