Sciencemadness Discussion Board - solar panels at Harbor Freight

solar panels at Harbor Freight

chemrox - 13-5-2008 at 20:57

Harbor Freight has a pair solar panels with 45 watt advertised output included are transformers and wires.. What else would I need to use the energy at night? Seems like a battery of some kind is indicated. I've no interest in 12v systems..anybody worked with this kind of setup?

ShadowWarrior4444 - 13-5-2008 at 21:15

Quote:

Originally posted by chemrox
Harbor Freight has a pair solar panels with 45 watt advertised output included are transformers and wires.. What else would I need to use the energy at night? Seems like a battery of some kind is indicated. I've no interest in 12v systems..anybody worked with this kind of setup?

Lead acid batteries are traditionally used for this sort of domestic energy storage, charging in parallel then discharging in series could be used to step up to the desired voltage, should you wish. Although, this is not recommended with batteries, an inverter system would likely be best--charge the batteries at 12v, inverter to pull it up to 120 at 60Hz. As they are including a transformer, this is what they probably intend for the system.

If you want to get extravagant, you can use supercapacitors configured in a large array, Zinc-Silver matrix batteries, a fuel cell system of sorts, or perhaps a sodium-bromine or sodium-sulfur battery. The lead acid way is generally the most economical, unless you have industrial applications in mind. Solar-to-hydrogen fuel cell systems are in these days, too.

12AX7 - 13-5-2008 at 21:34

You need to imagine your overall use. What are you going to use 45W for? That's hardly enough to run a desk lamp (incandescent). It's certainly insignificant in terms of offsetting your daily power consumption, which averages well over 1kW (us Americans are power-hungry, ain't we?). You'll need a whole bunch of them to do that, which will get expensive. And that assumes they work, which knowing Horrible Fright, they'll have lower output, efficiency or lifetime in exchange for the lower price (although I should check their actual price before ranting about a store I've never been to..).

45W is somewhat over 3A at 12V, which is a reasonable float charge current for a pair of car batteries. Over an 8-hour charging period, you accumulate maybe 45 * 8 * 3600 = 1.3MJ, which sounds impressive, but isn't even 45 * 8 / 12 = 30Ah in the battery. That said, if all you're doing is a few hours of "work", you can easily draw a reasonable rate of work in that time (30Ah over two hours is 180W, enough to, say, run a computer).

SW4444: supercapacitors are hardly 1% of 1% competitive with lead acid by weight, let alone lithium technologies by weight or volume. They are useful for smoothing out high peak power demands, much as large capacitors are usually used. Because voltage varies proportional to charge, a wide-range inverter must be used to store and draw energy from a supercapacitor bank. It will be interesting to see what future developments may bring, but likely chemical cells will always be several orders of magnitude ahead of any capacitor. After all, cells are improving too.

Tim

not_important - 13-5-2008 at 21:39

Batteries : while you could use any old rechargeable, in the long run you're better off with deep discharge batteries, especially those designed for solar service

http://www.oksolar.com/battery/

http://www.dcbattery.com/solar.html

although these also look interesting as they have a high discharge/charge cycle rating

http://www.fireflyenergy.com/index.php?option=com_content&am...

You also need aa charge that understands PV as a source of electricity, although you can fake a simple-minded one with a Schottky rectifier.

And the you need an inverter to get house current from, the specs depend on what you plan to power; some equipment can run off a near square wave while others want a pretty clean sine.

Remember that the power rating of PVs is usually a peak power rating, for optimal conditions. If you live in the US, go here http://www.nrel.gov/gis/solar.html then select from the "Flat Plate, Facing South, Latitude Tilt" set. Find where you live, find the rating for daily solar flux as kw per sq m per day.

Now it gets difficult, as the manufacture doesn't give an efficiency specification. These are amorphous silicon cells, conversion efficiency runs 5 to 6 percent, meaning that 45 watts out is from say 900 watts input; sounds about right as the panels are a snudge smaller than a meter square. That's noonday sun at the equinox continental US about the 40th parallel; around 4.5 kwhr/day of solar power would give 225 watt-hr/day of electricity at that time. Summer in the Southwest will yield about twice that.

So now you can get an idea of what your power generation will look like. Get clever will polished metal mirrors and you can stretch the peak output period, plus you can put some amount of additional sunlight on the panels to boost output.

here is an example of the daily variation in solar irradiation
http://www.victoriaweather.ca/stations/RaceRocks/RaceRocks.w...

[Edited on 14-5-2008 by not_important]

ShadowWarrior4444 - 13-5-2008 at 21:48

Use a flywheel compulstor! Then, craftily connect it to a free electron laser on the roof...

