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etienne

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Is solar thermal heating out of date ?
« on: June 01, 2017, 05:30:42 PM »
Hello,

I see always more systems using directly solar electricity to heat sanitary water, I even heard of a system from Solacal using DC current in order to save the inverter costs and losts.

I had an idea to use solar heat without having to change too much my heating system, send it to a supplier and didn't got any answer. See attachment.
Pumps and anti backflow systems are not drawn.

Does anybody has experience with such configurations ? Does it make sense ? Is thermal solar really more expensive than PV solar ?

My feeling was that thermal solar was seen as not so good because panels' surface was most of the time oversized, so ROI (and EROEI - energy return on energy investment) was too low, but looks like things are worse than what I thought.

Thanks for your comments,

Etienne

oren

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Re: Is solar thermal heating out of date ?
« Reply #1 on: June 01, 2017, 05:50:08 PM »
In Israel I believe a solar water heater is mandated by building codes for new buildings.
From Wikipedia "Solar Water Heating":
Quote
Israel, Cyprus and Greece are the per capita leaders in the use of solar water heating systems supporting 30%–40% of homes.

I'm not sure if this is what you were refering to. I can't say whether it's cheaper than PV and other stuff, but it is very convenient in a sunny climate.

rboyd

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Re: Is solar thermal heating out of date ?
« Reply #2 on: June 01, 2017, 06:00:08 PM »
One of the easiest policy fixes to out in place, mandate solar water heathers for all new buildings and subsidize retrofits. Good climate policy and good working class jobs!

TerryM

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Re: Is solar thermal heating out of date ?
« Reply #3 on: June 01, 2017, 07:18:54 PM »
The systems I've seen were all pre-heaters, in other words your present water heater is left in place, but the feed in is through a solar heater.
Your water temperature is still regulated by the water heater's thermostat, but especially during high usage periods, almost all heat is supplied by the solar heater. A large, well insulated water heater provides the best results.
Terry

etienne

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Re: Is solar thermal heating out of date ?
« Reply #4 on: June 01, 2017, 07:54:03 PM »
The systems I've seen were all pre-heaters, in other words your present water heater is left in place, but the feed in is through a solar heater.
Your water temperature is still regulated by the water heater's thermostat, but especially during high usage periods, almost all heat is supplied by the solar heater. A large, well insulated water heater provides the best results.
Terry

Well, this is really a good idea for retrofit. Do you know if this also works for the house heating part of the system ? The only issue is space in the heating room (in Luxembourg, the heater has to be in a separate room that has fire doors).

Thanks,

Etienne

etienne

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Re: Is solar thermal heating out of date ?
« Reply #5 on: June 01, 2017, 09:10:30 PM »
To continue the previous reply, since there is no fire related to a pre-heater were the feed is a solar heater, I could place it outside of the heating room, so space would not be an issue anymore.

Really a good idea.

Etienne

ghoti

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Re: Is solar thermal heating out of date ?
« Reply #6 on: June 02, 2017, 01:38:17 AM »
In locations where freezing is an annual issue solar domestic hot water  systems are expensive and mechanically much more complicated that PV. I have both in Ottawa, Canada. The solar domestic hot water is not economically efficient despite it being more solar efficient than PV.

I have it to reduce the natural gas I'd otherwise burn to heat hot water. PV installation prices dropped by half since I installed the solar hot water. It might well be economically better to heat water with the electricity from PV at this stage.

sidd

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Re: Is solar thermal heating out of date ?
« Reply #7 on: June 02, 2017, 06:52:34 AM »
" It might well be economically better to heat water with the electricity from PV at this stage."

this was actually true for the last commercial project i ran costs for. But i got to say, for a quick do it yourself project when resources are limited, solar hot water preheat is a no brainer. And incredibly easy to install. Freezeup can be beaten with thermosiphon or antifreeze with heat exchanger isolation.

sidd

etienne

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Re: Is solar thermal heating out of date ?
« Reply #8 on: June 02, 2017, 12:27:00 PM »
Well, about economics, my parents have thermal solar since something around 1996 and still very happy with it. They never talked of any specific issue with that part of the heating system, and they live in the Swiss Alps in a Ski station. The nice thing when you're up in the mountains is that you have much more sun than down in the valley.
Of course costs can be lower when you buy the systems with PV panels because of the huge cost drop of all the electronical systems. This is also valid for LED lights, also electronics.
But with the life span issue, I still wonder what's the best in a non business context. Business needs shorter ROI.

Thanks for the ideas and comments.

Etienne

numerobis

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Re: Is solar thermal heating out of date ?
« Reply #9 on: June 05, 2017, 01:54:19 AM »
Solar thermal is definitely still a thing.

