Feb 20, 2010

Alternative Energy

Yeah, that's right. Alternative energy. Say it with me. It's not a dirty word. Seven syllables. (Isn't a haiku 5/7/5? I might have an idea! See below.)

In any case. I've been looking at alternative/off-grid power for a long time. My truck has an inverter and deep-cycle battery hiding in the toolbox. Doesn't see much use, but it's there. I've been toying with the idea of a small setup for fuel-free backup power at home.

Conveniently, Northern Tool Co sent me an emailthis week advertising various items for sale. Among those were their 15W/12V solar panels. I talked to the Mrs and ordered two of them along with a charge controller. The intention will be to put a small battery bank in the garage along with a small inverter, big enough to run the coal stove for a few hours at a clip.

Yes, we have a generator - but our genset will suck down nearly eight gallons of fuel every 24 hours, and there is a limit to how much fuel we can store. On top of that, it takes time to get the generator hauled out, fired up, hooked up, etc. I wanted something that could simply be one switch and an extension cord until we have time to get everything else going.

I'll be adding a few deep-cycle batteries in the next couple months, probably to end up around 300-400Ah of capacity. 400Ah with a 300W inverter (coal stove draws 200W, adding a cushion is a good idea) should last up to six hours. I'm well aware that 30W of solar power won't keep up with the load, but they will be more than enough to maintain and trickle-charge the bank. If there's an extended outage, one of the things to do will be recharging the battery bank whenever the genset is being run, then allowing the inverter to run the coal stove when the power is off. (Est. charge time 400Ah @ 30W/12V = 160hr sunshine - but that's from zero charge.)

In addition to providing a backup power source, we will probably get a portable fence charger in order to move the goats around the yard to spots that would otherwise be un-grazed, or if they go to visit family/friends for a vacation.

Somewhere on down the road, I'd love to have enough alt-energy to be, if not off-grid, at least not completely grid-dependent. I think a small wind turbine would be feasible where we are, and a good-size solar array would be plausible for about half of the year. Our average monthly electricity use is around 500kW-h, so a 1500W system would cover the vast majority of our power needs.

I'm still waiting for replacement LED bulbs that are both affordable and realistic replacements in terms of light quality.

green power calls me
alternative energy
it's not a bad thing


doubletrouble said...

Hey Zerc-

I’ve got a small set up like you are describing- one Northern panel & 3 from Harbor Freight. Other than minor construction differences, they are electrically identical.

A few things to remember-
Battery a/h ratings are typically for a 20-hour draw;
A battery shouldn’t be drawn down to less than 70% of its rating (I think you know these based on your 400a/h req’t for a 17 amp load for 6 hours);
Inverters should be twice the size you think you’ll need (I’ve seen 400w inverters struggle with a <300w load).

Some good resources:

Backwoods Home energy forum

Otherpower forum

A neat idea for making a 12v generator from a small engine & an alternator (doesn’t use anywhere near the fuel a 3600-rpm genset does)

On the lighting thing- we made good use of a LED droplight during last year’s ice storm (Harbor Freight- ~$20/ea). They’re 12v, have 30 leds, & while fairly directional, they give a lot of light for little juice- 210mw is all they draw. I bought 2 more of them, & running 3 of these beauties is still way less than 1 amp- gotta love that.

Good luck- this is fun stuff to fool with!

Lemmeno if I can be of assistance…

ZerCool said...

DT - That little generator is pretty slick, nifty idea. If I come across some spare bits and bobs I may look into building one!

Doing more reading, I'm beginning to think I should look at a pair of 6V golf-cart batteries wired in series - those run around 225A-h each, and would provide most of the load capacity I'm looking for. As far as draw-down, are you talking 70-80% drained (i.e., 20% remaining), or vice-versa? Everything I've seen indicates most deep cycles can be run to 20-30% remaining without too many problems, but 50% will dramatically extend the lifetime.

I'm already starting to wonder how much I can convince the Boss to spend on larger cells to keep things charged. :-D

doubletrouble said...

Check out the Backwoods Home site- there's a guy who goes by the handle "12vman"- he's pretty knowledgeable on this subject, & has the home set up to prove it.

That's where I learned of the 30% rule- if you can keep the draw down at a safe slow rate (20-hour rating) & keep the discharge amperage to 30% or below, (70% remaining), you will radically extend the life of the storage system. Yeah, you can draw lower, but at the expense of battery life- everything's a trade off. But batteries are expensive!

The golf cart batteries are far superior for continual use, & will allow for a greater draw down than lesser "deep cycle" batteries.

I lurve this stuff...