Though, a more serious note that not_important reminded me of: Would it be possible to run water up through/around/under the PV, then bring it back to a Stirling engine in the house? Stirlings aren’t that hard to build, and besides, everyone should have one. *smirk* (Hence recovering a bit of those 855 wasted watts.)

not_important - 13-5-2008 at 22:01

Remember that Stirlings are just heat engines, and run within the Carnot limit. For a hot side of 100 C, this will be around 18% (cool radiator @ 30 C) to 24% (cool radiator at 10 C), and that's the temperature of the cold side, not the air. I suspect you'd be lucky to recover a tenth of the thermal energy as mechanical power. Better to use it to pre-heat hot water ( 1 m-sq is small for heating purposes).

While I've seen a number of home-built Stirlings, I've only seen one that ran well for any length of time. I've also seen a couple of liquid piston Stirling pumps that worked OK, but their efficiency was horrible - it was only their location that made them practical. I'm not sure that it's worth chasing, unless you have experience with and access to a machine shop.

ShadowWarrior4444 - 13-5-2008 at 22:22

Quote:

Originally posted by not_important
Remember that Stirlings are just heat engines, and run within the Carnot limit. For a hot side of 100 C, this will be around 18% (cool radiator @ 30 C) to 24% (cool radiator at 10 C), and that's the temperature of the cold side, not the air. I suspect you'd be lucky to recover a tenth of the thermal energy as mechanical power. Better to use it to pre-heat hot water ( 1 m-sq is small for heating purposes).

While I've seen a number of home-built Stirlings, I've only seen one that ran well for any length of time. I've also seen a couple of liquid piston Stirling pumps that worked OK, but their efficiency was horrible - it was only their location that made them practical. I'm not sure that it's worth chasing, unless you have experience with and access to a machine shop.

Stirlings are quite efficient as heat engines go, and as such are used in solar-thermal power generation schemes which achieve comparable results vs PV cells.

If you wanted to be excessively conservative, you could run the water from the external solar panels through a stirling, *then* into the water heater. Running the drain from your shower through a stirling might be fun as well. Stirlings can be designed to run on quite small temperature gradients, as demonstrated by the novelty designs that run on the heat of a person's palm vs the ambient temp.

I have also been toying with the idea of building a car/other vehicle based on a stirling engine powered by graphite encased mixed uranium ore. (Like the pebble-bed reactor designs.)

not_important - 13-5-2008 at 23:16

Quote:

Originally posted by ShadowWarrior4444

Stirlings are quite efficient as heat engines go, and as such are used in solar-thermal power generation schemes which achieve comparable results vs PV cells.

If you wanted to be excessively conservative, you could run the water from the external solar panels through a stirling, *then* into the water heater. Running the drain from your shower through a stirling might be fun as well. Stirlings can be designed to run on quite small temperature gradients, as demonstrated by the novelty designs that run on the heat of a person's palm vs the ambient temp.

But they still run below the Carnot limit, which was the 18 to 24 percent value I gave. Change that to a cool side temperature of 50 C, heating water as well, and you are down to a best-possible limit of about 12%, less in the real world. That's maybe 70 watts of electrical power for a few hours a day; the EROEI is likely to be low and maybe below unity. It can be improved with limited solar concentration and illumination time extensions, and with active tracking.

Engineers and scientists of the Victorian era were dumbfounded at the limits of efficiency they determined. It took decades to get the idea settled in, and it still is not accepted by a few.

Running a Stirling with 35 C hot and 10 C cold can only recover a maximum of 5% of the heat energy, given really effective heat exchangers. That's 5 watt-seconds per gram of water, 1.4 watt-hours per liter of 30 C drain water.

You can make all sorts of demonstrations that run off of small energy gradients, the Crookes radiometer is an example. But it's tough getting useful work out of these, and of getting a positive payback.

12AX7 - 14-5-2008 at 09:01

You'll have better overall efficiency if you pump the cold water directly to the solar array. Solar cells get *really* bad when they're hot.

Tim

chemrox - 15-5-2008 at 00:52

"...What are you going to use 45W for? That's hardly enough to run a desk lamp (incandescent). It's certainly insignificant in terms of offsetting your daily power consumption,." I wasn't thinking. A 15 watt fluorescent bulb puts out the equivalent f around 60w incandescant. But he's still right, 45w is not enough to run a hot water heater or a (good) stereo set. But I am intrigued with the Sterling engine idea ...

Solar Power and energy self sufficiency

franklyn - 4-6-2009 at 21:47

Have we attained solar breakeven and not even notice ? see image below
webpage here _
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?itemnu...

