How Water Heaters Have Evolved into Grid-Scale Energy-Storage Devices (2014)
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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.
This is not true, and the article specifically addresses this. A heating element can be switched on and off roughly five orders of magnitude faster (100 000× faster) than a heat pump.
I'm not actually sure that that would be the major problem. A heat pump is basically a motor, which can cause a lot of noise in electrical circuits. I'm not sure you would want 1000s of electric motors turning on in unison. I wouldn't like to say whether that is a solved/solvable problem though.
The grid has a lot of inertia and a motor can go from full load to none, or from no load to extra-high startup load, in a fraction of a second.
So we're back to "just as fast" for this use case.
Where does the inertia come from? I understood inertia in the grid to come from turbines and motors spinning up and down, which seems to be different from what you're suggesting?
Capacitance in the wires?
With something like a heat pump compressor, you're connecting or disconnecting it completely with the flip of a switch. It's also an asynchronous motor and unable to feed power back into the grid at all, it's a pure load.
To put it another way. Say if energy use jumps X%, inertia may make up Y% difference in the short term, you'd still have to put in more than X% in the slightly less short term, and it would take longer to make up the Y% shortfall. Is the Y% shortfall not big enough to be important here.
If you add more load, you start dragging down the frequency. The more inertia you have in the turbines, the less the frequency is impacted. I'm not sure what you mean by "spinning up a turbine" in this situation. Do you mean to produce more power? You don't spin turbines faster to do that.
> To put it another way. Say if energy use jumps X%, inertia may make up Y% difference in the short term, you'd still have to put in more than X% in the slightly less short term, and it would take longer to make up the Y% shortfall. Is the Y% shortfall not big enough to be important here.
Yes, you have to make up the deficit. But the alternative means having a brownout. In a choice between "drain some inertia to cover the increased load, then overproduce by .1% to refill the inertia" and "don't cover the increased load, voltage freefalls until load drops", I prefer the former.
Reading around, as the amount of renewables (solar) increases this might become an issue due to less turbines being in use.
"spinning up a turbine"
As in spinning up to speed. It can't go 0 to X000 rpm instantaneously. Inertia!
Didn't realise they were designed to spin at a constant speed though, thanks.
Solar is trickier but it's also more flexible in how it injects power. The real issue is not lack of inertia but the fact that it can lose production when a cloud comes by.
In addition such systems sometimes measure frequency deviation and switch off/on the load when it goes out of bounds.
The result is that this works really well for fast balancing as soon as you have few hundred installed spots in one grid. And there is real money in it with ROI 1..3 years for the service provider.
Disclaimer: my electronics engineering company has worked with research, design and engineering of such load balancing hardware
If you're talking about a heat pump used in air conditioning, at least, longer cycle times result in better dehumidification and higher efficiency. If you interrupt the cycle, you're effectively short cycling.
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?
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.
If the electricity is down, the. Internet will be down, and without this feedback mechanism working they wouldn't be able to keep the grid stable.
Nest (and I assume other internet-connected) thermostats are able to accept peak-usage notifications from the power company and dynamically reduce usage. In my case (Portland Electric), it's two-way communications, if Nest can prove to the power company that I let its device reduce usage during peak-load times, I get a credit at the end of the year. The Nest in my house has almost paid for itself.
This is exactly how Nest makes money. About 40$ per thermostat per year from the utilities.
1) getting into big data to help utils
2) shutting down (as a google does) a data service for users ---
https://www.forbes.com/sites/parmyolson/2014/01/13/nest-give...
http://fortune.com/2016/03/01/nest-shuttering-data-service-m...
---
Disclaimer: I do not know if this means they are/was/will-be providing data to utils/ users or not...
The point of having smart water heaters is to stabilize the market, not make it more chaotic in pursuit of more efficient trades. So instead of going with something complicated like a financial market, a simple feedback system controlled by the power company will do.
Additionally, the system is a lot more stable if a central utility can control these water heaters as a bank of shapeable demand, rather than having each individual device making independent decisions. It’s more efficient for them to give you a periodic rebate for participating in the program and have them manage the details.
I don't share your concerns with calling it a battery though, it stores energy. Combined with a peltier it could generate electricity with that energy.
If it eases marketing, and gets this into peoples homes, I'm all for it.
To your underlying point, none of the added complexity is worth the effort unless a) the utility is paying you to take the excess load and/or b) someone really innovates on a slick, simple package.
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.
But it doesn't work for "house heat" (storage heaters) as well as for water heaters
What you describe is how water heaters work in most households in France and Belgium, and - I assumed until now - mostly everywhere with a well developed electrical infrastructure.
