https://cdn-ilcjnih.nitrocdn.com/BVTDJPZTUnfCKRkDQJDEvQcUwtA...
https://reneweconomy.com.au/battery-storage-is-dramatically-...
Solar + hot water tank can provide any house in US with 100% solar hot water (from PV!) for 80% of time, remaining 20 % of time you can have 10-99% solar heated water.
So we should focus on saying to people that if they buy solar and add electric heating element to hot water tank, then PV system will pay itself much sooner and their batteries will last longer. Becasue it is known and predictable load, you need hot water every day. And hot water is order of magnitude more energy then TV, lighting...
By lowering household usage like this we can make energy transition faster, cheaper.
Also proper construction - house heated only 10 days in a year - https://www.youtube.com/watch?v=5KHScgjTJtE
I realize that some people won't be willing to have a very warm/very cold house that gradually shifts to the more ideal comfortable range, but for people who are willing to deal with that (it personally doesn't bother me), it's a pretty easy way to shift a lot of power use and, if you have Solar or Time of Use billing, save a lot of money.
time of use billing - tool to incentivie you to use "off-peak" power, but i guess it will be deprecated in favor of "realtime" billing in future, because there will be so much solar (almost zero $ per kWh on market) that your energy provider will incentivize you to draw energy during peak solar "activity" AND off-peak hours. it will be simpler for them to give you market price every 15 minutes window than 4hour window at same time every day.
But biggest expense is instalation costs(humans) so it depends how you calculate. But PV system can be used for hot water, tv, car, charging kids bikes, lawnmower etc. Solar thermal can be used only for hot water (or cooling if you use multistage heat pump but that is viable only in office buildings or hockey stadiums and such).
Imagine if everybody switched to EVs right now, en masse. Emissions over the next decade, and every subsequent decade, would be massively lower. Waiting for every gas car to reach end of life before switching is always going to be higher emissions, always.
Similarly, the "waste" already happened when the gas heater was manufactured. There's no additional waste when it's decommissioned. It's a sunk cost, there's no getting that back. The only question is if you switch to lower emissions now, or you switch to lower emissions later.
Now, if you bring money into it, sure, there could be a financial motivation to keep emitting higher amounts of emissions. But if you take monetary considerations out of it, it's always better to stop emitting sooner rather than later.
I'd love to have some serious push back against this. The best I've ever got is "that doesn't sound right..." without any engagement with the quantitation or the ideas. Which is exactly what I would expect if it was a fallacy.
There’s a bunch of different possibilities to consider, but if you drive more than the average person buying an EV and selling your ICE is great for the environment. If you rarely drive then keeping an old ICE car out of the hands of a frequent driver has real value etc.
As to the environmental impact vs retrofitting an ICE vehicle into an EV, the grid has gotten a lot cleaner over time so many of the old assumptions around EV’s are outdated. Comparing the emissions from extracting, transporting, refining, and then burning gas vs the same with EV’s built with a cleaner grid and more electrified infrastructure now heavy favors EV’s. And these calculations just keep favoring EV’s more every year.
Hopefully the new heat pump water heaters are better. The advantage of resistance heating is simplicity and cost, with no moving parts. Solar panels are so cheap now they make it hard to justify the expense of the heat pump, assuming you have room to mount the panels.
it disappoints me (but thrills me) that improvements in PV efficiency and cost have made solar thermal hot water more or less pointless.
i.e. rv propane refrigerator.
Most of the homes around me have somewhere around 3.5 to 6.0 kW of installed solar. This is barely enough to support these homes. With changing rates and TOU billing, everyone is paying hundreds of dollars per month for electricity (between billed power and leasing costs). Wasting --because it would be wasting-- the energy they produce to heat water would cause every single one of these homes to go back to bills they were getting in the pre-solar era.
Electric water heaters run somewhere between 3KW and 5KW...which is crazy. In a place like SoCal, in the summer, your air conditioning system is going to consume that much power. The monumental increase in energy usage cannot be understated.
I have THERMAL hot water heating, similar to this:
https://www.stiebel-eltron-usa.com/products/solar-thermal-ho...
Just two to four panels are enough for most homes. Instead of burning gas or electricity to heat water, you run a little circulation pump and get water hotter than you can handle, by far. This is supplemented with gas to keep the desired temperature when the sun isn't up. I've been using these systems for well over 30 years, they work well and they are the smart way to make hot water from the sun. My 13 kW solar array isn't being used to inefficiently turn photons into electrons to then burn the energy making water hot.