If you're doing a solar PV system, it might be cheaper to just add a few more panels on it, than to have two types of panels and get permits both for plumbing work and for electrical work.

I'm used to these systems having glycol in them, so there's no freezing problem.

ghoti

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Re: Is solar thermal heating out of date ?
« Reply #10 on: June 05, 2017, 04:50:11 AM »
No freezing problem but more complicated and more maintenance. Glycol loop, expansion tanks, relief valves, pump, control electronics, glycol replacement every few years....

numerobis

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Re: Is solar thermal heating out of date ?
« Reply #11 on: June 06, 2017, 12:44:51 AM »
Heating systems in Canada are often glycol already. That way if they fail you don't have to condemn the whole house.

Sleepy

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Re: Is solar thermal heating out of date ?
« Reply #12 on: March 19, 2018, 08:23:35 AM »
Lifting this thread since it's close to my own issue now. I've retired my solar hot water panels after the latest recent failure and temporarily placed PV-panels on top of them (at a 51° angle which is spot on this time of year).

I've ordered this unit together with a "harvi": *ttp://myenergi.uk/products/#eddi
A bit expensive but specs looks good and if someone in here has any real world experience of it, I'm all ears.

We still don't have net metering here and batteries are still too expensive, so this would be a nice intermediate solution for me. During winter I'd rather have the electricity the PV's can produce and during summer I can make full use of my, now capped, PV panels. I even turn off some of my inverters during summer, so dumping the excess into my hot water tanks and/or whatever I choose in the future should make this a sound investment.

But I won't know for sure until I start using it... The installation should go really fast though, just switch my old hot water control unit to this one and then fix the rest during summer.

Edit; adding a screenshot from the system overview.
« Last Edit: March 19, 2018, 08:34:13 AM by Sleepy »
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etienne

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Re: Is solar thermal heating out of date ?
« Reply #13 on: March 19, 2018, 08:32:14 PM »
It sounds good and should work. I manage at work similar systems from SMA. It becomes more complicated if you want to start the dishwasher and other appliance when the PV power is available because even if the machines are smart grid ready, the smart grid doens't really exist yet. The easiest way to work is to have electrical appliance that take hot water from the tap because heating water is often what uses the most power and warm water is an easy energy storage.

There should even be deepfreezers that can go to lower temperature (-30°C ?) when PV power is available so that the compressor doesn't have to work at night.

if you have a very old electrical meter (i guess only the ones with a turning disk), you have to make sure that the electricity you inject in the network will not be on your bill. There have been meters that were not able to detect in which direction energy was flowing, but counted everything. Don't know about the situation in Sweden. Is this why you turn off some of the inverters  during the summer ?

There are also some areas where you have to pay penalities if you inject electricity on the network without having a contract with somebody who would buy the electricity, so in Belgium, some people have an electrical heater in the garden just to consume excess electricity.


Sleepy

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Re: Is solar thermal heating out of date ?
« Reply #14 on: March 20, 2018, 05:29:45 AM »
It's the other way around etienne. Unfortunately we had our old meters replaced by the utility a long time ago, those were really good becuse they spun backwards when you produced energy (also the counter) so noone ever knew, real net metering. ;)

I have my fair share of commercial products that only works half the way, this should be configurable to whatever I need to do with it. It also has an optional relay & sensor board that can be attached to control other stuff. See the eddi manual at page 28. So in theory I will be able to do what I want with the output.

In Sweden, if you don't have a contract with your utility then you will pay the regular electricity fee for everything produced. If you have a contract, you will get payed but your payment will vary depending on which utility you have, but far away from net metering. The reason we don't have net metering is thanks to our government:
https://forum.arctic-sea-ice.net/index.php/topic,861.msg140148.html#msg140148
Another previous comment about solar sharing which is also taxed here:
https://forum.arctic-sea-ice.net/index.php/topic,856.msg140188.html#msg140188

Adding the pdf's from the link I posted above.
This solution measures the current direction via "harvi" on all three phases that we have here in Sweden. Eddi then directs the output to wherever I want it automatically, in my case (at least initially since I'm replacing my hot water panels), to one or two hot water immersion heaters.
« Last Edit: March 20, 2018, 05:36:08 AM by Sleepy »
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numerobis

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Re: Is solar thermal heating out of date ?
« Reply #15 on: March 27, 2018, 02:56:05 PM »
I've ordered this unit together with a "harvi": *ttp://myenergi.uk/products/#eddi
A bit expensive but specs looks good and if someone in here has any real world experience of it, I'm all ears.

Let me know how it works.