Except instead on people manually setting up timers, the utility send a signal over the electrical wires when off-peak hours begin and end, and a device (owned and installed by the utility. It can be integrated into the counter like in France, or a separate Zellweger device like in Belgium) turns that into a third wire that power hungry appliances can use to turn on during off-peak hours.
Usually, the utility guarantees a minimum amount of off-peak hours per day, with min/max times that are convenient enough (you will never have two hours of off-peak at 9am, then one hour at 2pm and then five hours from 4pm to 9pm, is going to be between 10pm and 8am in any case).
Water heaters will rarely be turned on during the day in this configuration. It doesn't work that well will storage heaters though.
Is that how they do it? In the UK, it was/is sometimes still done by piggybacking a signal on a BBC radio channel:
https://en.wikipedia.org/wiki/Economy_7#Timing_and_switchove...
It actually signals both the strict off-peak times (from 22:00 to 07:00 as well as Saturday and Sunday) and separately, a "night programme" that is variable and used to manage to grid more efficiently. Apparently, there are many different signals that go over the wire, and houses are more or less randomly tuned to one of them.
The strict times are used by the counter itself to know how to count usage, and the night programme is used for the appliances.
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!
The tariff is called Economy9 for reference. It's not widespread outside London.
Had the drafty Victorian building been properly insulated it might have worked quite well.
https://www.energy.gov/energysaver/services/do-it-yourself-e...
https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_tab...
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?
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.
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.
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.
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.
This comes with the downside of leaking energy a lot faster than batteries. Moreover, the more energy stored, the faster the leakage.
All that is not to say this is useless. Just to say the role played by heaters is different from batteries. Notably, neither are a good solo solution to the volatility of renewables.
I know that in the Netherlands, stuf like this would require infrastructure upgrades. There is simply not enough copper running to consumer houses to handle the amperages.
One-way conversation of energy to heat is a very common use-case: Warm water, heating are all things a lot of people use. Currently, most of that conversion happens on-demand, when someone turns on the tap. Heat is a form of energy that is fairly easy to store. Have a large bucket of water, well insulated and you’re mostly set. It’s dead cheap. There are similar concepts that use a generator to provide electricity for buildings on demand and store the waste heat for warm water and heating.
> Calling such a one-way sink a battery is even worse.
The article does not. They are a replacement for batteries in some use cases. The article may overstate how often that’s the case but it does not pretend you could regain the energy stored as electricity.
If heating loads are a significant amount of the total load, then this would help reduce the need for peaker plants or battery energy storage. And, if done properly, it provides a cost savings to the utility user too.
You can also use the same principle to store cold in summer: Cool down a vat of coolant (though water likely won’t do) at times when you have electricity surplus and use it later.
Certainly, that not solving all problems, but it can kill battery usage for some cases.
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.
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.
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?
Sure the water can absorb more energy, but what can I do with it?
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
Anytime vs Controlled.
[2] https://en.wikipedia.org/wiki/Load_management#Ripple_control
A smart dryer could react minute by minute to draw the cheapest electricity over 5 hours. Same with car charging
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.
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.
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.
This. I'd really wish something would be done to align incentives in this area.
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?
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.
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).
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.
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.
I assume that’s not bad for the food as long as you’re staying below freezing?
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.
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.
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.
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.
Also, see Gravity battery: https://news.ycombinator.com/item?id=17789456
Germany is trialling it for energy storage, has a number of trial sites running I believe, and already have some hydrogen powered trains.
Unless you need the energy density of hydrogen the simpler solutions are probably better.
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.
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.
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.
Eg in the UK we have absolutely no need for desalination, but wind speeds tend to be higher in winter, when most energy is used, so this tech could be combined with electric heaters also, as well as water heaters.
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.
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.
[0] http://www.fsec.ucf.edu/en/publications/pdf/FSEC-PF-464-15.p...
[0] https://www.phcppros.com/articles/5312-water-heater-regulati...
Obviously gas inherently involves digging carbon out of the grown and throwing it into the atmosphere, though, so there's that to think about.
Also, no, gas does not inherently involve digging carbon out of the ground, you can produce methane in bio reactors or via electrolysis from electricity (see https://en.wikipedia.org/wiki/Power_to_gas ), which is another method of storing surplus electric energy, either to be converted back later with a gas turbine, or to be injected into the natural gas grid.
It can be big deal for the environment. Compare "green" solar to heat water is much better than fracking your groundwater and creating greenhouses gases. If the electricity comes from coal burning, gas could be less worse.
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 ?