15kw Solar System with Solar Hot Water?

[Solarguy]

Another option for hot water is an electric tankless hot water heater. For some reason tank type hot water heaters don't last more than 10 years in Florida. After replacing two tank type I installed a tankless 11 years ago and love it. It is a large one and does require three 60 amp circuits to power it but provides constant hot water as long as the tap is on. Obviously it only draws power when water is called for so it uses a lot less electricity than a conventional tank type but not sure compared to the new heat pump designs. No tank so I gained space for a beer frig
Here is a picture of mine:

 

[GJ79]

Another option for hot water is an electric tankless hot water heater. For some reason tank type hot water heaters don't last more than 10 years in Florida. After replacing two tank type I installed a tankless 11 years ago and love it. It is a large one and does require three 60 amp circuits to power it but provides constant hot water as long as the tap is on. Obviously it only draws power when water is called for so it uses a lot less electricity than a conventional tank type but not sure compared to the new heat pump designs. No tank so I gained space for a beer frig
Here is a picture of mine:

View attachment 189382

Heat pumps use significantly less energy than tankless systems. If you drain the tank every 6 months and use a water softener than Tank Style heaters last much longer in FL.

 

[LoL Rick]

OP's price sounds high, but I'm not sure if that is because of the water heater and the pool. I just had a 10k system installed for $24,800 before the tax credit. 40 250w panels and 2 SunnyBoy 6000TL inverters.

On the other topic, my water heater is 19 years old and has never been touched.

 

[GJ79]

OP's price sounds high, but I'm not sure if that is because of the water heater and the pool. I just had a 10k system installed for $24,800 before the tax credit. 40 250w panels and 2 SunnyBoy 6000TL inverters.

On the other topic, my water heater is 19 years old and has never been touched.

eeeewwww, you should drain it and you will be disgusted to see what is resting at the bottom of it.

But I am sure there are many 19 year olds' that have never been touched

 

[nwdiver]

For some reason tank type hot water heaters don't last more than 10 years in Florida.

One reason tank hot water heaters die is the collection of scale. Heat pumps can help reduce scale buildup since instead of having high temperatures (>200F) concentrated on the heating element they have much lower temperatures (~140F) spread out on the refrigerant tubes. Heat pump hot water heaters basically heat the water by heating the tank. It's the high temperatures that cause the minerals to come out of solution and collect in the tank.

Another reason I'm far more favorable toward tanked hot water heaters is the potential for thermal storage. For ~$50 you can buy a 240v timer which effectively turns your hot water heater into a ~4kWh thermal battery. $50 for a 4kWh battery with a effectively infinite cycle life is a pretty good deal.

I shudder to think of the consequences if electric tankless heaters became popular... imagine the duck curve then since most people either shower in the mornings or evenings... ~15kW per shower

What REALLY irritates me is how electric tankless heaters somehow got the reputation of being efficient... regular resistance hot water heaters are ~90% efficient (already not much room for improvement). Tankless are ~99%. BUT the new heat pump models have a COP if 3.2... meaning you get 3.2 watts of heat for every watt of electricity. So you use ~10% less energy with tankless vs ~70% less energy with heat pumps.

 

[GJ79]

I shudder to think of the consequences if electric tankless heaters became popular... imagine the duck curve then since most people either shower in the mornings or evenings... ~15kW per shower

Well you will see that exact problem soon when EV's will become popular and the huge power demand will shift to nighttime when everyone charges their vehicles.

 

[nwdiver]

Well you will see that exact problem soon when EV's will become popular and the huge power demand will shift to nighttime when everyone charges their vehicles.

Well... you can program your car when to start charging... it's a bit harder to program people when to shower... and with demand response the utility can send a signal to your car to stop charging and no one would really care. I have a feeling people wouldn't like it if their shower water suddenly ran cold due to a surge in demand...

 

[GJ79]

Well... you can program your car when to start charging... it's a bit harder to program people when to shower... and with demand response the utility can send a signal to your car to stop charging and no one would really care. I have a feeling people wouldn't like it if their shower water suddenly ran cold due to a surge in demand...

interesting idea but I don't think it's sustainable. They can't just turn off my car charger, I still need to be in control when it's charging or not. I wouldn't want to give that decision to my utility company.

 

[nwdiver]

interesting idea but I don't think it's sustainable. They can't just turn off my car charger, I still need to be in control when it's charging or not. I wouldn't want to give that decision to my utility company.