I should be putting up solar panels in July/August. I'd love to dump excess power into my heating system. There won't be any excess until next March, so I have an extra year to research that bit.

Ideally though I'd dump it straight from DC so I can oversize the panels relative to my inverter.

Sleepy

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Re: Is solar thermal heating out of date ?
« Reply #16 on: March 28, 2018, 07:55:40 AM »
Will try to update when I have it installed, numerobis. Hopefully I'll recieve these during the latter part of April.

My panels are oversized (using micro inverters), so out of ~4800Wp in total I never get more than ~2400W (real power) but the power curve is almost flat over the entire day, I also have almost vertical panels mounted in W/E directions. I did that to get more power during summer mornings/evenings but later found out that those were really nice during winter as well.

I've also looked at using DC directly but then would have to replace my immersion heaters to DC ones or build a regulator for my existing immersion heaters. It's more hassle than at first glance and I would still be restricted to using the immersion heaters, it's important to keep things as scalable as possible.

-11°C here and looking forward to a crisp and clear sunny day. :)
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etienne

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Re: Is solar thermal heating out of date ?
« Reply #17 on: March 28, 2018, 07:28:16 PM »
If you want to heat water using DC power, there is the SELACAL solution from Wagner Solar in Germany.
http://www.wagner-solar.com/de/strom/produkte-strom/solar-elektrische-warmwasserbereitung/selacal
They also have a solution to install on existing boilers.

They also have a MyPV  solution that only heats according to the available PV power.
http://www.wagner-solar.com/de/strom/produkte-strom/solar-elektrische-warmwasserbereitung/my-pv

I know somebody using MyPV in combination with a Loxone Smart Home system and it works fine.

Unfortunately, the descriptions are only in German.
« Last Edit: March 28, 2018, 07:38:39 PM by etienne »

sesyf

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Re: Is solar thermal heating out of date ?
« Reply #18 on: March 28, 2018, 08:15:36 PM »
Perhaps that depends on the location... e.g. We have lots of trees - not on our yard so cannot do much about them... and so only solar water heating is so far only practical, as electrical solar panels would be shadowed by some branches most of the day. Also there are two hills that create shadow early morning and late afternoon, and I’d guess that people living in houses on those hills would not be very delighted if I’d try to level the hills.......

Sleepy

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Re: Is solar thermal heating out of date ?
« Reply #19 on: March 29, 2018, 09:19:24 AM »
@sesyf, hot water panels has been more efficient for a long time but not during winter. They are also not scalable as they are restricted to heating water, the same with off-the-shelf expensive DC immersion heaters, often priced from € ~800 (panels excluded) and upwards.

I have most of my panels on the ground, shadowed by my house in the morning and some trees throughout the day (mostly at this time of year when the sun is still low on the horizon). The solution is to use microinverters and avoid large strings, using smaller panels in parallel to avoid loosing power when they are shadowed. A lot of my panels are 36 cell panels, simply because they were cheaper per watt (inc. shipping) some years back. Adding yesterday from the inverters that are logged, I have another two from a different brand that are not logged.
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sidd

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Re: Is solar thermal heating out of date ?
« Reply #20 on: March 29, 2018, 08:05:09 PM »
Winter heat is possible with solar hot water in the Midwest (42N). As I have mentioned b4, I know a farmer has been using solar hotwater panels for about a decade now for his greenhouse. The panels are cheap chinese work, 200 US$ a pop ten years ao. He has about a dozen of them, mounted vertically (no snow cover)  on south wall of a barn. Several thousand gallon water tanks for heat storage and runs hydronic heat in the concrete slab of the greenhouse. Never runs out of heat, and of course he mostly turns it off in summer.

sidd

Rob Dekker

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Re: Is solar thermal heating out of date ?
« Reply #21 on: March 30, 2018, 08:32:40 AM »
If you want to do true solar thermal water heating, you are going to need a separate storage tank.
Something like this :



Think about it : If you have only ONE water heater, then the energy source (gas or electricity) will try to keep that water at a fixed temperature (something like 120 F or so).
So with a single tank, the heat from the solar water heating panels has no where to go. At best it will overheat your tank water, and at worst some temp/pressure valve starts venting.
So even at best, not much heat is gained from having solar water panels on your roof.

With TWO tanks the first one heating the inlet water by solar panels, and the second one your usual water heater, you capture the heat of the sun, and store it efficiently.
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etienne

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Re: Is solar thermal heating out of date ?
« Reply #22 on: March 30, 2018, 11:14:06 AM »
There are also boilers that can handle both circuits.
With the one on the picture below, during the winter, cold water is only pre-heated by the sun, but during the summer, the sun provides all the needed heat.

