Free Power From the Sun

[mivey]

I was curious about that, but since solar systems don't involve medium voltage, I was at a loss to understand what his point was.

Because you don't get much chatter about LV splices. The higher the voltage, the more dramatic the illustration, costs, consequences, etc.

He could have made the same point with tapping a low pressure water line vs. tapping a high pressure water line. The failure point is rarely in the middle of the pipe but at a joint. People usually don't talk much about leaks on a garden hose connection but let a high pressure water main have a leak and it might make the news.

Same with a roof. The failure point is usually not in the middle of the roof but at some point of discontinuity, like a penetration, valley, etc. because they are points of higher stress.

 

[weressl]

Because you don't get much chatter about LV splices. The higher the voltage, the more dramatic the illustration, costs, consequences, etc.

He could have made the same point with tapping a low pressure water line vs. tapping a high pressure water line. The failure point is rarely in the middle of the pipe but at a joint. People usually don't talk much about leaks on a garden hose connection but let a high pressure water main have a leak and it might make the news.

Same with a roof. The failure point is usually not in the middle of the roof but at some point of discontinuity, like a penetration, valley, etc. because they are points of higher stress.

You're correct. With MV splices having a dramatically higher failure rate, there are several general priciples can be observed and some specific to the application problem.

• The largest one is the human factor. Whatever have to be installed in the field - as compared to factory - the outcome is much more uncertain as it is not subject to the same quality control that you can excercise in the factory.
• The available skill in the factory will be higher as the individuals are much more specialized than the ones in the field, who may do a splice every 2-3 months while the factory/assembly worker does it day-in, day-out.).
• In the case of the old PILC MV cables and even in the early days of polymer insulation the stresscone buildup was done by applying overlapping tapes and buyilding a conical structure, very elaborate, an artform if you will.
• In the newer type splices or termination, it is dumbed down, but there are still a number of steps tha has to be gotten right.
• Environmental contamination, both mositure and dust will affect the life of the splice.
• Wherever you interrupt a manufactured, extruded insulation, the repair and restoration will be chaning the uniformity of the dielectric, where streesslines will be formed and a point of weakening is created. (Splices are designed to overcome that but will come up short of 100%.)
• There are other influencing factors why a field installed splice is never as good as an unbroken continuous lenght of cable, but the above summarizes the main issues as I know them. (I also just stayed on the low end of the MV insulation and did not go into higher than 15kV, wehre more exotic cables are used with even more complex problems.)

I thought that because of the above description it was a good analogy to the roof penetration.

 

[tallgirl]

I have no experience with solar power. I have seen my fair share of leaking penetrations from plumbing, HVAC, electric service masts, gas appliance outlet vents, or anything else that penetrates a roof and pretty much any type of roof.

In snow and ice country things are worse when there is snow or ice on the roof as it dams up water and allows it to penetrate small cracks that it may not otherwise enter during rain shower in warmer conditions.

Right, and the difference between a plumbing stack or other conduit-ish penetration is that it's going through the deck between two rafters. A PV penetration typically is going through the decking AT the rafter. The entire bore of the hole is filled with sealant, then the racking footer is screwed down, placing the entire hole in compression.

Most roof-top PV systems DON'T bring the PV conductors into the building because DC has to be run in pipe and it's easier to just run it over the edge to the disconnects. THEN deal with the AC.

 

[weressl]

Right, and the difference between a plumbing stack or other conduit-ish penetration is that it's going through the deck between two rafters. A PV penetration typically is going through the decking AT the rafter. The entire bore of the hole is filled with sealant, then the racking footer is screwed down, placing the entire hole in compression.

Most roof-top PV systems DON'T bring the PV conductors into the building because DC has to be run in pipe and it's easier to just run it over the edge to the disconnects. THEN deal with the AC.

Right, and you clearly have no idea how a leak occurs.

 

[tallgirl]

Right, and you clearly have no idea how a leak occurs.

I'd prefer to make a response that's not dripping with sarcasm, but I'm suddenly incapable.

 

[weressl]

I'd prefer to make a response that's not dripping with sarcasm, but I'm suddenly incapable.

..or non-sensical. Oh, the irony of it!:happyyes:

 

[ggunn]

I can't get too political here but the above is the root cause of many of our economic problems we face here in the US.

We have far too many people "making" money by moving money around and far too few actually producing anything.

Anything more I would say would be seen as political, so I will refrain.

I do have a solution to all our problems, though. Give every man, woman, and child a couple of million dollars to invest; we could all retire and live off the interest and dividends, and none of us would have to work another day in our lives. Wouldn't that be great?

And speaking of getting something for nothing, there was a story aired on NPR this morning about a program the US gov't. is running where you can buy $1 coins in bulk from the US mint at face value on line with a credit card with free shipping. People are buying huge quantities of them and just depositing them in their banks where they can use them to - you guessed it - pay off their credit cards, and the coins get sent right back where they came from. This generates airline miles from the CC companies, and these ripoff artists are flying all over the world for free with the rest of us footing the bill. What a country, eh?

 

[weressl]

We have far too many people "making" money by moving money around and far too few actually producing anything.

Anything more I would say would be seen as political, so I will refrain.

I do have a solution to all our problems, though. Give every man, woman, and child a couple of million dollars to invest; we could all retire and live off the interest and dividends, and none of us would have to work another day in our lives. Wouldn't that be great?

QUOTE]

Like the way you think, man!

How about this one?

• Give a Quarter million for every welfare recipient families, with the stipulation that they can never receive welfare again in their lifetime.

 

[ggunn]

Like the way you think, man!

How about this one?

• Give a Quarter million for every welfare recipient families, with the stipulation that they can never receive welfare again in their lifetime.

Well, even though they are a source of annoyance to all of us who work for a living, if every "welfare family" were cut off from the dole today, it wouldn't make a bit of difference to the predicament this country is in. It's deck furniture on the Titanic.

 

[kwired]

We have far too many people "making" money by moving money around and far too few actually producing anything.

Anything more I would say would be seen as political, so I will refrain.

I do have a solution to all our problems, though. Give every man, woman, and child a couple of million dollars to invest; we could all retire and live off the interest and dividends, and none of us would have to work another day in our lives. Wouldn't that be great?

QUOTE]

Like the way you think, man!


How about this one?

• Give a Quarter million for every welfare recipient families, with the stipulation that they can never receive welfare again in their lifetime.

I know of people that will have that spent in no time, and will find a way around the "never receive welfare again". If there is any way at all they will find it.

 

[ggunn]

I know of people that will have that spent in no time, and will find a way around the "never receive welfare again". If there is any way at all they will find it.

IMHO, we should focus on larger issues. Folks who take unfair advantage of the welfare system, reprehensible as they may be, are an insignificant part of the economic problem that this country faces. I could go on, but it would get political, and we don't want that in here.

 

[tallgirl]

..or non-sensical. Oh, the irony of it!:happyyes:

What is your personal, actual, direct, real professional experience with solar installations?

Or are you going on such notions as "people who don't speak English can't make holes in roofs so they don't leak", because that seems to be the basis for your (unfounded) assertions.