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1500 questions
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3 answers
Do solar cells age? Why, and how?
As I heard, the life expectancy of photovoltaic cells is normally some decades, as so. This is very long, regarding their high cost, it has significant (negative) effect on the total costs.
Why do they age? I can see the only possibility which could…
peterh
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Determining RTK parameters for runoff analysis
I am examining a watershed and determining runoff using the RTK method. I basically use a 'guess and check the hydrograph' method right now. I've seen calibrators that use a mutation and convergence criteria using root mean square but I've had…
RossV
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In aluminum machining, what are the most common factors that might cause a machined component to have warping issues?
I am currently having an issue where features of my machined parts are warping. I am using Alloy 7050 Type I and Type III in this particular case. Using a feeler gauge and a certified, calibrated granite slab, I am getting out-of-flatness…
Tim D
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Additional jacking force to overcome stiction/dry friction
It is common to lift bridges to replace bearings, etc.
In an ideal world the lifting capacity required of the jacks would be the self-weight of the bridge divided by the number of jacks (+ allowances for wind/snow, etc.).
From my (limited)…
thomasmichaelwallace
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Why are bird flight diverters shaped like a spiral?
I was out walking and saw these strange looking spirals on some power lines.
When I got home I did some research and discovered that they are to prevent birds form hitting the power lines, mainly used in conservation areas. I found this interesting…
jhabbott
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13
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3 answers
What is this Y-shaped screwdriver bit, and what is its purpose?
I found this strange looking bit in a bit set of uncommon bits, including Security Torx, hexalobular, tri-wing, spanner head, 12-point flange, Torq-set and others. It's the only one that I could not identify, what is it for?
jms
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3 answers
PID controller explanation
I haven't found a text that explains the PID controller in simple words. I know the theory: that it calculates the derivative and the proportional gain and the integral etc, but I need to know in reality what is the output of each function and each…
ergon
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Are there any materials known to be sound-insulating but thermally-conductive?
Are there any materials known to be sound-insulating as well as thermally-conductive?
Cost is not an overriding concern, but preferably costing "reasonable amounts" and much less than national defense spending levels.
This is a thought experiment…
Jimmy Hoffa
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Can Zinc/Aluminum coated anchor rods be used in concrete?
Bolts and anchor rods that are very high strength ($F_u$ > 150ksi) are not supposed to be galvanized. This is because of concerns about hydrogen embrittlement. This includes ASTM A 490 bolts and ASTM A 354 Gr. BD anchor rods.
The project in…
hazzey
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13
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1 answer
From an engineering standpoint, what is the purpose of the indent in a coffee lid?
I've see the same lids every day but I never really thought about their construction. There is an indent in a "Solo Travel Lid" for coffee cups that is just above the hole that you drink the coffee from.
You can see the crescent shaped indent in…
ruckus
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7 answers
What are the disadvantages of concentrated solar thermal power?
Concentrated solar power looks on the surface to be an excellent source of grid power. It's sustainable, has no obvious waste products to deal with either during construction or operation, and with thermal storage it can generate power at night or…
Stephen Collings
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Estimating whether the flow through a valve or nozzle cavitates
My understanding is that cavitation occurs in the flow of a liquid when the static pressure drops below the vapor pressure, even intermittently. So even if the time-averaged static pressure (what you might measure) is above the vapor pressure, the…
Ben Trettel
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13
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7 answers
Wind farms that wind up in the wind, and then unwind producing energy when the wind is still
Given the difficulty of producing energy for a region when the wind isn't blowing, why is it not possible to have half of each wind farm producing energy directly, and the other half working to lift a weight, that then descends and produces energy…
apg
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13
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2 answers
How does a multimeter protect itself from high voltages?
I have used a cheap multimeter to measure voltages in simple DC circuits, but I have seen pictures of them plugged straight into the mains and used to measure various home-built generators.
Why doesn't the higher voltage fry the multimeter, and also…
jhabbott
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13
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10 answers
How do heat pumps output more heat kW than the electrical kW used to run the heat pump?
I understand that a 2 kW electric heater will use 2 kW of electricity and output 2 kW of heat (apart from small losses of energy as infra red, vibration etc.. but let's exclude those for this example as they are negligible).
A 2 kW air source heat…
sam
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