perestroika
@perestroika@slrpnk.net
- Comment on ‘Suddenly energy independence feels practical’: Europeans are building mini solar farms at home 2 weeks ago:
It depends on the country one lives in, because to connect equipment to the grid, it has to be certified in that country.
As a good starting point, I would recommend to look at inverters sold as “hybrid inverters”, especially if the manufacturer advertises “off-grid” capability. Typically there’s a process of automatic switch-over and it has to take really few milliseconds (e.g. 10 ms).
Here is one, from the manufacturer whose devices (older version) I use. There are many others. If the user’s manual explains the process of automatic switch-over to off-grid (island) mode, then the inverter will provide autonomous power in case of grid collapse.
maximumsolar.online/product/hybridv2-6048/
…and here is another one, from a different company. Anything that becomes autonomous upon loss of grid freqency (disconnects from the grid and leaves only sensors to read its status) and then gracefully handles the return of grid frequency (does not connect before synchronization has been achieved).
- Comment on ‘Suddenly energy independence feels practical’: Europeans are building mini solar farms at home 2 weeks ago:
Colleagues, please do not downvote the poster. Most solar poewr installations in use today are grid-following, so it’s correct to point out: if the grid drops, most solar inverters stop. Your average Huawei is not capable of operating in island mode.
Of course, the grid drops rarely, but this is a real risk for example if your electrical grid should get bombed, or pelted with ice rain.
Myself I have a different kind of a solar power system, and it’s not commonplace. It’s easy and doable, there is plenty of instruction available, but it’s less profitable.
panels -> DC -> charging controllers -> DC -> battery bank -> DC --> consumers, among them an inverter --> AC --> possibly the grid
To get a safe system, ask a specialist or learn about balancers, interrupters and fuses. Everything is DIY-able with a willingness to learn. Avoid dangerously high voltage if you aren’t certified to work with electrical power.
- Comment on Can I assemble a metal building by myself? 5 weeks ago:
If you don’t mind divulging, how does that stack against timber for cost at least for the time?
It’s too expensive but practically indestructible, except in salt water. Unlike wood, it does not offer any favourable thermal properties, so you can only do unheated sheds with it. I came across a pile of it on a bankruptsy auction, which made it possible to afford its use.
- Comment on Can I assemble a metal building by myself? 5 weeks ago:
I recommend to find some assistance. Even one other person can help immensely at certain points.
I have built a 2-storey shed on a metal frame alone, and it involved highly inconvenient and more than moderately dangerous stages.
I managed only because I relied heavily on industrial aluminum profiles for machine building (engineer’s Lego beams).
- Comment on Cold weather stud finder 2 months ago:
If you don’t mind buying from Guangdong and being hit with import and customs fees, then on Linux, this gadget presents a standard V4L (Video4Linux) USB camera.
www.aliexpress.com/item/1005007938478574.html
Note: never ever point at the Sun. It has poor solar protection, I almost ruined it when my code erred and scanned across the Sun, leaving a massive black track which took several hours to fade.
- Comment on Cold weather stud finder 2 months ago:
Coincidentally, it is cold here too. Walked around the house with an USB drone camera. Window edges are radiating like crazy. There was no difference between a window with shades down vs. a window with shades up, but the edges need extra foam.
- Comment on The Ultimate Guide to Affordable NVIS Comms (How to Build a Regional Off-Grid Radio Box) 2 months ago:
What makes me worry is the size of the “reflector”. I wonder what symbol rate it is possible to get if the “reflector” is literally everywhere above you - the time delay between start of reflection and end of reflection might be considerable.
I found a resource with practical advise about using NVIS, including using meteorological data (ionograms) to determine the best frequency, antenna diagrams and such.
- Comment on The Ultimate Guide to Affordable NVIS Comms (How to Build a Regional Off-Grid Radio Box) 2 months ago:
Thanks for dropping the abbreviation. :) For those who want text:
- Comment on A giant 'Air Battery' emerges in the Gobi Desert 3 months ago:
Given that…
The potential energy carried by Liquid Air/Nitrogen is just over 200 Wh/kg (watt hours per kilogram).
…this is on par with battery storage, but likely doesn’t need any scarce minerals.
- Comment on Lead acid battery reconditioning question 3 months ago:
Some tips: listen for bubbling. If a battery makes bubbling sound, that means it produces hydrogen. That’s not supposed to happen outside a short period at the very end of charging.
