Energy and sand batteries (thermal energy storage)

In summary: I'm not familiar with the specifics of your project, but a rough calculation might be to use the following equation: Q=V*D*T, where Q is the heat transferred, V is the flow rate, D is the pipe diameter, and T is the temperature. If you want to transfer a fixed amount of heat over a fixed period of time, the best way to do this is to use a rate controller.
  • #1
Matt27RS
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TL;DR Summary
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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  • #2
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.)
 
  • #3
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
 

FAQ: Energy and sand batteries (thermal energy storage)

What is a sand battery and how does it work?

A sand battery is a type of thermal energy storage system that uses sand as the medium to store and release thermal energy. It works by heating sand to high temperatures using excess renewable energy (like solar or wind). The heated sand can then store this thermal energy for extended periods. When energy is needed, the stored heat is extracted and converted back into electricity or used directly for heating purposes.

What are the advantages of using sand batteries for energy storage?

Sand batteries offer several advantages, including high energy storage capacity, low cost, and long lifespan. They are also environmentally friendly, as sand is abundant and non-toxic. Additionally, sand batteries can help balance the grid by storing excess renewable energy and releasing it when demand is high, thereby improving the reliability and efficiency of renewable energy sources.

How efficient are sand batteries in storing and releasing energy?

The efficiency of sand batteries depends on various factors, including the quality of the sand, the temperature at which the sand is heated, and the design of the storage system. Generally, sand batteries have a thermal efficiency of around 70-90%, meaning that 70-90% of the stored thermal energy can be effectively recovered and used. This makes them a viable option for large-scale energy storage.

What are the potential applications of sand batteries?

Sand batteries can be used in a variety of applications, including grid energy storage, industrial process heating, and residential heating. They are particularly useful in regions with high renewable energy generation, as they can store excess energy during periods of low demand and release it during peak demand. Additionally, sand batteries can be used to provide heat for industrial processes that require high temperatures, such as metal smelting and chemical production.

Are there any challenges or limitations associated with sand batteries?

While sand batteries have many benefits, there are also some challenges and limitations. One challenge is the need for high temperatures to store thermal energy, which requires specialized materials and equipment. Another limitation is the relatively large space required to store significant amounts of sand, which may not be feasible in all locations. Additionally, the initial cost of setting up a sand battery system can be high, although this is offset by the low operational and maintenance costs over time.

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