Solar on houses

[hokie66]

Maybe some of you smart folks in the tech pub can explain for me the logic of placing solar panels on the roof of a house.

There are obvious advantages of centralized power generation, so why would solar be an exception? I suppose it could be because you don't have to transport solar fuel, but is that really enough reason?

Residential solar systems are expensive to buy, install, and maintain. And then, if excess power is generated which could be exported to the grid, the existing grid sometimes can't cope (according to reports I have read).

I wouldn't want panels on my roof. They have limited life, and I imagine require a bit of maintenance during that life. What happens if you need to get at the roof for maintenance? Surely all those penetrations will create some leaks.

Is this all just a political stunt inspired by greenies? Most of these schemes have government subsidies attached at the consumer end, and some have backfired. The manufacturer subsidy end seems to be dodgy as well (Solyndra).

 

[zdas04]

In my industry we use a lot of solar panels for field automation in places where is too expensive to get access to the power grid. To me the same would hold for a home. If I had a mountain cabin that I would have to spend $100k to bring in line power, putting in a solar system might be just the answer.

When line voltage is readily available, it sure seems to be a Green PR stunt to me. I read about one family that didn't even have a way to store power, so they used the PV power during sunny days (selling any excess) and used grid power the rest of the time. As I recall from the story the payout was very long (maybe 25 years, but it has been too long since I read it to be certain) and I remember thinking that there was no way the panels would last that long.

The panels used for solar heating seem to be pretty marginal too (you need heat during the winter when the days are short and the weather has a higher frequency of cloudy days). I've never heard of anyones solar hot water system providing all the hot water they needed. Compared to an natural-gas powered on-demand hot water system the payout looks to be unacceptably long to me.

David

 

[ivymike]

There are power companies in Houston who'll lease the equipment to you, all service included (even roof leaks), for a fixed monthly rate. they even offer performance guarantees. Haven't quoted it. 20yr payback is about right for the owned systems I've investigated.

Have been thinking about installing a mini split ac unit for my garage, with all solar input. Seems like I should be able to leave it on all summer. Don't know pricing yet.

 

[csd72]

I am very interested in this discussion as my wife wants to put some of these on our roof. The UK government gives a gurantee on the rate that it can be sold back to the grid and the payback looks around 15 years based on that. Still havent got my head around all the issues.

I do understand why solar is encouraged on rooftops though as the centralisation of this would require large chunks of land whereas a rooftop requires no land layout.

Part of the problem in the US is that the traditional dirty sources are too cheap because the price does not reflect all the hidden costs.

 

[VEBill]

As far as know, the only way to achieved a payback period less than 'several infinities' is via government subsidies. In other words, residential PV systems not only consume more resources than they'll ever produce, they also consume government money. This makes them not only environmentally irresponsible, but also a contributor to the fiscal crisis. Once residential PV systems can actually pay their own way, then that will be a sign that they're actually achieving the point of environmental break-even.

The real solution is a moderate and variable 'carbon' tax on oil. That's the simplest solution that'll bring market logic into alignment with environmental goals.

PS: It's great to see all the new highly-efficient auto engines coming out now. Amazing! How come nobody is celebrating this massive change?

 

[Eltron]

Yeah, I see a benefit to solar in large installations and off-grid applications, but not so much in residential areas. I ran the numbers a while back on my current house, and even with subsidies it would have been a 20-year payback for enough pv cells to account for 1/2 of my usage.

As a southern friend of mine says: That don't make no kinda sense.

Dan

http://www.eltronresearch.com

Dan's Blog

 

[IRstuff]

Well, the question would be, "Where else would you install the panels, if not the roof?" I, for one, do not have 800 sq.ft. or so of empty land attached to my property.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[zdas04]

The 20-25 year payback is a common theme. When I've done the math, it only works out with a simple payback. If I discount it at the current AAA bond rate, it gets much more grim. In field use, I plan on replacing panels every 3 years (and batteries every year) and the only way I get positive economics is compared to the capital of running grid power to remote locations.

VE1Bll, your quote

Once residential PV systems can actually pay their own way, then that will be a sign that they're actually achieving the point of environmental break-even.

is absolutely right.

CSD72,
By "hidden costs" I'm going to assume you are talking about global warming, because everything else that I can think of is currently contained in the unit costs (including things like stack scrubbers and desulfurization equipment on coal plants). We can get back into that, but in several threads with a combined activity approaching 3,000 posts (many of the posts quite long), no one has convinced anyone else to change their position on AGW so it may not be terribly productive to start again.

David

 

[VEBill]

Many EnvironMentals don't seem to realize that the capital costs (in $ etc., before subsidies) are a pretty reasonable measure of the initial environmental impact of the system. If the fiscal output of the system can't pay back the capital, then that's a strong clue that the net environmental impact is also detrimental.

The Toyoto Prius springs to mind as an example of a 'Green wash' product that does more harm than good.

