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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?
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").
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, 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.
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.
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"