Energy and sand batteries (thermal energy storage)

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SUMMARY

This discussion focuses on the feasibility of using sand as a thermal energy storage medium, specifically in the context of building a sand battery. The specific heat capacity of sand is noted as 830 J/kg·K, and calculations indicate that heating 1000 kg of sand to 400°C requires 332,000 kJ of energy, which translates to approximately 83,000 seconds (or about a day) when using a 4 kW solar array. Additionally, the conversation shifts to the heat transfer dynamics through a copper pipe, with a focus on flow rate and pipe diameter, specifically 28 mm, for effective temperature modulation.

PREREQUISITES
  • Understanding of thermal energy storage concepts
  • Knowledge of specific heat capacity calculations
  • Familiarity with solar energy systems and their output
  • Basic principles of heat transfer in fluids
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  • Research thermal energy storage systems using sand
  • Learn about heat transfer calculations for fluids in pipes
  • Explore the design and efficiency of solar thermal systems
  • Investigate the impact of pipe diameter on heat transfer rates
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Engineers, renewable energy enthusiasts, and anyone interested in thermal energy storage solutions and the practical applications of solar energy systems.

Matt27RS
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TL;DR
How much energy is required to heat a sand battery
Hi,
I'm new here, so apologies if this is covered somewhere else.

I'm just playing with the notion of building a sand battery.

Sand has a spec heat cap. of 830j/kg degrees K.

If I want to heat 1000kg of sand up to 400 deg c, by my rough calculations that will require 332 000 Kj of energy, or 332,000 KWatts of electrical energy.

If I haveva solar array producing 4Kw, this will take around 83 000 hours!

Is this correct? Or amI completely wrong?

Many thx
 
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Matt27RS said:
If I want to heat 1000kg of sand up to 400 deg c, by my rough calculations that will require 332 000 Kj of energy,

If I haveva solar array producing 4Kw, this will take around 83 000 hours!

Is this correct? Or amI completely wrong?
You're not completely wrong, but it's 83,000 seconds (not hours). Which is about a day (neglecting heat lost in the process.)
 
PeroK said:
You're not completely wrong, but it's 83,000 seconds (not hours). Which is about a day (neglecting heat lost in the process.)
Doh! Thanks very much. I knew it was a bit wrong somewhere!

My next question....does anyone know a quick and dirty calc for understanding the rate of heat transfer for a copper pipe running through a heated source? In this instance it would be the sand.

I'm sure there must be a graph which plots flow rate, temp,pipe length etc for a given pipe size? I'm looking to hear water flowing through the heated sand battery. Flow rate will be the control method for modulating the temperature transfer from the sand to the water in the pipe. The other variable will be the pipe diameter. Ideally I would like to use pipe sizes of 28mm.

The length of the pipe run within the sand is also variable, but I would start with a length of 8m.

Any thoughts....

Thank you
 

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