
How Water Heaters Have Evolved into Grid-Scale Energy-Storage Devices (2014) - camtarn
https://www.esource.com/ES-WP-18/GIWHs
======
ethagknight
This is not a battery, or a battery killer, and the author surely knows
better. This is a distributed load bank, located in places the heat can be put
to good use.

Interesting idea though. The paper seems like it’s pushing a product instead
of pushing concepts, because the applicability of this concept goes much
broader than the article goes into, for greater benefit to the consumer. A
heat pump (a compressor and some fans) can be switched on or off just as fast
as a heating element, at least as far as the article is concerned. The water
heater switch is a dead simple solution though, credit due for that.

A bit of a rabbit trail here: A heat pump would not provide as much potential
load, but it gives the flexibility of working for both heating and cooling,
and also puts the electricity to better use. The key would be to put a cheap
heat storage element in between the customer-premises heat pump and the final
use, so that the utility can fire up the heat pump regardless of the
customer’s need, and the customer has a huge bank of hot or chilled water at
their disposal. Combined with a radiant floor heating system, and tied into a
water-source HVAC system, this is a real energy efficiency boon by taking
waste energy and getting it past the meter into the customer premises. Go
ahead and throw a Steffes(tm) resistance heater in the water heater while we
are at it. Have your cake and eat it too.

~~~
radicalbyte
My father works in the heating world. He installed a large efficient storage
water heater in the house which would basically warm the water in one go at
5am and provide it to the house all day.

What I don't understand from the article is why this is being controlled by
the grid? The US is a market system, can't I buy a smart immersion heater
which can then react to real time pricing information? So I warm my water up
at times when the grid are paying people to use electricity?

That places the incentives correctly:

a) The entity making the investment in a new heater also gets the financial
benefits thereof.

b) What's to stop your electricity supplier making your water 5% hotter every
year to boost their revenues?

~~~
benj111
"What I don't understand from the article is why this is being controlled by
the grid? "

Hypothetically if you bought your own you would need a smart meter so you're
electricity company knew exactly when you had used power, there also needs to
be a system to communicate to your smart appliance, to tell it to turn on.
Neither of these really exist so I suppose its sensible for the utility to
take ownership to iron out kinks, feel out how in works in practise and stuff.

To clarify, smart meters do exist, I don't believe they have the accuracy of
metering needed for this application though.

~~~
bdamm
The modern smart meters are quite accurate, much more accurate than the
mechanical ones, usually to the ratepayer’s chagrin. The modern meters will
pick up an induction spike from a noisy motor such as in an inefficient
refrigerator or fan, where the older generation would not. How accurate does
it need to be?

~~~
benj111
Its the time accuracy that matters, if its for frequency stabilisation then
you need granularity in the order of seconds, rather than minutes as I believe
smart meters are at the moment.

~~~
bdamm
Oh no, they're way down in the milliseconds.

------
cnj
My uncle has implemented version 0.1 of this in his weekend house. Power is
cheaper during the night, so he has installed a clock timer that only powers
the water heater during the night. It holds enough hot water for two persons
to take a shower, and to wash hands during the day. (There is a separate water
heater in the kitchen).

Works great. If one should ever run out of hot water, it's simple to remove
the clock timer... but we didn't need that when we spent a week there.

With a well-insulated water heater, the idea to use them as energy storage
sounds like a great idea.

~~~
ddalex
I have version 0.2 in my London apartment - the bottom element of the water
heater is connected to a different electric supply, with a separate meter,
with energy that's almost 3 times cheaper than the rest of the wiring energy.
The catch? The circuit is powered only when the power company feels like it
(i.e. They need to dump excessive power somewhere), but they guarantee 2h
power on by day and 6h by night.

Since this is the bottom element, and the top element is controlled by a
thermostat (guaranteeing hot water on demand), this is a great setup for both
the consumer and the power company!

~~~
throwawaycanada
What an unusual arrangement. Are you allowed to connect other things to that
power source?

~~~
ddalex
I am not sure, I also have a storage heater on the same circuit. Probably I
need to speak to the power company if I want to connect a power bank of some
sorts, like charging a car.

The tariff is called Economy9 for reference. It's not widespread outside
London.

~~~
gambiting
Is it not? I know at least a few people who use Economy9 in Newcastle. And
yes, their storage heaters are hardwired to this secondary circuit.

------
rocqua
It sounds disingenuous to call one-way energy sinks 'heat storage'. Calling
such a one-way sink a battery is even worse.

On another note, I wonder how resisitve heaters compare to heat-pumps. The
article states that heat-pumps can react faster, but are more efficient. What
about putting a battery in front of the heat-pump to accelerate the response?

