Flat solar thermal panels or evacuated tube?

[MikeSolar]

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.

If you are at all familiar with flat hot water collectors, there is no difference in how the systems are piped and the specs you posted above are a very small part of the story so I would not focus on them.

First, a solar system to add to your electric tank would include another tank that is used to store the solar hot water (SDHW), no matter what type of panel you use. The cold water from the street goes into the tank,, gets heated by the solar, and then goes to your electric tank. This is the simplest way to explain that part. The rest is a bit more complicated.

Forget what the manufacturer says above. Why would any one want to drink the hot water from the solar is beyond me, boil water if you want it hot, solar is for showers and possibly heating etc. ANY solar panel will give you warmer temperatures when the sun is out, you will not see 250C in your tank (nor would you want to). A properly sized solar system will give you around 50-60% of your hot water annually, most of it in the spring/summer/fall and it doesn't matter much if it is a vacuum tube or a flat panel. A flat panel system will have a longer lifespan than a vacuum tube panel (most of the time) and needs less maintenance (typically).

As said above, a glycol (antifreeze) system pumps the antifreeze from the panels to a heat exchanger that transfers the heat to your solar storage tank then back to the panels to get hot again. It needs a small pump to do this, perhaps as little as 10w or as much as 90w which only runs when the panels are warmer than the storage tank.

a drainback system takes water which is stored in a smaller tank above your solar storage tank and pumps it (along with the air in the piping) up to the panels where they grab the heat in the same way as the glycol system, then it transfers the heat to the tank in the same way as the glycol system. The difference is that the pumped water drains back to the little tank after the heating cycle is finished. The pump needed is usually a minimum of 140w or more which must be accounted for in the cost to run the system.

The system you are looking at has a tank on the roof which heats the shower water directly. It is viable only if you live in a temperate climate that seldom sees freezing temps. In Canada and the Northern US, most of these system need an electric trace cable to keep the lines from freezing when the cold comes.

The Canadian govt tested this type of system verses a typical flat panel system. Typical performance of the above system is 600kwh of heat annually vs 2200- 2400kwh from a 2 flat panel solar system. You decide which one is more worth it.

[rainworm]

confused

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.

[Naptown]

Ok tubes seems better for around freezing point in winter and hot in summer.
But there are pressurised and non pressurised systems.
??? Why????
What is the reason for pressurise?

What you are referring to is an open or closed loop. An open loop would be as in a drain back system. This will provide freeze protection as the water used to heat is drained out of the collectors when the system shuts down. Generally it is an open tank and a pump that pumps water from the drain back tank to the collectors back to a heat exchanger and then back to the tank. If the collectors are very high above the tank it will take a very large pump to pump the water up to the collectors.

the alternative is a pressurized close loop where anti freeze is used for freeze collection. This simplifies things a bit and allows for a much smaller pump. When a pressurized system no matter how high the collectors are above the tank or pump it is the same as if they are at the same level as the tank. there is no additional effort to pump the fluid to a higher level.

[rainworm]

pressurised vx non pressurised

Ok tubes seems better for around freezing point in winter and hot in summer.
But there are pressurised and non pressurised systems.
??? Why????
What is the reason for pressurise?

[MikeSolar]

Mike, how does it help to know the consumption data?
Jonathan

The system may be capable of providing X amount of heat but its efficiency is best when the panels run cooler. There is an international standard for measuring the effectiveness of a system and it includes X volume draw over a period of time in the morning plus X in the evening and the testing also notes losses between the panels and the tank, HX and pumping power (I am looking for the actual numbers but so far I have found my test requirements for panels only). But.... If you look at some test data like this one:

SHSF154ST5en.pdf

You can see that the performance changes not only for each city but the daily consumption. As you use more water, the efficiency and ROI for the system gets better. The efficiency of the flat panel will drop off when we try to heat to a high temp such as 100C where the vacuum tube efficiency will still be reasonable at that temp (for the same flow rate). As we usually heat to between 30-60C most of the time, the added efficiency of the tube is not needed.

