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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?
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
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.