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.