Any of you guys have experience with solar energy systems?

[nateflanigan]

I've been thinking it would be a fun science experiment  to set up a small solar and battery array on my roof to power a window unit AC.  Just looking around online it looks like this would cost several thousand dollars.  If I could charge the batteries during the day then run the AC in my bedroom overnight that'd be pretty cool right?  Even if this is impractical if anyone has any advice on which vendors/products are reputable it's still fun to look at and think about.


The window unit draws about 5 amps.

[shooter]

I set up a 800watt array, charging 12 marine batteries, used an Outback Charge controller and a 3kw modified sinwave invertor.   I ran about 500watts of leds pretty well overnight.  Also ran my electronics shop, so most of my amps are green

I would NEVER roof mount my array.  The biggest reason for me - SNOW, it takes a day or 2 to build enough heat to get the snow off and since I've fallen from a roof in my younger days it just didn't make sense.  The odd thing, I took the tax credit back when it was 40% but the "law" stated the array must be roof mounted, I lied!

I since disassembled the array, mounted 400watts of panels, 4 batteries, charge controller and invertor on my red-neck camper and it worked great for water/filtration, lights, refrig, music etc, just couldn't handle a heater for more than 10min per hour.
The initial system set me back about 4K and saved me on average 15cents a day, about the same return I get from paying  taxes

[PRR]

> cost several thousand dollars

In that area. Perhaps more with batteries and the DC-AC conversion.

> window unit draws about 5 amps.

600 Watts? Sounds puny.

I'll assume 8 Amps at 120V, 1KW, for easy math.

1KW for one hour is 1KWH.

I pay at most $0.16/KWH for utility-company power.

8 hours a night, 100 nights per year, is $128 per year. (And an appropriately sized A/C should not run ALL night EVERY night, it should cycle on the thermostat.) $1,280 over ten years. And pay-as-I-go (weeks after I burn the power).

The solar system will be, as you say, "several thousand dollars".

Say that "several" is "3". $3,000.

That will have to be paid Right Now (this month on a credit-card).

It is not fiscally smart to pay up-front for a break-even many years down the road. Compare it against putting your money in the bank at interest. Even at today's pathetic rates you could probably place $3K long-term and get $100/year of interest. That almost covers the electric bill, and at the end you still have $3K.

If the solar array was a really LONG term investment, you might figure it different. I've gotten into 30-year mortgages to get a roof over my head. Houses usually last longer than 30 years (my last had survived 177 years) and usually have some resale value (mine doubled in sale-value in 19 years). The super-good solar cells used in spacecraft may last that long (though I think they do fade over decades). Consumer grade are not so defect-free, not so well sealed. By 5 or 10 or 15 years out you are replacing individual cells (messing with the panel seals and fragile solder joints). By 2025 (maybe sooner) you will be seeing better panels at lower prices, and toss the old ones. Very bad fiscal pay-back.

Since you want the A/C in evening and night, when the sun don't shine, you will need a battery. A car battery is rated 50 Amp Hours at 12V. At 120V that is 1 hour running your 5A A/C. So you need 8 or 10. Plus DC/AC conversion, say 11 or 12. But car batteries are not built to be drained flat every night. There are Deep Discharge batts made for the purpose. They are about twice the weight and cost per AH as car batts. So figure two dozen car batts, that's at least $2,000 just for batts. And for-sure they will be losing capacity in 5 or 10 years, need complete replacement.

So... "several" thousand dollars (perhaps $5K total), to save $128/year. That's a 39 year payback. And zero end-value (you'll probably pay to have the dead panels and tons of dead batts taken away).

There's also the fun of working on roofs, snow, dust/dirt/pollen! or giving-up garden/lawn space for solar arrays.

(I grant that snow may not matter in an A/C only application; tho we had snow upstate just a week before we had a steamy day on the coast.)

All this assumes you HAVE utility power. If you are back in the woods, it may be $20K on up to bring a power line to your house. If you want to light a shed it may be $500-$2K to get a proper/legal electric line run out to the shack. In such cases it may make good economic sense to run solar.

OTOH, I always am amazed at the school-zone flashing lights which have a solar panel, yet are right UNDER a power-line. Yes, the daily demand is super low (100 Watts 20 minutes a day?) and getting a power-drop may be more costly than a solar panel and a battery. (Around here the lights may be under a 13,000V line but the nearest 120V power is hundreds of feet away, and cable mechanically appropriate for overhead runs is electrically way over-kill for small loads.)

But maybe you just want to Save The Planet?

Are you? Burning coal (oil, gas) to make utility power is dirty, true. But making large-area semiconductors is dirty in other ways. One reason semi production moved out of the US is the pollution it causes. It has moved around the world, and gotten a bit better, but still un-clean. It may be mostly "local" pollution: pools of toxic waste behind a factory in China instead of smog in your area. I'd want to know more about this trade-off before getting too virtuous about it.

