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Cheap Solar Cooling Solution?
"I realize that the photovoltaic array will have to be of sufficient size to offer more power than will be consumed by peak load, causing excess power, that will need to be dealt with. Also, there will need to be some monitor so that if the available energy doesn't meet the minimum threshold, then the appliance is shut off (or the juice to the circuit is cut), and vice versa. As temperatures approach 120F and more this summer, I'm putting more aside for this project and at this point am not concerned with any but simple methods of using up 'excess' energy. Though thoughts have rattled around about a Linux controlled shading system to adjust the raw juice coming off the panels through selective shading."
If the concern is cooling, then one way of burning off any "excess" power might be creative use of fans (either single fans or a bank of them; small or large, depending on the amount of excess power available). What other ways might such "excess" power be used?
Flywheels are a really cool idea. I've never heard of one in practice, but they have been touted as a solution to peak hour power shortages. Just spin a heavy disk up with extra electricity in a low friction environment, and then siphon it off during peak hours. As a resident or a power company you could save money. It's not an option available right now, however.
If someone drops a fort on Will, he makes a reflex save.
Use excess power to pump water 300 ft uphill, then use the water to drive a turbine to power the A/C. From what I know of air conditioners, it would take a LOT of photovoltaics to drive one... I'd guess at least $20,000 worth.
"Freedom means freedom for everybody" -- Dick Cheney
As temperatures approach 120F and more this summer, I'm putting more aside for this project and at this point am not concerned with any but simple methods of using up 'excess' energy.
Don't most state regulatory bodies require that electrical utilities purchase any power that a customer generates?
Just feed your excess into the power grid, and let it offset the power you buy from the utility. Pay the difference on your lower utility bill.
Opinions on the Twiddler2 hand-held keyboard?
IANAEE (I am not an Electrical Engineer), so feel free to correct me where I stray from reality.. but here's some ideas:
1. Sell it back to the grid. Use the electrical power grid as a battery, drawing from it when you need and selling your power back when you don't. You can actually make some money this way, offsetting the cost of the solar panels.
2. Break the circuit when you don't need the cooling. (Any EEs want to comment on if this can damage the solar cells?) I believe this will just create a DC potential difference across the cells, and since the circuit is broken, there's no current flowing around to worry about storing.
Good luck.
Using your sig line to advertise for friends is lame.
Traditional air conditioning assumes cheap electricity, and plenty of peak capacity. (Ever try to start a compressor motor?)
You want to reduce you air conditioning need. Think awnings that reduce solar gain. Think reducing heat generation. Think insulation. Think how to be a bit more clever. There is a lot of work available on this aspect.
Once you do do some air conditioning, consider finding a cooler hot side for your heat pump. Something my wife wants us to look at for both heating and cooling is "geothermal", that is using the earth for the both hot side (in winter) and cold side (summer) of the heat pump. Also, if you are in a dry climate, consider if a little evaporative cooling might boost efficiency.
-kb
Maybe instead of using solar energy to make electricity, then converting that electricity to mechanical compression, you could use an ammonia type refrigeration unit -- like the type you see in RV's that are powered by propane.
They use heat to separate ammonia+water, condense the ammonia, then use the evaporating ammonia for cooling as it is absorbed back into the water solution:
http://home.howstuffworks.com/refrigerator5.htm
Not sure if this would be any more efficient than solar cells + batteries, plus you'd either need a large quantity of ammonia to give you long periods of cooling even after the sun goes down, or you'd need a large thermal mass to store heat (or rather to remove heat and store "cool").
In other words, take the total square footage of the area you want to cool and divide it by 3. That's a rough estimate of the square footage of solar panel you'll need. (Of course, the math WILL change depending on your installation: more efficient panels, better sunlight, more efficient AC unit, etc). This estimate is a worst-case scenario, and I can easily see getting a factor of 5 or better.
As for excess energy... if you anticipate needing a LOT of cooling, one option may be to "store" some of that cool. Use the extra juice to run refrigeration units to chill tanks filled with brine or antifreeze solution. Help cool off/dehumidify your house by running this chilled solution through some radiator coils. (Add small fans for better results!) The pump and fans can also be powered from the "extra juice" if there is any.
The added benefit here is that you can use energy collected in early morning/late evening hours to help reduce cooling load during the really hot parts of the day, allowing you to get away with smaller AC units and less solar panels.
