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Solar Thermal or Vacuum Tubes

I have had solar for 15 years now and the system cannot be upgraded.
I have been waiting a while to heat the house with clean energy. Throwing out perfectly good panels (or donating them) seems a bit extreme, and running the electric heat pump on grid energy seems like a weak choice.

I have recently heard about using Vacuum Tubes or Solar Thermal instead. Both these technologies seem great and even better choices as they both can operate in cold weather when you need to heat the house, whereas solar works better in the summer. So no need to shift energy around during the entire calendar year.

Unfortunately these seem unpopular here in the states, as we are pushing everything to be electrified, which is a good thing. But with old solar panels that are maxed out with the Model S's needs, not good for this house.

I am hoping I can find someone in the Tesla world that might know more and give me pointers.

There does not seem to be any major installers or companies locally. I have pointers for a few independent small operators that's it.

I am located near Tesla Headquarters in sunny California.

Any info or experience much appreciated.
 

nwdiver

Well-Known Member
Feb 17, 2013
8,855
12,936
United States
I have had solar for 15 years now and the system cannot be upgraded.
I have been waiting a while to heat the house with clean energy. Throwing out perfectly good panels (or donating them) seems a bit extreme, and running the electric heat pump on grid energy seems like a weak choice.

I have recently heard about using Vacuum Tubes or Solar Thermal instead. Both these technologies seem great and even better choices as they both can operate in cold weather when you need to heat the house, whereas solar works better in the summer. So no need to shift energy around during the entire calendar year.

Unfortunately these seem unpopular here in the states, as we are pushing everything to be electrified, which is a good thing. But with old solar panels that are maxed out with the Model S's needs, not good for this house.

I am hoping I can find someone in the Tesla world that might know more and give me pointers.

There does not seem to be any major installers or companies locally. I have pointers for a few independent small operators that's it.

I am located near Tesla Headquarters in sunny California.

Any info or experience much appreciated.

You mean your solar PV system can't be upgraded? Why? If the have the roof area for solar thermal to work IMHO adding more PV panels would be cheaper and more effective. Nothing wrong with taking another 3kWh/day in energy from the grid if you're exporting >3kWh/day more from PV...
 
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...I have recently heard about using Vacuum Tubes or Solar Thermal instead. Both these technologies seem great and even better choices as they both can operate in cold weather when you need to heat the house, whereas solar works better in the summer....
Not familiar with vacuum tubes used in this application? Where have you heard of them?

In winter, although Solar PV production with good exposure loses 50%+ production, Solar Thermal is much worse and nearly useless then in most places.
 
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You mean your solar PV system can't be upgraded? Why? If the have the roof area for solar thermal to work IMHO adding more PV panels would be cheaper and more effective. Nothing wrong with taking another 3kWh/day in energy from the grid if you're exporting >3kWh/day more from PV...

Well last time I checked and called around I was told 'your system is too old' we would just have to start from scratch. I think that was Tesla....and maybe a second person not sure.

I think I may have found someone that will upgrade my solar. They have been around for 30 years so they may not be as resistant as the new fangled people on the market.
 
Not familiar with vacuum tubes used in this application? Where have you heard of them?

In winter, although Solar PV production with good exposure loses 50%+ production, Solar Thermal is much worse and nearly useless then in most places.

My county has a new rebate program and an actual consultant team you can call for free. I explained my situation and they pointed to Solar Thermal and/or Vacuum Tubes.

 

nwdiver

Well-Known Member
Feb 17, 2013
8,855
12,936
United States
Well last time I checked and called around I was told 'your system is too old' we would just have to start from scratch. I think that was Tesla....and maybe a second person not sure.

I think I may have found someone that will upgrade my solar. They have been around for 30 years so they may not be as resistant as the new fangled people on the market.


How old is your system? Do you what wattage your panels are?
 
My county has a new rebate program and an actual consultant team you can call for free. I explained my situation and they pointed to Solar Thermal and/or Vacuum Tubes.


