Posts related to solar power and off the grid living.

the cliff

Falling off the cliff is always a surprise. I know it's there; I've been living next to it for months. I chart its outline daily. Avoiding it has become routine, and so comfortable, and so failing to avoid it surprises.

Monday evening around 10 pm, the laptop starts draining down from 100%. House battery, which has been steady around 11.5-10.8 volts since well before Winter solstice, and was in the low 10's, has plummeted to 8.5 volts.

With the old batteries, the cliff used to be at 7 volts, but now, with new batteries but fewer, it's in a surprising place, something like 10 volts, and I fell off it.

Weather forecast for the week ahead is much like the previous week: Maybe a couple sunny afternoons, but mostly no sun at all.

Falling off the cliff is not all bad. It shakes things up. It's a good opportunity to disconnect, to read paper books, and think long winter thoughts. It forces some flexability.

I have an auxillary battery for these situations. With its own little portable solar panel, it can charge the laptop and run it for around 6 hours. But it takes it several days of winter sun to charge back up.

That's enough to get me through the night. Then I take a short trip, and glory in one sunny afternoon. But I know that won't get me out of the hole, the batteries need a sunny week to recover. This evening, I expect to lose power again, and probably tomorrow evening too.

Luckily, my goal for the week was to write slides for two talks, and I've been able to do that despite being mostly offline, and sometimes decomputered.

And, in a few days I will be jetting off to Australia! That should give the batteries a perfect chance to recover.

Previously: battery bank refresh late summer

battery bank refresh

My house entered full power saving mode with fall. Lantern light and all devices shutdown at bedtime.

But, it felt early to need to do this. Comparing with my logbook for last year, the batteries were indeed doing much worse.

I had added a couple of new batteries to the bank last winter, and they seemed to have helped at the time, although it's difficult to tell when you have a couple of good batteries amoung a dozen failing ones.

The bank was set up like this:

+---- house ----
|              |
+( 6v )-+( 6v )-
|              |
+( 6v )-+( 6v )-
|              |
+( 6v )-+( 6v )-
|              |
+( 6v )-+( 6v )-
|              |
+( 6v )-+( 6v )-
|              |
+(   new 12v  )-
|              |
+(   new 12v  )-

Tried as an experiement disconnecting all the bridges between the old 6v battery pairs. I expected this would mean only the new 12v ones would be in the circuit, and so I could see how well they powered the house. Instead, making this change left the house without any power at all!

On a hunch, I then reconnected one bridge, like this -- and power was restored.

+---- house ----
|              |
+( 6v )-+( 6v )-
|              |
+( 6v )  ( 6v )-
|              |
+( 6v )  ( 6v )-
|              |
+( 6v )  ( 6v )-
|              |
+( 6v )  ( 6v )-
|              |
+(   new 12v  )-
|              |
+(   new 12v  )-

My best guess of what's going on is that the wires forming the positive and negative rails are not making good connections (due to corrosion, rust, broken wires etc), and so batteries further down are providing less and less power. The new 12v ones may not have been able to push power up to the house at all.

(Or, perhaps having partially dead batteries hanging half-connected off the circuit has some effect that my meager electronics knowledge can't account for.)

So got longer cables to connect the new batteries directly to the house, bypassing all the old stuff. That's working great -- house power never dropped below 11.9v last night, vs 11.1v the night before.

The old battery bank might still be able to provide another day or so of power in a pinch, so I am going to keep them in there for now, but if I don't use them at all this winter I'll be recycling them. Astounding that those batteries were in use for 20 years.

late summer

With days beginning to shorten toward fall, my house is in initial power saving mode. Particularly, the internet gateway is powered off overnight. Still running electric lights until bedtime, and still using the inverter and other power without much conservation during the day.

