*Energy payback* on PhotoVoltaic solar collectors

Note this is ENERGY PAYBACK, not financial payback. It explores the question of how much energy is collected by different types of PV in relation to the energy used to build them.

This is a vital area of comparison that nuclear proponents prefer to ignore as they try to convince the public that nuclear is our answer to fossil fuels. The assessment is based on these articles and is performed by National Renewable Energy Laboratories (NREL). It is a down-loadable report you can search google and find: NREL Report No. NREL/FS-520-24619

Producing electricity with photovoltaics (PV) emits no pollution, produces no greenhouse gases,
and uses no finite fossil fuel resources. These are great environmental benefits, but just as we say
that it takes money to make money, it also takes energy to save energy. This concept is captured by
the term “energy payback,” or how long a PV system must operate to recover the energy—and
associated generation of pollution and CO2—that went into making the system in the first place.
Energy payback estimates for rooftop PV systems boil down to 4, 3, 2, and 1 years: 4 years for
systems using current multicrystalline-silicon PV modules, 3 years for current thin-film modules,
2 years for future multicrystalline modules, and 1 year for future thin-film modules. With energy
paybacks of 1–4 years and assumed life expectancies of 30 years, 87% to 97% of the energy that
PV systems generate will be free of pollution, greenhouse gases, and depletion of resources. Let’s
take a look at how the 4-3-2-1 paybacks were estimated for current and future PV systems.

An average U.S. household uses 830 kilowatt-hours of electricity per month. On average,
producing 1000 kWh of electricity with solar power reduces emissions by nearly 8 pounds of
sulfur dioxide, 5 pounds of nitrogen oxides, and more than 1,400 pounds of carbon dioxide.
During its projected 28 years of clean energy production, a rooftop system with 2-year payback
and meeting half of a household’s electricity use would avoid conventional electrical plant
emissions of more than half a ton of sulfur dioxide, one-third a ton of nitrogen oxides, and 100
tons of carbon dioxide.

With those sorts of paybacks, I'd imagine that solar energy would be used very quickly to power solar manufacturing facilities, which would further reduce the payback times.

I have seen people put them in the shade. The shadow of just one roof vent falling on one panel will shut the whole system down.

That's something most people don't understand.

Photovoltaic panels produce power even in the shade, even on cloudy days, even when it's raining, though not nearly as much as in full sunlight.

The idea that the shadow from a vent being cast on one panel will shut down the whole system is utter nonsense.

I work with a major US utility company in solar-related projects. One in 20 Americans is one of our clients. I have a system. I have a solar boat. I know a thing or two about photovoltaics.

You need to provide a link or citation.

Then, those of us here that know better can debunk the claim for the benefit of all readers.

Most utilities won't accept a gridtie system unless there was a proper shade analysis done.

Solar systems consist of a string or strings of solar panels. Shading just one panel drastically reduces the system output.

I'm not trying to spread misinformation I just want to see it done correctly. The worst possible thing to do to a customer is have them pay tens of thousands of dollars for something that won't work.



FYI,a hard shadow of something close. like a vent pipe right next to a pannel is a bad thing.

Based on what you wrote:

"The shadow of just one roof vent falling on one panel will shut the whole system down." The whole system???

That would have to be one huge roof vent! I sounded alarmist to me. I don't know how often a contractor places a system in the shadow of large permanent structures but i've never heard of it.

Even if a single cell or row of cells is fully shaded, you lose one module at worst and/or become a drain on the system, but not shut down the whole system.

From your link: "If even one full cell is hard shaded the voltage of that module will drop to half of its unshaded value in order to protect itself. If enough cells are hard shaded, the module will not convert any energy and will, in fact, become a tiny drain of energy on the entire system. "



Having said all that, your original comment, that "correct installation is everything", is DEAD ON.

And, I support your effort to inform potential customers and to warn them of the problems that can result from negligently planned and executed installations.

