Cost effectiveness of solar panels

[rescueme]

This is certainly an interesting subject, and more so since our local utility will be raising their rates in the future.

However, I've found (upon initial investigation) that the current technology, along with the price will not give us a payback until many years in the future (we're currently in our early 60's).

Since our home will be sold when we pass (proceeds to charity), we don't see any advantage to "converting" at this time.

IMHO, if you are young enough, can afford the conversion, and plan to stay in your home till the anticipated payback (plus) years, then go for it.

When we built our current (terminal/retirement) home in 1994, we added an additional $30k+ in items that then were considered “state of the art” (e.g. insulation, off-peak heating recharge, passive heat retention, etc.) Of course, as time goes on technology changes and our current home would be considered outdated (as compared to today). However, it does provide the environment that we want in retirement and we can’t see pursuing what is currently in style (we know that it will become passé in time)

[FUEGO]

Quote:

Originally Posted by samclem Right. As an example, the typical alternator in a family sedan (e.g. Toyota Camry) puts out 80 amps max. At 12VDC, that would equal 960 watts. And, it is not designed to do that for very long--it will get hot and not last very long. And it probably won't produce that much juice at idle, so you'd have to sit in the car with your foot on the gas. Reving a 100HP+ engine continuously in order to produce less than 1000 watts is not an efficient use of fuel. I also thing you'd want a direct connection to the battery or main bus, that cigarette lighter accessory plug in most cars probably isn't built for this much juice. A smaller inverter might work okay for emergency use in a typical car.

That was what I was afraid of. I doubt my honda civic's alternator could power a beefed up inverter for very long without burning out and without revving the engine. I guess I'll stick with the 120 watt inverter plugged into the cigarette lighter plug. At least I can power my cable modem, router, and netbook so I can log on here and post while the power is out.

[scrinch]

I've had my home's 3 kW rooftop PV system in use for 4 full years now, and so am getting an idea of the real economics of the project. The system gross cost was $20583 (material, labor, permits, new TOU meter), and the net cost after rebates and tax credits was $10678. Operating/maintenance costs over 4 years have been about $20...to buy a pole-mounted PV panel washer/squeegier. I've found that I lose 10-15% efficiency with the accumulation of 6 months of airborne grime. There has been no significant permanent loss of panel efficiency in 4 years, though. My pre-PV power bill averaged about $1000/yr, and now my average annual bill is almost exactly $0 (I owed $6 this past year). So, assuming no big changes in the price of power, the zero-return payout on the investment will be at about 10 years, and the lifetime IRR will likely be about 6-8% (depending on inflation, system degradation, maintenance, etc).

[NW-Bound]

Quote:

Originally Posted by Nords In an RV I'd think that the PV system wouldn't get much use unless you went full time, and gas is cheap by comparison. Quiet boondocking would be the best use I could think of, but again it might cost $6-$8/watt to install a PV system that could power lights and a fridge. The PV would have a terrible time trying to keep up with A/C. I don't know if the reduction in gasoline/generator use would ever recover your costs, and if RV solar is like home solar then no one will ever pay you for the feature on resale.

Audrey has answered your questions, but I'd like to add the 2 cents I have learned by reading.

Full-time boondockers want to enjoy nature in solitude, and do not want to stay on RV campgrounds. They also save money by not having to pay campground fees, though they have to visit once every few days for tank dumping, fresh water refill, and a luxurious shower. A PV would not be economical for weekenders.

I have not read of any RV'er being able to run a fridge from the PV+battery. It just takes too much power, so has to be run off propane. The electricity is sparingly used for microwaving, lighting, laptop PC, small TVs, etc... and must be carefully rationed.

The ammonia-absorption RV fridge is pain in the rump, though. It is expensive, slow to cool, and does not last long. I have read of class-A owners getting rid of it and plugging in a normal residential fridge. Now, they cannot stray far from a 30-A receptacle, but these owners seem to not care about not being able to boondock.

About the AC, it is simply not possible to have enough solar cells for an RV to have a self-contained AC.

There is also the problem with the surge load at starting. The induction motor inside the AC compressor typically needs 2.5X its normal current to start. Just by reading the wattage consumption of a typical 15,000-BTU/hr RV AC, same as a mid-size window home AC which is run off a 15A home outlet and hence by definition needs less than 15A X 115V = 1725W, one would think he can run it with a 2KW portable Honda generator. No, not so. One would typically needs a 4KW generator for the job, even though the AC motor is an inductive load and actually consumes less than 1725W. Additionally, generator ratings are stated for resistive loads (because the numbers look better), but the only resistive loads we use are incandescent light bulbs.

