On Friday 09 September 2011 11:33:08 Stanislav Jakuba wrote: > Note: This e-mail was apparently "blocked" as some of the earlier ones > were. Here is a new attempt.
In "into", the first three letters are bold and the last isn't. > but the units are kWh/h, Btu/hr, hp, V·A, and others but rarely the W kW·h/h is of course kW. You may have meant kW·h/d. V·A is dimensionally equal to W, but when motors are rated in volt-amps, that's not equal to watts because the volts and amps are out of phase. The wire still has to have capacity to carry all the amperes, even those that don't contribute to power. I'm designing a solar house. I took a spring power bill to get a rough estimate of my electric consumption. The bill said I used 391 kW·h in a month, but I'm not sure how long that month was, so I had two estimates (526 and 543) of power consumption in watts. But a 550 W panel is not enough. I have to know how many hours per day the panel is producing electricity - a rule of thumb says 5, but it varies with season and location. Solar designers often use a figure in kW·h/d in this calculation. In your solar calculation, the 200 W/m² figure includes the 5 h/d. Insolation at noon on a cloudless day, with the sun's rays normal to the panel, is about 1 kW/m². For the hour per day figure, you should take not the yearly average, but the least monthly average, which is probably the one in December in the temperate north. What do you do in your house that takes 4.6 kW? I had two computers running continuously (three now, the third being a laptop, and soon a fourth which will be for my work), a water heater (my house will have it built into the roof), and a fridge (I'll get a more efficient one designed for a solar house). I've seen a solar panel comparison which lists watts per square foot. That irks me. Insolation is quoted in watts per square meter, and my lower slope is 20.6 m (plus end eaves) by 3658 mm (i.e. 12 ft, a common lumber length). Another unit you may want to mention, though it's neither energy nor power, is the ampere-hour. Battery capacity is quoted in this, instead of kilocoulombs. And to build a battery box, I'll have to find the dimensions of the batteries in millimeters. If you'd like to discuss solar design, feel free to contact me off-list. Pierre -- gau do li'i co'e kei do