Cold water always arrives at the bottom of the boiler, and warm water comes out on top.

Rob Dekker

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Re: Is solar thermal heating out of date ?
« Reply #23 on: March 31, 2018, 04:40:35 AM »
Hi etienne.
Yes you can do this with one tank.
But as I just pointed out, with one tank you don't have any heat capacity to store solar heat.
After you use some hot water (take a shower or so) then the heat source (gas or electricity) will kick in, and bring the temp of the water back to a set point (120 F or so).

After that, if the sun starts shining, the solar heat has no way to go, and at best would overheat the water in the tank.

Does that make sense ?
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etienne

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Re: Is solar thermal heating out of date ?
« Reply #24 on: March 31, 2018, 07:17:44 AM »
Hi Bob,

It depends which rules you put on the regulation. We manage houses with heat pumps and solar systems, (in this case, solar is PV + electrical heater, but it doesn't change the concept).

In the winter context, the sanitary water is heated at 50°C (122°F) because I don't trust bacteria, and when the PV power is available, we first heat the water up to 55°C (131°F) with the heat pump, than start the electrical heater up to 70°C (158°F) if more power is available. We want to have some more experience before increasing even more the temperature.

During the summer, we heat the sanitary water only at 47°C (116°F) because we have regular PV overheating, so bacteria is not an issue. When PV power is available, we do the same order change than during the winter, but go back to 47 °C (116°F) when PV power is down.

When you take a shower, if the hot sanitary water is at 70°C, you only need like 1/3 hot water in your mix for your shower, so if you reduce consumed volume and reduce temperature where non renewable heater starts, you really might make it through the day. Temperature sensor is in the middle of the boiler because of the heat pump technology, but we have 300 liters (about 80 US gal.) boilers, so you have 150 theoretical liters before the heat pump starts again.

Here, we have 3 issues :
  • the heat pump has a higher efficiency than the electrical heater, so we want to use it with PV power. The people I know who have solar thermal + gaz heater just turn off the gaz heater during the summer to make sure that it doesn't start.
  • we are not living ourselves in the appartments and have a contract for delivering hot water, so we can't say that people should go downstairs and restart the heater if solar power isn't sufficient
  • some people prefer to use mainly the heat pump because of the better effciency, so they limit the temperature of the electrical heater at 60°C (140 °F) or less. This is not really an issue, because as long as the smart grid doesn't work, you can't tell if the injected power is positive or negative for the network.

Sleepy

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Re: Is solar thermal heating out of date ?
« Reply #25 on: March 31, 2018, 07:34:37 AM »
If you want to do true solar thermal water heating, you are going to need a separate storage tank.
I use three. First two connected to utilize natural cirkulation.
The first two also has electric immersion heaters at the top of the tanks. One is controlled by my hot water solar controller (never used it...) and the other by a home built thermostat.

When there's enough sun, the heat pump in the second tank will drop it's output automagically.
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GrauerMausling

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Re: Is sr thermal heating out of date ?
« Reply #26 on: March 31, 2018, 06:07:20 PM »
Hi etienne.
Yes you can do this with one tank.
But as I just pointed out, with one tank you don't have any heat capacity to store solar heat.
After you use some hot water (take a shower or so) then the heat source (gas or electricity) will kick in, and bring the temp of the water back to a set point (120 F or so).

After that, if the sun starts shining, the solar heat has no way to go, and at best would overheat the water in the tank.

Does that make sense ?

But of course you have plenty of capacity to store the solar heat. I have such a system in my house, a 1000 liter tank, and can assure you that it works.
As you can see in the picture the heater (natural gas in my case) is only heating up the upper part (in my case the upper 1/3 of the tank, so approximately 300 liters. The remaining 700 liters are NOT heated up by the heater and stay cold when there is no solar heat available - there are some inserts in the tank to prevent to much mixing of the warm and cold water. The solar heat on the other hand is fed into the tank at the bottom and will heat up everything. So there are 700 liters of water which are exclusively heated by solar and this would be the storage capacity for the solar heat.
When using the hot water it is taken out at the top and fed back at the bottom. So there is a drawback, as the 'cold' water will have the temperature of the water which has been fed back. But as we are using a heat exchanger for the warm water and underfloor heating this temperature is rather low (less than 30°C / approx. 80° F).
And of course the whole tank can have a temperature quite a bit above of those 120°F in your example (which is rather close to the value in my system when using the gas heater). So there is additional storage capacity.

etienne

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Re: Is solar thermal heating out of date ?
« Reply #27 on: April 01, 2018, 06:50:33 PM »
The use of heat exchanger to heat hot sanitary water is very usefull because you don't have the bacteria issue since water is only heated when needed, so you can produce a lower temperature hot sanitary water.
Heat storage is done in a tank of water that can also be used to heat de house. There is a German company (don't remember the name) that makes a tank with a system that gets the water in different height in the tank depending of the needed temperature (floor heating, sanitary water...).

