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How Water Heaters Have Evolved into Grid-Scale Energy-Storage Devices (2014)

123 points by camtarn 8y ago

tomasien 8y ago
Why are these illegal?
- Fronzie 8y ago
  They are illegal above a certain capacity. I assume that's because to large storage is wasteful: heat will leak without being used efficiently.
  - deleted 8y ago
    [deleted]
  - rocqua 8y ago
    In general, the bigger the tank, the better the 'skin to volume ratio'. Hence I'd expect less % per second of loss. The total wattage of loss would still be higher though.
  - chongli 8y ago
    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 8y ago
      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.pdf http://www.fsec.ucf.edu/en/publications/pdf/FSEC-PF-464-15.p...
      - Xylakant 8y ago
        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.
  - Tharkun 8y ago
    Perhaps legionnaires' disease has something to do with it instead?
- skosch 8y ago
  They aren't anymore. This article is from 2014; the rule was amended a year later to make an exception for grid-enabled electric water heaters.[0] [0] https://www.phcppros.com/articles/5312-water-heater-regulations https://www.phcppros.com/articles/5312-water-heater-regulati...
  - tomasien 8y ago
    Great - and as I understand it the original ban was for efficiency reasons that don't apply here
stevespang 8y ago
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 ?
rocqua 8y ago
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?
- deleted 8y ago
  [deleted]
- ajross 8y ago
  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 8y ago
    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.
cnj 8y ago
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.
- raverbashing 8y ago
  A lot of houses in Ireland and the UK do something similar. But it doesn't work for "house heat" (storage heaters) as well as for water heaters
  - Havoc 8y ago
    Presumably you can still make a dent in that 1 hour peak energy demand spike in the evening though? But yeah overall not as convenient
    - laurencerowe 8y ago
      By the time I got home from work in the early evening heat from my storage heater had long since dissipated. If you were at home during the day or had better insulation maybe it would have been more useful.
- seszett 8y ago
  Honestly I was a bit lost at what was the innovation in the article, but reading your comment I think it's just that the US (?) didn't know about that. 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.
etaty 8y ago
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.
sjjshzvuiajhz 8y ago
It’s cheaper to use a gas-powered water heater, right? I assume that’s because it’s also more efficient?
- ajross 8y ago
  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 8y ago
    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.
  - zAy0LfpBZLC8mAC 8y ago
    Yeah, it is a lot more efficient, primarily due to conversion losses. A gas powered power plant loses about half of the energy fed into it as gas to waste heat, whereas a gas heater has essentially 100% efficiency. 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 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.
- rb808 8y ago
  Yes gas is cheaper measured in btu/$. An electric heat pump could be more efficient, but that's not normal for domestic hot water heating. 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.
danmaz74 8y ago
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 8y ago
  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.
  - benj111 8y ago
    "Landlords like them because they don't have to pay the bill" This. I'd really wish something would be done to align incentives in this area.
  - danmaz74 8y ago
    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 :)
mandelken 8y ago
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).
- Xylakant 8y ago
  The intention is to use primarily waste energy from times when production exceeds demand. The side effect is that you have a set of consumers that can take or shed load quickly and on demand, having a stabilizing effect on the grid. Grid stabilization is an important problem when using energy sources with less predictable power output such as wind and solar.
- ptero 8y ago
  Electricity transmission can be expensive, both in terms of initial and recurring costs (which include safety provisions, wire maintenance, surge handling, regulation compliance, etc.). If you have a solar 10m away generating unnecessary power, heating water might be an OK option.
- IfOnlyYouKnew 8y ago
  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 8y ago
    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.
ethagknight 8y ago
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.
- kragen 8y ago
  > A heat pump (a compressor and some fans) can be switched on or off just as fast as a heating element, 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.
  - ethagknight 8y ago
    You clipped out the qualifying phrase, “as far as the article is concerned”, dumping a few extra MW of electricity for 30 mins or a few hours. I don’t see a need presented in the article to rapidly switch a heating element on and off a few 1000 times a second.
    - benj111 8y ago
      Grid frequency stabilisation would require that. 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.
edent 8y ago
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 8y ago
  So which one would you go for if you did it again, battery or iboost?
  - edent 8y ago
    Battery. Electricity is more useful than steam.
    - benj111 8y ago
      Do the financials agree?
      - edent 8y ago
        Sort of. https://shkspr.mobi/blog/2016/03/meet-maslow-the-uks-answer-to-teslas-powerwall/ https://shkspr.mobi/blog/2016/03/meet-maslow-the-uks-answer-...
        benj111 8y ago
        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?
mabbo 8y ago
> 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 8y ago
  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.
- Havoc 8y ago
  Big water heater stay at a decent temp for 24hr+. So if they switch it off here or there for an hour you don't notice.
tonto 8y ago
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
mrfusion 8y ago
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 8y ago
  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 8y ago
    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
benj111 8y ago
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.
joezydeco 8y ago
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 8y ago
  Is it telling that your utility company is one letter away from comedy?
  - joezydeco 8y ago
    Perhaps. At least they’re not burning California to the ground.
gwbas1c 8y ago
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.
russfink 8y ago
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?
- benj111 8y ago
  Desalination is useful in certain areas, not so in others. 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.
- ddalex 8y ago
  I dunno, I prefer taking showers with hot rather than cold. Hot water helps with the dishes, too...
- thinkcontext 8y ago
  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.
danans 8y ago
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.
ox_cable 8y ago
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?
- pofilat 8y ago
  You are describing charging a battery: https://www.tesla.com/powerwall https://www.tesla.com/powerwall Also, see Gravity battery: https://news.ycombinator.com/item?id=17789456 https://news.ycombinator.com/item?id=17789456
- edoo 8y ago
  Electrolysis to hydrogen and back to electricity is notoriously inefficient. It makes a great place to dump extra energy that MUST be burned off, but it would be more efficient to just not have that much energy that needs to be burned off. It can make sense with solar and hydro but imagine what that means with dirty energy.
- NeedMoreTea 8y ago
  That is exactly how Orkney plans to enable the next ferries to be hydrogen powered, for the huge energy density compared to batteries. They already generate more from renewables than they can use for electric, heat and vehicles. Surplus is already splitting water. More here: http://www.surfnturf.org.uk/page/transport http://www.surfnturf.org.uk/page/transport 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.
- throwawaycanada 8y ago
  That is too inefficient and the problem of hydrogen embrittlement has not been solved.
- 8y ago
edoo 8y ago
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 8y ago
  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.
3pt14159 8y ago
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.
nobrains 8y ago
How does this compare to the cement blocks (aka gravity) energy storage?
- URSpider94 8y ago
  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.
rb808 8y ago
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/home-heating-systems/storage-heaters https://www.which.co.uk/reviews/home-heating-systems/article... 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?
jpollock 8y ago
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 8y ago
  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
deleted 8y ago
[deleted]
aj7 8y ago
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?
- IndrekR 8y ago
  Looking from the grid side it looks the same, you just shift the timing of the consumption. This can be done to limited extent.
- gwbas1c 8y ago
  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.
skookumchuck 8y ago
"it effectively turns the water heater into a battery" More like a capacitor.
mark_l_watson 8y ago
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 8y ago
  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 8y ago
    You might be right about that. Someone described this to me as a real emergency measure- not something that sounds good.
magicalhippo 8y ago
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.
URSpider94 8y ago
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.

