Thermal energy storage and usee

[helpP3T3R101]

i want to try use heat energy to power a small device, but i also want to be able to store some energy for use at a later stage... how could i go about doing this? also it needs to be as small as possible, and also very cheap
id guess that it could be relatively simple to do considering i just need something that absorvs the thermal energy (provided) and can store it; as well as use it

any suggestions or advice?

 

[russ_watters]

Welcome to PF.

We need waaay more information to be able to help you. How much energy? What is the source? How hot do you want to store it? How do you want to use it? Is the "power" mechanical or electrical?

 

[helpP3T3R101]

the purpose of the device is that when prompted, it produces a set of about 20 beeps of relatively high volume.. the entire device is intended to be no bigger then a $1 coin
thus the heat energy is required to be stored; so that it can be utilised upon request for the beeps - this shouldn't require much energy, yet how can it be captured, stored and then converted into electrical energy for the beeps

 

[Studiot]

Why store heat and not pressure or elastic energy in a spring, if you want to store mechanical energy rather than use a battery? You could, I suppose, convert heat to one of these.

 

[helpP3T3R101]

well the initial energy source is going to be thermal energy (or potentially solar energy); the final use of it is to produce a repeating tone.. how it is stored is whatever is most efficient

 

[Studiot]

Stored heat leaks away more readily than stored mechanical or electrical energy, so accept the conversion losses and convert it.

 

[russ_watters]

Does the "initial energy source" really have to be thermal? Can you have an external device to convert it to electrical energy to charge a battery in your beeper? Thermal energy itself is not very easy or efficient to store when space is a constraint or you need long term storage. You really don't want to try to put a heat engine and a generator on a device the size of a wristwatch...but what you are trying to do is a piece of cake if you keep it all electric.

 

[BrIDo]

This is not an easy to task to do properly, given it's a fairly new implementation in the energy sector. During the day heat from the sun warms oil in glass tubes which later turns turbines. Excess heat is stored using molten salt during the day, and utilized at night when there is no sun.

 

[russ_watters]

For comparison, according to the wiki, a 11.6mm dia x 5.4mm silver watch battery has a capacity of 200 mAh at .9 V. That's .18 w-h or 648 J. Water's heat of fusion is 333 kJ/kG so that's enough energy to melt (is released by melting) 1.5g or 1.9 ml of water...or a block 10mm x 10 mm x 19 mm, or about 4x the size of the watch battery (not including a container and insulation). And, of course, if you wanted to use a heat engine to convert to electricity, you'd need at least 3x as much.