Storing heat in sand?

[Whats_per_question]

Bought two end-of-run 415W panels for $280 ea - Longi LR5-544HPH - 21% efficient, half-cell, backwash-diode-equipped, and only about 200M from the guy I was buying the barrels from. Driving down tomorrow morning.

Bought two 2100W 200mm spiral elements for $29 ea
Bought some insulated 4" ducting and an inline 12VDC fan
Dug out some L298N DC speed controllers - I can hopefully use the same ESP that is running the thermocouples to do double-duty as DC speed controller for the inline fan.
Ordered some floor registers (vent plates) for hot air outlets. I've gone with two sizes - 85mm x 400mm for baseboard vents and 80x150mm for floor vents.
Ordereed a solar panel meter tool for testing panels, etc. It will come in handy over the next few years enough to justify the $100 cost. I could use a multimeter - I have a bunch of them - or my clamp meter, but this makes it so easy with the built0in MC-4 connectors and preset programs for testing.

I got a tip for steel cutting for a bloke in the next town just starting out with his home-based waterjet who will cut the baffles for a reasonable price. Submitted the vector files - will wait for a price.

I'm at around NZ$850/USD500 spent so far, with only the cost of the plates to come, but not including the stuff I already had on hand - motor controllers, ESPs, cable, MC-4 connectors, etc.

@MyK3y - how are you getting on with this project? I have a couple of acquaintances trying similar projects

 

[MattiFin]

You guys are still confused.

Panels in series wired directly to nichrome wire coil in a circuit. That's it. No other elements involved. I found a bunch of SSRs, so I will wire in a breaker just for safety.

So, further developments:

Just picked up aluminium tubing - 10M @ 50mm x 2mm - and redrew the diagram for the water jet. Cutting tonight. We've had a massive storm blew through for the last 6 or so days which really put a damper on things - I wasn't going to go out and wrestle with stuff in the high wind and rain when I could stay inside and read my book.

Nichrome arrives sometime this week, so I can start test wiring. I plan to make three elements in parallel, buried at three different levels in the sand. That allows me to run them hotter without the chance of burning out and are evenly heat the sand.

I was going to go through-hole with the baffle ducts, but have decided on flush-mount using exhaust gasket goo - good to 350C

46mm holes centred - the gap is to allow fuss-free routing of wiring, temp sender, etc.

View attachment 170651

How is the project going?

probably beating old horse here but maybe worth mentioning for others that connecting pv panels directly to resistive heater results really bad utilization of available power most of the time.
when sun is at angle or behind light clouds you lose big time compared to mppt controlled load.

 

[Ampster]

...... connecting pv panels directly to resistive heater results really bad utilization of available power most of the time.
when sun is at angle or behind light clouds you lose big time compared to mppt controlled load.

That is why I prefer a heat pump for heating water. Of course the biggest benefit is the efficiency. In my case that compensates for the high initial cost.

 

[Hedges]

probably beating old horse here but maybe worth mentioning for others that connecting pv panels directly to resistive heater results really bad utilization of available power most of the time.
when sun is at angle or behind light clouds you lose big time compared to mppt controlled load.

Assuming no shadows (uniform illumination, even if off angle or through clouds) you can come pretty close to MPPT by simply connecting a capacitor to the PV array and doing PWM into a resistive load, controlling on/off time ratio to maintain constant voltage Vmp on input.
No inductor necessary.

 

[orangezero]

Any projects that have progressed with the sand batteries?

In the US there has been a recurring joke about retailers selling 8 hot dogs in a pack vs 10 hot dog buns. This happens with solar panels and heating elements; both come in fixed and often incompatible combinations.

I like the idea of using a custom length of nichrome (or copper wire, or diodes) as a "heating element" so you can get really close to the optimal resistance that best suits the solar panels with zero electronics in the middle. In other words, low cost and less failure points.

I tend to notice most of the time when efficiency is discussed, the less expensive answer is often to just add another panel (if space is available).