123 points by camtarn 8y ago

tomasien 8y ago

Why are these illegal?

Fronzie 8y ago
They are illegal above a certain capacity. I assume that's because to large storage is wasteful: heat will leak without being used efficiently.
- deleted 8y ago
  [deleted]
- rocqua 8y ago
  In general, the bigger the tank, the better the 'skin to volume ratio'. Hence I'd expect less % per second of loss. The total wattage of loss would still be higher though.
- chongli 8y ago
  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 8y ago
    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.pdf http://www.fsec.ucf.edu/en/publications/pdf/FSEC-PF-464-15.p...
    - Xylakant 8y ago
      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.
- Tharkun 8y ago
  Perhaps legionnaires' disease has something to do with it instead?
skosch 8y ago
They aren't anymore. This article is from 2014; the rule was amended a year later to make an exception for grid-enabled electric water heaters.[0] [0] https://www.phcppros.com/articles/5312-water-heater-regulations https://www.phcppros.com/articles/5312-water-heater-regulati...
- tomasien 8y ago
  Great - and as I understand it the original ban was for efficiency reasons that don't apply here

stevespang 8y ago

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 ?

rocqua 8y ago

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?

deleted 8y ago
[deleted]
ajross 8y ago
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 8y ago
  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.

cnj 8y ago

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.

raverbashing 8y ago
A lot of houses in Ireland and the UK do something similar. But it doesn't work for "house heat" (storage heaters) as well as for water heaters
- Havoc 8y ago
  Presumably you can still make a dent in that 1 hour peak energy demand spike in the evening though? But yeah overall not as convenient
  - laurencerowe 8y ago
    By the time I got home from work in the early evening heat from my storage heater had long since dissipated. If you were at home during the day or had better insulation maybe it would have been more useful.
seszett 8y ago
Honestly I was a bit lost at what was the innovation in the article, but reading your comment I think it's just that the US (?) didn't know about that. 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.

etaty 8y ago

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.

sjjshzvuiajhz 8y ago

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

ajross 8y ago
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 8y ago
  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.
- zAy0LfpBZLC8mAC 8y ago
  Yeah, it is a lot more efficient, primarily due to conversion losses. A gas powered power plant loses about half of the energy fed into it as gas to waste heat, whereas a gas heater has essentially 100% efficiency. 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 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.
rb808 8y ago
Yes gas is cheaper measured in btu/$. An electric heat pump could be more efficient, but that's not normal for domestic hot water heating. 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.

danmaz74 8y ago

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 8y ago
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.
- benj111 8y ago
  "Landlords like them because they don't have to pay the bill" This. I'd really wish something would be done to align incentives in this area.
- danmaz74 8y ago
  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 :)

mandelken 8y ago

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).

