First, I used all prices and specifications from materials available at Home Depot. [2] I want to make sure that the materials I use are generally available to the public. Outside of a retail store, the only question becomes price. This is the cheapest you could install it unless you can buy wholesale because I did not estimate labor and assumed you did everything yourself.
Efficiency
The efficiency limit of silicon based solar panels is theoretically about 29% due to the Shockley–Queisser limit. [7] In simple terms, this is talking about how much of the energy received from the sun (1000 m/w2) can be converted into usable electrical energy. You can push the limit up to 86% using multilayer solar panels. [8] The most widely available panels are about 18% efficient and the best are about 22% efficient. The better the panel the higher the price. This probably also assumes that conversion is taking place at the equator on a clear sunny day. (The further north you go the less energy is received from the sun.)
Recently, new records were set for 18.7% efficiency. [9]
The Project
The next problem is how much space do you need? I will use an example project I heard about recently to illustrate the use of solar panels. The idea is using shipping containers like the one above and converting it into a green house. The problem is the container is completely closed off from the environment so the light and water must be supplied. We will attempt to use alternative energy sources to keep the environmental impact to a minimum. The idea is to convert this into a green house with as few modifications as possible so that it can be massed produced. (After all if you cut 90% of the container away then why not just build a steal frame instead of using a closed box producing a lot of waste?)
The container dimensions is about 20 X 8 (feet) with a total square footage of 160. The main idea here is to demonstrate solar panels and not refine the design of a garden in a surplus steel box.
On the inside, we mount three shelves on both sides for hydroponics. We would end up with four (double bulb) light fixtures per row and a total of 24 bulbs. (4 X 3 X 2) (See picture above) For our demonstration, we will assume these are 40 Watt Bulbs and 120V.
That equals 960 watts per hour (40 X 24). We will use a 390W fixed solar panel at a cost of $969 each. These panels produce about 3 amps with dimensions of 6 X 4 (feet) using 24 square feet each. This means we need at least three solar panels just to power our bulbs using a total of 72 square feet. The panels needed to power only our bulbs would cover half of the container's roof.
40 / 120 = .33 (amp per bulb)
.33 * 24 = 8 (total amps)
8 / 3.25 = 2.46 (panels needed)
3 X 969 = $2,907 (cost)
This assumes perfect conditions, where the sun is always directly overhead and never a cloud in the sky at the equator. The reason is that solar panels are dependent on the sun. (duh) We know the sun's angel changes as the day passes. A fixed panel doesn't produce as much power if the panel faces directly up and the sun is at a 30% angel from the horizon. The power production suffers even more if the sky is cloudy. You can help this by installing motorized panels that adjust their tilt so they are always facing the sun. These panels are really expensive and consume power by themselves. So you would spend more money and require additional panels.
The amount of sun light also depends on where you live and what season it is. You get less sun light for shorter periods of time during the winter months. On average, you would probably only have 8 hours of usable day light to run the garden. I hope your plants can survive in those conditions because not all plants have the same environmental needs.
The other major problem is weather. In the central parts of the USA have severe weather. High winds, hail, and tornado's could cost you $3,000 every spring by damaging your solar panels. Solar panels also lose efficiency over time at a rate of .5% a year because the material degrades.
On the Home
You can install panels on your home and reduce your electric utility use. This will save you money. Such a kit is available for the do it yourself group for about $10,000 consuming about 350 square feet and producing an average of 5,400 kwh per year. For comparison, I personally use that in about 3 months. On average, I pay about $250 per month for electricity. Assuming perfect sun conditions, I would get 3 months for free and it would take 14 years to break even on my investment. You can reduced the time to break even by cashing in some government subsidies which makes everyone pay for your bad investment.
In a Power Plant
The largest solar power plant in the USA is Nellis in Nevada. This facility takes up 140 acres and produces about 14 Mega Watts at maximum capacity. To replace a single 140 mw coal fired power plant would require ten times the cost and space using 2.18 square miles of land. To replace the total power generated in the United States would require more land than the state of Maryland occupies and that doesn't consider the space needed for transmission lines. It would require 14,000 square miles where Maryland only has about 12,000.
It would not even do away with the fossil fuel power plants since they would remain as a back up power source. The reason why is most conventional power plants boil water and use the steam in turbines to generate the power. If the plant were completely turned off then there would be a delay from the time the pilot was lit and the volts started to flow out. This would lead to blackouts and general interruption in service when a cloud rolls in the area until the sky was clear or the back up power plants came online. For this reason, installing solar panels does not reduce CO2 emissions because we can not store the power we generate on an industrial scale.
Germany
Germany has emerged as the leader in solar panels. The biggest problem with solar panels is if there's no sun then there is no power. In fact, for the first part of 2012 Germany's solar panels didn't produced much because the country had cloud cover for several weeks in row which is often the case in the winter.
Energy storage methods have not kept up with technology. During the cloudy days, Germany has to import most of their electricity from conventional power plants in neighboring countries since they no longer have many of their own. At the low point, they had to restart old oil fired power plants to prevent an interruption in service. No matter how many solar plants Germany builds, they will always be dependent on conventional sources when the sun is unavailable due to weather or the spin of the Earth. Simply put, you have to build two power systems; solar and conventional. The conventional plants must always be on stand by to fill gaps in supply. This isn't just a switch you can flip. The power plants must be running even when not in use.
Since solar panels are so expensive the German government provide subsidies to businesses and individuals to install the panels to the tune of $10 billion in 2011. This amounted to the most unreliable 3% of power supply. None of the private owners can automatically switch between utility and their panels because without a storage method it isn't possible to send excess power back to the grid. It is expensive to dispose of unused power on the grid. In the end, Germany pays the second highest rates for power in Europe. The highest rates are paid by citizens of Denmark who is the leader in wind energy. They have created a government supported sector that will end up costing over $200 billion Euros in the next 20 years.
The cost of solar panels have dropped in Germany but this is misleading. The drop in expense is due to labor cost and not materials. Companies in Germany are really good at installing new panels. The German manufacturing sector has been unable to keep up with demand and so most of the panels come from countries like China.
The proponents claim that all the solar panels can generate 20 Gw but this can only occur if every solar panel has perfect environmental conditions which don't occur outside of a laboratory. As a result, Germany has cut subsidies for solar panels.
Sources:
- http://www.usatoday.com/
- http://www.homedepot.com
- http://www.spiegel.de/international/germany/
- http://www.hawaiireporter.com/germanys-solar-failure
- http://en.wikipedia.org/wiki/Nellis_Solar_Power_Plant
- http://en.wikipedia.org/wiki/Energy_in_the_United_States
- http://jap.aip.org/resource/1/japiau/v32/i3/p510_s1
- http://en.wikipedia.org/wiki/Shockley
- http://phys.org/news/2011-05-efficiency-percent-flexible-cigs-solar.html
No comments:
Post a Comment