Can Adding a Lens to a Small Solar Dish Increase Its Heat Output?

[BurnIt0017]

Increase reflector output?

Greetings, I have been workings on a Solar Tracker. I have some small TV sat dishes that I am planning to cover with Mylar to create the reflector. After viewing some videos on YouTube I noticed that a larger dish produces more heat. Would adding a lens increase output of a smaller dish?

 

[sophiecentaur]

Greetings, I have been workings on a Solar Tracker. I have some small TV sat dishes that I am planning to cover with Mylar to create the reflector. After viewing some videos on YouTube I noticed that a larger dish produces more heat. Would adding a lens increase output of a smaller dish?

Alas, no. Your dish already collects any energy that's available. You can focus it on a large or small target (depending on what you want) but all you will achieve is a different surface temperature, depending on how small your 'spot' is. There is something to be said for using a large spot because a small spot at high temperature is more likely to re-radiate some of the energy you have received.

I once used a 0.5m diameter microwave dish and coated it with cooking foil. It would boil small quantities of water, in a black metal can, very quickly. The effective power would have been a couple of hundred Watts, I guess, in full sunlight. The 'optical' quality wasn't too good but, as the target was several cm across, it didn't matter.

The optics of combining a number of small dishes would be hard because their focus is too close to each dish to get all the spots to converge. The overall received power would be the sum of all the dish powers. Do you actually need it all focused on one spot?

 

[BurnIt0017]

Greetings, my goal is to make one simple working unit using one small dish and if that works then make more. So if use this configuration all I am doing is changing the location of the focal point. I have seen thermal storage unit that just use liquid like water, could you store more heat if a combination of liquid and stones where used in the thermal mass? Thanks for the heads up and best regards.

 

[sophiecentaur]

Water is an ideal thermal storage medium as it has the highest specific heat capacity of all common materials and your maximum temperature will not need to be very high (which is where rocks can be an advantage, in electric night storage heaters for instance).

Your idea of focusing the sunlight is a good one, particularly where the Sun is 'feeble'. Some of the up-market panels use cylinders with clear fronts and reflective backs, focussing the sunlight onto narrow tubes along the axis. They give hot water (albeit small quantities) in almost any daylight conditions because of this focussing advantage and resulting high temperature.
They do not use fancy tracking - they just use a larger area than strictly necessary to cope with the pointing losses.
I fancied using them until I saw the PRICES!