Cost effectiveness of solar panels

[audreyh1]

I'm surprised to see this. Our RV has a built-in controller that staggers the start up of our two A/C units whether we're on shore power or running the generator. I thought that was SOP on all dual A/C RV's, but I suppose not. (This is our first).

I guess not, even though it seems like an obvious thing to do. We have the Dometic Duo-Therm "Comfort Controller" and I would expect the brains to be in there.

Audrey

 

[Nords]

Thanks for the RV info, everyone. I was wondering where all those propane fridges were being sold.

And as for the PV payback, it's always better to reduce your consumption through a home energy audit, solar hot water, upgraded (reflective) insulation, EnergyStar appliances, and maybe even new windows.

Our PV inverter is a Xantrex, too, and I guess its conversion algorithm is a lot more finicky than I realized. Our array pumped out over 10 KWHr yesterday with less than 10 hours of sunshine, although history for this time of year has been more like 7-8 KWHr. I'll need a couple months of data before I'm ready to declare victory, but the trend is encouraging.

 

[NW-Bound]

We had solar hot water on our roof in Portland, in a shaded area. That puppy melted dip sticks and blew off steam regularly. This was a while back and I see the current home owner has removed the set-up. Based on my experience, it doesn't take much of a system to get water boiling. Doubtless there are better control systems today.

And you are in Portland! Imagine what you can get in the Southwest. Solar water heating is simpler, less expensive, and more efficient than PV electric. It should be investigated first. Some countries like Israel will not issue a building permit if it does not include a solar water heater.

If solar water heating is a no brainer, why hasn't it been more popular? It was in the early 80s, after the oil crisis, but then died out. Simple as it is, it still requires some maintenance. I have had solar water heating in my houses since 1980, but finally lost my panels due to some dumb overlook. I am still kicking myself over it. My story was told here.

http://www.early-retirement.org/forums/f27/solar-hot-water-heater-45665.html#post843159

 

[NW-Bound]

Audrey and REW have said a number of times that they don't do their scale of RV to save money, although I guess some full-time RVers manage to reduce their housing costs...

Just a brief sidetrack from PV discussion if I may.

In some posts, I half-jokingly talked of moving into an RV to save money. Does that contradict what other posters say? Not so. Still an armchair RV'er here, but I have learned a few things by reading.

There are different types of RVs, as well as different types of houses, of course. R-i-T and REW use theirs for vacationing. Even with the smallest RV, you DO not save money compared to the traditional fly-and-hotel accomodations. I am trying to make the case for long treks, but it still looks iffy due to the gas cost.

Even for a full-time residence, you lose big money if you buy a new RV. No doubt about that. The depreciation of RVs makes me cringe when I shop around. Of course people buying new know that, and are willing to pay for that intangible pleasure. I do not know if I would like RV'ing that much, and in fact still reluctant to buy a good used one.

The only way you save money with RV-full-timing is to get a clean used class C, do not drive it much, and boondock as much as you can. It's not for everybody, though I do see the allure of it. By the way, many of these are single guys. I can see how. I would have to drag my wife out, while she was clinging to the drapes of our stick-built house.

 

[brewer12345]

Hmmm, I guess life is all about choices NW. For our short trips (a week and under), our small trailer is pretty economical at least as far as marginal cost is concerned. Its hard to tale a family of 4 and 2 dogs anywhere for $100 a weekend, but in decent weather this is a regular thing for us. But even if it cost more we would still go on our trips.

 

[Brat]

Back to solar panels... I hear that their efficiency is increasing and cost per KW decreasing. They will be cost effective options for many more conditions soon.

I think that we are so enamoured by technology that many are overlooking water heated by solar as another energy source.

 

[Nords]

If solar water heating is a no brainer, why hasn't it been more popular? It was in the early 80s, after the oil crisis, but then died out. Simple as it is, it still requires some maintenance. I have had solar water heating in my houses since 1980, but finally lost my panels due to some dumb overlook. I am still kicking myself over it. My story was told here.

Maintenance?

We found our two 4'x8' water panels on Craigslist. When we arrived (Kahuku country, an hours' drive from the house) we learned that they'd been sitting in a vacant lot for about a decade after being used for "a while". But hey, I have engineering training. I know how to rig up a hydrostatic test system to see if they leak, and I can solder copper. We bought them for $75 (the copper is worth more than that, let alone their function) and took them home. They spent the weekend at 75 PSI. When I put them in the sunshine you could watch the pressure gauge rising. I figured we'd be OK at our house pressure of 60 PSI.

When we were mounting the panels we found a couple label plates from a California solar company. I called our local solar company and found out that the panels had been made in the mid-70s.