~~~
ajross
Why, exactly? It's not electrical power storage, sure. But a water heater is
_by definition_ energy storage. You want hot water, it takes time to heat, so
keep it in a buffer.

And in fact a well-insulated modern tank is a very efficient store for energy
that you're going to use at some point anyway. It makes perfect sense to use
it as a flexible load to buffer grid management.

> On another note, I wonder how resisitve heaters compare to heat-pumps.

Heat pumps are sort of an orthogonal trick. Ultimately they work by using a
lower temperature state to "steal" energy from the cooler outside
temperatures. They don't make "heating" any more "efficient" per se. But if
you have such an outside environment (i.e. colder than whatever the operating
temperature of the heater is, but still warm enough to provide energy to the
coolant) they are worthwhile.

~~~
SigmundA
Heat pumps are no trick any more than solar panels or solar water heaters are.
Resistive heat is 100% efficient while heat pumps are over unity usually
300-400% efficient although usually denoted as coefficient of performance
(COP) as number ex 3 or 4. For every 1 watt put in 3-4 watts of heat come out.
Real efficiency in terms of energy paid for vs energy provided to heat is what
matters.

The reason they are over unity is they are taking heat from one place and
moving it somewhere else. If they are pulling heat from outside air they are
basically solar assisted. Technically anything above absolute zero has heat
energy, even very cold outside air has plenty of heat to pump into your living
space. Temperature is not heat, you can raise temperature by putting the same
amount of heat in a smaller space, its like using a transmission to increase
torque by lowering rpm.

~~~
ajross
Not sure you're disagreeing with me. That's indeed how they work, and it's...
a pretty neat trick! So are phototransistors, for that matter. Not sure I'd
put radiative solar water heaters in the same boat, but semiconductors and
thermodynamics make for great tricks.

~~~
SigmundA
I am disagreeing with "They don't make "heating" any more "efficient" per se."

They definitely do make it more efficient at least in the ways that matter to
people, less energy paid for the same heat.

I guess all technology is a trick, but normally that denotes its not really
doing what is said, which you reinforced by saying it is not more efficient.

Air source heat pump water heaters and direct solar water heaters are similar
in they both utilize solar energy to heat water. Then again if you really get
down to it you could argue everything is indirectly solar powered, just some
forms you must pay for the energy, while heat pumps and solar collectors get
it directly from outside your home heat pumps just require some energy to
collect it.

~~~
dannypgh
I think you just mean different things by "heating" \- if you're talking about
heating in a closed system, they're the same - 5 joules of energy are needed
to increase the total heat energy by 5 joules, with either approach.

The advantage of the heat pump is that we are, for, say, 3 joules of energy,
heating part of the system by 5 joules and heating the other part of the
system by -2 joules.

This is great for home heating and the like because we don't care about making
the outside slightly colder.

~~~
SigmundA
Good thing we don't live in a closed system and instead have a giant fusion
reactor in the sky to heat the outside air.

------
danans
This kind of tech was actually investigated several years prior, at PNNL,
where they experimented with using electric water heaters to provide grid
frequency regulation:

[https://availabletechnologies.pnnl.gov/technology.asp?id=287](https://availabletechnologies.pnnl.gov/technology.asp?id=287)

Soon after, I worked on an team that, inspired by PNNLs work, created a
research demand-response system using a variety of real and simulated loads,
including electric water heaters. IIRC we used the current Texas wind output
as our input power signal.

At least at the time, our finding was that a collection of smart loads could
replace natural gas peakers for frequency regulation on the demand side, so
much that the service (therefore economic opportunity of) frequency regulation
would be met with a small percentage of actual loads.

The real long term and large scale value of dispatchable loads was thought to
be the ability to adapt to the intermittency of renewables. I think that is
still the case.

------
etaty
France has been doing it for the past 40 years. France has nuclear power
running through the night, so electricity is very cheap. We have a special
overnight tariff. France is a big user of water heater and electric radiators.

------
edent
I have one of these! A domestic Solar iBoost. If our solar panels are
generating excess energy, it automatically switches on an immersion heater. So
the electricity heats up water rather than flowing back into the grid.

And, sadly, it is kinda pointless when combined with a battery. The days we
produce more power than we can use and store - are generally warm and sunny
days where we don't need as much hot water.

It saves very little money compared to the cost of gas - but it was a hell of
a lot cheaper to install than the 2kWh battery.

