Renewable energy storage technology

[skyking1]

In the example posted, they used boreholes to store the heat deep below the surface. That is part of the high cost. The other factor is the bitter cold winters they are dealing with. It takes significant energy, and yet they managed to get 100% of it fromthe solar in 2015.
I'd like to hear what parts and pieces are failing.
The collectors have vacuum tubes around the copper. Those tubes have about a 15 year life before the vacuum goes away.
Perhaps they are facing the replacement of the collectors. The interesting thing about that is the tubes are replaceable. They slip over the copper collector, which is a pipe within a pipe and the soldered collector looks like a comb with only a top header.
When they ship out the collector they include spare tubes to cover for shipping breakage, so they are easy enough to replace.
The other complication is that system is all done with water to air with an air handler. That adds another layer of complexity.

 

[skyking1]

In comparison, we live in a mild climate. Winter extremes are ~25F. ( Just enough to snow LOL!)
The thermal mass we can construct ourselves, using an excavator and some sand for bedding the pipe, and about 1600' of SDR11 HDPE pipe. My last quote for 3/4" was 0.26$ per foot. I have good connections.
I think I will look for the higher temperature version of that pipe. I'm sure it is more $$ but worth it so it is not the limiting factor.
For rough figuring our cost for the mass is under 5K.

 

[skyking1]

Things are moving forward with this design idea. I'm meeting with the source of free installation on Wednesday. It's production scrap from a process and it will do just fine.
Now I am definitely splitting the rectangular thermal storage mass in half. I'll put a demising wall in there.
At the heart of the business is Delta T.
The collectors are certified by SRCC and they specify how much heat they put out at various Delta t's.
By having a hot mass and a cooler mass I can cruise that line a lot better.
I'm thinking the initial collector array will be four of those 25 tube units, which will gather about 80,000 BTUH per day in my latitude and weather conditions.
The plumbing will be in place for the 5th and more panels and they'll be room on the roof too.
One very legitimate concern with this idea is hail damage. Those tubes are not as resistant to hail as regular photovoltaic solar panels.
Thankfully that area does not have much in the way of convective activity.
Back to the Delta T; for the collectors, that's the difference between air temperature and fluid outlet temperature.
At the thermal mass it's the difference between the inlet and outlet fluids. I would try and run the Delta T around 20° or so, so I'm not forcing the solar panels up into a less efficient temperature.
That's when having two different masses comes into play On the shoulder part of the year, I could be warming up the cooler of the two masses and also using heat out of that overnight. In the hot summer I'd be jacking up that hotter mass for the winter.
Because of the hotter air temperatures, the panels would still be efficient with output temperatures approaching 70C.

 

[Exchme]

I have always wondered why they don't use the excess to do industrial tasks which don't have a specific time requirement.

An example might be to use excess power to do cryogenic separation of gasses for storage and later use in the industry (or for rockets!)

Who wants to idle the process, stop production and send the workers home when a cloud passes over or the wind calms?

In your example of cryogenics, it can take days for the process to cool down and establish levels, flows and compositions, so that's not going to work with intermittent energy sources. That's a typical result for a lot of industry, from steel mills to breweries to refineries, you can't start them and stop them on a whim.

Even the now-defunct Ivanpah solar concentrator power plant actually fired the boiler with natural gas at night to keep it up to temperature, otherwise it spent most of the morning reheating water.

Folks are searching hard for answers, but nothing is remotely close to taking over.

 

[ERD50]

....
My tentatlve plan is to build a thermal mass from a mix of existing soils and possibly some imported sands, measuring 12' wide by 6' high by 60' -ish long. ...

It's all very interesting. I'm not sure I understand how you get the thermal transfer in/out of the soil/sand chamber?

Is water going through the 3/4" 1600' of SDR11 HDPE pipe? Then to a water coil in the HVAC 'furnace'?

-ERD50

 

[skyking1]

It goes from the roof collectors in well insulated copper down to the the equipment room, then out to the mass using that 3/4 plastic pipe.
I'll build a layer cake out there. First a foot of insulation, then a foot of dirt. Lay out the first course of tubing 1' apart.
add 2 feet of dirt. Repeat the tubing layer.
2 more feet of dirt. Repeat the tubing layer.
Cap with the final foot of dirt and then 12"~18" of insulation, a plastic cover, and cover with ~12" of soil.
The walls will be 12"~18" of insulation also.
This fuid will be common with the hydronic floor heat system.
This system will only have enough pressure to overcome the difference in elevation, the head pressure. That's about 25 feet of head for ~11 PSI.
I will draw heat from the mass(s) and use a mixing valve where necessary to get a maximum of 40C hydronic heating. No heat pump, no heat exchanger or other monkey motion.
The only external energy is pumping with relatively small Grundfos type pumps.

