solar question

[nvmike]

I would like to heat water with solar, assuming the same area of sun for a flat panel with tubing  and a parabolic reflector,  one should get the same amount of energy, is my thinking correct?  I think you could get higher temp at focus point of parabolic reflector (old tv dish lined with mirrors) but less volume of water heated, therefore the same enegy transfered to the water.  Assuming the cost is the same for materials, which would be the better way to go.  I figured both would need a tracking device for best results.  My goal is to preheat water before entering existing water heater and if any extra, do pump through a radiator for space heat.

Nothing new here, just looking for suggestions.    

[farmerfrank]

Personally I would go flat plate. A flat plate collector will provide you with more temperature than you need as a good collector will reach the boiling point. Concentrators are good with other high temperature transfer mediums. Remember that the higher the temperature above ambient, the higher the heat loss due to radiation. It would be fun to make steam with a concentator I will admit.

[pyrocasto]

If you're just wanting to preheat the water then I would go with a flat panel, since it will simplify things like no tracker needed. Only time you usually want to use a collector for is to keep it warm on cloudy days, or if you need higher temperatures for like a hot tub.

[nvmike]

Thanks for your input, i will try the flat collector,  have one stated but need time to finish, and would like to add glass over the top this summer.

[tecker]

 the flat panel will alow for mabe two 50 gal heatings in realworld aplcations in full sun . You need several to have panels to give good prformance . With a tracking parabla the heating is very quick and you can percolate through a tracking collector to a holding tank.I am building a unit like this with a drain down for cold weather.

[mcgivor]

I made a flat pannel solar hotwater pre-heater, it worked great.  It would be better if your hot water heater was above the solar collector for thermal flow.  Mine is mounted on the roof, above the water heater with a small storage tank (5 gal).  The hardest thing for the wife and kids was time the "batches" of hot water.  It took about 2 hrs to recover a batch.

[BT Humble]

A flat panel is simpler and cheaper to construct, and doesn't need a tracker.  They won't produce temperatures as high as a parabolic reflector, but I'm personally not all that fond of bathing in boiling water! ;-)

It's worth checking at your local scrap-metal dealer for collector panels.  The panels and tank are typically disposed of as a unit when the tank rusts and needs replacement, and I've bought factory-built 7'x4' collectors for $25 each.

In the type of system I'm talking about, the tank is mounted on the roof directly above the panels, like this:

(They're the most common type here in Australia, where 99% of the country doesn't get covered in snow in the winter).

BTH

[Ungrounded Lightning Rod]

Sounds like you need a minor plumbing change - adding a circulation pump and a check valve and maybe rerouting some pipes - to bring the hot water down from the roof and store it in your big tank.

You can use a low-flow pump or cycle a larger one intermittently (a few minutes every half hour or so - long enough to turn over the water in the collector and its little tank), and cut it off during nighttime or when the bottom of the main tank is at the desired temperature.

[Ungrounded Lightning Rod]

A tracking collector and a flat panel of the same cross-section will collect the same amount of usable HEAT.  The sole advantage of a tracking collector is that it collects the heat at a higher temperature, thus yeilding a larger amount of usable ENERGY.

If you are using this collector to heat water or air for your house, a flat panel should do just fine.  No hassle and expense for tracking, and you can make it big very cheaply.

If you want process steam you can go with a one-dimensional focus - a parabolic trough oriented to the seasonal angle of the sun.  (Doing this for hot water might cause an explosion or scald someone trying to take a shower or wash their hands.)

If you want to melt metal or run a heat engine you might want a two-dimensional focus - a dish that tracks the rise/set as well as seasonal angle of the sun.  (Heat engines like big temperature differences - the higher the temperature difference the more energy they can extract from a given amount of heat.)  Doing this for forced-air heat could set your house on fire, especially if the fan runs to slowly.  B-)

[healerenergy]

I am a big fan of the parapolic trough becaush of what you can do with it. With a closed loop system you can store lots of heat underground after you use it to run a steam turbine to generate power. Then you can preheat your hot water before you heat your house and a hole lot more. I love closed loop systems probably because I was on submarines for a number of years and they use a lot of closed loop systems.