~~~
benj111
So which one would you go for if you did it again, battery or iboost?

~~~
edent
Battery. Electricity is more useful than steam.

~~~
benj111
Do the financials agree?

~~~
edent
Sort of. [https://shkspr.mobi/blog/2016/03/meet-maslow-the-uks-
answer-...](https://shkspr.mobi/blog/2016/03/meet-maslow-the-uks-answer-to-
teslas-powerwall/)

~~~
benj111
Thanks for the writeup. I couldn't find a breakdown for the iboost but the
Maslow was 2kwh for £2000.

Given that a water heater could absorb much more energy for less money,
wouldn't that be the way to go, or at least go water heater first until you've
achieved some maximum utility, then go for battery?

~~~
edent
I think the iboost was under £100.

Sure the water can absorb more energy, but what can I do with it?

------
jpollock
New Zealand has this for grid attached water heaters. They can be placed on a
lower tariff, but will be turned off during times of peak load. It is
implemented by putting the stored heat device (water heater, air heater) onto
a separate meter with something called "ripple control" [2].

This gives the power company the ability to avoid spinning up peaking plants -
which are very expensive compared to base load. Nest also offers this as a
service to power companies - they allow the power company to shift cooling
load the same way.

The power company then passes this cost savings on to the customer. It ends up
being about 1c/kwh [1].

Personally, I had to turn it off, our ripple control kept going bad. Nothing
worse than a cold shower in the morning. Instead, I went with a timer and
switched to a night rate. The heater would come on after hours and warm up the
next day's water.

[1] [https://www.genesisenergy.co.nz/plans-and-
pricing](https://www.genesisenergy.co.nz/plans-and-pricing)

Anytime vs Controlled.

[2]
[https://en.wikipedia.org/wiki/Load_management#Ripple_control](https://en.wikipedia.org/wiki/Load_management#Ripple_control)

~~~
Scoundreller
I know people would complain incessantly about it, but I wish we had real-time
electricity pricing.

A _smart_ dryer could react minute by minute to draw the cheapest electricity
over 5 hours. Same with car charging

------
3pt14159
My takeaway from this article is a little different.

Thermal loss is a function of three things.

First, thermal difference: A hot water tank is at around 50C / 120F, but it
could be higher. Let's assume a 10C / 50F basement temperature.

Second, R-value: Dividing the temperature difference to compare loss rates.
For example, an R-value of 20 that insulates a 40 degree difference will be as
effective as an R-value material that insulates a 20 degree difference, all
other things being equal. R-values can go as high as R45, but typical
wood+insulation walls are about R15. Pure wood is around R1 per inch
thickness.

Third, surface area of exposure. This is pretty self-explanatory.

But if you put all these ideas together, then making a heat battery becomes
basically a matter of raw scale.

Say we design a cube storage tank. It is governed by these equations, where L
is the side-length of the cube.

R = InsulationR * InsulationLayers

IA = InsulationArea = 6 x L^2

TIC = TotalInsulationCost = IA x InsulationUnitAreaCost * InsulationLayers

VS = VolumeStorable = L^3

WVHC = WaterVolumetricHeatCapacity = 4.2 ( Joules / K ) / cm^3

MTD = MaxTemperatureDifference = MaxTankTemp - RoomTemp

TES = TotalEnergyStorable = MTD * WVHC * VS

EL = EnergyLost = Time * AverageTempDifference * IA / R

Cost = ( TES - EL ) / TIC

Basically I think this is a great idea for power storage if that hot water is
need _anywhere_ in the semi-near future. The larger the pools of water you
have the cheaper it gets, economies of scale aside.

------
danmaz74
Our rented apartment here in London has storage heaters in each room which
only turn on at night, when tariffs are off peak; they then release the heat
during the day.

I think there is a separate power circuit for that. There are also two
separate switches for the main water boiler, one for off peak power and one
for peak power.

It's not ideal - it gets too warm at night - but I'm sure it saves quite a lot
in the energy bill.

~~~
tonyedgecombe
_it gets too warm at night_

Most storage heaters have a flap you can move that affects how quickly the
heat is released. Ours are marked "Room Temp Boost". We leave them on the
lowest setting because there is usually someone home during the day.

In general they aren't very good, they are more expensive than gas and
difficult to control. Landlords like them because they don't have to pay the
bill. I looked at converting our house to oil but the figures didn't look very
good at the time.