=Smidge=
As for alternatives, I agree. Solar isn't very efficent. As for wind, in the right area and done the right way it can be fanstastic. I live in eastern Kansas and let me tell you it can get VERY windy on some of the highways that I drive that are surounded (basically) by farms. Now, you would lose some crop if you put the windmills up in the middle of your fields, but there are also a large number of cow farms around (mostly meat cows, not dairy I think). Now you have all this land that's just used for grazing. You add some windmills and all of a sudden your land is now producing energy for free for you. You'd only lose a tiny ammount of grass (wouldn't effect the herd). You get money (that will cover the maintence) and it works year round. As for the cost of putting up the mills, you could almost certainly get grants from the Government and private groups to help pay for 'em (or band with other farmers to buy in "bulk"). The biggest problem is "environmentalists" complaining about the what it will do to the view (I think they're neat, personally) or how it makes the landscape unnatural (and ripping everything down for cattle grazing doesn't, let alone building "real" power plants). With all I've heard about the plight of family farms, this could be a fantastic way to suppliment income. Wind won't work everywhere, but in some areas you could get a LOT of power.
In fact, just 10 minutes or so down the road from me is a company's headquarters that has a few small windmills outside their building. I think they design/manufacture them.
Comment forecast: Bits of genius surrounded by a sea of mediocrity.
No, without a disconnect you will not be the only guy with his lights on durring the black out. You will, however, be the only guy on the block to recieve a visit from an electric company expert skull cracker and solar panel smasher, after a linesman gets cooked working on supposed-to-be dead lines. There is a reason you *must* have an incoming undervolt cutoff to even maybe legally connect your generating equipment to the grid.
For a typical panel you will not have any trouble if you just leave it out in the sun open-circuited. However, if you parallel several of them and don't use anti-backflow diodes, you can dump the power of one or more back through the one with the lowest voltage (typically the hottest). This can lead to thermal runaway (voltage drops with temperature) and fire. Ergo, anti-backflow diodes are one of the most basic elements of a properly designed solar system using parallel panels.
Read Home Power and you'll know this too.
Time is Nature's way of keeping everything from happening at once... the bitch.
Sometimes I think the average slashdot poster must be about 14 years old judging by how much thought goes into some of these comments.
I agree. Unfortunately your post shows exactly the sort of thoughtless knee jerk reaction you are complaining about.
The fact of the matter is that the US economy is
drastically and negatively influenced by the current status quo of statisfying energy needs by cheap oil imports. The costs of the foreign policy needed to support this situation are in the 100's of billions per year. The current ballooning deficit ($500 billion this year) and military budget are the direct result of this oil dependence. Do you think Americans would give a rats ass about what happens in the Middle East if oil didn't come from there?
And it can only get worse as these finite reserves of oil are consumed. What is the end game we are heading towards? Surely it is nuclear war or nuclear terrorism. We cannot tolerate where this is heading, yet we seem to ignore the clear signposts.
The taxes and the huge balance of trade deficits that drain the life blood from out economy are the distortion that is the direct result of our dependence on foreign oil, and the erroneous percieved need to keep the price down. It is distorting the true market forces through massive government intervention. Any sane economist will tell you that this is incredibly wasteful.
What is the solution to this? Other countries have partially found it in more efficient use of energy. The US uses over 12,000 BTU per $1 of GNP. That is only SLIGHTLY more efficient than the Dominican Republic. Switzerland manages 2,900 BTU per $1 GNP. Japan even less. Now this says to me that the US could potentially reduce its energy consumption by a FACTOR OF 4 with NO reduction in standard of living.
To me the idea that the economy of what is supposed to be the most technologically advanced nation on earth is driven by an energy balance no more efficient than the Dominican Republic, and it must sustain this by imposing its political will on another part of the world by military intervention is nonsense on the face of it, and history will record it as insanity.
I think that the US *MUST* face the music and realize exactly what this current economic fallicy is costing the country. Instead of the giant balance of trade deficits and military budgets, we should be investing in sustainable development - efficient utilization of the resources we have, and new technologies to expand their use. The result will be those oil and defense budget dollars going into technologies that are being surpressed due to an artificial and ultimately untenable situation.