Indeed, I had two laptops running cpu-melting keysafe benchmarks for much of today and one of them had to charge up from empty too. That's why the house power is a little low, at 11.0 volts now, despite over 30 amp-hours of power having been produced on this mostly clear day. (1 week average is 18.7 amp-hours)

September/October is the tricky time where it's easy to fall off a battery depletion cliff and be stuck digging out for a long time. So time to start dusting off the conservation habits after summer's excess.

I think this is the first time I've mentioned any details of living off grid with a bare minimum of PV capacity in over 4 years. Solar has a lot of older posts about it, and I'm going to note down the typical milestones and events over the next 8 months.

solar year

I've been at the cabin, on solar power, for a year now. I have a year of data!

Everything went pretty well until last month. There was an April rainy spell where power felt slightly tight. Then over the summer, plenty of power, no need to conserve. The last month though had what seemed like weeks of continual grey clouds, where I never saw the sun.

high noon today

Of course, even on a sunny day in winter, it does not get far above the hills, and the peak production window is only a few hours. This bad combination had my battery power dipping below the 10 volts that I consider low, down to 9, and even to 8 volts.

I use kerosine lamps in the winter. (I prefer the light anway.) I've also started unplugging my Thecus server at night to conserve power, meaning no internet late or early. For four or so nights, I had no power to run even my laptop after sunset. On one notable day, there was no power even in the daytime.

Even when it turned sunny again, I found that the batteries would seem to charge to 12 volts during the day, but then precipitously drop to 10 and 9 volts at night. I think the problem was not damaged batteries, but that these Nicads charge most efficiently above 12 volts (14 volts is best), and there was never enough power saved up to get them full enough that they could charge really efficiently.

So, I reluctantly spent three days away this week, to let the batteries soak up sun and recover. It seems to have worked; they've been holding a 12 volt charge overnight again.

more solar data

Entered in 6 months of the house's solar power data.

Power system voltages.

When I last did in mid-December I was seeing the expected slow decrease, but did not anticipate the dip in mid-January, which I think was due to snow and bad weather.

At the end of February, I doubled the size of the active battery bank, and this damped out many of the spikes and lows. The mid-April low is bad weather paired with much higher than usual (24x7) inverter use, and possibly with some batteries that were still being conditioned after spending all winter off power.

I'd expect the last couple of months to be higher, but perhaps I'm just not needing to conserve power here at all (come to think, I have a radio, an inverter, a flourescent light, an electric shaver charger, a sheevaplug, a laptop, and 4 USB pepherials going right now).

infrastructure update

I'm surprised to be on the porch hearing rushing water. I tend to think of up here as high and mostly dry, but not this time of year. Yesterday was such a soaking rain, very annoying at the time as I did chores and drove out from town. Now there are two little creeks here. That's a sound I've missed..

Pity that all the water is going to waste. I discovered the reason the large cistern is not filling up is simply because the pipe into it is not connected to the feeder pipe in the spring. It seems like a complete shambles really, with layer upon layer of pipes, all broken. I will have to wait until the water is down to dig and find out what's going on, and fix it.

In the last of the evening light today I got the house's two battery banks finally combined into one bank. I had planned this out long ago, and bought one long cable I'd need, so was surprised to find I needed two long cables. Had to slide batteries around like a big sokoban puzzle, and swap several cables to make it work. While I was away I'd charged up the bank that had gone unused most of the winter. So they were near equalized and the combination seems to have gone ok. I got through the lean part of the year with only half the batteries; there never seemed to be a good time to combine them. It remains to be seen if the solar panels can keep my increased capacity filled.

I hope this was only an early taste of spring. Would be nice to have some more icy weather so I can put off dealing with refrigeration a little while longer. I have my eye on a 12v/propane fridge.

snow and stats

It's been an intense couple of days out at the Hollow. Did it only start to snow yesterday? It feels like a long time in winter. Yesterday was the first day that the solar panels produced no power, it was too cloudy and snowing most of the time. I cleaned an inch of slushy snow off the panels to no avail, and wondered if the power would last.