~~~
danmaz74
Thank you for the suggestion. For us it's not a flap, it's a very cumbersome
dial and, honestly, I gave up on moving it every day. We just sleep in lighter
pyjamas :)

------
rb808
Most other countries have a cheaper rate at night which encourages such
behavior, eg Economy7 in the UK. The other device is a Night Storage Heaters
which warm up thermal stores like bricks that release heat during the day.
[https://www.which.co.uk/reviews/home-heating-
systems/article...](https://www.which.co.uk/reviews/home-heating-
systems/article/home-heating-systems/storage-heaters)

The US is really behind on Real Time electricity pricing. Smart devices should
run when electricity is cheap and avoid in peaks. eg don't run clothes dryer
in peak times, heat room at cheaper times. This isn't complicated stuff, some
states have started, but should be urgency on this.

I did see some other comment on here that comed provides this. In IL? Anywhere
else?

------
joezydeco
I'm on real-time electricity pricing ([https://hourlypricing.comed.com/live-
prices/](https://hourlypricing.comed.com/live-prices/)) and have been thinking
about this for a while.

I have a gas-powered main water heater, and my idea involved installing a
_second_ electrically heated tank to use as a feed/preheater to the main water
heater and would only kick on when the real-time price was near zero or, as it
happens in the summer sometimes, slightly negative which indicates a load-
shedding situation.

At the end the cost of installing this all meant the ROI was really long. But
I like this concept.

~~~
benj111
Is it telling that your utility company is one letter away from comedy?

~~~
joezydeco
Perhaps. At least they’re not burning California to the ground.

------
mandelken
Using electricity to heat water is a waste of a high quality (i.e. low
entropy) energy source. Carefully tuning when to use electrical water heaters
and calling this energy storage is not quite right.

There are much better ways to heat water for domestic use, depending on the
climate and context, such as solar panels, heat pumps with ground drilling,
industrial heat waste, etc. These are standard technologies being used in
large parts of the world.

For more info I recommend the excellent book Sustainable Energy Without the
Hot Air by MacKay (pdf freely available at withouthotair.com).

~~~
IfOnlyYouKnew
Residential heating with electricity is obviously wasteful, at least in
temperate and cold climates when they are regularly used.

But for he tap on your kitchen sink, it can in many cases be the most
efficient solution. That’s because an electric heater is a far smaller
investment than running a gas pipe installing a furnace. Or, with a central
furnace, to run th gap until warm water gets to the tap, then letting warm
water in the long pipes go to waste when you turn it off.

~~~
gwbas1c
As a rule of thumb, when using fossil fuels to make electricity, grid
electricity is 1/3 efficient, and cost three times as much as having an
appliance that uses the fossil fuel directly.

Of course there's plenty of details that make that statement an over
simplification! The point is that you can recuperate your investment in a
fossil fuels based heater extremely quickly.

Another problem with using electric water heaters is that they pull a high
amount of amperage. Assuming you're going tankless, a water heater necessary
for the temperatures in the northeast states could easily use over 100 amps.
If you fill the bathtub, turn on the oven, and charge the car at the same
time, you could trip your main breaker.

------
edoo
It seems like a much simpler solution would be to have dynamic rates based on
demand needs. There would be a near overnight rollout of dirt cheap gadgets
designed to help you regulate your energy use based on the pricing. You could
have a simple web interface that lets you set the rates you are willing to let
your appliances run at. The end result would be exactly like this without
having anything centralized and letting people determine their own demand. The
average smart home can probably do this already with a little extra software.

~~~
URSpider94
The core issue is that customers don’t want to do this kind of work. People
are gradually being moved to a 2- or 3- tier time-of-use strategy that
customers can adapt to over time, but nobody wants to get their utility bill
and find that the spot price for power spiked up to 100x the nominal rate
while you were cooking your Thanksgiving turkey.

------
mrfusion
A chest freezer might also work well. Lower the temp to -5 or so when power is
available and let it creep up to 20f or so when not.

I assume that’s not bad for the food as long as you’re staying below freezing?