I was perusing an advertisement offering 3 foot square 45 watt rated solar
panels for sale at 180 dollars. That comes to 4 dollars a watt. 100 of these
forms a section 30 feet by 30 feet with a combined output of 4500 watts,
more than enough for a normal household and can be had for 18000 dollars.
If not done by yourself, installation may cost another 6000, so say total
cost is 24000. That amount invested at a return of 5 percent compounded,
a very good return these days, will double to 48000 in 15.6 years.

The alternative is utility supplied electricity at a current residential cost
( to me ) of 22 cents a kilowatt. Consuming 500 kilowatts a month this
amounts to 110 dollars times 12 months is 1320 dollars a year current
market price. Multiplied by 15.6 years comes to 20600 dollars.
It's fair to expect current cost will likely more than double in the
forthcoming years so this fruit certainly appears to be hanging low.

Supplemental electric power can be provided by a 4500 watt auxiliary
backup generator powered by utility supplied natural gas. A useful thing
to have on its own. This can perhaps be had for 1500 dollars which comes
to 33 cents per watt, and would free you from being subject to general
power brownouts and blackouts. The prospect of accumulating and storing
a reserve of gas when it is cheaper for use later also beckons investigation.

Globey - 5-6-2009 at 14:33

I have 6 Global Solar 55 Watt P3's now. Thinking of inverting and tying into the grid. Might as well put them to work, aay? I'm thinking those might reduce my electrical bill by perhaps $1-$3 a month?

BTW, although those (above coupon) are amorphous CIGS, not flexible. That's why I went with the P3's. No, didn't pay anything close to the retail price.

Franklyn don't forget there may be other factors your not considering. This rating in open sun? your exposure may vary? Generation/inversion losses? Cell depreciation? There may be more. Still, good point...very reasonable fixed cost. I think solar will get WAY cheaper though. Like your above equivalent for about $20 USD.

[Edited on 5-6-2009 by Globey]

not_important - 5-6-2009 at 17:22

Quote: Originally posted by franklyn

...
I was perusing an advertisement offering 3 foot square 45 watt rated solar
panels for sale at 180 dollars. That comes to 4 dollars a watt. 100 of these
forms a section 30 feet by 30 feet with a combined output of 4500 watts, ...

That's 4500 watts peak. Actual power output averaged over time is less, the capacity factor for PV is in the range of 0,15 to 0,24. This makes the power output more like 675 to 1080 Watts, say 16 to 26 KWH per day. Typical houses in North America seem to run 22 to 65 KWH per day, meaning your 4600 Watt array might be able to power your house provided the house is energy efficient for N.A. and is in a decently sunny climate.

Utility scale wind still is the lowest cost renewable power source, getting near coal fired power plants, followed by utility scale concentrated solar thermal. Photovoltaics are still several times as expensive as those.

franklyn - 5-6-2009 at 18:02

Photovoltaic preformance peaks when demand on a utility's electric grid
is also at it's peak, hot sunny days. This is also when supply cost rises.
Matching the energy source to demand or application is key.

not_important - 5-6-2009 at 18:56

Quote: Originally posted by franklyn

Photovoltaic preformance peaks when demand on a utility's electric grid
is also at it's peak, hot sunny days.

Be nice if that were true, but it's not. For non-tracking panels PV peaks at solar noon, with a fairly narrow curve. Demand peaks mid-afternoon to early evening, air temperature continues to rise for several hours after solar noon plus heating from building usage accumulates during operating hours. See the attached image for examples. Photovoltaic is the magenta curve in the 2nd chart.

franklyn - 5-6-2009 at 19:35

It appears there is a phase shift of 5 hours. That's not to say there isn't
concurrence of power supplied with demand. Notice that the light blue
line ( grid peak demand ) coincides where PV ( Photovoltaic ) output has
dropped by a third, and at this point grid demand also drops off.

Windy
http://www.clariantechnologies.com/main/page_plugin_wind_pow...

Another twist on the same, old same old
www.solar.tm/RSi%20PV-Glass-Window%20press%20release%2012-12...

franklyn - 8-4-2012 at 07:38

Price point on commercial solar panels is down to $ 2.50 a watt.
At the lower nominal expected output this will produce $ 600
worth of electric power per year in the cheapest regions. The
payback period for the purchase price is 22 years. If it can be
kept clean of birdshit.
www.costco.com/Browse/Product.aspx?prodid=11630267

.