And the lead batteries, though lead-batts tend to be 98% recycled. The batt-factory takes back the trade-ins, chop and melt, neutralize the acid and sludge, and build new batts. (LiOn etc offer more energy density, but still less KWH/$, and the recycling process is not so well developed.)

[PRR]

I didn't see your post before I wrote the above.

system set me back about 4K and saved me on average 15cents a day

$0.15/day is $55 per year.

$4,000/$55 is 75 year break-even.

Since costs and benefits WILL vary widely, my "39 years" wild guess and your 75 year prediction from actual practice are remarkably close agreement.

In energy-saving appliances, we usually want payback in more like 5 years. Here in Maine (and maybe where you are), I got the low-efficiency A/C because the $10/year savings will not justify the $100 extra cost for high-SEER any time soon. OTOH I willingly paid for really-high (96%) efficiency on the Heating side, because it may pay-off in a few years. (Not that simple because I also changed fuels for sheer personal preference.) My friend in Texas sees it the other way: A/C costs suggest all the SEER you can find, but the heat is trivial (and probably 80%).

about the same return I get from paying  taxes

Canada has not invaded the US since the gang in DC got a substantial tax base. If we paid no taxes, you might want to erect walls and mount canons to keep the Canadians away from your land. Generally a tax-supported army is cheaper over-all than every home a well-defended castle. (Tho where I sit, closer to Canada than most of the US, if the Canadians invaded I'd buy the beer.)

[nateflanigan]

Thanks for the input guys.  The 5 amp window unit is pretty puny, my bedroom has an old bay window, the large center panel doesn't open anymore, the side panels are pretty narrow.  So I can only fit about the smallest AC unit available.  The motivation for the idea was really just science/fun.  But several thousand bucks is too steep for that, and a little array that charges my laptop just isn't very exciting.  I'm in philadelphia, so snow is a concern.  Oh well, back to building amps.

[DummyLoad]

something to think,about....
http://www.teslamotors.com/powerwall

--pete

[shooter]

$4,000/$55 is 75 year break-even.

That was a time in my life when I had disposable income

I did a lot of experimenting with it, taught a few people about the ins and outs of solar, including the how impractical it is/was at the rates I paid.   I also built a 500W wind system, just as impractical in my windless zone, but the pieces parts were mostly free.
We're prone to power outages about 5-10 times a yr for 24hrs or so, so it was very handy for lighting, I designed n built a rainwater, micro controlled solar powered toilet flusher so I wouldn't have to lug 5 gallon pails of water. And it is great for back-country camping, or Wal-Mart parking lots.  Bottom line PRR is right, even the bankrupt goldmine I'm holding stocks on is making me more money than solar saved!

[MadMax]

Since we're on the subject, I have a solar question I hope someone can answer. Since solar energy is created in the form of DC (as opposed to most other generator based energy), is there any loss in the inversion to AC? If so, there are cases (such as a small hunting camp) where it could be more efficient to run 12 or 24 volt lights and small appliances, right?

Mad Max

[shooter]

loss in the inversion to AC?

my 3KW continuous, 6kw peak modified sinewave invertor is about 90% efficient based on manufactures spec and the data I collected jives with that, although it's a 110Vac based unit so anything "motor based" is a little doggy.  It also sucks as a power source for guitar amps, the EMF is crazy high.  For a small off-grid cabin I would suggest 250-300 watt panels, which now only take up the same space as my 120w panels, at about the same price per watt.  I'd configure it as a 24 or 48vdc system(mine was 24vdc)  And the Ausies build one hellava charge controller, pricey, but worth it.

[MadMax]

Thanks Shooter. By the way, I get the rainwater part, but what exactly is a micro-controlled, solar powered toilet flusher? Did you need to power a pump to refill the tank?

[nateflanigan]

something to think,about....http://www.teslamotors.com/powerwall

Hey DL, that's what got me thinking about this.  It just seems like cool technology to mess around with.  I wish it wasn't quite so expensive, I don't need it to make me money, but thousands of dollars to say "Gee Whiz the lights work" isn't a very good wow factor investment.

Bottom line PRR is right, even the bankrupt goldmine I'm holding stocks on is making me more money than solar saved!

Maybe me should be investing in lithium ion mines?

It also sucks as a power source for guitar amps, the EMF is crazy high

Damn, this is the other direction I was going.  The wall power in my home studio isn't awful but it can get pretty noisy sometimes.  I was thinking maybe I could run the studio off of rechargeable batteries for pristine noiseless power. 