The boilers in the projects I manage store hot sanitary water, and the water coming back from the circulation in the house come back more or less in the middle of the boiler so that it doesn't heat the bottom of the boiler. Most people don't use the water circulation (pump off) and wait until hot water arrives to the tap.

Rob Dekker

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Re: Is solar thermal heating out of date ?
« Reply #28 on: April 02, 2018, 06:22:18 AM »
GrauerMausling and etienne thanks for sharing your experience. I can understand how with a few tricks, using the temp difference between bottom and top water, and some over-heating and a large enough tank you can make solar thermal work with a single water container, and you don't need a separate solar thermal storage tank.
 
One question : Etienne, you mention a system where you use PV solar and electric water heating. In your opinion what are are the advantages and what the drawbacks of such a system compared to direct solar thermal water heating ?

Thanks Sleepy, nice system you have there, using solar thermal AND heat pump to minimize fuel use. Compliments !
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ghoti

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Re: Is solar thermal heating out of date ?
« Reply #29 on: April 03, 2018, 03:07:16 AM »
Once upon a time solar PV was much more expensive than solar hot water systems. That's no longer true. Most people consume much more energy for everything other than heating water so PV is much more applicable to offsetting energy consumption. PV provides much more flexibility and as shown here by others surplus electricity can also be used to heat water.

Note:
I have both and I'm not getting rid of the solar hot water but it very clearly returns far less when compared to my roof top PV even though the water system hogs the best location on my roof.

etienne

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Re: Is solar thermal heating out of date ?
« Reply #30 on: April 03, 2018, 09:37:42 PM »
One question : Etienne, you mention a system where you use PV solar and electric water heating. In your opinion what are are the advantages and what the drawbacks of such a system compared to direct solar thermal water heating ?

Well, the main advantage of PV are that it is cheaper, it is easier to install, it is easier to maintain, you have more possibilities with electricity than with heat,  and you can sale overproduction.
The main advantage of solar thermal is that it is easy to repair with standard components you can find anywhere, and under some condition, it can work alone without electricity and it probably has a longer life expectancy.
Sidd said once that if you do it yourself, that solar thermal is a very good option. My experience is that electricity work and material is always much cheaper than plumber work and material.

I don't know if there are issues regarding electrosmog with PV, I guess not because this is more an AC problem, furthermore with production mainly during the day, and houses having sleeping rooms under the roof, I guess it's ok. I also have an attic that's only for storage, so it would even reduce that issue.

I don't have any panels on my roof yet and I don't know what I should do. Right now the budget is limited so it's not directly an issue (I'm quite conservative in the way I manage my money). My feelings go for thermal, and my brain for PV.

sidd

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Re: Is solar thermal heating out of date ?
« Reply #31 on: April 03, 2018, 10:19:03 PM »
" My experience is that electricity work and material is always much cheaper than plumber work and material."

These days with PEX tubing and sharkbite fittings, plumbing is a lot ezier than it used to be. Pricewise, it really depends on the current load for the electric, copper cable for large current gets expensive.

There's another aspect to look at too, which is safety. In both cases, you really want to know what you are doing. But screwing up electricity can burn you down or kill you. Plumbing, you mostly make a big mess if you screw up, and may run a lot of money to fix, but it rarely kills you outright.

Of course you could combine two screwups, run the water leaks to the electric, and have the best of both worlds.

sidd

TerryM

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Re: Is solar thermal heating out of date ?
« Reply #32 on: April 03, 2018, 11:08:15 PM »
DIY plumbing is within the ability of most. The oldest working system I've seen was in Death Valley and it was built and installed in the 1930's by a bunch of drunk cowboys. Hot water plus radiant heat at night!


Just looked up "electrosmog". Can't imagine it would be any kind of concern with low voltage DC panels. Site your inverter away from the living area if you really do have a concern.


Terry

sidd

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Re: Is solar thermal heating out of date ?
« Reply #33 on: April 04, 2018, 12:29:14 AM »
The other bit is ease of repair. PV fix means go to the store; usually very few people can fab a panel or inverter at home. But anyone can fix a solar hot water heater thats a black hose in a black box with plexiglass top, fix leak, unclog pipe. Repair is usually possible in a pinch, without a trip to a hardware store. After a disaster there may be no hardware store.

sidd

Rob Dekker

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Re: Is solar thermal heating out of date ?
« Reply #34 on: April 06, 2018, 06:34:12 AM »
I don't have any panels on my roof yet and I don't know what I should do. Right now the budget is limited so it's not directly an issue (I'm quite conservative in the way I manage my money). My feelings go for thermal, and my brain for PV.

