PV Gap

Ruben Said:

Saran wrap on solar heating system?

We Answered:

If you had a picture it would be better to diagnose your situation. Also it might make a difference where you are located and what you are heating, hot water or house heating.

I would guess you live in a relatively warm environment with little or no freezing and you are heating hot water. Yours may be a Thermo-siphoning system (doesn't use pumps) and may work quite well on some days but not enough of the days for you so you are trying to make the system more efficient.

There are 3 main types of solar thermal collectors. The latest are vacuum tube collectors. These produce high temperatures and work better in cold and cloudy conditions. The next would be flat panel collectors. These typically have a collector surface located in a box with glazing over the top of the box. The last would be some sort of open loop that may be placed on a roof. This last is the simplest and the least effective.

The primary issue is heat gain vs heat lost. The considerations are the way heat is transferred by convection, conduction and radiation. You want your collector to heat up and then transfer heat to the medium you are using to move the heat to a useful place. But as the system heats up it will tend to lose more heat to the surrounding environment.

A box collector makes several improvements over open tubes. A flat black collector area will absorb more of the sun's radiation. If the area is conductive like copper sheets painted black it can then conduct heat to the copper pipes it is in contact with. But as the collector area becomes hotter than the surrounding environment the heat loss also increases. Glazing changes this my making a little micro environment within the box. Glazing helps to hold the heat against convective losses. Some sunlight is also bounced off of glazing.

In cold environments double glazing is important because the losses are greater and the heat gain may not be as much as a warmer environment. Glazing is like insulation as it prevents heat loss. In general it is better to insulate at night than to add a second layer of glazing. This is because glazing blocks some solar radiation.

The difference between different forms of plastic as glazing and glass is slight. Glass may be more conductive for heat loss but it also allows more light to enter and is opaque to infra red radiation.

But glazing is only going to work if their is a relatively air tight environment. There has to be a box. Just putting glazing on top of exposed pipes is not going to be as effective.

Timothy Said:

Is it true that the other planets in our solar system are heating up too?

We Answered:

There are three fundamental flaws in the 'other planets are warming' argument. Not all planets in the solar system are warming. The sun has shown no long term trend since 1950 and in fact has shown a slight cooling trend in recent decades. There are explanations for why other planets are warming.The basis of this argument is that the sun must be causing global warming and in fact, warming throughout the solar system. There are several flaws in this line of thought. Firstly, the characterization that the whole solar system is warming is erroneous. Around 6 planets or moons out of the more than 100 bodies in the solar system have been observed to be warming. On the other hand, Uranus is cooling.Secondly, the theory that a brightening sun is causing global warming falls apart when you consider the sun has shown little to no trend since the 1950s. A variety of independent measurements of solar activity including satellite data, sunspot numbers, UV levels and solar magneto grams all paint a consistent picture. Over the last 35 years of global warming, sun and climate have been moving in opposite directions.Martian climate is primarily driven by dust and albedo. Global dust storms increase the surface albedo by settling brighter dust on dark surfaces. Higher albedo leads to more sunlight being reflected which has a cooling effect. Snapshots of Mars' surface in 1977 and 1999 find that the surface was brighter in 1977 and darker in 1999. However, this doesn't necessarily point to a long term warming trend - the 1977 snapshot was made shortly after a global dust storm while the 1999 snapshot occurred before a dust storm. Consequently, there is little empirical evidence that long term global warming on Mars is occurring.Neptune's orbit is 164 years so observations (1950 to present day) span less than a third of a Neptunian year. Climate modeling of Neptune suggests its brightening is a seasonal response.Eg. - Neptune's southern hemisphere is heading into summer.Neptune's largest moon, Triton, has warmed since the Voyager space probe visited it in 1989. The moon is approaching an extreme southern summer, a season that occurs every few hundred years. During this special time, the moon's southern hemisphere receives more direct sunlight.Jupiter's storms are fueled by the planet's own internal heat (sunlight is 4% the level of solar energy at Earth). When several storms merge into one large storm (eg - Red Spot Jr), the planet loses its ability to mix heat, causing warming at the equator and cooling at the poles.Pluto's warming is not clearly understood. Pluto's orbit is much more elliptical than that of the other planets, and its rotational axis is tipped by a large angle relative to its orbit. Both factors could contribute to drastic seasonal changes. As Pluto's orbit is equivalent to 248 Earth years and observed warming spans only 14 years, it is likely this is a seasonal response.

As far as your second question is concerned,yeah,the sun's activity is winding down, triggering fevered debate among scientists about how low it will go, and what it means for Earth's climate. NASA recorded no sunspots on 266 days in 2008 - a level of inactivity not seen since 1913 - and 2009 looks set to be even quieter. Solar wind pressure is at a 50-year low and our local star is ever so slightly dimmer than it was 10 years ago.Sunspots are the most visible sign of an active sun - islands of magnetism on the sun's surface where convection is inhibited, making the gas cooler and darker when seen from Earth - and the fact that they're vanishing means we're heading into a period of solar lethargy.

Clara Said:

Which of these methods of heating a planet is least likely to decline over the lifetime of the Solar System?

We Answered:

E- Gravity does not grow weaker nor does the mass change that much.
I am defining the lifetime of the solar system as up to the point were the sun goes red giant because at tha point, the 3-4 inner planets might be vaporized.

Accreation is over, radioactive decay get weaker as less material is around to decay, and the sun will remain relatively constant by my defined endpoint. So I guess c could count as well.