We bought the solar water heater & pump for $50 from a guy in Waialae Iki (another hour's drive). It was three years old and the anode rod still looked perfect. I had to use a little mechanical agitation to get the pump going, but it worked fine once it was wet.

Our house was "pre-plumbed" for solar water. That meant there were two pipe stubs in the garage and the copper piping went through the attic to the underside of the roof. Unfortunately one end of each pipe was open, not capped, so who knew what had crawled in there during the 15 years they'd been sitting around. But, hey, I knew how to blow out piping and I had a dive tank full of air. 100 PSI was enough to blow out all the centipede carcasses. After that it was just a lot of soldering and connecting the thermocouples for the temperature controller.

We haven't done a lick of work on the system in the five years we've had it. The foam pipe insulation is getting pretty brittle from the UV, but we already have more hot water than we can possibly use. I'll get around to replacing the insulation when it crumbles to the touch.

I think that we are so enamoured by technology that many are overlooking water heated by solar as another energy source.

Hawaii just made it a state law for new construction as well.

 

[NW-Bound]

The solar water heater is usually simple and takes little maintenance. However, failures due to the panels freezing are ALWAYS catastrophic.

The typical systems that were sold in AZ in the past used a bimetallic thermal switch contact to sense near-freezing temperatures. If the switch fails to snap when it is supposed to, you do not know you've got a problem until a freezing night.

This anti-freeze electrical switch is embedded in the panels. An average home owner usually does not know to remove it to test in a glass of ice water, using an ohmmeter. And how often should one climb up to the roof to remove it for testing?

 

[Nords]

The solar water heater is usually simple and takes little maintenance. However, failures due to the panels freezing are ALWAYS catastrophic.

Yeah, I'm blissfully ignorant of that one...

 

[youbet]

Hmmm, I guess life is all about choices NW. For our short trips (a week and under), our small trailer is pretty economical at least as far as marginal cost is concerned. Its hard to tale a family of 4 and 2 dogs anywhere for $100 a weekend, but in decent weather this is a regular thing for us. But even if it cost more we would still go on our trips.

Brewer,

We went ahead and ordered the A-Liner I mentioned in another thread. You mentioned you'd be interested in an update if we did so. I'll put something together with a pic or two if there is any interest.

I've been reading the owner's club board and have been surprised by the level of modifications going on including many of the heating, cooling, refrigeration, electrical (including solar panels) and boondocking suggestions mentioned here.

NW - note, this is camping with your butt off the ground as opposed to "RVing."

Nords - Sorry for the hijack. Carry on. Very interesting.

 

[brewer12345]

Brewer,

We went ahead and ordered the A-Liner I mentioned in another thread. You mentioned you'd be interested in an update if we did so. I'll put something together with a pic or two if there is any interest.

I've been reading the owner's club board and have been surprised by the level of modifications going on including many of the heating, cooling, refrigeration, electrical (including solar panels) and boondocking suggestions mentioned here.

NW - note, this is camping with your butt off the ground as opposed to "RVing."

Nords - Sorry for the hijack. Carry on. Very interesting.

Cool! I would be very interested in how it works, how you like it, experiences, etc. Our hard sided trailer is not a lot above an A liner in terms of amenities, and I am always interested in alternatives.

 

[inquisitive]

With the cheaper alternatives for solar cells, what would be the current ballpark cost to cover the roof of an average-sized house entirely with solar cells?

Cost of installation?

Right now it is 94 degrees outside and ~ 87 degrees inside. I live in a 3rd/4th floor condominium converted from a house. I'm wondering how much cooler it would be if all of the sunlight beating down on the roof was not there (ie hitting solar panels). While it might not make sense if I was using it just for the electricity, the question is could it significantly cool down the house?

Does it matter if I have a slate roof?

 

[Brat]

Kill a slate roof? Remove carefully, there is $$$$$ in those tiles!! For God's sake don't walk on them. Have them removed by a professional slate tile roofer (society member) but bid it out - there may well be cash coming to you.

That aside, the roof is a common asset so other owners must consent.

Frankly I would wait a couple years, solar panel technology is rapidly improving and costs are being driven down.

 

[samclem]

With the cheaper alternatives for solar cells, what would be the current ballpark cost to cover the roof of an average-sized house entirely with solar cells?

Cost of installation?

Right now it is 94 degrees outside and ~ 87 degrees inside. I live in a 3rd/4th floor condominium converted from a house. I'm wondering how much cooler it would be if all of the sunlight beating down on the roof was not there (ie hitting solar panels). While it might not make sense if I was using it just for the electricity, the question is could it significantly cool down the house?

Does it matter if I have a slate roof?

I'm with Brat--messing with/carving up a slate roof in order to save a tiny amount of energy seems very extreme. As far as heat transfer, you'd be better off (winter and summer) to add some additional insulation up there and possibly improve ventilation in the attic. If it is often hot where you are, then installing a radiant barrier in the attic might make sense, but usually added insulation is the better bang-for-the-buck.