Dr.Bob - 9-4-2012 at 10:21

Not important,

Just put a really big mirror in space to reflect light down on it from 2-6pm, and then it will be creating power at the best time. :-) Solar Electric is best where the cost of electricity is already very high, there is ample sunlight, and/or where the grid is poor or non-existent. In other places, it is still not economical for most individuals.

Also, the costs of most of the systems mentioned are for grid based systems, which means that if there is blackout, the system shuts down. The cost to put in a useful battery storage and switching system for non-grid use is quite high, maybe 50% of the cost of the panels. So that does not help much for the infrequent blackout.

So the most cost effective solar is thermal, like hot water production. For PV, the best use is large commercial grid tied systems, since they can be maintained correctly (cleaning off the pollen and bird poop) and the loads matched correctly. Smaller systems are more expensive per watt, just like most systems where cost goes down with size/scale/quantity (Costco, for example.) The cost per watt of a large inverter is only a fraction of the cost of a small one, for example (up to a point), and the wiring is much cheaper and easier if designed for very high voltages like most commercial systems use.

Those are some nice figures, and explain the problem well.

[Edited on 9-4-2012 by Dr.Bob]

Polverone - 9-4-2012 at 15:20

Quote: Originally posted by franklyn

Price point on commercial solar panels is down to $ 2.50 a watt.
At the lower nominal expected output this will produce $ 600
worth of electric power per year in the cheapest regions. The
payback period for the purchase price is 22 years. If it can be
kept clean of birdshit.
www.costco.com/Browse/Product.aspx?prodid=11630267

Where I live, anything else has a hard time competing with the cheap hydroelectric power. If you live in Hawaii, a setup like this is a good investment. Residences and small businesses on the big island pay about 40 cents per kilowatt hour from the utility company; most of their generating capacity is from diesel generators. At 40 cents per kilowatt hour and 700 kilowatt hours generated monthly, this system reaches payback in under 4 years, and that's without any tax breaks/credits. Hawaiian solar households have already proliferated to the point that utility companies are complaining they don't buy enough power to cover meter reading and other fixed expenses. I suspect it's just the beginning of Hawaiian utility company headaches.

In many sunny locales, peak energy usage is for cooling on hot summer days. If the actual peak demand from cooling arrives a few hours after peak solar output, thermal buffering should be a cheap way to shift the load. Chill a tank of water while sun shines and use it to regulate building temperature into the afternoon and through the night. The marginal cost of supplying that last megawatt of peak demand is much more than the median marginal cost to supply a megawatt, so it seems like there should be a common interest between utilities and their customers in making use of distributed solar in hot sunny regions.

chemrox - 9-4-2012 at 19:54

"Though, a more serious note that not_important reminded me of: Would it be possible to run water up through/around/under the PV, then bring it back to a Stirling engine in the house? Stirlings aren’t that hard to build, and besides, everyone should have one. *smirk* (Hence recovering a bit of those 855 wasted watts.)"

Wouldn't one want to use a low heat capacity fluid rather than water"

Dr.Bob - 10-4-2012 at 13:14

Actually, if you could keep the water cooled, and cool the cells, it would be great, as they make higher voltages as low temperatures. But that takes either a lot of fresh, cold water, or a chiller, which uses up all of the electricity produced.

But if you are trying to heat the water, it is a terrible idea, as the PV output plummets with higher temperatures. So most solar PV systems are designed to air cool themselves, such they stay near the ambient temp, thus produce to most power possible. Plus water and high voltage are a bad mix in most cases. I thought that same thing until I took a course and actually did a PV installation and saw the effort that went into keeping the cells cool and then understood why.

So the ideal place for solar is on top of a mountain (cooler and less atmosphere to block sunlight), near the equator for most light, and far from cheap power. Mouna Kea is the best place I can think of (that I would want to visit at least). And solar is a great idea in HI, I saw a ton of it on the big island, but not as much on Oahu. But I think most new buildings are required to have solar thermal water systems installed. And one of the locals was talking about his PV system that he would add a panel to every year. It was nearly at providing all his power.

franklyn - 10-4-2012 at 17:38

Quote: Originally posted by Polverone

@ Polverone
If you have Grand Cooley Dam for power , who needs alternatives.
Electric vehicles for commuting also make great sense in such areas.
I think Hawaiians should take the example of Iceland and develop
geothermal sources.

.

497 - 11-4-2012 at 02:36

What's wrong with concentrating solar? It doesn't have to be as high tech as most large systems are these days.

The problem with nearly all home made stirlings is their low operating pressure. The pressure makes a huge difference in efficiency and power! Also heat exchangers and regenerators are rarely well designed or built. There are potential ways around these problems, but more work needs to be done, and hardly anyone is doing it...