If all you want to do is heat water, the choice is easy : Go with solar thermal.
The efficiency of solar thermal is some 85% while the efficiency of PV is an abysmal 17% if you are lucky. That means you need to install 5 PV panels for every single solar thermal panel.

If you want to do more than just heating water, the story gets more complicated.
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Sleepy

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Re: Is solar thermal heating out of date ?
« Reply #35 on: April 06, 2018, 06:43:52 AM »
The other bit is ease of repair. PV fix means go to the store; usually very few people can fab a panel or inverter at home. But anyone can fix a solar hot water heater thats a black hose in a black box with plexiglass top, fix leak, unclog pipe. Repair is usually possible in a pinch, without a trip to a hardware store. After a disaster there may be no hardware store.

sidd
That is an important consideration, often forgotten.
My own damaged pipes to my hot water panels are unfortunately in the (still) frozen ground so I can't do much about them for a while.

Thanks Sleepy, nice system you have there, using solar thermal AND heat pump to minimize fuel use. Compliments !
Thanks Rob, lost that comment. I actually have two heat pumps heating the radiator water and another on my top floor. Also a pellets stove with DIY water piping that adds a bit of heat when it's used, it's more expensive with pellets than heat pumps though. I also have a stove cassette on the bottom floor and two +100 year old tile stoves on the upper floor, so I don't have a heating problem here. :)
« Last Edit: April 06, 2018, 06:55:53 AM by Sleepy »
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Re: Is solar thermal heating out of date ?
« Reply #36 on: April 06, 2018, 12:20:12 PM »
I don't have any panels on my roof yet and I don't know what I should do. Right now the budget is limited so it's not directly an issue (I'm quite conservative in the way I manage my money). My feelings go for thermal, and my brain for PV.

If all you want to do is heat water, the choice is easy : Go with solar thermal.
The efficiency of solar thermal is some 85% while the efficiency of PV is an abysmal 17% if you are lucky. That means you need to install 5 PV panels for every single solar thermal panel.

If you want to do more than just heating water, the story gets more complicated.

There are now hybrid panels, heat and electricity. https://dualsun.fr/en/
But I'm not sure that all the issues are clarified. I wonder what happens when the heat tank is full.

TerryM

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Re: Is solar thermal heating out of date ?
« Reply #37 on: April 06, 2018, 02:04:33 PM »

But I'm not sure that all the issues are clarified. I wonder what happens when the heat tank is full.


In the systems I've seen the heated water in the very well insulated tank is returned to the panel(s) for additional heating or is drawn off as input water into the equally well isolated gas or electric heater that keeps your shower so toasty.
It might also be drawn off to provide radiant heat for the domicile if the thermostat calls for heat.


The only problems I've seen were when DIYers attempted to use PVC or ABS piping. They simply expand to much from thermal expansion to be useful. Sweating copper tubing isn't difficult.
In California and Nevada those using solar to heat a pool or hot tub used a separate panel and with the pool pump for circulating the water as it exits the filter.
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Re: Is solar thermal heating out of date ?
« Reply #38 on: April 06, 2018, 02:36:39 PM »
Re hybrids: STC PV cell temp is rated at 25°C. Cooler=more power, warmer less.
Regular flat hot water panels can reach ~150°C and vacuum tubes ~220°C.

Hybrid stagnates at 80°C. NOCT for hybrid listed at 46.9°C.
Image below from the link etienne provided.
Quote
Power output as a function of the temperature of the water in the panel (by application)
Power values are calculated using the a0, a1 coefficients and the panel surface (1.654m 2 ) in STC conditions(Text = 25°C, G = 1000 W/m 2 ).

Edit; NOCT is normally during 800W/m2, 20℃ ambient temperature, AM 1.5 Spectrum and 1m/s wind speed.
« Last Edit: April 06, 2018, 02:48:45 PM by Sleepy »
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ghoti

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Re: Is solar thermal heating out of date ?
« Reply #39 on: April 06, 2018, 05:47:04 PM »
Energy efficiency of PV versus Solar thermal has very little meaning because the sun is free but the equipment is expensive.

I think when comparing PV versus solar thermal you should focus on dollar cost efficiency. These days cost of purchase, installation, and maintenance usually will put PV as more cost efficient most of the time. This advantage would be enhanced if you already heat water with a heat pump.