So the emissions stayed the same and you added the carbon embedded in the new EV.
I do really appreciate shifting this from the "the consumer must make the right choice" to "what choices result in overall better outcomes" but we must do the full accounting.
No, it might or might not, depending on (a) the embodied emissions of creating the new product and (b) how soon it will be replaced by something even more efficient.
It's easiest to understand the importance of point (b) by going to extremes: Suppose that, every week, a new model of EV comes out that uses 99% as much energy as the previous year's model. If some nonzero proportion of electricity is generated from fossil fuels, then ignoring point (b) would imply that the rational thing to do would be to buy the new car each week, regardless of how much CO2 went into building it.
So blindly converting a gas water heater to electric will roughly quadruple your water heating cost.
Yes, heating DHW with a heat pump is not that trivial. There could be problems when the tap water is hard (limescale problems in heat exchangers), you often need 2-3 times larger tank in order to cover the daily cycle, but still looks more efficient than a big battery and an electric heater.
PS: I've accumulated lots of knowledge on the topic. DM me if you are interested in exchanging on this.
I've got a heat pump, and I'm in Germany.
Also, if you're in Germany, you can get a balcony PV system from half the supermarkets a few hundred euros, and those are designed to be installed DIY without needing an electrician. Limited power, sure, but way cheaper than €0.39/kWh delivered:
• https://www.lidl.de/p/vale-balkonkraftwerk-ecoflow-820-w-800...
• https://www.kaufland.de/product/502015379/?search_value=balk...
15kWh battery - 5.5k NZD + and hour of DIY.
So technically battery is more expensive but more useful.
Also easiest with water heater would be cranking up the temperature, but I really hate dealing with scolding water coming from taps (especially with small kids around).
Another thing with battery I can charge with whatever solar excess I have, but with hot water my only option is 16A.
Either way I do not care ATM - I export using spot price which has been 2x of what I actually pay for power - https://www.emi.ea.govt.nz/Wholesale/Reports/W_P_C?DateFrom=...
If you aren't limited by roof and other outdoor area for PV panels, US$4000 buys you about 50000 watts of "low cost" solar panels at current wholesale prices: https://www.solarserver.de/photovoltaik-preis-pv-modul-preis...
At a nominal capacity factor of 15%, that works out to about 5000 liters per day of domestic hot water:
~ $ units -t '50000W 15%/(30K 1kcal/kg/K)' kg/day
5162.5239
That's still about six times the cost of wholesale low-cost solar panels: https://www.solarserver.de/photovoltaik-preis-pv-modul-preis...
64 watts is about 40–50 liters per day of hot water heated resistively, presumably closer to 150 liters per day with a heat pump. But it seems like the heat pump is only saving you the 700€ for two more such balcony systems, assuming you have the space. Moreover, you don't need a microinverter for a resistive heater.
I'm not sure if you're allowed to just resistively dump an off-grid PV system into a resistive heating system, but I guess if you did, you could indeed save on the cost of the inverter.
Losses are higher but you store more energy per L, which is often the limiting factor.
Your water heater temperature isn't exactly my business but please look into sanitary norms on minimum safe temperature. Water heaters have standing water and bacteria might start living there if the temperature isn't sufficient. I think legionnaires' disease is one of the most prevalent dangers.
my PV system is paid after 6 years of use. if i use current prices for energy. last two years market/spot prices were even higher than that. so in reality it was paid even sooner.
and pv system does not disappear as soon as it is paid, it continues to work. so i have next 4-10 years remaining of lifetime of a inverter.
so for next 4-10 years i am having 100% REALLY REALLY FREE hot water, again for 80% of time... etc vis original comment.
when inverter ends its life in next 4-10 years then i will buy new one, without changing panels. so payback time will be even quicker.
calculations/models of biggest engineers, experts, etc. do not involve thinking about using pv system after it is paid... ( not insult, just exposing state of things )
Well no, there will be a chain of people all upgrading their cars to better ones. The final car will drop off the bottom of the chain, so you trade an EV for what is likely to be the worst performing car environmentally.
I think that what actually costs money is not the space but the tank. Higher temperatures mean not only more expensive materials and shorter lifetimes for tanks and piping but also higher conductive losses.
Also, if you are heating with solar you could heat water directly. But that path is also only available to house owners.