This is completely isolated from the HVAC Ground Source Heat Pump (GSHP).
That system has ~4 loops 600' long in 6 pass trenches, at least 6' under the surface.
Each 600' of pipe is considered a ton of load.
The heat pump is a 3 ton, so the system has excess loop, which is great for efficiency.
The 6 pass trench is dug about 7' wide and the pipe goes up and back to make 6 pipe runs a foot apart.
Then you move over an additional 4' to dig the next trench. This avoids the saturation effects of a continuous grid of pipe.

 

[Chuckanut]

They better get this solved. In the last week, wind power energy production has collapse in my home state. Thankfully, it’s not a high usage time. But, last winter when we had a week of highs that barely passed freezing if they got above it at all, we also had a big drop in wind generated power. That along with less than nine hours of weak sunlight caused the local power company to request people turn down their thermostats.

The latest Northwest energy generation statistics are available from the Bonneville Power Administration and they are sobering: wind energy generation (green line) has collapsed over the past several days (see below). Spring is normally a time when wind generation increases robustly, but not this year.

 

[RobLJ]

We're in the midst of replacing our AC with a heat pump but found that, for financial reasons, we still needed a gas furnace for backup on the coldest nights (below 25 degrees or so). Heat pump only would have cost about 1.5-2x more, unfortunately, although that may be the unfamiliarity of companies in Reno with heat pumps and limited supply of cold climate pumps. We'll spend more in electricity in winter despite the solar panels (although the decrease in expensive gas will mitigate) and save in summer and the solar panels will help a lot in summer and help a bit in winter.


Next step next year or 2026 is to look into a small battery, although more because when the big winter storms hit, we can be without power for 6 hours to a day or so. Doubt a battery will save any money since we get 81% of retail in metering--we have fixed cost-- and Nevada Utilities' price for peak power if we switch is like 4x our fixed rate. I guess if Nevada Energy increases a battery rebate, then it might be worth considering, but the peak price is so high it will be a big risk.

 

[gwlbe]

There are 8760 hours in a year. The mode for wind and solar is zero. Grid size storage is a challenge based upon the energy required. Fossil fuel based generation is going to be required. Remove all subsidy’s and let the market figure it out.

 

[skyking1]

The free insulation looks promising.
It is SIP panels with 2lb EPS foam.
I can get plenty to build a 150Mt storage mass.

 

[Alan]

One of the big energy companies here are now offering a V2G tariff. Plug your EV in on an afternoon, such as when you come from work, and during the peak evening hours it will feed the grid discharging down to 20% and then charging up overnight to 80%.

They have been trialling this for about 3 years so it is good to see it go live.

 

[bjorn2bwild]

Keep it simple.
This team of engineers at Sandia National laboratories is making the case for using landscaping gravel, easy to scale.

Thermal energy is very energy-dense — you can basically use any material that could withstand high temperatures to store heat and then deliver it when you need it. “Say you have a PV or a wind farm and you're overproducing in the middle of the day. You can take that excess electricity and heat up air using a big resistive heater,” said Sandia engineer Luke McLaughlin. You can then use a blower to push the heated air through a bed of gravel, which is quite porous. That transfers the heat from the air to the rocks. You then close some valves, and the system goes into “hold” mode for hours, days, or weeks, until it needs to be released by reversing the flow.

https://www.techbriefs.com/component/content/article/50101-hot-rocks-store-energy

 

[skyking1]

That's interesting but does use an additional change of form from electricity to thermal energy.
Why not collect the heat and skip that step?
One reason, a big one is transmission.
PV is about 21% efficient in terms of capturing the totality of insolation.
Vacuum tube thermal collectors average 60% across the year, going up and down with the shift in delta T due to the seasons. This is just a comparison in terms of area.
PV has come down so far, there will never be a good comparison.
My 4 sq meter panels are ~$1000 each. a couple of solar panels to get the same area are less than $300 each these days.

 

[ERD50]

That's interesting but does use an additional change of form from electricity to thermal energy.
Why not collect the heat and skip that step?
One reason, a big one is transmission.
PV is about 21% efficient in terms of capturing the totality of insolation.
Vacuum tube thermal collectors average 60% across the year, going up and down with the shift in delta T due to the seasons. This is just a comparison in terms of area.
PV has come down so far, there will never be a good comparison.
My 4 sq meter panels are ~$1000 each. a couple of solar panels to get the same area are less than $300 each these days.

I was wondering that, but I see they are using the PV to run resistance heaters to heat the rocks to 500 °C (932 °F) air. So much smaller gravel bed needed, and high temperature air can be better utilized, even turned to steam if needed.