TerryM

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Re: Is solar thermal heating out of date ?
« Reply #40 on: April 06, 2018, 06:21:58 PM »
Energy efficiency of PV versus Solar thermal has very little meaning because the sun is free but the equipment is expensive.

I think when comparing PV versus solar thermal you should focus on dollar cost efficiency. These days cost of purchase, installation, and maintenance usually will put PV as more cost efficient most of the time. This advantage would be enhanced if you already heat water with a heat pump.


The efficiency question is one worthy of discussion.


I can build a very efficient heat pump for a residence. However, it will take up a large space both inside and outside the residence. It will use large amounts of potable water. It will be noisy and at times create quite uncomfortable drafts. It will cost some multiples of any reasonable system. But it won't use a lot of electricity.


Is the efficiency of a solar system related to how many sq ft it occupies, how many Watts the pumps draw, if it has pumps? Does it's maintenance, initial cost, or survivability make a difference? Will efficiency be effected if it only operates during certain seasons, certain times of day, or if lots of work is needed to keep it snow free, leaf free, or safe from wild animals?


Inducing a cold breeze with an inverted chimney is very efficient, but it only works in dry conditions, requires water at above roof height, and is difficult to design into an existing structure. - but it requires no electricity.


What are we asking when we ask how efficient a system is?
Terry

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Re: Is solar thermal heating out of date ?
« Reply #41 on: April 06, 2018, 07:44:23 PM »
Quote
I can build a very efficient heat pump for a residence. However, it will take up a large space both inside and outside the residence. It will use large amounts of potable water. It will be noisy and at times create quite uncomfortable drafts. It will cost some multiples of any reasonable system. But it won't use a lot of electricity.
Current heat pumps usually use no net water - they are either air source or closed exchange fluid loops. Even open loop systems just circulate river or lake water and consume no water.

Ground source heat pumps have no above ground outdoor components and are quiet inside.

Heat pumps are another example of systems that currently are very energy efficient but are still very dollar cost inefficient for heating. They can use 1/4 the input energy compared to natural gas systems but the electricity still costs more than the natural gas ( at least in North America).

And then there is one more type of efficiency to consider - carbon use efficiency. That's the one driving me to replace my high efficiency natural gas furnace with a ground source heat pump.

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Re: Is solar thermal heating out of date ?
« Reply #42 on: April 06, 2018, 09:12:33 PM »
...

Heat pumps are another example of systems that currently are very energy efficient but are still very dollar cost inefficient for heating. They can use 1/4 the input energy compared to natural gas systems but the electricity still costs more than the natural gas ( at least in North America).
Burn natural gas in an ICE and then you could have 200% efficient instead of 95% with combustion alone.

And then there is one more type of efficiency to consider - carbon use efficiency. That's the one driving me to replace my high efficiency natural gas furnace with a ground source heat pump.
One idea I've had is a glass box big enough for your house and an air cycle heat pump moving the heat from the glass box back into the house.

Sebastian Jones

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Re: Is solar thermal heating out of date ?
« Reply #43 on: April 06, 2018, 09:51:34 PM »
Burn natural gas in an ICE and then you could have 200% efficient instead of 95% with combustion alone.

One idea I've had is a glass box big enough for your house and an air cycle heat pump moving the heat from the glass box back into the house.

[/quote]

Oh wow!  If everyone did that...perpetual energy creation!

TerryM

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Re: Is solar thermal heating out of date ?
« Reply #44 on: April 06, 2018, 10:27:35 PM »
Quote
I can build a very efficient heat pump for a residence. However, it will take up a large space both inside and outside the residence. It will use large amounts of potable water. It will be noisy and at times create quite uncomfortable drafts. It will cost some multiples of any reasonable system. But it won't use a lot of electricity.

Current heat pumps usually use no net water - they are either air source or closed exchange fluid loops. Even open loop systems just circulate river or lake water and consume no water.
Quote
That's one of the reasons they aren't optimally efficient. California was the first to ban potable water connections for heat pumps, A/C and commercial refrigeration. The others followed but there is a small energy cost to run the recycling pumps through the cooling towers now mandated.
I never claimed my system would be legal. :)
Ground source heat pumps have no above ground outdoor components and are quiet inside.
Quote
I never promised you a ground source heat pump. I promised a super efficient one. As a side note don't listen too closely when your unit slams into and out of defrost. It might make your cat jump.
Heat pumps are another example of systems that currently are very energy efficient but are still very dollar cost inefficient for heating. They can use 1/4 the input energy compared to natural gas systems but the electricity still costs more than the natural gas ( at least in North America).
And they can be made more efficient- if that is your only criteria.
Quote
And then there is one more type of efficiency to consider - carbon use efficiency. That's the one driving me to replace my high efficiency natural gas furnace with a ground source heat pump.
A ground source, or water source heat pump can be a reasonable choice. Much depends on the skill of the installers if it is a large or complex installation, and much depends on the quality of the unit. I've recently run into three Air/Air units in a row with no provisions for lubricating the bearings in the blower/fan motor. Two were Chinese, one was German, all were so inexpensive that it wasn't worth the trouble to replace the poorly located frozen motors.