Now that the sun is out for longer periods each day we are "wasting" energy to the grid a lot. I don't really see how to capture that energy though.
1. Buying a battery quickly shifts the break even points to decades. Without a battery I estimate 3-4 years. 2. I would love to heat water, but renting a place limits my options a lot. I was looking at electrical boilers to supplement the gas heater. But we are limited on space for small heaters below the sink and big heaters in the main water path. (Also we can't change the plumbing for legal reasons.) 3. The next best thing is some imaginary insulated water heating kettle that I can control to only use exactly the excess energy. No idea if such a thing exists.
If you don't have net metering (or just a terrible power purchase rate), why not just sink that extra solar energy into a water heater?
1. Consider PCM heat storage (still relatively new technology, but works well with heat pumps)
2. Maybe the problem shall be solved at the building level, not individual apartments.
Someone that that switches to EV today will pass that EV to a second owner down the line. The sooner the fleet starts switching to electric, the sooner the carbon emissions, primary energy needs, gas usage and particle emissions dive.
Try this: if everyone in the US suddenly purchased EVs, and ditched their ICE cars, flooding the market with old ICE vehicles, would emissions decrease in the world or increase? I think it's pretty clear that the vast majority of the old ICE vehicles would be junked, and there'd be marginally more vehicle-miles-travelled, so the huge wins of everyone using EVs would counteract any increase in vehicle miles from suddenly having cheaper ICE available around the world.
So I would argue that the single person doing that action would have the general same trend as if everyone did it.
It is certainly true that energy-intensive buildings cannot be self-sufficient on solar, but perhaps you can put the solar panels near your house instead of on it.
Another issue was that they were not available for a long time (around 6 months delivery time with no guarantee), something not relevant here but it also affected decision of owners.
Welcome to public policy.
> Try this:
No, I’ll stay in the real world. Your thought experiment isn’t possible, and extrapolating from it isn’t useful.
With respect to the duty cycle, obviously if you have solar power, you would prefer to use it predominantly and only add up some extra power from the grid when needed. This is the essence of the sizing problem, because that leads you to 2-3x power overprovisioning and the need for heat/cold storage. Heat storage can be two types - DHW and space heating. Space heating is the easiest to estimate. You need to know your house's heat loss (either by specification or just figure it out empirically if you have already lived in it). DHW storage is more difficult to estimate, because it depends on the usage (e.g. how many showers per day). Cold storage is the most problematic, because the fluid needs to be at least 16C or lower to do useful cooling work, however you cannot go much lower than 7C unless you are using propylene glycol (expensive) and even then your indoor units may start to freeze (I am not even mentioning indoor humidity management and dew points).
Lately, the industry has been exploring PCMs (phase change materials). The idea is to store heat/cold not as sensible heat, but as latent heat of the phase change. In practice the substances used are either salts (efficient, but corrosive to the storage tank) or paraffins (more expensive, less efficient, but still viable). These come rated at a specific temperature, but usually have some hysteresis/drift and other issues. I guess you are now feeling a bit frustrated from the engineering complexity :). If batteries were cheap, long lasting and environmentally friendly, this complexity would not be needed. However, I really doubt it that in the foreseeable future batteries will beat heat storage. Given that most of our domestic energy use is space heating/cooling and DHW, I think that PCMs may actually have some moat. There are already offerings on the market, but IMHO they are still not very compelling. What I see lacking is some integrated offering, that would take into account the PV schedule and also grid prices. One a side not, batteries still have an advantage if you can sell back to the grid at a high premium or if you need to e.g. charge your car in the night. So these technologies may be complementary, rather than competitive.
A very big factor is climate. Just to give you an example, I live in the mountain with a colder climate. Cold water from the faucet is around 10C. I rarely need cooling if at all, but I need space heating around 8-9 months during the year. Just 300 km south and by the sea (Greece), cold water from the faucet is around 20-25C, you need 4-5 months of cooling and only ~4 months of heating. Some countries, such as UK have very moderate climate without extremes and things are more predictable. Where I live, we get -15C in the winter and 38C in the summer.
Every taxi I rode in the Bahamas was a 2nd gen Jeep Grand Cherokee with the CEL on.