Not really turning it off... the way to think about it is this... say you need 10kWh in the car by 6am. You're definitely going to get those 10kWh but the demand response program will determine when. It could be 10kW for an hour from 1am - 2am or 2kW from midnight to 5am. You can also override this if needed.

You obviously get paid for providing this service.

 

[Ulmo]

From what I understand the most current thinking about solar hot water is that it breaks down physically too quickly (no cost-effective material can handle the daily cycles) and is not cost-effective, with the possible exception of just for pool heating alone. The idea in hotter climates, perhaps like in Florida, is to use an electric heat pump water heater. Either way, they say that solar electric + electric hot water is the way to go, and I'd try mightily to make that water heater a Heat Pump Water Heater. The range of operation of that thing is pretty limited for the model we got, since it has to be above about 60°F and below about 108°F. We have an un-ideal climate for that, but we went ahead and got a Stiebel-Eltron, and it seems to be working fine, although not as well as if it were in a hotter climate like the California Central Valley. Also, I don't like that it doesn't have a built-in temperature projections for auto specification ambient temperature. Maybe the GE model has that built-in since it has a lot more computer electronics (Internet diagnosis of operation of the machine, firmware upgrades, Wi-Fi connection, whereas the Stiebel-Eltron is all mechanical electronics).

 

[nwdiver]

The range of operation of that thing is pretty limited for the model we got, since it has to be above about 60°F and below about 108°F.

That doesn't sound right... the GE Geo Spring temperature range is 35F-120F... I've never heard of a heat pump that can't work at ~45F...

But you're spot on with the economics... it's hard to find a solar hot water heater for <$3k... at that price you can buy a GE Geospring and 1kw of solar PV. That combo would easily provide 100% of the hot water needs for a typical family AND you can export your excess production if you're away.

The other reason I kinda have a hard spot for solar thermal is that if I meet someone that's had a bad experience with solar... 90% of the time it was solar thermal and they use that experience to also negatively color solar PV. The two could not be more different.

San Jose appears to be the ideal climate for your Steibel-Eltron; It can operate as a heat pump down to 32F.

 

[GJ79]

That doesn't sound right... the GE Geo Spring temperature range is 35F-120F... I've never heard of a heat pump that can't work at ~45F...

But you're spot on with the economics... it's hard to find a solar hot water heater for <$3k... at that price you can buy a GE Geospring and 1kw of solar PV. That combo would easily provide 100% of the hot water needs for a typical family AND you can export your excess production of you're away.

The other reason I kinda have a hard spot for solar thermal is that if I meet someone that's had a bad experience with solar... 90% of the time it was solar thermal and they use that experience to also negatively color solar PV. The two could not be more different.

San Jose appear to be the ideal climate for your Steibel-Eltron; It can operate as a heat pump down to 32F.

I couldn't agree more ^^^^^ Spot on !!!

 

[Ulmo]

Not really turning it off... the way to think about it is this... say you need 10kWh in the car by 6am. You're definitely going to get those 10kWh but the demand response program will determine when. It could be 10kW for an hour from 1am - 2am or 2kW from midnight to 5am. You can also override this if needed.

You obviously get paid for providing this service.

Absolutely 100% correct, when it eventually gets correctly implemented. HOWEVER, political enemies and other power-brokers will INTENTIONALLY INCORRECTLY IMPLEMENT IT in order to cause INTENTIONAL problems that for one reason or another MIGHT help them with one of their agenda items. This WILL be fixed by the civilization(s) that utilize such systems (pretty much 100% of future civilizations), as people EVENTUALLY read through all of the subterfuge and sabotage, and erase those problems. But please expect a one or two decade period in which implementations will be faulty (much like NSA took out advertised features of cell phones in order to have space to put in malware). For now, if you want such systems to actually work as nwdiver explained, then INSIST on them working properly, and they will reluctantly make them work that way, either by charging you extra, or by you waiting a few years for the "feature" of it working properly to be made "available".

 

[nwdiver]

HOWEVER, political enemies and other power-brokers will INTENTIONALLY INCORRECTLY IMPLEMENT IT in order to cause INTENTIONAL problems that for one reason or another MIGHT help them with one of their agenda items.

That's why the Supreme Court ruling on Order 745 earlier this year was so critical.

That Supreme Court ruling states that by law the markets are required to treat 1MW of curtailed demand the same a 1MW of increased generation. So Tesla Energy could network 100k Teslas and 'sell' 200MW of capacity. Tesla Energy has a profit motive for keeping their 'power plant' happy because if people don't have the charge they need in the morning they'll drop out of the network and Tesla will lose capacity. By law that 200MW is no different than 200MW available from a peaking plant... expect it's a fraction of the cost since the power plant is a power plant and 100k cars are controlled by software.