This economic approach would have drastic results in the revitalization of American industry. Productivity of energy will soar, and the distortions in the current national policy disappear. Investments in new technologies other than pinpoint bomb delivery will lead to the end of the need for oil wars. The development of new energy technologies will lead to a whole new economic growth vector that will complement and amplify the silicon revolution, and hasten growth in other (bio- and nano-) technologies.
This is why I said a rise in the price of oil is a good thing.
In terms of batteries... you only ever use batteries if you are off-grid or if the grid is really unreliable. If you are tied to the grid you do not usually use batteries... the Solar system goes through an inverter and powers the house, and any excess is fed back to the grid (running your meter backwards). The grid acts as the 'battery' in this case. If you are not producing enough to power your house, the remainder is fed to you from the grid. Grid-tie systems without batteries are the *simplest* and *cheapest* type of PV system you can buy, but you are still talking about $15-$20K for the system you see above. Systems with batteries cost a lot more (add another $5-$10K at least) plus you have maintainance requirements (Batteries wear out), and you need an ATS (Automatic Transfer Switch) which itself is expensive. On the otherhand, systems without batteries are nearly 100% maintinance free. Without batteries means that if the grid goes down, you go down too. Most people live in areas where the grid is reliable enough that there's no point doing battery storage. Also keep in mind that battery systems have much higher losses then grid-tie systems because you have a loss charging the battery and another one pulling energy out of the battery on top of the inverter losses.
Typical home AC systems eat 3kW while larger home systems eat 5kW (for homes, not apartments). Lets say you had an AC unit that eats 3kW while operating. A 2.5KW grid-tie system producing 16KwH/day would be able to run such a unit for 5 hours. As you can see, the PV system itself would not be able to power the AC unit alone, it would definitely need help from the grid, but if you only ran the AC for 5 hours the PV system would run your meter backwards the rest of the time and make up for it.
Five hours is not usually enough running time to really be able to cool a house unless you live in dessert conditions where it gets cold at night, in which case you really need to cool the house down at night so it stays cool enough so you don't have to turn on the AC until the afternoon (12-5p.m.)
So, generally speaking, trying to run an AC system with a PV (solar power) system is a bad investment. You could try running a smaller AC system but the sun generates something like a kilowatt of heat per square meter and it will easily overpower a small AC system if you do not have good insulation. Note, in particular, that if you do not have good wall insulation the sun is likely to overpower your AC during the afternoon when the sun is hitting the side of the house instead of the roof.
You would be far wiser to invest in passive technologies such as improved insulation and infra-red reflective shading. If water is cheap (or even if it isn't), a swamp cooler (rooftop evaporator) is often a great investment... it's cheap and it provides some cooling at a far lower cost then AC in electricity use. I've heard people mention GeoThermal, and it does work, but if GeoThermal is not put in when the house is actually built it can't take advantage of an under-the-house installation. Getting enough suds out o
Ammonia is widely used in industrial-scale compression refrigeration systems. It's a heck of a lot cheaper than fluorine/carbon compounds.
Time is Nature's way of keeping everything from happening at once... the bitch.
Try this. Direct refrigeration from the sun - and it doesn't even use salt water and ammonia.
If you just want cooling (er, you can also get heating with this) and you have the property, it's even easier. Dig a buncha ditches and lay some pipe. You combine these inlets with a decent solar chimney and you have a completely "passive" (ie no machine moving parts, no electricity needed) means of circulating 60 degree air throughout the house.
Oh, and here's a DIY solar ice maker - just for the heck of it.
Feel free to message me about this. Solar energy is something of an avocation of mine.
Of course, you could never make Keanu Reeves movie about bacteria...
Walt Dismal suggests:
One solution is to not use electricity.
OK so far.
Build a solar-powered steam engine and use it to run a Carnot cycle in reverse (heat pump) during the day. All mechanical, no electricity. Cheaper than solar cells plus batteries plus charger/inverter.
While we're at it, we can make the air conditioner even more efficient by making it out of point masses and assuming no friction.
[Hint: The Carnot cycle is a theoretical model from the thermodynamics unit in physics class, it's not a real heat pump to cool anything. It makes some assumptions (eg. a fully reversable process, no entropy increase) that we don't know how to engineer. It's the oversimplified ideal heat pump, not a real one.]
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Open mind, insert foot.