[TerryVierhout]

The solar energy is one of the ideal sources of renewable energy. This energy can be used incessantly as long as there is sun. It is believed that the earth absorbs nearly 3,850,000 exajoules (EJ) of solar energy. In one hour, the energy absorbed by the planet's oceans and landmasses is more energy than the world consumes in an entire year. With lower costs and increased efficiency of solar technologies, solar energy is becoming a rage in renewable energy market.

Solar energy can be tapped in two ways: Passive and Active. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and positioning buildings to maximize sun exposure. Active solar techniques use photovoltaic panels, pumps, and fans to convert sunlight into electricity.

Active technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies. Investment in solar energy can be done keeping in mind the favorable aspects of tapping sun’s energy and the ways of doing it.

[fizzissist]

~360watts per square meter.

How'd I do?

[mozmozmoz]

~360watts per square meter. How'd I do?

I dunno, what was the question? If you're talking insolation, 1000W per square metre peak, 250 average, but it depends a lot on all sorts of stuff.

My answer is: passive. Every time.

I'll accept a fan or pump if I have to, but since so much of the energy I use I want as heat it makes little sense to use intermediate forms with large conversion losses. I'm hanging out for the heat-powered air conditioning units to be available in smaller sizes because a 10kW unit would turn my house into a freezer. I suppose I could run the solar heating to counter it :idea:

[fizzissist]

...The minimum power output, not the peak or average, is the main factor governing solar power’s economic viability. The capital cost would be 25 times more than nuclear power. The least-cost solar option would require 400 times more land area and emit 20 times more CO2 than nuclear power...

http://carbon-sense.com/wp-content/u...-realities.pdf

[Geof]

...The minimum power output, not the peak or average, is the main factor governing solar power’s economic viability. The capital cost would be 25 times more than nuclear power. The least-cost solar option would require 400 times more land area and emit 20 times more CO2 than nuclear power...

http://carbon-sense.com/wp-content/u...-realities.pdf

What!! Heresy, Blasphemy; to the stake with the un-believer.

[mozmozmoz]

The least-cost solar option would require 400 times more land area and emit 20 times more CO2 than nuclear power...

Sure, since all they're talking about is the hardware. Take into account the lifecycle cost of the whole system and nuclear falls apart. And of course since we don't have nuclear powered mining machines we still need fossil fuels to run our mines etc, and in Australia their water consumption is a bit of an issue. Then if you like we can talk about the waste problem, and how breeder reactors are another theoretically possible thing that have been ten years away for the last thirty years. Excuse me, I'm feeding the trolls again.

[Geof]

.....and how breeder reactors are another theoretically possible thing that have been ten years away for the last thirty years. Excuse me, I'm feeding the trolls again.

Breeder reactors are not theoretical they are real. The reason they have not been used is because the fuel they use/produce can also be used for weapons.

[martinw]

Hello,

1100 watts per square metre is the maximum incoming solar radiation if you are sitting on top of Mount Everest on a cloudless day with your green energy gizmo pointing directly at the sun.

Oh dear, at altitudes where ordinary mortals dwell, there are clouds, and , at less than ideal times, there is daytime and night. Alas, the green gizmo probably does not track the sun either. So what is the average level of solar radiation available to a static gizmo optimally aligned? In the UK, I would hazard a guess at a lot less than 100 watts per square metre over the course of a year, day and night.

What is the conversion efficiency of PVs or water collectors ? About 10% tops overall.

You do the math, as they say...

Best wishes,

Martin

[Geof]

....What is the conversion efficiency of PVs or water collectors ? About 10% tops overall....Martin

You are too pessimistic I think. PV starts out at 15% or a bit higher for some of the newer stuff and I am not sure it degrades to 10% for a number of years.

Thermal collectors can be well over 50% depending on the exit temperature but I think the best overall for thermal through all the steps to electricity is in the region of 20% using focussing collectors and steam turbines.

[martinw]

You are too pessimistic I think. PV starts out at 15% or a bit higher for some of the newer stuff and I am not sure it degrades to 10% for a number of years.