The bottom exists, but it’s not here.
solar PV is order of magnitude cheaper in small systems (per actual provided output per year, not just rated wattage)
AND because hot water energy needs are much higher than for example tv, notebook etc, so after your hot water is heated, you can charge your devices with it, you can not do that with solar thermal. so if people size their systems for winter sunny day, they will have excess in summer so you can use that for other things like bikes, lawnmowers ...
of course there is ratio of people living in blocks of flats / townhouses and people living in family houses / rural, so every situation is unique. so townhouses should be connected to central heating network and heating network provider should chase efficiencies of scale, that is better, faster, cheaper for everyone ( europe / germany context ) if urban density does not allow otherwise.
similar situation with electric cars, a lot of people is crying that there are not enough chargers for them, those are "city" people, but in reality most people live in rural setting or family houses and in germany every house already has more than enough electrical capacity to charge from outlet, you can charge car from 2.5kW which is same wattage as most electric kettles. yes it charges over night (10 hours) only 100 km but every house can do that already. faster charger can be bought. of course situation in cities is quite different, you can not just put extension cord from window. which is feasible in rural setting / family houses. even in berlin roughly 50 % of people do not live in townhouses / high rises.
which is higher latitude than 99.99999999% of USA or 80% of canada population
then it will work even in USA too.
Again read my first post, it is NOT about reaching 100% offgrid which is expensive, and nonsensical for most people
it is about reaching 100% offgrid for 80 % of time and 10-99% offgrid 20 % of time. Which is so cheap in europe that youre generating totally free energy after 6-7 years PV system paid for itself.
per $ invested
then solar thermal system.
rated output is not what you get 100% of time. price per performance is crucial. price per imaginary watts is nonsense.
It sounds like you might be interested in my notes and calculations on thermal energy storage in phase change materials, some of which are listed at https://dercuano.github.io/topics/phase-change-materials.htm.... But I think TCES systems are likely to be more significant because of their technical advantages, among other things for managing indoor humidity and possibly even for seasonal thermal stores; some of my notes on the topic are at https://derctuo.github.io/notes/desiccant-climate-control.ht... and https://dernocua.github.io/notes/shower-heating-tces.html. Various kinds of thermal energy storage do seem to beat batteries on cost by around three orders of magnitude; some of my relevant notes are listed at https://derctuo.github.io/topics/thermal-storage.html. I agree with you that there is no real prospect of batteries catching up with thermal energy storage in the foreseeable future.
With respect to the particular problem you mention with needing expensive propylene glycol in your heat transfer fluid to keep it from freezing, ice rinks commonly use brine systems instead, despite the corrosion problems you mention. Brines are very cheap, some like dipotassium phosphate are minimally corrosive, and the commonly used ones are pretty nontoxic.
Consider running the dishwasher (if you have one) or washing machine / dryer (if you don't dry that in the sun directly) during the day.
Granted, we work from home _a lot_ and also have an EV so it's a lot easier to do load shifting for us, but just shifting the dishwasher and washing machine to 'sunlight hours' already made a pretty decent difference.
E.g. our washing machine uses 1000W over a prolonged period of time which would be perfect to run on a sunny day. But it does so by switching the 2000W heating element so it averages to 1000W ...
So we repeatedly export 800W (without any form of reimbursement) and import the missing 1200W back.
And that is the case for all of our appliances. (I have a sensor to monitor that)
Don't know if more modern machines are better in this regard, our machines are about 5 years old now.
edit: I don't want to sound bitter about it. The Balkonkraftwerk works perfectly fine to power our base energy load.
energy generated by big wastewater plants is methane from microbial activity. also waste water plant can not remove a lot of stuff like medicine, hormones...
you can construct wastewater tank with integrated coil connected to heat pump. so you can take all heat back. if you have house with integrated waste water treatment, this should be no brainer. houses with existing heat pumps can "just add another heat exchanger circuit"
but i do not personally like heatpumps because working fluid can be in orders of 10 000 times more harmful to greenhouse effect than co2. and compressors using CO2 as a working fluid are rare.
heatexchangers connected to vertical wastewater pipe are showed in tradeshows. but i do not understand how that makes sense price wise. im not sure they recover as much heat as advertised.
If you're saying electric cars are pointless, and we should keep making ICE cars, because for a period of transition from ICE to EV some older ICE cars will go overseas, then I'm not sure there's much else to say. I disagree that that's good logic, I suppose.
You seem to have concluded energy use for hot water cannot go lower by excluding any approach that would lower it, not because it's physically impossible, but simply because such technology isn't being used.
Isn't this a vacuous argument?
