12 VDC Heaters

I've been looking for a way to come up with a renewable energy solution for some time--and I have not been terribly impressed with the options.  Photovoltaics are still not cheap enough to pay for themselves over any economically sensible time.  Our wind speeds aren't high enough here (or in many other parts of the U.S.) for most wind generators to pay for themselves in any economically sensible amount of time.


Part of the problem is that someone needs to come up with a wind turbine that can produce power at very low speeds.  If you can produce electricity at 5 mph, your generator will be running almost continuously in places like this (and probably where you live, too).  The problem is that the power that you get out of wind isn't linear based on wind speed.  The power is the cube of the increase in wind speed.  As a result, if you want to use low speed wind generators, they either have to be incredibly inefficient, or incredibly cheap.

Windtronics has an elegantly clever idea that Honeywell is marketing--a gearless wind turbine where the generator is the housing!  Brilliant design, and one that might actually be useful in places that have consistent but low speed winds.  But it's an expensive unit, and the last I checked, not actually shipping yet.  Worse, the price tag (because someone has to pay for the development costs) means that it still not economically sensible.  (Note: factoring in big tax credits by your state and local government doesn't make it economically sensible; it means that taxpayers are subsidizing your "Look how much I love Mother Earth" posing.)

Part of what makes all alternative energy systems spendy isn't just the cost of the wind generator, or the photovoltaic panels--it is what you do with the electricity now that you have it.  Because both wind and sun are intermittent, you have to store the electricity in batteries (for use when the sun or the wind goes away).  Or you use a grid-tie inverter to feed excess electricity back to your utility company when you are producing excess power.  This runs your electric meter backward.

Both of these are good things, no question about it--but there's a pretty sizable capital investment in either the battery backup or the grid-tie.  Battery backup has additional problems: regular maintenance; storage space; occasional replacement of batteries.  Suddenly, whatever merit the PV panels or wind generators had has become a lot more expensive--and that much harder to justify as economically sensible.

Let's simply the model.  What if you didn't need the battery backup or the grid-tie?  My oldest sister was talking to some people who build small wind generators from surplus, and apparently pretty cheaply.  (How cheap?  Still waiting to get an email back.)  They produce 12 VDC output (as do most PV or wind generators).  Instead of all the complexity of trying to make the generators replace the grid--identify something useful that you can do with 12 VDC.  That means that you need some system where 12 VDC supplements an existing system--but does not replace it.  More importantly, it needs to supplement an existing system of your house without requiring any changes to your existing house systems.

Lights?  Nope.  Even if you changed everything over from 110 VAC to 12 VDC, the power from wind generators is necessarily intermittent--and you don't want intermittent lighting!  Refrigerator?  Same problem.  It is too expensive to use an inverter that switches back and forth.

But what about heating?  At least where we live, our strongest and most consistent winds are in winter--when we get some real howling storms through here.  My guess is that many parts of America have that same experience.  Take the 12 VDC output from the generator, and feed a couple of 12 VDC electric heaters to warm your house.  It isn't going to replace your current forced air furnace--but if that heater warms your house even five degrees, that reduces the amount of LPG or natural gas your forced air furnace uses, and the amount of electricity to run the fan on the furnace.

The electric heater does not have to be terribly efficient, as long as the electricity from the wind generator is free, and as long as the wind generator isn't hideously expensive.  Where I live, even a five degree gain in overall house temperature would probably knock about $10 a month off our our gas bill, and perhaps $3 a month off the electric bill.  As long as the purchase costs of the wind generator and the heater is low enough, this can make economic sense.

I am still waiting for word on the cost of the surplus wind generators.  Any suggestions on inexpensive 12 VDC space heaters?

UPDATE: Of course, if you take this bare bones direct to application approach, maybe even photovoltaics start to make sense.  Sun Electronics is offering 190 watt blems for $338.20.  (That's less than $2/watt--very impressive pricing.)  I'm not sure how much loss there will be from running a hundred feet of 12 VDC wiring to a heater--but the goal is to provide heat.  All the loss that takes place within the house turns into resistance heating, right?  If you managed to get 140 watts of the output of this panel released inside the house as heat, and you managed to get it to happen for 3-4 hours a day during winter, that's 420-460 watts that don't have to be produced with a forced air furnace.

Another attractive aspect to this bare bones approach is that you don't need to hire an electrician to do something like this (unlike anything that involves connecting to the grid, or your house wiring).  Any reasonably competent handyman can install one of these panels outside, and run wiring into the house.  Making it look pretty might be a bit challenging, of course.

Here's a 1 Kw wind generator for $429.  That's at 22.5 mph, of course, which we don't get very regularly up here.  At more typical speeds for our location (5-8 mph), I suspect it will be more like 150 watts--but perhaps for a big chunk of the day.  Again: this probably doesn't make economic sense, once you spend several hundred dollars on the grid-tie inverter, and a couple hundred for an electrician to install it, and couple hundred for a tower.  But if you can get something like this directly running a DC heater, the capital cost comes way down--and even a continuous input of 120 watts of heat for ten hours a day into the house in winter makes sense.

UPDATE: This is discouraging.  A couple of readers tell me that gearboxes on wind generators are actually not life of the unit--and are effectively common maintenance items, as are various generator parts.  There's a reason, I guess, that all this alternative energy stuff needs gobs of subsidies: it probably doesn't make any sense, except as a fashion statement.   Eternity Road has a depressing example of what happens when environmental activists decide to help the downtrodden with their alternative energy needs.