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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?
Rather than generating and then trying to store the power, have you considered selling it to your local utility? This would offset the cost of having to buy energy to run the air conditioner when it is required. Most of the time it won't be because, presumably, you'll need your air conditioner most when the sun is out. Perhaps I don't fully understand the question as it seems to me that you're over-engineering the problem.
Caterpillar makes a flywheel-based UPS system.
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").
Why not just setup a Wind turbine and a 2way grid connection? A good (but large) wind turbine can generate up to 1MW of power.
With it, when its windy, you generate and use your own electricity, and sell off excess to the grid. Its quite exciting watching an electrical meter run backwards.
Of course, when its calm, the grid sells off electricity to you.
Either way, its a guaranteed supply of power for your house (AC included), and can really reduce your electrical bills.
Call your local electrical company about setting up a reverse grid hookup. Some will be more than pleased to set one up (likely for a cost), while others may advise otherwise. Be also sure that the hookup is done properly and legally. Elsewise, the electrical company will be extremely pissed off, and may resort to legal action.
Frink: Nice try floyd, but you were designed for scrubbing, and scrubbing is what you shall do.
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=
No. What the above poster is thinking of can be found in Superconducting Magnetic Energy Storage (SMES). Google for it, there is a lot of information out there. Batteries are generally assumed to be the chemical reaction type of storage we've all come to know and love/hate.
You wont be on the producer side of the equation, but your net savings will be much MUCH higher by installing a geothermal system. They're cheaper to install, are pollutionless (well as compared to oil/gas burners), and provide central air and heat. Also... look at evaporative roof cooling systems if you have a flat roof. Are you well insulated? how about planting a tree or two on the south side of the house to provide some shade? Point being is that there are far more effective ways of lowering your energy bills than installing solar, though I do see the draw to producing your own power. Still, saving 1kw*hr of energy per day is better than producing 500w*hr each day.
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One myth about solar in most systems- you will NOT be the only one on your block w/ lights during an outage. The power grid is a two way street, and your power will flow right back out to the grid in most setups. You will have to install special equipment to disconnect you from the grid in these cases.
There are programs out there where you can finance geothermal heat pumps so you dont feel the pain upon installation of the system. most of the time, youre cost savings in your energy bill is greater than the loan, so youll actually have more money in your pocket (and a brand new heat system- increased resale value).
for more info:
http://www.nrel.gov/clean_energy/geoheatpu
Search for Solar Powered Ceiling Fans.
They're not (that) expensive, they run when the sun's out, when you need it most.
I've spent time in Africa and India, and everyone has really good ceiling fans, and it makes a heckuva difference. Some places, like banks and airports, are augmented by these neato wall-mounted oscillating fans.
There's a fellow in CA who has solar cells on his house. The power co buys back his excess power during the day, at the peak rate, and at night he uses power off the grid. His night usage is paid for by the difference between peak and evening rates. Check out homepower.com -> Home power magazine. There are lots of people out there who want to power their stuff in a safe way.
Good heavens, solar technology is mature and installers are standing by to set up a system for you. Photovoltaic panels today are completely capable of running from no load to full load without any special care, and you can purchase inverters that do not need batteries. Since you mentioned you are only interested in running an air conditioner during the day, go get a Sunny Boy(tm) 2.5KW inverter and panels to drive it. The panels will cost you about $15,000 to deliver that much power (and most house air conditioners run at around 2KW. If you have the system hooked up to the grid, in many states you will qualify for a rebate ranging from 30% to 50% of the cost of the system.
A less expensive alternative is to spend your money upgrading the insulation in your house, adding verandas to the south and west exposures.
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.
Net Metering is the issue here.
Electric companies buy the electricity from you at wholsale rates. Then they sell it back to you at retail rates.
You end up paying the electric company the same for your own electricity as you would if you bought it from them directly, without any solar cells, windmills or whatever. The concept of Net Metering allows the consumer/generator to sell back to the electric grid at the same price for generation or consumption, based on net usage.This way you get a real incentive for building your own small facilities and put power on the grid.
Power companies don't like it because they loose money on the deal: transmission efficiencies are well below 100%, the power is not reliable in peak hours (because you are probably consuming it), and they don't get their administration and maintenance costs.
But I like the idea of generating your own electricity, espically for something as engery-intensive as cooling.
More power to ya!
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.
Don't use an air conditioner when tha application requires low voltage. Instead use a fan (or group of fans) vented to the outside. The net affect will be around -5 to -10 degree delta. Plus, fans can operate on the voltage solar panels can provide (read no battery bank)
Actually there are fywheel energy systems around.
But for the small home user, they are not practical. Also, something spinning that fast with that much mass makes me quite nervous.
Most people do not live near a creek and do not have space for a water reservoir storage system. This is probably the case here as he is wanting to use photovoltaics.
This is why everybody is clamoring to get a fuel cell to work.
He could use the excess energy to generate hydrogen and feed it to a fuel cell later to use as he needs.
Fuel cells are available, but they are beset with problems. They are expensive because many use rare metals as catalysts. They have limited lifetimes, needing repalcement every couple of years, making them very uneconomical at today's prices.
So while fuel cells may be the ideal, he may be stuck with batteries.
Take the cheese to sickbay, the doctor should see it as soon as possible - B'Elanna Torres, "Learning Curve"
As a starter, here's a page with a number of stats, but being from a site called "ecotopia" makes the engineer-cynic in me want to take it with a grain of salt. They are, however, citing other studies. The more facts, the merrier, so if you've got any links, post.
The short version is that amorphous (thin-film) panels yield a 400%-2000% payoff on energy investment. That range is worst-case to best-case lifetime for the panels. Thin-film is the way to go anyway, as it's around $15/sq. foot instead of the $60/sq. foot for the crystalline panels. Sure, crystalline is twice as efficient, but thin-film is cheap enough to use as siding on your house, and you'll make up the difference in area. Now, as to convincing your significant other that shiny purple-blue panels are the way to clad your house is the tough part.
Look at it this way-- based on the energy costs, even if the return was only 110%, it would be worth doing. Is there any other way to turn a barrel of oil into 1.1 barrels of oil?
Many flywheel systems use smaller flywheels spinning much faster. Take this one, for example, at 60,000RPMS and 23Kg.
Still, if you can't afford lead acid batteries, you probably can't afford flywheels for the scale of the system.
Electric cars, maybe, although hybrids seem to be doing pretty well with plain old lead-acid batteries.
Lead-acid batteries are considered to heavy for most hybrids, since every bit of weight counts, especially when you have a weaker powerplant. The Toyota, Honda and Ford hybrid vehicles use sealed nickel-metal hydride (Ni-MH).
It's odd that you're worried about the cost of batteries but not of the panels. As a point of reference a recent issue of home power, HomePower.com shows 3 100W panels for $1680 while a 105AH battery is only $400.
The solar panels are going to be easily thousands of dollars. By spending some money on batteries you'll be able to do away with a bunch of extra panels which is going to save more in the long run and will allow you to cool in the evening or on a cloudy day to boot. Still the cheapest is going to be all the tricks you can use to reduce the need for AC like shade, swamp coolers and such.
This is the time of day rate for "peak demand" - 12:00 PM to 6:00 PM - electricity in California.
This is, according to PG & E and the CSPUC, the marginal cost of providing/generating a KWh duing this time period.
Of course, folks that aren't on time of day metering pay 7 cents/kWh due to regulation and overburden the system during peak demand.