The manufacturer-suggested retail price of the Stiebel Eltron SOLkit 2 you link is US$7870, according to https://www.stiebel-eltron-usa.com/sites/default/files/pdf/s.... This includes two SOL 27 Premium flat-plate solar thermal collector panels, about which that page says, "The net absorber surface of over 25 square feet results in a maximum output of 31,300 btu/day per panel (SRCC clear day rating)."
In modern units, that's 2.3m² (per panel) and 382 watts (per panel), so you're paying US$7870 for 764 watts (on a clear day). That's US$10.30 per average watt. We don't really care about peak power, since the system comes with thermal energy storage built in, but if we assume a capacity factor of 20% (which would be about right if it were fixed photovoltaic) then it's about US$2 per peak watt. (Incidentally, that's a very-well-designed panel, because, assuming the same 20% capacity factor, it's about 80% efficient!)
That's a very high price. The SEIA calculated a cost breakdown for US residential solar PV installations in early 02024 (https://www.seia.org/research-resources/solar-market-insight...), of which 20¢ per peak watt (Wp) was the PV module. The rest of the US$3.25/Wp price (even higher than Stiebel Eltron's!) was things like batteries, inverters, installation labor, etc. You don't need those for water heating; you only need low-voltage wiring, an electric heating element (a resistor) in the water tank, and some kind of safety thermal cutoff. So if all you're interested in is getting a solar water heater, you can almost certainly get it more cheaply by running wires to your roof, or to panels in your yard, instead of pipes.
20¢/Wp at a 20% capacity factor would give you a nice round US$1 per round-the-clock watt, so 764 round-the-clock watts would cost you US$764 of panels, as compared to Stiebel Eltron's US$7870 MSRP. (Which one were you saying was "the smart way to make hot water from the sun" again?)
But the situation actually favors solar PV much more strongly than that, for two reasons. First, PV modules are cheaper than that; the "mainstream" price on https://www.solarserver.de/photovoltaik-preis-pv-modul-preis... is now 0.115€/Wp (US$0.125/Wp) wholesale, though the US's anti-renewable-energy policies presumably make them a little less cheap than that where you live. Second, in most cases, even if a home PV system provides less power than you need on average, it still provides more power than you need at times. If you're choosing between turning some of the panels off in the daytime and heating up the hot-water heater, the latter sounds like a better choice. If you're just burning up surplus energy, instead of buying extra panels just for your hot water, it won't even cost you US$764.
But wait, you might ask, why not batteries? And batteries are certainly more flexible than a hot-water heater. If you use your excess solar power production to charge batteries, you can use the energy later to run your computer, cool your house, run a circular saw, heat your house, or take a hot shower. If you use it to heat up a hot-water heater, you can only use it to heat your house or take a hot shower.
But batteries have a countervailing disadvantage: they're expensive. If your hot-water tank is at 65° when incoming water is at 20°, and the tank is 300 liters like the one in the Stiebel Eltron system you linked, it's storing 56MJ of energy, or, in cursed folk units, 16kWh. Lead–acid or lithium-ion batteries generally cost in the range of US$50–150/kWh (US$15–40/MJ) so the same amount of energy storage in batteries would cost US$700–2400. The hot-water tank only costs about US$500, if you don't have it already.
There are cheaper solar hot-water systems than Stiebel Eltron's. Looking locally, this no-brand locally-made 300-liter one sold by "Energía al Sol" only costs about $2.1 million: https://articulo.mercadolibre.com.ar/MLA-1683162470-termotan...
That's about US$1600 at today's exchange rate, one fifth of the much more complex system you're talking about. Still more expensive than the PV option.
The solar-thermal option might still beat PV if you're limited on space, because, at around 80% efficiency, it requires about a fourth of the area as the equivalent mainstream 23%-efficient photovoltaic panels. Even garden-variety solar thermal collectors can often exceed 50%. They're just much more expensive than photovoltaic. I know that's crazy, but what can I say? We live in a crazy world.
As for your unfortunate neighbors, I suspect that the reason they are paying hundreds of dollars a month for under 6kW is that they installed their solar systems when prices were much higher than they are today, and that all their energy storage is in electrical batteries. Some thermal energy storage—whether in primitive "sensible heat storage" systems like an insulated tank full of hot water, or more advanced phase-change and TCES systems—would probably have gone a long way toward bringing those costs down. See https://news.ycombinator.com/item?id=43468177 for a recent comment where I did a brief sketch of an LCoE estimate.