Thursday, March 24, 2011

Solar Power

Let's talk a little more about solar power.  I got started a little bit yesterday, but I'm a geek about it so I'm diving back in.

As I said, the rule of thumb is a kilowatt of energy lands on every square meter of full sun.  That's pretty good.

The best photovoltaic panel returns maybe 25% of that as electricity.  The rest gets converted into heat, which is why it hurts to touch a car hood on a sunny day.  That's converting nearly all of the energy into heat, and reflected light.  But you don't have to settle for such a low rate of return if you don't want to, and you don't have to go through the hassle of wiring it up to your house.  Read on:

Visible light is only a small portion of the energy the sun sends our way, but that's the only part we consciously use.  There's also a huge amount of heat, which we don't think about. We can make use of a bigger piece of the spectrum.  Simply acknowledging that infrared light is there, but we don't see it, and that's the wavelength where heat radiation lives, we can tap into that energy stream.  It's stupid easy to make a solar heat collector: just park your car in the sun.  That's a real quick demonstration of a flat plate collector, and a really lousy one.  Sure it's crazy hot to you, but let me tell you - you ain't seen nothing yet.

Spend $100 on materials and you can make a solar heat collector that will make a dent in your heat bill.  Spend more, and make a solar water heater that keeps your home's water heater warm without relying on the utilities.  Some of these things can get pretty expensive, but once they're paid for, you're done.  Everything it does after that is knock a few bucks off your utility bill.  Utility rates gone up recently?  Wouldn't it be nice to pay what the bill was last year...or the year before that?  It can be done.

Got windows in your house?  Of course you do, code requires windows at least in the bedrooms.  Do they face south?  Excellent, open the curtains on a sunny winter day, make the most of that light.  Let the heat in.  You haven't spent a cent, but already the solar power is right there, just knocking to come in!

My front door faces south, and a big picture window in the living room, dining room, and kitchen.  On sunny days, we open everything.  After a couple of hours, we might open the slider on the storm door a little, to let some of the excess heat out.  Without turning the first screw or building the first gadget, in the right conditions my house climbs into the middle 70s on solar power alone.  If you have anything like that kind of asset in your favor, put it to use.

Summertime though - wow.  Then there's too much solar power.  Well - maybe not.  If you have a solar water heating system, then you might just not have the electric elements in your water heater come on at all.  Size the system right and there's enough hot water for everybody's shower, and then it just regenerates over the next day.  Add the fact that the solar collector is interposed between your home and the sun, and there's less sun load on your home, less heat load on your air conditioning.  Again, a few bucks off the utility bill.  Less stuff for equipment to do, so your AC system lasts longer.  One expense when you install or build the solar collector, then a little off the bottom line for however long it lasts.

How long does it last?  Decades.  A cheap solar collector made with plastic and lumber might be good for five years.  Drop a hundred bucks on that, save a few hundred, you're coming out ahead.  A high quality system with an aluminum frame, copper water pipes and soldered connections is a lifelong item.  That should be good for however long the house can hold it up.  Replace the pump motor every once in a while and forget about it.

Circulator pump motors are notoriously well designed.  I have one pump motor here at work I've been watching since it was 1997!  It's been running continuously since then, that's over 120,000hrs without a failure.  Your mileage may vary, but don't be shocked if you do better, either.

What about solar electric, photovoltaics?  Well, more good news there.  No moving parts.  Barring actual breakage, solar panels are pretty much foolproof.  The industry standard is a 25 year warranty, which means you can expect it to last longer.  The technology is getting better all the time, the prices are getting better all the time.  Nanosolar recently perfected a roll-to-roll production process that generates photo panels in a manner not too unlike how a big printing press works.  They can generate miles of solar panels.  They're pushing hardest at the dollars-per-watt envelope, making it affordable and even economically smart to install photo panels.

Unfortunately, they're currently only offering at the bulk utility level, selling megawatts of capacity at a time.  Megawatts, as in 100 = Norris Dam on a good day.  But someday, they're going to be open the phones to retail buyers, and when that happens, I'll have my wallet open.

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