Flat solar thermal panels or evacuated tube?

[J.P.M.]

Since heat-pump systems are not capable of providing enough heat for 100% of home heating needs, they are best suited as a tertiary heat system, behind your primary home heating system and a secondary home heating system. Heat-pumps work great for supplemental heat during the limited span of when they work, to lessen demand on your primary heating system. But since heat-pump systems are so much more expensive then Solar-Thermal systems are, I am not sure I would recommend them over Solar-Thermal.

When you look at Net-Zero homes in my area, you see a lot of Solar-Thermal systems on application. You don't see so many heat-pumps being used in Net-Zero homes.

How much heat pump systems can provide is a function of climate and system size. Supplying 100% of a space heating load is certainly possible in mild to moderate climates as my neighbors continue to prove every year. To a point and depending on application, heat pump systems become less, but perhaps still economically viable as the length and depth of the heating season grows.

Similarly, as with space heating applications, heat pump H2O heaters are less viable in winter for colder climates, but still possible, and competitive or more so in many/most applications w/ electric resistance heat. Additionally, in mild to moderate climates, there can be some additional benefit from additional reduction on the A/C equipment loading.

Since superinsulation is more/most common in cold climates, and despite recent improvements, Thermodynamics dictates that heat pumps are less efficient as the temp. drops, many well thought out low energy use dwellings use downsized fossil fuel fired equipment. for space heating.

Tertiary systems as you speak of are usually used in more severe climates such as yours and usually for space heating only, or space/DHW combos. Truly well designed (read well insulated/sealed) low energy dwellings usually do quite well with simple fossil fuel fired space heating systems. I've seen a built design in a cold climate that is so well insulated/sealed that a 40,000 BTU domestic water heater was used to supply heat to a rad. floor heating system.

In cold climate and cloudy winter combos, solar thermal DHW systems can get expensive to the point of getting less robust systems, operating them less than 12 months/yr. and buttoning them up for the winter. Buffalo and environs for example, are such a climate.

I haven't done a cost analysis at this time, but I suspect that a PV/heat pump system for domestic H2O heating can be life cycle cost competitive with a closed loop solar thermal flat plate collector system in moderate to cold climates.

[organic farmer]

Since heat-pump systems are not capable of providing enough heat for 100% of home heating needs, they are best suited as a tertiary heat system, behind your primary home heating system and a secondary home heating system. Heat-pumps work great for supplemental heat during the limited span of when they work, to lessen demand on your primary heating system. But since heat-pump systems are so much more expensive then Solar-Thermal systems are, I am not sure I would recommend them over Solar-Thermal.

When you look at Net-Zero homes in my area, you see a lot of Solar-Thermal systems on application. You don't see so many heat-pumps being used in Net-Zero homes.

[J.P.M.]

First off, great forum..been reading the past hour and now I have a question. We want to put solar panels on our roof to heat our water. Is it better to go with the flat panels or the evacuated tubes? We want the most of it because it is so expensive to get it set up! Thanks in advance.

Before you do solar for any DWH applications, your best off to first reduce your hot water load load as much as possible through water use reduction by shorter showers instead of baths, low flow shower heads, flow restrictor faucets and other measures.

Also, before solar thermal, know that in many but not all applications and locations, it is becoming more cost effective to combine PV with a heat pump H2O heater rather than solar thermal by itself. Probably less maintenance for the solar portion of such a system as well.

If solar thermal is still a choice, evac. tube is usually thermal overkill in many applications. That is, it can heat water way hotter than needed. such high temp. potential comes at a cost in both $$'s and maint. that can be avoided y using less sophisticated and simpler solar flat plate with glycol/H2O flowing in the collector loop transferring heat to the DHW via a heat exchanger. If in a completely frost free, and I mean never freeze climate, a direct system w/ the domestic H2O flowing directly through the collectors back to the main storage tank may be possible.

Either way, PV + a heat pump H2O heater may be the best way over a solar thermal collector system.

[saniconenergy]

I do not see why you say this, since the working fluid does not pass through the tubes, just the manifold connected thermally to the top of each tube.