In climates where cooling is the main power consumer, why bother even using electrically powered A/C? It doesn't make sense when you could directly couple the compressor to a (solar, biomass, geothermal powered) heat engine. There are even cheaper/simpler systems that don't require any mechanical power at all (see Einstein refrigerator and Icyball), but efficiency is sacrificed. Should efficiency really be the priority if dirt cheap solar heat is available?

Just to illustrate how insanely cheap and easy solar heat can be, I present this lovely site
http://www.aquaflector.com/technology.html

Can it get any easier?

More fun reading:
http://www.google.com/url?sa=t&rct=j&q=porous%20plat...
This could probably be applied as a low cost design for a concentrating collector too.

http://www.google.com/url?sa=t&rct=j&q=parabolic%20s...
I really like the looks of this, but I'm not in a hot climate...

watson.fawkes - 11-4-2012 at 05:17

Quote: Originally posted by 497

In climates where cooling is the main power consumer, why bother even using electrically powered A/C? [...] There are even cheaper/simpler systems that don't require any mechanical power at all (see Einstein refrigerator and Icyball), but efficiency is sacrificed. Should efficiency really be the priority if dirt cheap solar heat is available?

Economic efficiency is largely the only driver here. What's perfectly conceivable, though, is that an ammonia absorption refrigerator, which could use solar heat directly, could have better cooling efficiency that a two stage process that used conventional photovoltaic conversion and then a conventional compression refrigerator operating on electricity. Furthermore, for a true comparison in a residential context, you'd need two scenarios: one where the house was occupied during the day, and one where it wasn't. I can't say I know offhand what all the optima for these two two technologies in both scenarios.

The relevant efficiency is the analogue of well-to-wheel efficiency, use to compare different transportation technologies. I've never seen a name for it, much less an actual comparison. Perhaps sky-to-ice efficiency?

497 - 12-4-2012 at 00:46

Seasonal heat storage is more of an interest for me. It has been improving a lot over the last decade or so. This stuff looks really ripe for DIY exploration!
The most current (idealized) plan in my head for a heating dominated climate basically consists of the following:

A simple tensioned mylar strip heliostat array similar to the one I posted above would provide heat to a collector of some sort, a simple heat pipe will transfer it to a high pressure free piston linear alternator stirling engine (or steam engine if you prefer). The cold side of said heat engine would be cooled with a heat pipe that transfers the low temperature heat to dry a sorbent bed. In an "open system" air is heated and blown through the sorbent to dry it. In a "closed system" a heat exchanger transfers it to dry the sorbent in a vacuumized vessel, and the vapor is condensed seperately. There are several effective, low cost options for sobents such as silical gel and CaCl2 impregnated fibers. The waste heat exiting the sorbent could be used to heat a borehole field or suitable aquifer if desired. When heat is required in the (green)house it can be provided by either A. Blowing humid air over the sorbent (in an "open system" style) which causes a temperature rise and then the hot dry air is blown into the building, or B. By adding external heat (optionally recovered from borehole field/aquifer) to evaporate water (in a vacuum, "closed system") out of a separate vessel and then absorb it into the sorbent, a heat pipe carrying the released heat into the building. The electricity produced by the heat engine could potentially be stored seasonally in a simple home built flow battery. I like the bromine/polysulfide couple, but vanadium, zinc/bromine, even ionic liquids may become better options. If you didn't want to mess with large scale battery storage, you could also just run the stirling in cogen mode with any available fuel over the winter. Preferably the system would be combined with a simple cellulose --> chloromethylfurfural --> ethoxymethylfurfural batch process to provide some transportation/backup generator fuel. Duckweed based aquaponic systems could be easily integrated and provide a semi-self sufficient (emergency?) food supply, and the starch from the duckweed could be used to make the ethanol required to form ethoxymethylfurfural.
Hope that all makes sense..

If anyone is interested here is some really useful reading.

Salt impregnated fibers
http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=59...
http://www.springerlink.com/content/m142r88182234250/
http://www.springerlink.com/content/b21636638t713r11/

Salt/zeolite/silica gel sorbent systems
http://www.ecn.nl/docs/library/report/2009/m09102.pdf
https://docs.google.com/viewer?a=v&q=cache:TKeEYFDFuoYJ:...
https://docs.google.com/viewer?a=v&q=cache:xPOVQbKCFY0J:...
https://docs.google.com/viewer?a=v&q=cache:WkVNR99NWUwJ:...

Any takers?
IMHO even a prototype that was too small to fully supply a modern household would be extremely valuable to have "in storage" if any sort of disaster/collapse where to halt shipping and utilities.

[Edited on 12-4-2012 by 497]