[shooter]

need to power a pump

madmax,
Yup, the rainwater was stored in my basement, used a Ping-Pong ball with a magnet attached, floating in a pvc tube to close a reed switch connected to a pic controller to turn tank water on/off (the pump).  Used a similar setup to control a valve to turn the rainwater feed on/off to regulate storage tank levels.  the pump was a submersible pond pump.  had a couple fault - read flood warning alarms wired also.  ran the in and out water thru 10micon filters.  ran it about a year off the solar array and did notice a savings over my normal 220 15amp well pump use.  But at the end of the day, it was just another tinkering project

[Ritchie200]

Nate

Bnwitt (longtime member but not on that often anymore) installs solar systems (haha! sorry....) for a living.  I was hoping he would jump on here and give his two cents.  He also has wholesale connections.  You may want to PM him if you would want any advice/suggestions on the latest and greatest.

Also, your AC might run at 5amps but startup on the compressor is going to be a lot higher than that.  Batteries don't like those high current spikes and will adversely affect charge/capacity.  The electric cars have been fighting that battle for years - hence the supercap applications to absorb some of the shock.

Jim

[PRR]

.

[nateflanigan]

That's great.  I wonder to what extent they implemented that program?  Thanks for the tip Ritchie.

[drew]

So... "several" thousand dollars (perhaps $5K total), to save $128/year. That's a 39 year payback. And zero end-value (you'll probably pay to have the dead panels and tons of dead batts taken away).

On the other hand, if there is a hurricane, earthquake, tornado, or other disaster that doesn't obliterate your place but knocks out the electrical grid in the area for multiple days or even a week or two, your house still works.  That's worth something.  Is it going to cost less than $5k to put in the kind of serious back-up gas or diesel generator that you would otherwise need to provide that kind of capacity?  I doubt it.  And the generator isn't going to make you $128/year while it sits there.

[shooter]

hurricane, earthquake, tornado

That was my main reasoning, no Gas, noise, mechanical failure, to deal with generators.
I also wanted to have valid data to argue the complete nonsense in most cases that you could "save the planet"" with solar.

[John]

On the other hand, if there is a hurricane, earthquake, tornado, or other disaster that doesn't obliterate your place but knocks out the electrical grid in the area for multiple days or even a week or two, your house still works.

Actually, with the systems they're putting in around here, that's not the case. If the grid goes down, you're still without power.

[shooter]

you're still without power.

Ya, that's a "grid-tied" system, no batteries, no inverters, you become just another node on the grid.  Again, another bad investment

[Ritchie200]

Just got a flyer from harbor freight they have their 45 watt three panel amorphous solar panel "kit" for $129. That's the cheapest I've seen it. Comes with all the wiring, some lights, and what looks to be a charge controller - I haven't looked it up for the details. A couple of these, some deep cycle batteries, an inverter (also on sale), and you are good to go.

Jim

[jjasilli]

Ditto to PRR.  Especially on the hidden "external costs" (pollution) of "clean" energy.


Also, an array of batteries is an inherently dangerous thing.  See:  http://www.allaboutcircuits.com/textbook/direct-current/chpt-11/practical-considerations-batteries/


Even if the batteries in an array are spec-matched initially, they are subject to age differently.  This can lead to fire or explosion.  So this is not a plug & play situation.  The batteries in the array need to be properly monitored; and the array shut down if needed. 

[shooter]

batteries in the array need to be properly monitored

A MUST, I set up a 3 week maintenance schedule, check fluid level, use hydrometer?, check lead corrosion, look for sweating- swelling, monitor I and V.   In less than a week I had 2 batteries go *catastrophic* - all fluid gone!, some plate welding, case swelling.  So ya, 12 deep cycle marine batteries is one very scary explosion potential!

[Ritchie200]

Another option is to visit a fork lift dealer/repair and see if they have any small packs with some life left.  Obviously not a 1000lb pack.  Keep them well vented.  Lots more water capacity.  Loads of amp/hr capacity.  You can also get a watering kit to easily keep them topped off without having to pull caps...

Jim

[bnwitt]

you're still without power.

Ya, that's a "grid-tied" system, no batteries, no inverters, you become just another node on the grid.  Again, another bad investment

Well now that depends.  Out here where we have aggregated costs per kilowatt hour of 32 cents and  a grid tie system is not a bad investment.  I regularly see simple payback periods of 3 to 5 years.  Now that is on a system that will probably last 30 years, so there is a lot of gravy after the payoff.  By the way, I don't install systems anymore, I design them.  Grid tie, Off Grid, Grid tie with battery backup, commercial, micro grid and utility scale systems.  If anyone in here needs advice I'd be glad to assist.

I love the Ma bell "solar battery" ad.  Solar modules haven't been called that in many years.

[bnwitt]

batteries in the array need to be properly monitored

A MUST, I set up a 3 week maintenance schedule, check fluid level, use hydrometer?, check lead corrosion, look for sweating- swelling, monitor I and V.   In less than a week I had 2 batteries go *catastrophic* - all fluid gone!, some plate welding, case swelling.  So ya, 12 deep cycle marine batteries is one very scary explosion potential!