Thermal collectors can be well over 50% depending on the exit temperature but I think the best overall for thermal through all the steps to electricity is in the region of 20% using focussing collectors and steam turbines.

Dear Geof,

OK my figures are ball park. I will not argue with the PV efficiencies. The solar water heating figures are based on flat panel domestic installations in the UK. There was a report published about six years ago which indicated a net yield of 2500 kWh per year from a number of (approx.) 1.5 metre square roof mounted panels. That represents a saving of about £120 a year at off-peak electricity rates. The installations typically cost £2000+ to install. Add to that, the cost of capital, maintainance and depreciation, and the economics look grim.

Large scale concentrating, industrial plants are a different ball game, but in terms of land useage, I would guess that the efficiency in output per metre square is no better than a domestic panel on the roof of a house.

Tin hat time...

Best wishes,

Martin

[Mariss Freimanis]

Far from ideal; solar energy is a miserable energy source. If it were, everyone would be falling all over themselves to replace oil with solar. That isn't happening so it means one of two things. Either people are too stupid to know what's good for them or there is something wrong with the premise of "free and renewable" solar energy. I humbly submit it's the latter.

Solar is 1,000W peak and 250W average per meter^2 insolation. At a 10% conversion efficiency, it is 100W peak, 25W average per meter^2, or 0.6 kWh per day on average. The sun doesn't shine at all at night and it shines poorly at dawn and dusk.

An average US household consumes 10,000 kWh per year or 27kWh per day. It would take a 180 meter^2 (1,920 ft^2) solar cell collector to meet this demand. Why so big? The sun doesn't shine at night. Forget about it on snowy, cold days in January. Sad fact #1: Electricity cannot be stored.

About storage batteries. It would take a 2,250 Ah 12V battery to store a day's worth of electricity use. That's 40 automotive type batteries and if it's overcast for 10 days, make it 400 batteries.

Solar cell panels cost about $5 per Watt uninstalled. 4,500W peak is needed so that's $22,500 uninstalled. Automotive batteries are about $100 for the 60Ah variety so that's another $40,000. Add $5,000 for the inverter (got to have AC instead of DC) and add another $10,000 for installation and wiring. You will need a special ventilated room in your house for all those batteries. You are up to $80,000 now just to set up a realistic solar energy home; I didn't count the value of the former bedroom you gave up to turn into the battery room. Sad Fact #2: Free, renewable solar energy costs a lot.

Automotive batteries last about 5 years. You have 400 of them. You will be replacing one every 5 days. Who sweeps the snow off of your solar collector in the winter? Who sweeps the leaves off in the fall? Who washes the dust off during the summer? Who repairs corroded wiring that is exposed to the elements? Who replaces panels when cells go bad? They are silicon after all; ever had a blown transistor? Figure on $8,000 a year in maintenance. Sad Fact #3: Complex systems cost $$$ to maintain them in a working condition.

Solar cell panels, inverters and batteries don't grow on ecologically friendly and renewable trees. They are manufactured. Their manufacture is energy intensive and involves the use of many "toxic" chemicals. Sad Fact #4: The up-stream pollution costs for all down-stream environmentally friendly solutions have to be taken into account.

There are over 300 million people in the US. Let's call that 75 million 4-people households. $80,000 times 75 million is 6 trillion dollars. The US GDP is 14.3 trillion dollars making this "investment" nearly 50% of the GDP for installation and 5% of the GDP for annual maintenance. Sad Fact #5: Free solar energy will make everyone poor.

Nuclear energy is the only sane choice once oil runs out and becomes too expensive. It integrates with the existing power grid.

Other than that, I'm all for solar energy. My Texas Instruments TI-36X scientific calculator runs off of a solar cell. Sadly a misname because it's never powered by the sun but rather incandescent light-bulbs and fluorescent lighting. I rarely have the inclination to use it at the beach so I don't bring it along. It is in fact a fossil fuel powered calculator.