I'm curious about the prototypes though. All this stuff is very well understood, a model wouldn't need to be any more complex than a spreadsheet. If it pencils out, just do it (at a small scale obviously, but a 100-kilowatt-hour trial seems unneeded.

-ERD50

 

[bjorn2bwild]

Why not collect the heat and skip that step?

That was my first thought too.
They did qualify with “You can take that excess electricity and heat up air.“
I will leave it up to the system designers to decide when thermal storage makes the most sense.
A better comparison would ask how their idea stacks up against existing thermal storage technology that employs molten salts, tin or sulphur.
Perhaps a combination of storage substrates will prove to be best.

 

[Gumby]

Anything that you can heat enough to undergo a phase change will store and release the most heat.

 

[ERD50]

Anything that you can heat enough to undergo a phase change will store and release the most heat.

Very true, but most phase change materials will require a much more complicated and expensive system than just gravel and air.

That was my first thought too.
They did qualify with “You can take that excess electricity and heat up air.“
I will leave it up to the system designers to decide when thermal storage makes the most sense.
A better comparison would ask how their idea stacks up against existing thermal storage technology that employs molten salts, tin or sulphur.
Perhaps a combination of storage substrates will prove to be best.

Yes, that needs to be seen. As above, this is simple and cheap, so it may have more applications, where space isn't a major factor?

-ERD50

 

[skyking1]

The high temperatures demand more expensive materials and insulation that can take the heat. One of the really neat ones my brother read about was essentially a container of salts, and you park them next to the source of excess energy. Heat up and dry out the salts.
This is tailor made for processes that release heat, not near where you need it.
Now you have a container of latent energy to be released when you add water. It is now portable heat energy you can truck to where you need it.

 

[skyking1]

Anything that you can heat enough to undergo a phase change will store and release the most heat.

I remember an expiriment and article in popular science or similar, it had to be 40 years ago.
It was a system that had eutectic salts contained in foot square wafers of plastic that had bumps cast into it to allow for airflow.
The example had a few tons of the salts, which changed phase around 95 degrees IIRC.
They were in well insulated boxes in the basement, and the heat collection was douible paned solar heat collectors. There was no change of form and the delta T was kept low, which helps with the losses.
The hot air from the day went through the pile and then heat was extracted the same way.
I suspect the plastic technology of the day was the weak point there. I never saw anything about it again.

 

[bjorn2bwild]

A interesting seasonal approach.
This massive project in Utah is utilizing hydrogen gas to store excess electrical production for future use.
Note - an archive link, takes a little time to load.

Two caverns, each as deep as the Empire State Building is tall, are being created from a geological salt formation, using water to dissolve and remove the salt. When completed next year, the caverns will be able to store a huge amount of energy, but in a form that is vastly different from the chemical batteries found in everything from flashlights to cars.
Here, the energy will be stored as hydrogen gas.

https://archive.is/20240117163612/h...12/climate/green-hydrogen-climate-change.html

 

[Chuckanut]

A interesting seasonal approach.
This massive project in Utah is utilizing hydrogen gas to store excess electrical production for future use.
Note - an archive link, takes a little time to load.

https://archive.is/20240117163612/h...12/climate/green-hydrogen-climate-change.html

Storing hydrogen gas underground sounds like a real test of engineering. My understanding is that H2 is such a light small molecule. H2 will find its way into any hole or crack no matter how minor, and work its way out.

 

[Koolau]

Storing hydrogen gas underground sounds like a real test of engineering. My understanding is that H2 is such a light small molecule. H2 will find its way into any hole or crack no matter how minor, and work its way out.

Yeah, I think engineering is the real key to all of these. The theory is sound, but making them w*rk (with little human intervention) is the key. Most folks want a thermostat to turn up or down on whatever system they end up with. They don't want to worry about things that might leak or plug up or require significant monitoring. Some sort of turn-key heat storage system will be the ticket to such systems being accepted by "regular" people.

I recall NW-Bound talking about how much he had to "play" with his electrical system. He loved it. Most folks just want to flip a switch or turn a tap or dial a thermostat - just like they do now with fossil fueled systems. I'm actually surprised the heating systems haven't become turn-key by now, but YMMV.

 

[skyking1]

I am a tinkerer too, Koolau. My hope is to take it to the logical conclusion of automated microcomputer control.
The core of the system could be a $27.50 Arduino.
https://store-usa.arduino.cc/products/uno-r4-wifi

Get the operating parameters sorted out, then get the code written by others to make it happen. Note this is only for the collectors and storage operations.
The actual room by room control is quite simple. One room equals one zone, with a few exceptions where I will combine them.
Each zone gets a thermostat and a pump.
No valves, no computers, just a programmable themostat that monitors both the floor temperature and the air temperature.
Having individual pumps adds cost but it vastly improves simplicity.