[russ]

Hi Russ, I have been busy drinking beer so I can use the empty tins for the collector.

Its been hard work, but I keep telling my self it all for a worth while cause.

Reminds me better have another beer. Tony

Salude Tony - Be sure to enjoy while working hard!

[cssolar]

100% agreed Tony! Same for solar air heating.

Hi Russ,

Ive been busy building my solar air heater.

Or maybe I should say I have been busy drinking beer so I can use the empty tins for the collector.

Its been hard work, but I keep telling my self it all for a worth while cause.

Reminds me better have another beer.

Cheers

Tony

[russ]

Mike, how does it help to know the consumption data?
Jonathan

It shows the total amount of heat collected

[jtellerelsberg]

This is good data but what needs to be added to it is consumption data. It would be nice to know how much and at what time the water is drawn out.

Oops...I spoke too soon. The graph exists for consumption although I cannot tell if it is for both systems or just one.

Mike, how does it help to know the consumption data?
Jonathan

[MikeSolar]

Bob Nape, a solar installer in Ithaca NY, decided that the theoretical arguments were't satisfying and put up side-by-side systems. You can see the ongoing data comparisons and historical behavior at http://goo.gl/EMMM9. Here's a link to the previous 12 months of data of thermal output from the systems: http://goo.gl/2ZfX1. It shows the flat panel system producing slightly more BTUs in every month. The difference is rather small.

Will you get the same results? Maybe, maybe not -- depends on the particulars of your system and the particulars of your climate. Given that I'm in a similar climate (in mid-Vermont), this is convincing evidence that I should go with a flat panel system and plow my savings into other energy saving or generating efforts.

This is good data but what needs to be added to it is consumption data. It would be nice to know how much and at what time the water is drawn out.

Oops...I spoke too soon. The graph exists for consumption although I cannot tell if it is for both systems or just one.

[jtellerelsberg]

The evidence in Ithaca, NY

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.

Bob Nape, a solar installer in Ithaca NY, decided that the theoretical arguments were't satisfying and put up side-by-side systems. You can see the ongoing data comparisons and historical behavior at http://goo.gl/EMMM9. Here's a link to the previous 12 months of data of thermal output from the systems: http://goo.gl/2ZfX1. It shows the flat panel system producing slightly more BTUs in every month. The difference is rather small.

Will you get the same results? Maybe, maybe not -- depends on the particulars of your system and the particulars of your climate. Given that I'm in a similar climate (in mid-Vermont), this is convincing evidence that I should go with a flat panel system and plow my savings into other energy saving or generating efforts.

[russ]

100% agreed Tony! Same for solar air heating.

[cssolar]

I think flat plate and vacuum tube collectors and solar water heaters are both good.

And both have good and bad points.

But I think the most important thing is that, Solar water heating works and is worth while. ( here in Spain anyway )

I do feel it is a shame that in most country's its so little used, the other day I was up at Alicante castle looking down over the roof tops, I only saw 2 solar collectors , on the thousands of roofs I could see.
The sun was strong and I couldn't help thinking , what a shame so much free energy not being used.

Cheers Tony

[jtellerelsberg]

Tubes aren't that new on the scene

Flat solar panels are less expensive to install. The tube type solar heat panels have no history. Flat solar panels have been around over 20 years.

It's true that evacuated tubes are a more recent technology with less of a track record, but they aren't that new. They've been around since the 1970s, so plenty of time for people to have figured out their pros and cons. Flat panels have been around since early in the 1900s, so have lots more history, but anyhow...

[Peter69_56]

Solar Town

Funny part is that the site is sponsored by Solar Town. Their only request is that they be a suggested supplier in the event we name any names.

Quite fair on Solar Town's part I think.

Russ

I agree, if they sponser the whole forum, then they are entitled to get mentioned as a supplier if people are going to discuss where to get stock. If we couldnt agree to do that we would probably not be talking now.