There's an EnvironMental Showcase Home a few miles from here that also proves the same sad point. It has some PV and HW panels on the roof, but they've added about $150k+ to the price of the house. They'd have gotten a better ROI from lottery tickets.

 

[BigInch]

You have to include an assumed electric rate inflation factor. You can't think that electricity will remain the same price for the next 20 years.

Most silicone crystal mfgrs will guarantee at least 80% of nameplate output for 20 years (linear decline of 1%/yr) and it should be expected that you will average 90%. Some of the latest studies suggest 95% after 20 years for the better panels. Panels can last up to 35 years.

Of course it is better to put them on a new roof, but they can be removed for roof maintenance if necessary.

In Europe it is not uncommon to see a 12 year payback, with no inflation factor for a kWh.

Many of the companies that are in the leaseback business package the debt, investment credits and tax writeoffs and sell them on to investors that can make better use of the credits than the average homeowner.

Net paybacks into the grid are one method of making a system 30% more affordable, paying back in 12 years rather than 20a, since no batteries are required which can add to the cost of about 30% to store the electricity. That is my biggest gripe with the Spanish system which requires that you chose either to use all of your own electicity, OR sell all into the grid. To me it is positive proof that the utilities own the Spanish legislators, as it makes private systems so costly since batteries are almost always necessary in a normal household, or unused daytime power is mostly lost. It also costs about 8000 Euros to get the design and permits to construct a grid connected system, whether it is 1 W or 10 MW. With that kind of deal the only feasible method to build is to use all your own power, generally requiring batteries, unless you have some kind of immediate afternoon power requirement for a cottage industry, farm or vinyard, some kind of irrigation pumping need, etc.

Solar power in Spain, where they have the most potential and most need for distributed power, as the grid is relatively weak for wheeling power around from city to city. They could do much, much better, but it is a club exclusively for the big boys .. as is so typical for Spain.

It seems to work VERY well in Germany, France, Italy and of course Greece, and I think England's proposed payback scheme was a good one too. At least it sounded like it would pay back pretty well the last time I heard about it. I would suspect that the Greek subsidy might have gone offline lately.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[VEBill]

According to some TV documentary that I saw, in Germany they're willing to pay something like 8x normal for green power. That legislated rate made (makes?) Solar very fiscally attractive. Unfortunately this masks and distorts the fiscal (and thus, also the environmental) trade-offs.

 

[msquared48]

Solar and wind do make sense to me if you are in the boonies with no utilities closeby and need power. You can start small and build your system gradually, making the panels yourself with components bought from the internet if you are handy. I intend to do just that.

The thing I do not agree with is "green roofs". Structurally speakling, I think the idea is seismically ridiculous and a big nightmare for roof maintenance.

Mike McCann
MMC Engineering

 

[hokie66]

I agree that solar power makes sense in areas remote from the grid. I wouldn't try to make my own, but...

IRstuff, the answer to your question is in a big solar power plant which feeds power into the distribution system, rather than on the roof of thousands of houses. The land area could be an issue in some areas of the world, but there are plenty of suitable spots. I don't think these stack up economically yet either compared to other types of plants, but perhaps in the future they will.

 

[stanier]

Without the subsidies it doesnt stack up on roof tops so why should we pay for the "feel good moments" of those who want them?

What about the cradle to grave carbon footprint taking into account the embodied energy of the devices?

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[LionelHutz]

It seems to me that subsidies are based on 2 things.

The party wants to look green, which I believe is the most important. They don't have to be green, just look it because most consumers don't understand that solar panels and Prius cars are not the solution today.

They may also be hoping that creating demand will result in cheaper panels one day.

 

[VEBill]

...cheaper panels one day...

That's easy. Have them made in China. One can save ~75% almost immediately.

 

[hokie66]

Most of the panels presently being installed in Australia are from China. A few made here, and the better and more expensive ones from Germany. So as well as not being logical economically, we are again just importing stuff we could be making here.

 

[KENAT]

Zdas - I swear I'd seen figures that made solar hot water look much more attractive than what you suggest.

Anyway, if my 'top priority' project works well, I may be helping to develop the organic/polymer solar cells which, while less efficient, promise to be much cheaper - if you believe the hype.

Given where I live (Mojave Desert maybe 45 minute drive from some of the big commercial solar farms/proposals) then I suspect my payback time might be a bit less than quoted above;-).

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[MintJulep]

Just noticed a little article in ASHRAE journal that claims that the installed cost of PV panels is decreasing steadily.

 

[MikeHalloran]

I'm waiting for PV panels to become competitive with shingles as a roof covering. Actually, the implementation rate could skyrocket if they just get competitive with 'wet' ceramic tile roofing.

I'm serious. If the panels can be made reasonably damage resistant and collectively waterproof, it makes no sense to bother installing a separate roof under them. That has to change the economics a bit.






Mike Halloran
Pembroke Pines, FL, USA