"@inetdog
Correct, to be specific
If it's Indirect Heating in ETC then the system would continue to run, but if it's direct heating then it has to be shut down!"

[inetdog]

3. In case of ETC, even if one tube gets broken then you have to shut down the entire system unlike FPC which due to its strength doesnt encounters so much of breakage issues.

I do not see why you say this, since the working fluid does not pass through the tubes, just the manifold connected thermally to the top of each tube.

[saniconenergy]

The application for ETC and PFC is now perceived to be different. ETC is efficient and effective wherein you have to heat up the water more than 70Deg C / 160F, in other words where the applicatioin relates to generation of steam or its near tempearature then ETC for sure would be the bet on any given day. However when it concerns to the heating up of the water to the safe limit of 60 Deg C and around for domestic consumption then Flate Plate is much more efficient. Plus there are sevaral othe advantages of FPC: 1. Much more strong and sturdy, much less issue of breakage and ultimate shutdown of the system. This holds true particularly for the areas which gets heavy hailstorm. 2. Snow would get melted easily if it gets accumalated on FPC rather than ETC. 3. In case of ETC, even if one tube gets broken then you have to shut down the entire system unlike FPC which due to its strength doesnt encounters so much of breakage issues.

[manoharan]

based on your requirements, flat plate collectors are mostly recommended for residential and commercial use. i both cold and hot regions the flat plate collectors can be the right choice to achieve the adequate domestic water temperature (say 60 oC). on the other hand, the vacuum tubes, besides being more expensive, can deliver temperatures as high as 120 oC for industrial use and manufacturing processes.

It doen't make sense to use a vacuum tube system for residential and relatively smaller scale installations if you have the flat plate collectors available.

Also, modern solar water heating systems with flat plate collectors are capable to avoid Frosting and Over Heating problems of the collectors field on your rooftop by utilizing certain technologies such as DRAINBACK technology.

eventually, as long as we are depending on the sun to heat up our water or spaces then we are definitely on the right track. makes both options better than other fossil fuel based solutions.

Nice

[russ]

Hi Omar - Welcome to Solar Panel Talk!

Russ

[zeidan.omar]

Both are Better!

based on your requirements, flat plate collectors are mostly recommended for residential and commercial use. i both cold and hot regions the flat plate collectors can be the right choice to achieve the adequate domestic water temperature (say 60 oC). on the other hand, the vacuum tubes, besides being more expensive, can deliver temperatures as high as 120 oC for industrial use and manufacturing processes.

It doen't make sense to use a vacuum tube system for residential and relatively smaller scale installations if you have the flat plate collectors available.

Also, modern solar water heating systems with flat plate collectors are capable to avoid Frosting and Over Heating problems of the collectors field on your rooftop by utilizing certain technologies such as DRAINBACK technology.

eventually, as long as we are depending on the sun to heat up our water or spaces then we are definitely on the right track. makes both options better than other fossil fuel based solutions.

[AIT Solar]

I love solar thermal and solar hot water! I think its a huge part of what will be the cure for the global "Energy Crisis".

please check out our website at

Mod note - If you wish to advertise contact user name Jason

[Twexcom]

Evacuated tubes are better, but if you live in a snowy area, then flat panel maybe better. The evacuated tubes do not melt off the snow as good as the flat panel does.

Thank you for pointing this out.

I have no experience with flat-plate thermal collectors. However, in the tropical climate I live, I use an evacuated tube solar water heater, and it paid for itself in about a year. It worked reliably year-round, despite the fact that the backup electric heater was not plugged in. That backup heater was never used.

Mod note = forget the links

[Kobayashi]

flat plate

First off, great forum..been reading the past hour and now I have a question. We want to put solar panels on our roof to heat our water. Is it better to go with the flat panels or the evacuated tubes? We want the most of it because it is so expensive to get it set up! Thanks in advance.

Flat plates will perform better in most climate zones and they are cheaper.