Mariss

[martinw]

Dear Mariss,

Absolutely...

Best wishes,

Martin

[fizzissist]

I was just looking at some panels, and a 10Watt panel was $90 uninstalled, without controller.

With the cost of the hardware, installation and maintenance, the cost to power a home, amortized over the life of the system, would be about $.25/kwh....or almost twice the rate we pay here from our coal-fired utility.

[TomB]

Lang’s “Solar Power Realities” is like many other articles in the field of alternative energy, partially right and distorted because it takes a too focused viewpoint. As engineers we were all taught that we need to define the domain then address it. Lang defines the domain to be solar energy and gets an outlandish answer. But just suppose he had considered a combination of wind and solar. Wind tends to blow at night and it is normally much stronger on a cloudy winter day. (That’s not really a scientific based observation but as a skier and snow maker I know there are clear windless days on the mountain that are followed by night time winds that blow my man made snow where I did not want to put it down. Likewise, most cloudy ski days include enough wind that we have to watch the kids for frostbite.) Studies that address just the viability of wind power tend to show that it requires an outlandish generating and storage capacity because wind power is not maximum during the day. Combine the two approaches and you get a completely different answer.

Lang also casually compares the land use for solar with the land use for nuclear. Theses are not the same acres so the comparison is not very valid. Nuclear requires prime acres next to a river or ocean, while solar can use desert acres. I’m not sure if the use of desert acres is significant to very many people. (Don’t tell me about the ‘Protect the Desert’ Club in California, I‘ve read the story.)

Finally several comments have touched on nuclear because of spent fuel storage, fuel reprocessing or nuclear proliferation thoughts. Most of that is simple not true. France is and several other countries are or shortly will be reprocessing spent fuel. It can be done and like any other process would get more efficient if used. The Pu in spent fuel is a combination of Pu239 and Pu240 plus some Pu241 and Pu242. The odd weight isotopes will sustain a bomb reaction while the even weight isotopes poison it. No country has built a bomb by separating these isotopes. (The actual process used involved adding thin removable U238 blankets around the reactor. The blankets are removed after some U238 is converted to P239 but before a significant amount of the P239 has been converted to P240. U238 and P239 can be separated chemically while P239 and P240 require extensive centrifuge or diffusion separation.) The mix of Pu isotopes isolated during fuel reprocessing can be used to fuel a high speed neutron reactor and you get out heat and thus electricity while disposing of the boogeyman.

But all is not perfect with nuclear either. A reactor can not be turned down at night and up in the day. As such you have to have a place to sell nighttime power or you have to set the reactor output too low to meet 100% of daytime demand. Again you have to get back to hybrid approaches.

Tom B

[martinw]

I was just looking at some panels, and a 10Watt panel was $90 uninstalled, without controller.

.

Dear fizzissist,

There is something else that you should seriously consider. The invertor (controller), the electronic gadget that converts DC to AC. The box of electronics runs 24/7 even when there is no useful energy generated by the greenie gizmo, and the invertor uses energy all the time. There have been cases where the net electricity generated is negative. Over the long term.

Best wishes,

Martin

[martinw]

Dear TomB,

Sorry for being a nit-picker, and I am sure you made excellent points in that post, but can I take issue with this one?

Wind tends to blow at night

In the UK, an island, the lowest windspeeds are actually at about one hour past midnight according to the records. Night tends to be calm. Things liven up later as the weather rolls in from the West.

Best wishes,

Martin

[Mariss Freimanis]

There is only so much you can do with hot water. After you have showered, washed the dishes and your hands you are done with its utility. Stands to reason, its energy content is barely above background thermodynamic entropy.

Even heating your house this way has drawbacks. Due to solar's low energy content, a house has to be aggressively sealed and insulated against the environment. Sealing works both ways, while it keeps the cold out, it necessarily keeps pollutants inside. Depending on where you live, that includes natural but thoroughly radioactive radon gas. A house is not meant to be a sealed space capsule; the health of the inhabitants depends on the warm air inside being replaced with the cold air outside. Replacing warm air with cold requires more energy than solar has to offer.