Well now a days you can use gel or absorptive glass mat type batteries and eliminate much of the maintenance.  Monitoring however is very important.  Most charge controllers today use sophisticated software and sensors to keep track of the bank.  If explosions were common, you'd be hearing about it in the news.  Flooded lead acid batteries are still the best bang for the buck though.  Now don't get me started on Lithium ion.  And the Tesla Powerwall will never pay for itself at the price they are selling it.

[bnwitt]

Of course solar power is not going to save the planet.  Frankly, I don't think the planet needs saving.  There have been many periods in the life of our planet where it has not been a carbon based life friendly place.  There will me more of those same periods coming in the future.  The planet will be fine, though we may be gone.

Is solar power a solution for all problems?  Of course not.  You can't get food to the space station with solar power.  There are some things that only fossil fuel does well.  You won't see any commercial aircraft carrying passengers with solar panels on the wings.  Also, as has been said, not every use of PV is financially wise.  You have to do your math before you invest in anything.  I deal with starry eyed tree huggers out here in SoCal all the time who want to do things with PV which make no financial sense at all.  Sometimes I am able to set them straight and sometimes they march head long into disaster.  If you live in an area with inexpensive power, then the only reason to go with PV is to get out from under the thumb of corporate utilities.  Because even if your power is cheap now, that doesn't mean it will be cheap forever.  Energy independence protects you from the arbitrary will of the power company.  There are people who sell PV that will try to convince you it is a panacea and plenty of others (with interests in the fossil fuel world) who will tell you it doesn't work.  You have to sort through all of the propaganda and do the math yourself to find the truth for you situation.  PV technology has improved immensely since the PV boom began.  People are constantly making qualification statements about the efficacy of PV based on old data.  When I started designing PV in 2005 the all in cost to a homeowner of a Grid-Tie system was around $14 per watt installed.  Today I see it as low as $3.25.  I would imagine that if the FTC is allowed to expire, the industry will get costs even lower on equipment to make PV profitable without it.

[Paul1453]

Electrical conversion of solar energy is poor.  Heat conversion, on the other hand, is quite good.

For people living up north, PRR and many other of us, heating is a reasonable consideration.

You can make quite a heater from pop cans, steel wool, etc. spray-painted black and enclosed in a simple box.
The most expensive component will be the sheets of glass.  I saw one a guy made, that he said could heat his 2 story garage/workshop in the winter.
He had a large South facing collector that he said could heat his workshop to 50F when the outside temp was below 0F.

[sluckey]

Of course solar power is not going to save the planet.  Frankly, I don't think the planet needs saving.  There have been many periods in the life of our planet where it has not been a carbon based life friendly place.  There will me more of those same periods coming in the future.  The planet will be fine, though we may be gone.

You did see what happened to Krypton, right?

[bnwitt]

Electrical conversion of solar energy is poor.

Tell that to the folks on the space station

[bnwitt]

Of course solar power is not going to save the planet.  Frankly, I don't think the planet needs saving.  There have been many periods in the life of our planet where it has not been a carbon based life friendly place.  There will me more of those same periods coming in the future.  The planet will be fine, though we may be gone.

You did see what happened to Krypton, right?

I did indeed and even those braniacs couldn't stop it.  For us to think we can impact the fate of a planet is the epitome of hubris.

[sluckey]

Those braniacs caused it! 

[bnwitt]

Well of course we are speaking about a comic book tale

[sluckey]

What? No way! I went to school with a kid named Clark and he said...

[Paul1453]

Electrical conversion of solar energy is poor.

Tell that to the folks on the space station

Well if you remove our atmosphere, with all it's debris and clouds, the conversion improves significantly.   
Until I can move my workshop to the space station, I think I'll just try to keep it warm in the winter with solar energy instead of trying to power my electrical devices.

[bnwitt]

Paul,
Heating with electricity which is a secondary energy source is a fool's endeavor regardless from where the juice comes.  Using primary energy sources like gas, oil, wood etc. is the best way to achieve economical heating.  Now a days, there are some really good solar thermal exchangers out there with which one can heat, but you have to have at least "good" irradiance.  Northern latitudes or heavy weather areas just won't work.  However, you don't have to be in space for good irradiance.  Southern latitudes in many north American areas are great.  That being said, electric ovens, space heaters, toasters and other such appliances are power hogs.  Propane, natural gas and wood are more economical for such tasks.  As I said in an earlier post, photovoltaic electricity isn't smart for all uses but it can be incredible for others.  It's not a thumbs up or thumbs down thing like some people like to paint it but it can be great or terrible depending on how it is applied.  You have to do the math.