 

[Mart Hale]

I made a video of my progress.... I have been tied up with gardening I may have more time this winter to move forward.

This video is quality about sand battery storage ->

This is my progress I have made with my sand battery.

Testing different types of sand batteries.. Results of testing I have done.

My progress and videos I have gained info from: Overview of the sand battery: 1752 A DIY Sand Battery - The Theory, Practice And Use https://www.youtube.com/watch?v=Icai6OOIh2M Using the waste heat of

rumble.com

On my thread on Permies on this subject I ran into a guy who uses this to cook food for a school in Kenya.

 

[orangezero]

Watched your video, thank you for sharing. I like the idea of using your sand to get water out of wood or to make quick lime.

Cleaning out the garage today, and found two bags of sand. At the very least I should do an "experiment" where I heat the sand enough to dry it out...

I know this is the "sand thread" but a serious disadvantage of sand compared to water; sand doesn't magically get pumped into my house when I turn a faucet handle.

 

[Mart Hale]

Watched your video, thank you for sharing. I like the idea of using your sand to get water out of wood or to make quick lime.

Cleaning out the garage today, and found two bags of sand. At the very least I should do an "experiment" where I heat the sand enough to dry it out...

I know this is the "sand thread" but a serious disadvantage of sand compared to water; sand doesn't magically get pumped into my house when I turn a faucet handle.

Yeah, that is why I do both... After my batteries are charged from my solar panels, my system auto magically flips a relay to my hot water heater and it heats my hot water. I have had to only use propane for back up for a few days.... Storing heat in water is indeed the way to go.

 

[Michelle Konzack]

I'm quite sure it's physically impossible to achieve a heater greater than the source..without more work input, say, from a compressor or something. This is a fundamental limit if you're using hot water as the heat source. If it was a steel bucket of sand, you could of course just place it over a fire and it will get hotter than that.


Hmmm.. if you can seal an engine, there will be sealing materials out there that can withstand very high temperatures. But you are right that heat is a concern and does deserve some engineering attention. You would have to make your vessel out of uniform material, so that it all expands evenly.


Is there any need for a pressurised vessel? It could be vented, unless I'm missing the glaringly obvious? I had in mind something like a steel drum? You can get some that secure the top on with a band clamp, allowing you to remove the lid to add fittings to it easily and place items on the inside.

Regarding mold, you would have the option of treating the water of course - though many cooler towers do just dump the water periodically as far as I know. The addition of chlorine, or keeping a low pH, to prevent stuff growing are options is potentially damaging to process equipment - certainly the mild steel drum as above would not fare well in either of those situations.

Simply add Glycole to it (minimal 20%) to prevent mold and reduce rusting of the barrel

 

[Michelle Konzack]

Sounds like you are off by about factor of five.
Specific heat of Water is 1 btu/lbs/F but sand is only 1/5 of that. https://www.engineeringtoolbox.com/specific-heat-capacity-d_391.html

Water is hard to beat as heat storage medium. Easily available, easy to heat and extract the heat from and excellent heat capacity per weight and volume.

This was my first idea too,

But it would require under my Greenhouse 5 bunker cells 4,0x6,8m, insulated with 50mm EPS and then a bag of HDPE or EDPM, which can be even ordered from Chinaman for a resonable price. Heated up to 70degC, you can store per Meter hight roughly 1.250kWh of energy. The make it 2m high and you have already 2.500kWh. My Greenhouse is 21,5m long and I can have 5 cells...

1.250kWh at a temperatur difference of 40degC (70-30 because of the underfloor heating system)

12,5MWh of Energy.

On top of it put 10cm of EPS and 50cm of sand as insulator.

This should be enough to keep the Greenhouse over the winter nicely warm and additional you can heat your house.

Hahaha, I need roughly 50kWh a day to heat my house at -20degC and the Water Storrage would keep my house 250days warm MINUS losses for the Greenhouse.

And there is another option, by using washed Gravel together with the water.

Mixing Sand with Oil give a nice problem with the authorities.