So, lugging around a 4-5 KW generator is no fun. When I buy an RV, I would not want to do without a built-in genset either. It is just too tough to do without, though I would rather use it just for emergencies. I have done a bit of reading and do not think that full-time boondocking is for me either. Too much of a spartan lifestyle for us. Our 2nd home in the boonies is close enough to nature. When traveling, we would want to stay close to the cities and their restaurants. Cajun food anyone?

Quote:

Originally Posted by audreyh1 As an EE who has designed power supplies for electronics systems...

Alright! Do you still have a Tek scope tucked in the basement of your Alpine? I was wondering if there would be room inside an RV to have an electronic bench with an antistatic top, and shelves for the instruments :-)

[audreyh1]

You are right about the extreme surge needs for the A/C starting up - in fact our generator has trouble switching both on simultaneously. We have to leave one off until the other starts running. If only I could program in a 15 sec delay between the two - darn! Just a tiny bit of additional intelligence needed in the controller to stage them....

We have no complaints about the performance of our absorption RV fridge (knock on wood that we don't jinx it, it is expense and we've had one serious repair). I'm really glad we don't have a residential fridge. When we are camping with 30A hookup, we actually switch it to gas because sometimes it makes a difference in being able to run both A/Cs.

No - no Tek scope hooked up to monitor our system, that was definitely a past life. You can just tell by absolutely no flickers and all electronics completely oblivious to any switching.

Our inverter is a Xantrex, and we also have a Surge Guard system monitoring shore power and switching over to the inverter if something goes wrong (here you might see momentary light-dimming if it's a brown-out type situation). Anyway - these modern RV power systems are very impressive.

We've done most of our boondocking either overnighting at Walmart on cross-country travel or because we are waiting somewhere for service and they don't have hookups or we got stuck somewhere over a holiday weekend and we are using the overflow camping area. At many of the most scenic locations if they have a decent road to get there, they also tend to have at least some minimal RV hookups, but even if not, we're set for quite a while.

The thing is, some of the serious boondocking areas can be pretty tough off-road situations or just roads not suitable for a heavier, larger RV or have campsites to small to accommodate a larger RV. We do a great deal of state/national park type camping because we really like to be out in the boonies and many of these places have some level of facility for RVs.

If you have a more expensive RV you absolutely do not take any risks with driving it on off road or on inadequate roads or in very heavily treed areas. This is where the camper vans and Class B type vehicles shine.

The only places I hear about serious boondocking is the BLM out in Quartzite and it always sounded like a madhouse so we never wanted to go there.

Audrey

[NW-Bound]

That explains why I have seen some RVs boast of having a genset capable to start both ACs simultaneously. Did not know it was a big deal.

No, Tek scope is for when one has the itch to troubleshoot that !@#$ piece of consumer electronics that fails :-) Perhaps time to sit down and design and add in that delay timer yourself?

[REWahoo]

Quote:

Originally Posted by audreyh1 You are right about the extreme surge needs for the A/C starting up - in fact our generator has trouble switching both on simultaneously. We have to leave one off until the other starts running. If only I could program in a 15 sec delay between the two - darn! Just a tiny bit of additional intelligence needed in the controller to stage them....

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).

[audreyh1]

Quote:

Originally Posted by NW-Bound That explains why I have seen some RVs boast of having a genset capable to start both ACs simultaneously. Did not know it was a big deal.

Some RVs come with a 10KW gen - wow! Ours is 7.5KW. But seriously, all you need is a short delay. Nope, I'm not touching the controllers in our RV - recipe for disaster! Who knows - there might be an upgrade to our H&AC controller box. Now we could replace that no problem - it's been a while since we looked at our options.

Some RVs have a "power management system" that can be set up to only run one A/C at a time - this would be a useful feature for camping with a 30A connection.

Of course there are some RVs out there with 3 and 4 A/Cs !!!!

It's too tough to mess with consumer electronics! Most of them are so cheap too. At most we've debugged some of the switches/solenoids in our RV and this was easily accomplished with a voltmeter/ohmmeter/ammeter. We more likely to have trouble with plumbing, wall leaks, mechanical components, hydraulics and our hydro-hot in our RV than with the regular electronics systems.

Audrey

[NW-Bound]

Kidding again. Yes, these things are now way too small and too complicated to fix. No schematic, no replacement parts. One would also need a SMD facility. It won't fit in an RV.

[Brat]

To hear you guys talk of a Tec oscilloscope brings tears to my eyes. What a great company it used to be.

[audreyh1]

Quote:

Originally Posted by REWahoo 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]

Quote:

Originally Posted by Brat 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]

Quote:

Originally Posted by Nords 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]

Quote:

Originally Posted by NW-Bound 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.

Quote:

Originally Posted by Brat 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]

Quote:

Originally Posted by NW-Bound 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]

Quote:

Originally Posted by 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.

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.