Sand battery heater

[tetrasect]

That doesn't sound to promising.

Doesn't matter whether you're heating sand, water or strawberry milkshake.

You get out what you put in.

Roughly.

So if you have 10kwh of excess power going into your water during the day, then at night you will get the equivalent heating output of running a 1000W electric heater for 10 hours.

If you have 5kwh of excess power then you get the equivalent of running a 1000W electric heater for 5 hours, or a 500W heater for 10 hours.

 

[BBSA]

Doesn't matter if you're heating sand, water or strawberry milkshake.

You get out what you put in.

Roughly.

So if you have 10kwh of excess power going into your water during the day, then at night you will get the equivalent heating output of running a 1000W electric heater for 10 hours.

If you have 5kwh of excess power then you get the equivalent of running a 1000W electric heater for 5 hours, or a 500W heater for 10 hours.

The actual energy you get out depends on the efficiency of the storage and retrieval process. Some energy is typically lost due to heat loss, especially when using thermal storage systems.

 

[animal531]

I think the real problem here is that we don't have a great solution for heat<->power conversion, too much power is lost with heat. That's why on larger scale they use other means such as mechanical<->power. For example use power to pump water up a mountain, or to raise a giant weight.

 

[tetrasect]

The actual energy you get out depends on the efficiency of the storage and retrieval process. Some energy is typically lost due to heat loss

As long as your storage tank and the pipes going to your radiator are in your house, that heat is not lost as it goes into your house.

, inefficiencies in conversion (like converting electricity to heat),

Heating elements have a 1 to 1 conversion ratio. They are 100% efficient.

or other factors, especially when using thermal storage systems.

The only thing I can think of is the ~10W you need to run the circulation pump.

 

[BBSA]

My roof is flat, so the geyser has to go outside. it'll lose energy, even with insulation.

 

[tetrasect]

I think the real problem here is that we don't have a great solution for heat<->power conversion, too much power is lost with heat. That's why on larger scale they use other means such as mechanical<->power. For example use power to pump water up a mountain, or to raise a giant weight.

He wants to warm up his house in winter. So he doesn't need to convert heat back into electricity.

 

[BBSA]

A sand battery can go inside my bedroom, so any energy loss will go inside the room.

 

[tetrasect]

My roof is flat, so the geyser has to go outside. it'll lose energy, even with insulation.

Well the energy lost will be a drop in the bucket compared to not using the excess solar at all.

 

[animal531]

He wants to warm up his house in winter. So he doesn't need to convert heat back into electricity.

My point was mainly that storing the power as heat is wasteful.

If I had to do it I'd rather look at some pipes on the roof that pumps down to underneath the floor or into a room at night.

 

[BBSA]

Well the energy lost will be a drop in the bucket compared to not using the excess solar at all.

Indeed, if the medium is inconsequential, then I should consider the most cost-effective option. The sand battery seems to be the clear winner here.

 

[tetrasect]

A sand battery can go inside my bedroom, so any energy loss will go inside the room.

Like I said earlier, 1 bucket of sand going from 20-450 degrees has around the same energy storage capacity as 2 buckets of water going from 20-80 degrees, and the water only weighs slightly more (storage capacity of 1.6kg sand = storage capacity of 2kg water).

So to match a 150L geyser holding 150kg of water you would still need 75L of sand which weighs 120kg.

Don't see that going on top of any cupboard...

 

[tetrasect]

My point was mainly that storing the power as heat is wasteful.

He has excess solar power that he isn't using.

If I had to do it I'd rather look at some pipes on the roof that pumps down to underneath the floor or into a room at night.

Pipes on the roof cool down as soon as the sun stops shining on them. Also, in winter they wont even heat up.

That's why solar water heaters use vacuum tubes.

 

[tetrasect]

@BBSA How many kwh per day of excess solar do you actually have? Cause that's kinda important.

 

[BBSA]

Like I said earlier, 1 bucket of sand going from 20-450 degrees has around the same energy storage capacity as 2 buckets of water going from 20-80 degrees, and the water only weighs slightly more (storage capacity of 1.6kg sand = storage capacity of 2kg water).

So to match a 150L geyser holding 150kg of water you would still need 75L of sand which weighs 120kg.

Don't see that going on top of any cupboard...

Never said I want to put it on a cupboard.

 

[BBSA]

@BBSA How many kwh per day of excess solar do you actually have? Cause that's kinda important.

About 5kwh.

 

[tetrasect]

About 5kwh.

So you'd need about 70 liters of water.
If heated to a more safe 200 degrees, you'd need 75 liters of sand.
If heated to 450 degrees, you'd need around 32 liters of sand.

For the water, you could 75L tub for 45 bucks:

75L Jumbo Tub | Rashida Plastics

www.rashidaplastics.co.za

For the sand, if you wanna use a 35L potjie pot, it will cost about 4,000 rand.

Best Duty Pot 3-Leg #14

Best Duty Pot 3-Leg #14Traditional quality, heavy duty and very robust 3-legged pot for the best potjie experience. Oil-cured & ready to usePrice includes VATPrice excludes deliveryServes: 50-60Volume: 34.5LPot Diameter: 405mm

bestduty.co.za

 

[BBSA]

So you'd need about 70 liters of water.
If heated to a more safe 200 degrees, you'd need 75 liters of sand.
If heated to 450 degrees, you'd need around 32 liters of sand.

For the water, you could use 3 of these polypropylene buckets at 42 bucks each and the water is free:

Blue 25L Bucket + Handle + Lid - Foamy

25l Tamper-Evident Bucket—a sleek solution with a breakable tag for unmistakable proof of product integrity. Comes with a handle for easy carrying. Can be used for and more: Food Storage Craft and DIY Projects Cleaning Supplies Pine gel Gardening Personal Care Pet Care Sampling Office...

foamy.co.za

For the sand, if you wanna use a 35L potjie pot, it will cost about 4,000 rand.

Best Duty Pot 3-Leg #14

Best Duty Pot 3-Leg #14Traditional quality, heavy duty and very robust 3-legged pot for the best potjie experience. Oil-cured & ready to usePrice includes VATPrice excludes deliveryServes: 50-60Volume: 34.5LPot Diameter: 405mm

bestduty.co.za

I already have a potjie.

 

[tetrasect]

I already have a potjie.

What size/No.?

 

[wingnut771]

Doesn't matter whether you're heating sand, water or strawberry milkshake.

You get out what you put in.

Roughly.

So if you have 10kwh of excess power going into your water during the day, then at night you will get the equivalent heating output of running a 1000W electric heater for 10 hours.

If you have 5kwh of excess power then you get the equivalent of running a 1000W electric heater for 5 hours, or a 500W heater for 10 hours.

What if it’s 10 000W for 1 hour?

 

[wingnut771]

A sand battery can go inside my bedroom, so any energy loss will go inside the room.

My shower heats my bedroom nicely.