If it happens early, there could be one or several dead cells, causing other cells to experience overcharging. If it doesn’t hold a voltage of 2V per cell (6 cells = 12 volts), discontinue using, as a dead cell is then very likely present in the battery.
- Comment on How would I replace this possibly load bearing wall? 3 months ago:
Disclaimer: not an engineer, but I’ve built a house and squatted half a dozen.
Questions:
- how much load might it be supporting (what is the porch made of?)
- how high and long is the concrete beam and approximately how many decades old?
Ideas:
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don’t remove woodwork until you have investigated the cracked concrete, removing anything that comes loose without striking; determine for sure if the concrete is fully compromised or partly so
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if concrete is only partly compromised, one method would be cutting off the compromised layer and casting a filler, but you should re-calculate the load bearing ability of the beam as if the filler was nothing
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after this you have a concrete that can be effectively supported from below
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if you use a jack and a pillar, prefer a mechanical (not hydraulic bottle) jack, people sell and rent such instruments for temporary support, it’s a steel pillar made of 2 parts that you rotate against each other to extend
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your plan to offer support from the center and replace the framework from sides makes sense
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if water if a frequent visitor there, use treated wood
- Comment on The design behind the world's most efficient 27.81% silicon cell 4 months ago:
Pretty damn neat.
If it’s expensive, I would still think that people needing to charge cars, power up boats or supply electricity to high altitude pseudo-satellites (read: balloons that are permanently up there) or satellites will buy some.
If the price drops, solar power with far less surface is nice to have elsewhere too.
- Comment on Li-Ion fire safety, inert atmosphere 4 months ago:
Most likely, it could help slow the process (buy time for firefighters to arrive) in some percentage of cases.
Provided large amounts of nitrogen and an already empty battery (devoid of chemical energy), in a small percentage of cases, it might prevent a fire.
However, having seen a lithium polymer cell heat up from mechanical damage (a drone crash), I can confidently tell that very high temperatures can be achieved without oxygen.
- Comment on China lets fly world's largest kite in Inner Mongolia for electric power generation 4 months ago:
What puzzles me: what is the risk of wind lull at high altitude? I know that winds are terrifically fast there (100 km/h would be considered a slow day at 10 km altitude) and slow down approaching the surface, but do lulls exist at all?
- Comment on China lets fly world's largest kite in Inner Mongolia for electric power generation 4 months ago:
Yep.
5000 m2 is more or less “the size of a football field” (50 x 100 m).
5 km2 is 5000 x 1000 m, not a practical thing to get airborne with current technology.
- Comment on How to Remove Burn Mark from (acrylic ?) Sink 5 months ago:
I would likely try the methods of car headlight repair:
- fine sandpaper (e.g. 600)
- followed by ultra fine sandpaper (e.g. 900)
- followed by polishing sandpaper (e.g. 1200)
- followed by polishing paste (cerium oxide)
However, since I see that the sink has a glossy surface… I would be deterred by that. The method I mention may reach a layer which isn’t burnt, but may wear off glossy finish.
What paint to use - sorry, no idea.
- Comment on Charging the Future with Wood-Based Battery Breakthroughs 5 months ago:
This looks like it could credibly improve both safety, cost and ecological footprint. Nice. :)
(I was previously aware of peat-derived materials being used in batteries, but lignin seems to fit considerably better.)
- Comment on Creating microbial fuel cells using bacteria in your garden 5 months ago:
it doesn’t really say how much power you can get out of it, but it sounds interesting!
Not much. The manual says you can run one LED off 5 mud cells. That would imply about 3 volts and maybe 10 milliamps. Enough to show that there’s a gradient of potential, not enough to accomplish much of anything. :)
- Comment on Acquired a sliding mitre saw 7 months ago:
I cut aluminum with mine, but I will second the “be careful” part.
Aluminum can snag your saw blade with dangerous results (saw jumping upward and losing teeth in the procecess).
Ensure the work piece is clamped down very well. Ensure that the saw is either on a large level surface or better yet - bolted or clamped down. Ensure that the saw jumping cannot hurt you in any way.
When cutting aluminum, push very gently.
- Comment on Engineering Breakthrough Opens Door to Cheap Hydrogen Power 8 months ago:
Most of it, yes.
But there is no requirement to do it that way.
