Contrary to what I thought going into it, I’ve discovered that it’s not yet all that easy or cost effective to be really green, when it comes to being electrically self sufficient - at least in my neighborhood. The past few weeks, I set off to try to look at how I could self generate a good chunk of the electric power for my house. This is part 2 of a two part blog on green power. Why not solar? My house sits on the top of a hill with a moderate line to the southern and western skies. As a reminder, my house uses on average about 24,000 kWh per year. At an average rate 10.5 cents per kWh, electricity costs me over $2,500 per year. Like most, the usage goes way up during the summer months. Further, like its wind counterpart, there appears to be up to a 30% tax credit for solar installations as well. But unlike the wind, it appears that you can grossly overpay for little capacity and still potentially get the full credit. I admit I haven’t figured out how that all works yet. In addition, like wind, it appears that my local utility may also provide another 20% or so credit. And of course, with the right electronics, the solar system ties to grid, obviating the need to get a bunch of batteries or charge controllers. So if you don’t generate enough power for your home, you can still buy some from the utility and if you make too much you can generally sell the surplus back to the utility.The equation for solar is primarily surface area and sunlight - the two don’t mix very well because if you want a lot of power, you need to have a large surface area that maximizes sunlight. The general rule of thumb with current solar panel technology is 15 watts of peak capacity per square foot at a cost of $6 per watt - notice the focus on the word peak. The sun actually has energy of about 95 watts per square foot, but conventional of the shelf solar technology is about 16% efficient. In the hinterlands of the northern hemisphere, the best hope for sun light is a roof angling toward the south, specifically at an angle close to your latitude. The second best is the east and west and there is no hope for a roof that faces to the north. Of course the ideal is a panel that moves with the sun. This is popular for large flat areas, but they tend not to be very practical on our sloped roof tops.
In order to account for the movement of the sun as well a periodic cloud cover, we use a conversion factor. In Minnesota, the conversion factor for west facing panels tilted at 30 degrees is 12.7% and for south facing panels tilted at 30 degrees is 16.4%. This conversion factor of 16.4% means that a 1 kilowatt peak capacity panel, in place for a year (8,760 hours) would generate 1,432 kilowatt-hours of energy (16.4% of 8,760). Of course this varies as the seasons change and is only an approximate value based on historic cloud cover for different geographic regions. The following table illustrates the energy output of the same 1 kilowatt panel by month.
For my own roof, I identified a 15 x 15 spot of south facing roof and a 25 x 10 spot of west facing roof for a total of 475 square feet and 7,125 watts of peak capacity. Next comes the math. Using the values from above, the 250 square feet of west facing panels (3.75 kilowatts capacity) will generate about 4,175 kWh and the 225 square feet of south facing panels (3.375 kilowatts capacity) will generate about 4,825 kWh, netting a total annual energy of 9000 kWh - 38% of my power needs. After the 30% tax credit, the original investment of $42,750 is reduced to $29,925, a payback period of about 32 years. Ugh! Of course, if you live in Phoenix, that south facing conversion factor goes to 21% because of more sun light and a more consistent sun arc. If you add sun tracking into the mix, the total power for the south facing panels goes up by about 40%, but adds more cost.
In this new Design News feature, "How it Works," we’re starting off by examining the inner workings of the electronic cigarette. While e-cigarettes seemed like a gimmick just two or three years ago, they’re catching fire -- so to speak. Sales topped $1 billion last year and are set to hit $10 billion by 2017. Cigarette companies are fighting back by buying up e-cigarette manufacturers.
Advertised as the "Most Powerful Tablet Under $100," the Kindle Fire HD 6 was too tempting for the team at iFixit to pass up. Join us to find out if inexpensive means cheap, irreparable, or just down right economical. It's teardown time!
The increased adoption of wireless technology for mission-critical applications has revved up the global market for dynamic electronic general purpose (GP) test equipment. As the link between cloud networks and devices -- smartphones, tablets, and notebooks -- results in more complex devices under test, the demand for radio frequency test equipment is starting to intensify.
Much of the research on lithium-ion batteries is focused on how to make the batteries charge more quickly and last longer than they currently do, work that would significantly improve the experience of mobile device users, as well EV and hybrid car drivers. Researchers in Singapore have come up with what seems like the best solution so far -- a battery that can recharge itself in mere minutes and has a potential lifespan of 20 years.
Some humanoid walking robots are also good at running, balancing, and coordinated movements in group settings. Several of our sports robots have won regional or worldwide acclaim in the RoboCup soccer World Cup, or FIRST Robotics competitions. Others include the world's first hockey-playing robot and a trash-talking Scrabble player.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.