[cssolar]

vacuum tube swh assembly

[ATTACH=CONFIG]2592[/ATTACH]Thank you for this. Can I ask you for pointers in assembling when i try to put this toghether? This will be mid April. I will probably need someone to keep the head cool haha. I will try to keep the tubes inside the house untill filling up time. I adjusted an existing drawing. Is this correct? The small cannister then should be the heat exchanger?

Hi Rainworm,

Assembly is quite easy,

1.First build the frame , it is normally in kit form and can be assembled at the point of use

2. drop the solar tank onto the frame , dont do the bolts up yet

3. if assembling in the sun, take the vacuum tubes out of the box one at a time ( close the box each time )
prime the tubes with water ( fill them with a hose ) slide the dust cap over the open end of the tube, lubricate the end of the tube and the silicone rings in the tank with some cooking oil,

4. push the tube into the tank with a slight twisting action, seat the bottom of the tube into the frame bottom rail ( some units have plastic cups to support the tube ends )

5. fit all the tubes in the same way

6. if your unit is a pre heat type ( with copper coil heat exchanger ) feed cold water to the coil and the assistant tank ( small tank that sits on top of the main tank with float valve to maintain water level )
remember to fit a safety valve on the cold feed to the coil

7 return the hot out of the coil to feed your existing electrical cylinder, or feed in direct to your hot water system. ( optional by pass is good )

8 if your swh has a back up heater , normally they do not have thermostat in built so it is best to fit a temp sensor to the main tank, with an electronic controller to control the heater.

9 also as the main tank is not a pressure vessel it is very important to make an open ended vent ( normally up to just below the level of the assistant tank over flow.

These are for guidance only, for pre heat model ( with a non pressure tank )

Good luck Tony

[rainworm]

thanks

water solar system 2.gifThank you for this. Can I ask you for pointers in assembling when i try to put this toghether? This will be mid April. I will probably need someone to keep the head cool haha. I will try to keep the tubes inside the house untill filling up time. I adjusted an existing drawing. Is this correct? The small cannister then should be the heat exchanger?

[cssolar]

vacuum tubes for solar water heaters

Ok now I am truly confused. I must apologise I am truly new to this tube invention.
I have a watertank. It runs on electricity from the grid. It is very expensive to use. I want to add to this a solar system. My watertank has not got any extra inlets or outlets. The solar goes maximum 1.5 metres above the tank. Here it can only be slight winter. Almost or just freezing. But very windy. Enough about the weather and chit chat. I read from a manufacturer the following.
Water is pure and drinkable
Heat insulation of water tanks adapts polyurethane foam
Silicone rings to connect and seal them
Tubes and supports are adjustable
Power bearing average and can assure vacuum tubes to use for long time
Whole glass vacuum tubes adapts super hard borax and silica glass
Absorption rate: 93%
Thermal radiation rate: 6% (100)
Resists MM hail
Lifespan: 15 years
Temperature when exposed to sun without water: 250°C
2.5 hours to boiling if using single tube
Used in electrical appliances to aid heating and switch off power supply before bathing
So I think there is tubes with own water system and then there is a collector with spiral that heats up from the tubes. The collector has water flowing through it and the spiral gives the heat to the water. Now this suplier states that water can be drinkable. ???
MayI ask advise to explain in easy words what it is I should go and look for on the market?
Thank you in advance.

Hi Rain worm,

I have quite a lot of experience working with the type of Chinese swh you are describing,

I am in Spain and that type of system works great, climate is important, mainly clear sky with sunshine is best , out side temperature is not to important as long as it dose not go below freezing for long periods

The unit you describe is a direct non pressure unit with gravity feed, I would recommend you use a pre heat unit, it uses the same non pressure tank but has a mains pressure copper coil heat exchanger inside for high pressure water.

These are self contained compact ( plug and play ) systems very simple, low cost and work very well.

you can feed your existing electrical cylinder with pre heated water via the swhs heat exchanger, also recommend fitting a by pass so you can use the solar heated water direct if you choose.

The vacuum tubes can reach 250 degrees Celsius DRY so be very careful not fill them with cold water when hot as the thermal shock may cause them to shatter.

It is true that a single vacuum tube ( in Spain with sun ) will boil in under 3 hours

Best Regards Tony