 

[David_Cary]

Absolutely 100% correct, when it eventually gets correctly implemented. HOWEVER, political enemies and other power-brokers will INTENTIONALLY INCORRECTLY IMPLEMENT IT in order to cause INTENTIONAL problems that for one reason or another MIGHT help them with one of their agenda items. This WILL be fixed by the civilization(s) that utilize such systems (pretty much 100% of future civilizations), as people EVENTUALLY read through all of the subterfuge and sabotage, and erase those problems. But please expect a one or two decade period in which implementations will be faulty (much like NSA took out advertised features of cell phones in order to have space to put in malware). For now, if you want such systems to actually work as nwdiver explained, then INSIST on them working properly, and they will reluctantly make them work that way, either by charging you extra, or by you waiting a few years for the "feature" of it working properly to be made "available".

Well isn't that a bit cynical?

The nighttime charging of EVs is very easy. Especially compared to tankless hot water. Tankless doesn't play well with the grid and solar. EVs are a dream for the grid. I don't see giving control to utility. I see demand charges and robust (and complex) TOUs. That is the logical answer. Now - wind does demand some curtailing ideally. But with big battery cars, people can be very flexible.

I have solar hot water. No significant issues in 7 years (after some small install issues). It was $7k, but net of incentives (fed, state, utility) it was less than $1000 more than a typical tank. So not terrible.

 

[nwdiver]

Here's something for the guy that's done everything to save energy but still wants to do more...

I installed one at my Rental. They run ~$700 but they should last forever since it's basically just a bunch of copper tubing. It's a nice compliment to solar and heat pumps since their performance in the winter is actually better than in the summer.

 

[digitalboi]

Another reason I'm far more favorable toward tanked hot water heaters is the potential for thermal storage. For ~$50 you can buy a 240v timer which effectively turns your hot water heater into a ~4kWh thermal battery. $50 for a 4kWh battery with a effectively infinite cycle life is a pretty good deal.

I am totally confused by this... What about the timer is turning the water heater into a thermal battery? Won't it cool down when its off and require that you heat the water back up to temp once the timer trips back to ON?

Here's something for the guy that's done everything to save energy but still wants to do more...
I installed one at my Rental. They run ~$700 but they should last forever since it's basically just a bunch of copper tubing. It's a nice compliment to solar and heat pumps since their performance in the winter is actually better than in the summer.

This is an awesome idea! I wish I could install this in my house... but we'd have to dig up the slab and install them underground so I think the dirt would suck the heat out to fast for it to work well...

 

[nwdiver]

I am totally confused by this... What about the timer is turning the water heater into a thermal battery? Won't it cool down when its off and require that you heat the water back up to temp once the timer trips back to ON?


This is an awesome idea! I wish I could install this in my house... but we'd have to dig up the slab and install them underground so I think the dirt would suck the heat out to fast for it to work well...

There's two parts of a battery as far as the grid is concerned. Charging and Discharging. The whole point if grid storage is to use energy when there's a surplus and to not use energy or export when there's a deficit. If you can program a water heater to only heat the water you use off-peak then you're accomplishing the same effect as a ~4kWh battery for 1/50th the cost.

The power pipe does not work horizontally. It requires the 'falling film effect' for effective heat transfer.

 

[digitalboi]

There's two parts of a battery as far as the grid is concerned. Charging and Discharging. The whole point if grid storage is to use energy when there's a surplus and to not use energy or export when there's a deficit. If you can program a water heater to only heat the water you use off-peak then you're accomplishing the same effect as a ~4kWh battery for 1/50th the cost.

The power pipe does not work horizontally. It requires the 'falling film effect' for effective heat transfer.

Oh! I see, so for municipalities like ours that don't have TOD rates for electricity, it really doesn't make much sense to mess with a timer for the water heater. Thanks for the clarification! I am trying to squeeze every watt of efficiency out of my house wherever possible, so any suggestions are welcomed!

 

[nwdiver]

Oh! I see, so for municipalities like ours that don't have TOD rates for electricity, it really doesn't make much sense to mess with a timer for the water heater. Thanks for the clarification! I am trying to squeeze every watt of efficiency out of my house wherever possible, so any suggestions are welcomed!

Yep; timing your water heating only makes sense if you have TOU but I would expect TOU to expand as solar does. Electricity is going to become less valuable at noon and more valuable at 6-10pm.

Do you have a heat pump water heater?