Most everything else we depend on requires the near universal energy conveyor called electricity. It is way above entropy and therefore it is more difficult to obtain from solar (10% efficiency) and costs far more to maintain. The Third Law of Thermodynamics is always working against you (I call it the Las Vegas Law: You can never win).

The whole thing comes down to choices of energy. Diffuse against concentrated. Oil is concentrated, nuclear is concentrated. Everything else (geothermal aside) is diffuse because in the end solar driven: wind energy, direct solar, fuel instead of food (ethanol), algae farms, tide energy, burning wood, even hydroelectric, the folly list is endless.

Particularly egregious is any plant matter energy source (corn to ethanol). Like all lifeforms, the business of plants is to grow and procreate. Any residual energy left over from those two requirements is incidental and small if the plant is the least bit competent. If you have any question, compare the energy content of ethanol from an acre of corn versus the insolation energy deposited on that acre for the growing season time for that crop.

Mariss

[Mariss Freimanis]

Uh,.. You drop the control rods, absorb excess neutrons and you throttle the reactor back. Daytime demand versus night time demand is about 2:1, well within the throttle range of commercial nuclear reactors.

The sun shines during the day, not at all during the night. Wind power is even worse; the air can be a dead calm for a week, then blow harder than wind turbines can safely accommodate. They have to throttle back or you get that absolutely terrific video on youtube of wind turbine tearing itself to pieces, tower and all.

All these are highly intermittent power sources. The most stable is solar yet it has a 4:1 ratio between peak and average power. Guess what, to get the average power you must design the system to the peak value. That means a 4:1 overbuild and a 1:4 return on your investment. Bad facility utilization. It's like teachers taking 3 months every 12 months only far worse.

Mariss

[Santa Fe Al]

Hi All,

Just want to get my 2 cents in before this thing shuts down.

The following has been suggested every few years and, to the best of my knowledge, never acted upon. At least not in a serious manner.

Todays technology allows for drilling miles into the Earth. This would allow for the magma to heat water, or its equivelant. Pump the water through the heating system at the appropriate speed to the desired temperature to convert water to steam. Pump steam into a heat exhanger, etc, etc.

Basically, just like a fossil fueled or nuclear fueled power plant would work, except the magma heats the water. What's nice about this, is that there are many places on this Earth where water can be heated without drilling too many miles into the Earth.

Over the years, I have attempted to find out why this was never done. Itr seems to have fallen off the edge of the Earth. Is technology not up to par yet? Is it too expensive with present technology? Is there not enough profit to cost ratio to make it worthwhile? Why hasn't this been done at least once?

I would like to know.

Al

[mozmozmoz]

Todays technology allows for drilling miles into the Earth. This would allow for the magma to heat water, or its equivelant. Pump the water through the heating system at the appropriate speed to the desired temperature to convert water to steam. Pump steam into a heat exhanger, etc, etc.

It's being done, and it's a very old idea. Look at geothermal electricity - Iceland and New Zealand have both been using it since the 1960's. Using close to surface heat sources, because that's easy.

These days companies like Geodynamics in Australia are trying to commercialise the "first drill a hole" type, but it's less trivial than we'd all like to hope. Going to magma is hard work, so they're just going down to big hot rocks but the key part is "big" - past attempts have tended to stall when the rock they're using cools down so now they aim for rock that fractures easily (but not so easily that they lose all their water).

Broadly, it hasn't been done before because you do need to drill a fair way down so we had to wait for something profitable to develop the technology and also for deep earth imaging to be developed to the point where we can be pretty sure of what's down there[1]. Effectively it requires cheap second hand oil drilling gear to be doable. Once the technology is proved I expect that will change, but proving has been a long slow process - those holes are not cheap even today.

[1] "deep earth" in the shallow, anthropocentric sense of "further down than I can dig with my hands" rather than "most of the way into the planet". The deepest hole we've made is ~12km of the 6000km to the middle, and detailed imaging is still limited to ~2km on a good day.