Flat solar thermal panels or evacuated tube?

[sundug]

Flat solar hot water panels have been around for close to 100 years, and evacuated tubes for more than 30 years. The flat panels deliver more BTU's per $ than evacuated tubes in clear, moderate conditions, but evacuated tubes perform better in cloudy and/or cold conditions. Doug

[sundug]

Evacuated tubes have such good insulation (vacuum) that they [I]do not[I]get hot to the touch. See my videos-

Evacuated tube-

http://www.youtube.com/watch?v=Z8ctn41ColA

Evacuated tube array-

http://www.youtube.com/watch?v=b-5dK5JNu0k

Making a heat pipe

http://www.youtube.com/watch?v=LU4eynU6R-8

Installing the heat pipe in the evacuated tube-

http://www.youtube.com/watch?v=zw6s9EObIPE

Completed heat pipe demo-

http://www.youtube.com/watch?v=xsx7BX0l5uQ

Solar water heating-

http://www.youtube.com/watch?v=Xdif6xVpQtQ

[netttech]

Solar Air heating...

I experimented with Solar Air heating for about 4 years. The panel was successful in generating very hot air. The panel would heat-up by 9am, fan turn on (@ 100 degrees) & progressively get hotter. It was not uncommon to heat-up beyond the thermometer's limit of 160 degrees, with the fan blowing
(300cfm) constantly.

I had remote wireless thermometers installed on the input (cold air) & output vents. It would effectively heat-up the air from 68 to 150 degrees on sunny days.

My problem was my house has 10" front deck, with the panel that far away from the nearest window. I would lose 20-30 degrees between the panel & the room. Still it would heat the house warm enough to keep the furnace from running.

My attempt at creating solar hot water for radiant heat failed though. It wouldn't heat up & sustain hot enough water for radiant heat.
Jeff

[mountain]

efficiency = 100% * (EH - Losses) / EH
where EH : Energy Harvested

so if you minimize losses, you obtain maximum efficiency.

It is important to understand all losses including
> Pump energy (fluid) or Fan energy (air)
> radiation losses
> distribution losses

People often confuse efficacy with efficiency. Efficacy is defined as the
capacity or power to produce a desired effect. So the proper semantics would
be which type of panel is the most effective at harvesting energy, for your unique situation.

Measure efficacy in $EH/$SC
So the best system is the one which achieves the highest $value in Energy Harvested per $System-Cost

Some folks don't care about $$$ cost, because perhaps they are either
rich or else naively idealistic : "We must generate energy via alternate sources regardless of the financial cost."
However, $$$ is how we keep score in a manner that cannot be argued with.

The best system is simply the one that is the most cost-effective. The term that is most often used is : "What is the payback period?"
If it (alternate energy) becomes a no-brainer “do-it” for the poor, then there may be hope for our planet.

We owe it to the planet to develop simple technologies for harvesting energy
from the sun/wind/uHydro, that are affordable by even the poor in our society. For this reason, it is a disservice to the planet to pay any credence to systems that are not cost effective. Energy must cease to be a commodity.

Solar Air Heating systems are more effective in sunny cold climates, whereas in a sunny warm climate, hot-water systems are more effective. In a non-sunny climate, then perhaps wind/uHydro is most effective. If you live in outer-space, or Germany, then PV. Each unique installation requires a separate comparative cost analysis.

M

https://www.mountainelectric.ca/hotbox

[Mike90250]

Evacuated tube panels will gather some heat on a cloudy day, flat won't

[armstrr]

actually i was just reading an article that states flat panels are more efficient IF the temperature of the fluid at the panel inlet is low compared to ambient. the higher the inlet temperature, the less efficient the heat transfer is for the flat panel. the evacuated tube looses its efficiency more slowly. eventually, the to curves cross. but from my reading, it appears they end up being quite similar in performance at the temperatures people use them. the moral of the story i would guess is: get as much heat out of the system before returning it to the panels.

[Off Grid Solar]

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.

[JoeyC]

I don't think there is really a right answer because there are different factors.

1. tubes are more efficient, but cost a lot more. The lower efficiency of panels isn't necessarily a problem, since the sun is effectively unlimited, so you can put up more panels (unless you have limited space). So you need to know the specific costs of each compared to the amount of water they heat; this varies with suppliers, but in many cases, tubes will be cheaper.

2. how robust they are. Tubes can be a little fragile, where as you can usually jump on a panel without damaging it. So are you likely to get anyone throwing rocks?

3. how accessible they are; tubes can get extremely hot. You don't want children or animals touching them.

[n3qik]

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.

[RchnFms]

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.