 

[Nords]

With the cheaper alternatives for solar cells, what would be the current ballpark cost to cover the roof of an average-sized house entirely with solar cells?

The "Rain-Man" answer is $30K without air conditioning and $60K with A/C. But you don't want to rely on those numbers because they don't apply to your particular situation.

Federal tax credits can reduce this cost by as much as 30% and state credits can knock off another 30-40%. It depends on the total system costs and on how the systems are installed (all at once or over several years). Then there's the issue of your payback-- it's fairly quick at 25 cents/KWHr (less than two decades) but a lot longer at eight cents/KWHr.

Another issue is how much of a system you need. It's always cheaper to reduce your consumption than to build a bigger system. Ask your local utility about a whole-house energy audit before you start pricing photovoltaics. Consider investing in solar water heating, energy-efficient insulation/windows, house-shading landscaping, and EnergyStar appliances before you buy a panel.

Cost of installation?

Again the Rain-Man answer is that installation has usually been about 50% of the total cost, but you're asking the wrong questions. You want to know about the total price and the quality of the installation & materials. Make your comparisons on the basis of the equipment and the durability of the techniques, not on the price of the installation. There are many cheap/fast installation techniques that will "save" on the costs, but will also come off your roof over the next 10 years (or at the first hurricane/snowfall). If a contractor is selling his cheap installation, then you don't want to use that contractor. You want the guy who's invested in advanced training, techniques, and tools... one who will also warranty his labor & materials for a long time, and be around to honor the warranty.

Right now it is 94 degrees outside and ~ 87 degrees inside. I live in a 3rd/4th floor condominium converted from a house. I'm wondering how much cooler it would be if all of the sunlight beating down on the roof was not there (ie hitting solar panels). While it might not make sense if I was using it just for the electricity, the question is could it significantly cool down the house?

I don't think it makes much of a difference, at least not on our house. South-facing roofs are the hottest parts of the house to begin with, so cooling them 10-20 degrees won't make much difference in the heat transmitted through the roofing materials. We saw that reflective foil roof insulation and good wall insulation will make a much bigger difference than the blocking effect of the PV panels.

Does it matter if I have a slate roof?

Holy cow, I'll say it matters.

First, any sunlight hitting the slate is very efficiently transformed into heat and transmitted to all other parts of the roof. So covering half of your roof with PV panels might reduce the solar impact on the slate but it'll just allow the remaining exposed slate to transfer its sunlight heating to the other half that much more quickly. Net effect won't be noticeable. You'll only keep the heat from coming into your attic by installing radiant foil roof insulation and good wall/attic-rafter insulation.

Second, slate roofs are expected to last 75-100 years. Have it thoroughly inspected/repaired by a slate-roof expert before you let any solar installers up there. Make sure the slate guy knows what you're planning so that he can make the appropriate recommendations & repairs. Then invite him back after the solar job is done to check that no new problems have been created.

Third, I suspect you'll have a terrible time finding a solar contractor who knows how to handle a slate roof-- let alone one who has the proper tools & roof racks. Their profit margins depend on speed & efficiency, and they're optimized for composition shingle roofs. You're looking at high-end custom racks with special mounts and painstaking installations, plus scaffolding and additional safety gear to move around up there. I doubt that they would want to drill through the slate tiles, which means that they'd have to remove some of them or build around/over them. I'm sure that they could eventually figure out what they need to do, but it'll be expensive.

An option for a slate roof might be photovoltaic roof tiles, not PV panels. This would involve removing slates (or clipping/gluing the PV tiles on top of them) and not using racks at all. However the PV tiles aren't used very much and are at least 2x-3x the price of PV panels. Again it's a lot of finicky work.

The best long-term option might be to ditch the slate roof and start over. You could build the new roof the "right" way, with insulated/reflective foil/foam panels under the sheathing, and add in the mounts for the PV roof racks as you're putting the roof together. While you have the roof off you might get more access to the walls for adding insulation (if necessary) to minimize heat intrusion. You could also route conduits for ceiling fans and photovoltaic cables instead of having to mount them externally to the ceiling/roof. The new roof would have ridge vents or solar-powered attic-exhaust fans to keep the voids cooler and reduce heat transmission to the house ceilings. You could use reflective shingles to drastically reduce the heating effect in your house, which should cut way back on cooling costs. Or you could go aluminum with integrated PV panels. But while the result would be elegantly integrated and aesthetically pleasing, it might not meet neighborhood style codes and could be horribly expensive. In this case, though, the "expense" would be in the up-front costs of doing it right instead of in the years of dealing with all the compromises of mounting PV racks on a slate roof.