~~~
thatcat
Ice changes densities at different temperatures. I'm not exactly sure what
that would do to food, but you can add water jugs as a thermal mass to reduce
the temperature swing.

~~~
pofilat
Great question.

There's some debate, apparentl, but the basic result is that temperature
variation has side-effects, but superfreezing (keeping temp below < -20F, or
below 0F, depending on the studied and what is studied) avoids the problems.

[https://pubs.acs.org/doi/abs/10.1021/ie50464a017](https://pubs.acs.org/doi/abs/10.1021/ie50464a017)

------
URSpider94
Electric cars will end up being a much better choice for this application.
Even today, there are a number of companies selling connected EVSE’s
(“chargers”) that can be grid-tied to modify the charging rate on demand. The
J1772 charge port standard includes a carrier signal that tells the car the
max current its allowed to draw, so it’s just a matter of modulating that
signal as needed. If there are 100,000 EV’s each charging at 5kW across the
state of California every night, that’s 500MW of demand that can be shaped
pretty broadly - assume each car needs 4 hours of charging between 9 PM and 7
AM, you have plenty of room to adjust rate and timing.

In the future, it’s likely that EV’s will be designed with bidirectional
charging capability, at which point they will be able to return power to the
grid in times of high demand, acting as a giant distributed battery.

------
magicalhippo
Was just discussing with my buddy the other day how having a large fleet of
electric vehicles will change the grid. You essentially have a Tesla power
wall with wheels.

If the charging circuits were modified to allow discharge as well, then your
car could act like a "household capacitor", handling high loads like induction
cooktops during peak demand, reducing the strain on the grid. The car would
then recharge later during low demand.

Not sure how electricity is billed around the world but here in Norway they'll
be introducing a power element, that is you'll have to pay a certain amount
each month for the peak power you want to be able to draw. This is typical in
the industry I understand, but until now consumers here have just paid per
kWh.

Thus, treating your car like a power wall would allow you to reduce the peak
demand you need to satisfy, which would be reflected in your bill.

------
tonto
This webpage is a pretty sweet highly obsessive guide to making water heater
timer controls... Or a tome for groceries style web design.. However you want
to look at it!

[http://waterheatertimer.org/index.html](http://waterheatertimer.org/index.html)

------
gwbas1c
The author notes that this system doesn't work well with heat pump water
heaters. I use a heat pump water heater because it uses significantly less
electricity and is cheaper to operate. Overall, efficiency is important.

A system like this might work better with hot tubs, where it's less common to
use a heat pump. Offering a subsidy, so the hot tub is 5 or 10% cheaper, would
probably make them very popular!

Another alternative would be tankless electric water heaters paired to a
battery, or even just having better integration of whole house batteries, like
the powerwall, into the grid.

Another alternative is figuring out how to retrofit this system into existing
resistance electric water heaters.

------
ox_cable
Pardon my ignorance, but wouldn't one way to solve the "store electricity for
later" problem we have with renewable energy be to use the unused power
generated at peak times to produce a stable, long term material that can be
used to generate energy on demand? Example: using excess energy collected at
peak times to convert large amounts of water into oxygen and hydrogen by way
of electrolysis, store the hydrogen for later, and then depend on hydrogen
fuel cells during periods of little to no energy collection?

~~~
strommen
The reason why stuff like this (electrolysis, desalination, etc.) is not
widely done is that the capital cost of the facilities is too high. If you
spend a bunch of money on an electrolysis plant and only run it 10% of the
time, you'll never make your money back, even if your electricity is free.

------
benj111
Can anyone comment on why larger resistive water heaters are being phased out?
Heat pumps are ok when its not too cold, you aren't going to be using one in
an Alaskan winter though.

Are you just going to be expected to buy a heat pump water heater and rely on
the resistive backup 6 months of the year? That may be preferable from an
energy use point of view, but massively more expensive, to the point of
pushing people back to gas.

------
mark_l_watson
Another safety tip someone told me about but I have never tried it: in an
emergency if you have no drinking water: drain a hot water heater for water.

~~~
zozbot123
Isn't this a rather bad idea due to the potential for bacterial and parasite
growth in warm, non-flowing water? AIUI this is the whole reason that it's
considered important to avoid the possibility of warm water entering the cold-
water pipes.

~~~
mark_l_watson
You might be right about that. Someone described this to me as a real
emergency measure- not something that sounds good.