Yeah, these had come up on top of my Google search. In theory, looks like could work in the winter for heating needs (as opposed to solar thermal).
But a few concerns include:

-10-year limited warranty
-how does this compare to solar PV for energy production from the same surface area
-how does this compare to solar PV for production in terms of cost
-thermal systems produce most of their hot water in summer when needed the least, least in the winter when needed the most
-solar PV also produces least in winter, but more versatile year round and well used in summer for electricity to power cooling
-competition for limited roof space exposure with solar PV
-the energy market has not caught up on them which usually means they are not economically competitive
 
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Yeah, these had come up on top of my Google search. In theory, looks like could work in the winter for heating needs (as opposed to solar thermal).
But a few concerns include:

-10-year limited warranty
-how does this compare to solar PV for energy production from the same surface area
-how does this compare to solar PV for production in terms of cost
-thermal systems produce most of their hot water in summer when needed the least, least in the winter when needed the most
-solar PV also produces least in winter, but more versatile year round and well used in summer for electricity to power cooling
-competition for limited roof space exposure with solar PV
-the energy market has not caught up on them which usually means they are not economically competitive

Good points. But could make sense if I can't add to my existing panels... in a sense buy electricity again

rarely use A/C -- so summer I generate a lot of excess power

Flat roof -- more than enough space for expansion
 
Good points. But could make sense if I can't add to my existing panels... in a sense buy electricity again

rarely use A/C -- so summer I generate a lot of excess power

Flat roof -- more than enough space for expansion
Are you in SF proper or substantially further inland "bay area"? If proper or within a stones throw of that part of the bay, it may be too foggy or overcast on most days as well. Of course that's a problem with solar PV too.
 
Are you in SF proper or substantially further inland "bay area"? If proper or within a stones throw of that part of the bay, it may be too foggy or overcast on most days as well. Of course that's a problem with solar PV too.

Substantially inland. Almost no fog. Even overcast seems to have died down completely in the last few years! Climate has drastically changed. Solar in general works great here.
 
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I have had solar for 15 years now and the system cannot be upgraded.
I have been waiting a while to heat the house with clean energy. Throwing out perfectly good panels (or donating them) seems a bit extreme, and running the electric heat pump on grid energy seems like a weak choice.

I have recently heard about using Vacuum Tubes or Solar Thermal instead. Both these technologies seem great and even better choices as they both can operate in cold weather when you need to heat the house, whereas solar works better in the summer. So no need to shift energy around during the entire calendar year.

Unfortunately these seem unpopular here in the states, as we are pushing everything to be electrified, which is a good thing. But with old solar panels that are maxed out with the Model S's needs, not good for this house.

I am hoping I can find someone in the Tesla world that might know more and give me pointers.

There does not seem to be any major installers or companies locally. I have pointers for a few independent small operators that's it.

I am located near Tesla Headquarters in sunny California.

Any info or experience much appreciated.
Vacuum Tubes are fantastic for heating water. The do not generate electricity. We have had them for about 15 years, alongside a small PV system. The have probably saved us much more than the PV panels as we have year-round hot water for free. There is a gas backup but that is almost always turned off. We only turn it on if there are several completely sunless days and/or we have multiple guests who shower etc.
 
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nwdiver

Well-Known Member
Feb 17, 2013
8,855
12,936
United States
Vacuum Tubes are fantastic for heating water. The do not generate electricity. We have had them for about 15 years, alongside a small PV system. The have probably saved us much more than the PV panels as we have year-round hot water for free. There is a gas backup but that is almost always turned off. We only turn it on if there are several completely sunless days and/or we have multiple guests who shower etc.

I've always wondered about the resistance or gas back up that solar thermal water heaters use. Love to know what uses less energy on average. A heat pump water heater or a solar thermal water heater.
 
Vacuum Tubes are fantastic for heating water. The do not generate electricity. We have had them for about 15 years, alongside a small PV system. The have probably saved us much more than the PV panels as we have year-round hot water for free. There is a gas backup but that is almost always turned off. We only turn it on if there are several completely sunless days and/or we have multiple guests who shower etc.