Xylakant 8y ago
The intention is to use primarily waste energy from times when production exceeds demand. The side effect is that you have a set of consumers that can take or shed load quickly and on demand, having a stabilizing effect on the grid. Grid stabilization is an important problem when using energy sources with less predictable power output such as wind and solar.
ptero 8y ago
Electricity transmission can be expensive, both in terms of initial and recurring costs (which include safety provisions, wire maintenance, surge handling, regulation compliance, etc.). If you have a solar 10m away generating unnecessary power, heating water might be an OK option.
IfOnlyYouKnew 8y ago
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 8y ago
  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.

ethagknight 8y ago

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.

kragen 8y ago
> A heat pump (a compressor and some fans) can be switched on or off just as fast as a heating element, 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.
- ethagknight 8y ago
  You clipped out the qualifying phrase, “as far as the article is concerned”, dumping a few extra MW of electricity for 30 mins or a few hours. I don’t see a need presented in the article to rapidly switch a heating element on and off a few 1000 times a second.
  - benj111 8y ago
    Grid frequency stabilisation would require that. 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.

edent 8y ago

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 8y ago
So which one would you go for if you did it again, battery or iboost?
- edent 8y ago
  Battery. Electricity is more useful than steam.
  - benj111 8y ago
    Do the financials agree?
    - edent 8y ago
      Sort of. https://shkspr.mobi/blog/2016/03/meet-maslow-the-uks-answer-to-teslas-powerwall/ https://shkspr.mobi/blog/2016/03/meet-maslow-the-uks-answer-...
      - benj111 8y ago
        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?

mabbo 8y ago

> 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 8y ago
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.
Havoc 8y ago
Big water heater stay at a decent temp for 24hr+. So if they switch it off here or there for an hour you don't notice.

tonto 8y ago

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

mrfusion 8y ago

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 8y ago
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 8y ago
  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

benj111 8y ago

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.

joezydeco 8y ago

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 8y ago
Is it telling that your utility company is one letter away from comedy?
- joezydeco 8y ago
  Perhaps. At least they’re not burning California to the ground.

gwbas1c 8y ago

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.

russfink 8y ago

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?

benj111 8y ago
Desalination is useful in certain areas, not so in others. 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.
ddalex 8y ago
I dunno, I prefer taking showers with hot rather than cold. Hot water helps with the dishes, too...
thinkcontext 8y ago
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.

danans 8y ago

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.

ox_cable 8y ago

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?

pofilat 8y ago
You are describing charging a battery: https://www.tesla.com/powerwall https://www.tesla.com/powerwall Also, see Gravity battery: https://news.ycombinator.com/item?id=17789456 https://news.ycombinator.com/item?id=17789456
edoo 8y ago
Electrolysis to hydrogen and back to electricity is notoriously inefficient. It makes a great place to dump extra energy that MUST be burned off, but it would be more efficient to just not have that much energy that needs to be burned off. It can make sense with solar and hydro but imagine what that means with dirty energy.
NeedMoreTea 8y ago
That is exactly how Orkney plans to enable the next ferries to be hydrogen powered, for the huge energy density compared to batteries. They already generate more from renewables than they can use for electric, heat and vehicles. Surplus is already splitting water. More here: http://www.surfnturf.org.uk/page/transport http://www.surfnturf.org.uk/page/transport 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.
throwawaycanada 8y ago
That is too inefficient and the problem of hydrogen embrittlement has not been solved.
8y ago

edoo 8y ago

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 8y ago
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.

3pt14159 8y ago

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.

nobrains 8y ago

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

URSpider94 8y ago
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.

rb808 8y ago

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/home-heating-systems/storage-heaters https://www.which.co.uk/reviews/home-heating-systems/article... 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?

jpollock 8y ago

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 8y ago
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

deleted 8y ago

[deleted]

aj7 8y ago

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?

IndrekR 8y ago
Looking from the grid side it looks the same, you just shift the timing of the consumption. This can be done to limited extent.
gwbas1c 8y ago
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.

skookumchuck 8y ago

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

mark_l_watson 8y ago

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 8y ago
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 8y ago
  You might be right about that. Someone described this to me as a real emergency measure- not something that sounds good.

magicalhippo 8y ago

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.

URSpider94 8y ago

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.