------
aj7
Bunk. A water heater is a purely dissipative device. You cannot regain the
energy, and it dissipates or is wasted if not put to good economic use. At
best, it can be turned off when demand peaks, as lack of hot water won’t kill
anyone. At worst, it dissipates during excess supply. What inefficiency is
that highlighting?

~~~
gwbas1c
Load balancing. The grid cannot react quickly enough for a certain kinds of
changes in load and demand.

This goes both ways, sometimes there isn't enough electricity, and sometimes
there's too much!

So, turning on everyone's water heater to heat up the water an extra degree or
two helps when there is too much electricity. It's considered storage, because
now everybody's water heater is already hot if you need to turn them off
temporarily when there is too much load.

I think the main point is that this particular system is cheaper than
installing grid-scale batteries.

------
mabbo
> In times of overgeneration, fleets of water heaters can be switched on to
> absorb excess power, and in times of undergeneration, they can be switched
> off to shed load and redistribute the existing electricity on the grid

I don't want my public utility deciding when I should and should not be using
my water heater. They don't know me, and they don't know my wants or needs. A
much better answer: provide consumers with high frequency data regarding
current electricity prices and a common API for devices, like water heaters,
to utilize that information.

The water heater can pay attention to it's owners needs (either learned or
configured) as well as electricity prices and optimize to reduce costs while
never running out of hot water. The same goes for freezers, electric car
chargers, battery systems, really anything where power can be used at varying
times.

This has the disadvantage that customers don't have easy-to-follow rules
regarding what the price will be in the future. It has the advantage, however,
that consumer demand will rise and fall to meet supply, leveling out (and
lowering) prices for all. And I can avoid letting a public utility I don't
trust controlling devices in my house.

~~~
ethagknight
I got the sense from the article that the controller makes the process
invisible to the customer. I.e, water heater maintains temp just like before,
but the utility can overheat the system or add heat to the striated capacity,
and then (potentially) blend with cold water back down to the desired temp.

------
russfink
So what does one do with all this hot water? Would it not be better to power a
desalination system that produces a useful byproduct rather than just bleeding
off excess joules into a water tank?

~~~
thinkcontext
Running a desalination plant intermittently would only make sense if the
capital cost of building a plant is low compared to the electrical costs of
operating it. My guess is they want to run those things 24 hours a day and
store the water.

Making smarter use of existing hot water heaters on the other hand is in some
cases just a software upgrade or the installation of a smart controller.

------
tomasien
Why are these illegal?

~~~
Fronzie
They are illegal above a certain capacity. I assume that's because to large
storage is wasteful: heat will leak without being used efficiently.

~~~
chongli
But that's not how heat works. A larger water tank has a higher volume-to-
surface-area ratio. This makes larger tanks more efficient than smaller ones,
not less.

This is why elephants need such large ears. Their bodies are otherwise
incredibly efficient at retaining heat. Those massive, thin, flappy ears
provide them with a way to expose their blood to a much larger surface area of
skin.

~~~
skosch
Your average household uses somewhere between 30 and 60 gallons of hot water a
day [0], and a bigger tank will just have water sitting in it, going cold. Any
extra surface area costs you extra heat, even if the marginal loss decreases
with growing tank volumes.

[0] [http://www.fsec.ucf.edu/en/publications/pdf/FSEC-
PF-464-15.p...](http://www.fsec.ucf.edu/en/publications/pdf/FSEC-
PF-464-15.pdf)

~~~
Xylakant
You can use warm water to power your heating in winter. So it might be less
efficient in summer, but the amount of energy you’d save in winter would
exceed the losses in summer.

------
sjjshzvuiajhz
It’s cheaper to use a gas-powered water heater, right? I assume that’s because
it’s also more efficient?

~~~
ajross
No, it's because gas is (if your property is plumbed for it, obviously)
cheaper to produce and transport than electricity for the same amount of heat
energy. It doesn't make sense to talk about "efficiency" for heating itself --
energy is energy. I don't know whether it's more "efficient" in the sense of
transport losses or not, my guess is it's a wash.

Obviously gas inherently involves digging carbon out of the grown and throwing
it into the atmosphere, though, so there's that to think about.

~~~
opencl
For a lot of people the choice is between heating with gas and heating with
electricity produced by burning gas- obviously using the gas directly for heat
is much more efficient in this case because you are skipping the generation
and transmission losses.

------
skookumchuck
"it effectively turns the water heater into a battery" More like a capacitor.

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nobrains
How does this compare to the cement blocks (aka gravity) energy storage?

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URSpider94
It uses capital equipment that already exists, with some minimal cost to add
the control circuitry, so it’s extremely low cost to build, virtually free to
operate, and takes up no extra space.

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stevespang
First of all, although water heaters may be lowest cost to install, they
"leak" or bleed off energy in the form of lost heat over time. Obviously super
insulating them can cut some of this loss.

2nd, the "bidirectional control" seems a bit misaligned, water heaters as
storage devices cannot give back energy into the grid to lessen overall load,
they can only be throttled down to lessen load. Perhaps a solution will be
obtained from energy storage salts or thermal electric devices to allow for
energy harvesting and conversion ?