From the consultant I was talking to he implied that the only reason they haven't taken off in the US is that we have insisted just basic solar to simplify the message.

So glad to hear this is successful in France!

I found a contractor that has been around the block for a long time and is not afraid of my old solar or the thought of Solar Thermal! :)
 

nwdiver

Well-Known Member
Feb 17, 2013
8,855
12,936
United States
From the consultant I was talking to he implied that the only reason they haven't taken off in the US is that we have insisted just basic solar to simplify the message.

Not sure about that. For ~$2k you can get a heat pump water heater and enough solar PV to 100% offset the use of 4 people. What’s the equivalent cost of solar thermal? I have a friend that paid $7k about 6 years ago for a solar thermal water heater. Crazy.
 
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So in summary: you have a flat roof with room to put another (thermal) system, and don't want to remove a working 3.8kW PV system.

Maybe I'm missing something here- why not just add a second independent PV system? Even if Tesla said no, that doesn't mean all installers will say no.

I've also run the numbers on thermal solar vs PV increase + heat pump water heater, and only the second one made sense. Any I already have my hot water heater in the attic (very easy thermal install, in theory). What it really came down to is that a thermal system needs a thermal backup (water heater of some sort) while a PV + heat pump just uses the grid or powerwall as a "backup" energy source, which is "free" because the rest of the house can use the electricity directly from the extra PV.
 
I paid $6k for solar thermal back in 2010. Got so many incentives (state, fed, utility) that my net was $1500. Try buy a good quality 80 gallon heat pump hot water heater for $1500 - installed. I am not sure in what world you can get a HP hot water heater and solar PV for $2k installed. Maybe DIY and a cheap hot water heater.

Back in 2010, there were plenty of longevity concerns with HP hot water heater as they were using pretty crappy compressors. They seem to be better today and when I made the choice in 2019, I maxed out PV and did a HP hot water heater. I also didn't have the same great incentives and PV had come down in price.

PV has gotten so cheap, it is hard to do anything else. It is not an oversimplified message - it is just the value of mass production and simple installation. Solar thermal can't compete with that.

My solar thermal was supposed to have coolant changed every 5 years. No issues with PV there. Now - if you have zero risk of freezing, then you can't put a super cheap system in and the economics change a bit.
 
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nwdiver

Well-Known Member
Feb 17, 2013
8,855
12,936
United States
I am not sure in what world you can get a HP hot water heater and solar PV for $2k installed. Maybe DIY and a cheap hot water heater.

DIY or after incentives and adding watts to a PV system. You only need ~500w of PV to offset the consumption of a HPWH. Adding watts is ~$0.50/w DIY. If you catch them on sale the Rheem HPWH is ~$1400.
 
Latest Update on trying to figure this out. I called a number of solar companies yesterday. Very few will upgrade any system unless they installed it.
One company who says they will do it will install a second system in parallel. But they were not very enthusiastic about it and did not follow up with a promised email. The second company who was interested has not called back either after 2 days.

Contractors around here are very busy. No one is waiting for business so anything 'non standard' gets shoved off the list.

Folks are more than happy to throw away a perfectly good functioning set of panels because they 'are old'

You also get no rebates if you ever got one in the past.

I think at the moment I'm going to try to replace the gas using hot water tank and/or the boiler with something electric and just live with the extra costs for a few years till my current inverter dies or another 10 years till the panels are out of warranty.

Not very optimistic about this either as I have 'non standard' radiant flooring....which is surprisingly not serviced by most HVAC companies.
 

nwdiver

Well-Known Member
Feb 17, 2013
8,855
12,936
United States
I think at the moment I'm going to try to replace the gas using hot water tank and/or the boiler with something electric and just live with the extra costs for a few years till my current inverter dies or another 10 years till the panels are out of warranty.

IMHO the Rheem heat pump water heater is far and away the best choice. AND... AND ~70% of the energy it uses to heat water is technically solar. ~100% if you count the energy from your PV :D I bet there's tons of rebates in SF for installing one.

Rheem HPWH
 

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