You may have noticed a number of members who do not support solar energy. I rail against them. I apologize for over-reacting if you are not among that group of naysayers!


:hi:

A hard shadow falling on one panel of a solar array consisting of one string of solar panels will go down...the output will be trivial...meaningless.

This is a really bad installation. The array consists of several strings of solar panels. The contractor had no idea of what they were doing.

Without hard numbers, it's absolutely meaningless.

Solar Pathfinder Demonstration

Solar Pathfinder Use

Solar Pathfinder Software

that power my co-ops well take a big hit in output when clouds move overhead.
Normally,in clear sunlight,it produces power at around 35-38 volts.When clouds obscure the sunlight that number drops to around 10 volts.That is low enough to shut off the controllers for our system
Then again,these are ten year old cells.I have seen newer cells that do a lot better.I have seen a demo setup of the latest and greatest cells produce 30 volts and half an amp of power on a totally overcast day.
Proper testing and installation is crucial.A house I am working on was deemed unsuitable by a solar company after they did their sunlight survey due to to much shade from trees.The homeowner almost wasted tens of thousands of dollars until me and a roofer talked him into getting surveys done befor buying a system.

or grass grows up in front of the array low to the ground. It's easy to lose effiecieny, but when i works right it is a dream. There is no electric hum. I used propane for the refrigerator and there was no sound at all.

Check your output. Clean the dust/dirt off when the output drops.

Site them properly and check their performance periodically and they will give you years of excellent performance.

they are so pretty when they are first washed off...so shiny

Who travelled around the country fixing expensive commercial photography machines.

He used a UPS truck to get from one state to another, and often lived in his truck as well.

he had an array of solar cells that he had placed in a serial circuit to produce 12 Volts worth of power. These were small enough to fit inside a backgammon set, and he would plug his specially adapted coffee pot or stereo into this circuit.

Now he paid about $ 200 for the cells - but they were guaranteed for 150 yesars - he planned on his great great grand kids to use them!

He loved the free electricity - and also that he could have that 12 Volts no matter where he was - at the edge of a canyon far from a utility line - he still had stereo and hot coffee.

construction option for new homes.

It is literally CRAZY that we haven't already been doing this for 20 years. It is beyond lunacy that we aren't even considering it now.

I would love to put solar panels on my roof and install that switch that automatically clicks back and forth between solar and grid depending on what is available, and withthat function, so they say, that will allow you to return excess energy BACK to the grid during times when you aren't using it all.

They say the meter spins backward when that happens. Gawd, I would love to see that one day!

But for the moment, solar panels are prohibtively expensive unless a person is Uper Middle Class or at least Moderate Wealthy.

For me to buy solar panels on my own would liquidate much of my savings. Sorry, I very much want solar panels, but I won't risk my emergency funds/nest-egg to do it.

Now, if they had been built with my house and I was paying for them as part of the mortgage...

It's a pity, nationally a tragedy, that here is one way we could decrease our oil dependancy and CO2 emissions in one fell swoop with technology that has been available for two decades, maybe more.

And yet, no one has gotten this simple thing, which would payback so many dividends so fast, done.

Sigh.

this year, an outfit called Nanosolar got a continuous-flow, thin-film production line running, dropping prices into the $1/watt range. Their production is sold out for a year into the future - all big commercial installations. You can't buy it yet for residential.

The last time I priced an old-fashioned, cut-silicon-wafer system, it was running at about $8/watt installed. At the ~3 kW needed for average US household electricity consumption, I was looking at a $25k system cost to save myself about $1,200/year. (21 year payback time) I could not justify that, except on environmental grounds.

But, cut that by a factor of 8, and payback is 3 years. I, and everyone else who is sane, will do that.

arendt

I keep hearing about their orders pegged and then some meaning they have hit something pretty damn good.

It's like the Wii even today it is sort of difficult to get one in some areas more than a year from release. The difference is a Wii isn't a must have. Energy is.

...why are you OP'ing a paper from 1999? Isn't there anything more recent?