Planned obsolescence has long been a problem with domestic appliances. Commercial grade costs more initially but they are designed to be repaired, not replaced.


Watch the beautiful fountains in Las Vegas, all of them evaporating water to get rid of those unwanted BTUs. Best looking cooling towers in the West.
Terry


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Re: Is solar thermal heating out of date ?
« Reply #45 on: April 06, 2018, 10:29:32 PM »
How did we go from solar heat to heat pumps, and why?
Terry

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Re: Is solar thermal heating out of date ?
« Reply #46 on: April 06, 2018, 10:52:11 PM »
How did we go from solar heat to heat pumps, and why?
Terry
Milk and cookies.  Some things are more than the sum of their parts.

If you have 25% T.E. and get 4X the heat out of a heat pump that you do out of the mechanical work. You have 75% plus 4 times 25% or 100% for a total of 175% heat in the fuel going into the house.

Now if your house is in a glass box the heat goes from the house into the glass box and back into the house with the heat pump. And you get solar heat as well.

etienne

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Re: Is solar thermal heating out of date ?
« Reply #47 on: April 06, 2018, 11:10:57 PM »
Re hybrids: STC PV cell temp is rated at 25°C. Cooler=more power, warmer less.
Regular flat hot water panels can reach ~150°C and vacuum tubes ~220°C.

Hybrid stagnates at 80°C. NOCT for hybrid listed at 46.9°C.
Image below from the link etienne provided.
Quote
Power output as a function of the temperature of the water in the panel (by application)
Power values are calculated using the a0, a1 coefficients and the panel surface (1.654m 2 ) in STC conditions(Text = 25°C, G = 1000 W/m 2 ).

Edit; NOCT is normally during 800W/m2, 20℃ ambient temperature, AM 1.5 Spectrum and 1m/s wind speed.
The interesting thing is that thermal power goes really down when temperature rises. Doesn't it  look like too much lost power compared to the temperature difference  ? I guess this is made on purpose so that PV panels don't overheat.
The heat pump discussion comes from this graph. These hybrid panels are made to work with a heat pump so that they can work with a higher efficiency.

I don't agree or don't understand Iceismylife's calculation. Here we talk about COP (coefficient of performance).
If you have a COP of 4, it means that for 1 kWh electricity you get 4 kWh heat/cold. COP is always better when heating than when cooling. The reason is quite easy.
You have 3 kWh heat on the cold side, you use 1 kWh of electricity to move them to the hot side, but doing so, the 1 kWh of electricity is also transformed in heat and you will have 4 kWh of heat on the warm side.
When cooling, you get a COP of 3 (3 kWh heat removed per 1 kWh electricity) and when heating you get a COP of 4 (4 kWh of heat added, 3 from the cold side and one from the electrical compressor per 1 kWh of electricity).
« Last Edit: April 06, 2018, 11:22:29 PM by etienne »

Rob Dekker

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Re: Is solar thermal heating out of date ?
« Reply #48 on: April 07, 2018, 10:24:29 AM »
Re hybrids: STC PV cell temp is rated at 25°C. Cooler=more power, warmer less.
Regular flat hot water panels can reach ~150°C and vacuum tubes ~220°C.

Hybrid stagnates at 80°C. NOCT for hybrid listed at 46.9°C.
Image below from the link etienne provided.
Quote
Power output as a function of the temperature of the water in the panel (by application)
Power values are calculated using the a0, a1 coefficients and the panel surface (1.654m 2 ) in STC conditions(Text = 25°C, G = 1000 W/m 2 ).

Edit; NOCT is normally during 800W/m2, 20℃ ambient temperature, AM 1.5 Spectrum and 1m/s wind speed.

Sleepy, where did you find this graph ?
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etienne

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Re: Is solar thermal heating out of date ?
« Reply #49 on: April 07, 2018, 11:32:13 AM »
The graph comes from the data sheet that can be downloaded at the bottom of the description page.

https://dualsun.fr/en/product/2-in-1-solar/
https://dualsun.fr/wp-content/uploads/DualSun-EN-Datasheet.pdf