- Comment on Engineering Breakthrough Opens Door to Cheap Hydrogen Power 8 months ago:
Anything that brings operating temperatures down by a half while maintaining efficiency is good news. :)
- Comment on Finland warms up the world’s largest sand battery, and the economics look appealing 9 months ago:
As much as I’ve understood, yes - heat pumps have difficulty with reaching high temperatures.
- Comment on Finland warms up the world’s largest sand battery, and the economics look appealing 9 months ago:
They use resistive heating, so they can only charge it dirt cheap when there is surplus solar or wind.
- Comment on Finland warms up the world’s largest sand battery, and the economics look appealing 9 months ago:
It’s a pretty neat system:
- can be set up anywhere
- can supply high grade heat (process heat, not space heating heat)
However, heat stores are subject to scaling laws which don’t favour sand on the large scale. Large thermal stores benefit from storing heat in water, and placing the water deep underground so the boiling point rises.
For comparison Helsinki (.fi) has a 10 GWh underground thermal store. Where I live, Tallinn (.ee) will soon get a 1 GWh thermal store. And Vantaa (.fi) will soon complete a whopping 90 GWh thermal store that’s located 100 m underground, so their water will boil at 140 C instead of the usual 100 C.
- Comment on New fuel cell could enable electric aviation | MIT News 10 months ago:
With this technology, it’s just the combination of fuel and exhaust that makes it unlikely to reach peaceful applications sooner. A user of this technology must be willing to tolerate (and cause) considerable inconvenience just to increase the range of their electric aircraft.
Fuel distribution would be an annoying but surmountable problem. Not the easiest, but doable. Sodium needs to be stored either in mineral oil or inert gas. Otherwise it will spontaneously oxidize quite fast. Airports would need sodium warehouses with specialized equipment (either oil baths to submerge it or an unbreathable atmosphere). Trucks with the same kind of equipment would be needed to deliver the stuff.
Fuel production efficiency would be a problem. I don’t know the efficiency of sodium production, but intuitively this is likely to be around 80% (plus road transport). Charging a battery from the grid is more efficient, so the user of this technology must either have cheap electrical energy (this might be true in future with lots of renewables) or be willing to ignore the cost of energy (military users will do that already now).
Finally, the debate over a caustic exhaust stream is likely to be non-trivial. I predict that people will be quite worried about the direct effects of NaO and NaOH air pollution - it’s one of those things which is clearly health negative, even if climate positive. Unsurprisingly, military users are pretty unconcerned about being health negative.
- Comment on New fuel cell could enable electric aviation | MIT News 10 months ago:
Thanks for the tip, both the popular and scientific article are interesting.
Short summary of the pros an cons:
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energy density: 3 x better than lithium ion
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power density: really poor (if they raise their power density by 10 times, it will suffice for cruising, takeoff will require supplementary high-current batteries)
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exhaust: sodium oxide, converted by moisture in air to sodium hydroxide (caustic), converted by CO2 into sodium bicarbonate (harmless) --> this is a tech for cruising up high, not for takeoff or flight above settlements
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operating temperature: reasonable (about 100 C)
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mass production of sodium: doable, but somewhat messy (electrolysis of seawater?)
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fire safety: sodium burns just as bright as lithium, nothing cheerful here
My personal conclusion: currently, this is a potential military technology (“electric cruise missiles with 500 km range”), but likely won’t reach passenger or cargo aviation soon.
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- Comment on Questions on how to connect a PC to a washing machine (USB→TTL serial) 11 months ago:
Note: another really common baud rate is 9600, 8, 1.
- Comment on Questions on how to connect a PC to a washing machine (USB→TTL serial) 11 months ago:
You don’t need to connect the 5V pins. Otherwise it seems sound.
- Comment on Wind/solar motorcycle [with 50 km solar/wind range] looks like an April Fools' joke ... but it's legit 1 year ago:
I would think the drag is considerable.
I would also worry about stability in a strong side wind.
As a result, I would not like to ride the 2-wheeled version in strong side wind. The 3-wheeled version looks OK, but also suffers from drag.
Besides, to generate power from wind while parking, you would have to choose your parking direction. But you can’t always choose the parking direction - location dictates it often. That kind of a wind generator on a vehicle looks severely half-assed. They should have though two steps ahead.
- Comment on Flow Battery Research Collective: Building an Open-Source Battery for Stationary Storage (FOSDEM 2025) 1 year ago:
Nice project, I hope they arrive at good recipes. :)