But the wood stove has kept it nice and warm, so yesterday was spent cosily in the living room enjoying the snowfall, nethack, and podcasts. Also, I'm very much enjoying cooking on the wood stove. I've never been in a position to cook on one before; when I lived at Wortroot the stove was in the cabin, and the cold kitchen in a different building. So cooking on the stove, or even keeping a kettle on, was mostly only done in emergencies. Here, I am constantly using it, and the propane stove is still on its first 20 pound tank. Long slow cooked beany or roastish stuff does especially well. Yesterday I did a great pork loin roast with homemade quick sauerkraut.

Today, after cleaning another 3 inches of snow off the solar panels, and scraping off a layer of ice, I am getting a decent amount of power for a cloudy day with some snow still falling. Turns out it was good I cleaned them yesterday after all, since a part I missed has a inch+ layer of hard ice, which I don't dare chip away at for fear of damaging the panels. I'd not want to live someplace where it snowed a lot with solar panels that didn't have some kind of a heating system.

I wish I had a camera to show the long walk down the driveway, through the winter woods, and past the field where the wind blows gusts of snow into the air. But my cell phone is on a Caribbean cruise.

I have been recording data ever since the fall equinox, and it's almost to the winter solstice now. Time to geek out with some graphs! Solar production has surely been falling off with the waning days, but it seems like it will get through the shortest day with enough, and from then on, no worries.

Highest watt production seen each day I've been here.
Zero all day yesterday.
Power system voltages.
Charge controller limits it to a maximum of 15 volts during the day.
Originally, it was limiting it to 13 volts.
chop chop

I've always loathed cheap particle board and peg bookcases, and when I broke one while reorgaising the living room at the Hollow today, I finally found a good use for them. They're great fun to chop up with an axe, and make for a very hot fire in the stove later.

I released git-annex 0.03 today. The main improvements are being able to configure the backend to use on a per-extension basis in .gitattributes, a fsck subcommand that will find dangling annexed content, and bugfixes, including massive memory use savings. The big feature under development next is an idea Josh Triplett and I batted around; a way to checkout annexed files to edit their contents.

Today I also got the radio working well here. Set up a car radio with a 40 foot wire for an antenna, and I finally got it almost static free. Pity that running a nslu2 on the same power circuit causes interference, so I am not able to use that to feed in music via the radio's AUX jack yet, which is the eventual plan. And the radio's powered USB outlet is wasted, I had hoped to run the nslu2 from that. Seems I can run the radio for 9 hours and still have plenty of solar power, even this time of year.

Wish it were colder..


I brought my cat Leo to the house in the hollow a week ago. He settled in quickly; this was his 7th move. He seems both more kittenish, and more predatory out here. This was a trial run, I'll bring him back to town soon for a few weeks. Since early August, I've for one reason and another been away every other week, and I got tired of worrying about the cat home alone.

With a cat, and with electricity seemingly sorted, it's getting homelike here. As the days shorten, I'm being power wasteful with computers and radio and lights, and the batteries still never drop below 13.5 volts. Bodes well for winter. All that remains to be done is refrigeration that does not involve hauling ice, and more water. Winter will help with both.

Still remains to be seen if I will continue bouncing back and forth, or if there will be an inflection point.

I've regained a tranquility that had been eluding me for ages. It's been a lot of work, but it seems worth it.

(git-annex announcement soon!)

getting to know my batteries

I should probably have researched the batteries in this old solar-powered house before I installed a charge controller. I had assumed that the 24 6-volt batteries in the house's battery bay were standard lead-acid deep cycle batteries. It wasn't until I stumbled over a receipt from 1997 that I learned that the batteries are really NiCads. Specifically Saft model STM5-180.

Thirty of these were purchased in 1997 from TVA in Chatanooga, for $350 total. An amazing price, since a single deep cycle battery is in that ballpark, new. These batteries were used, they had been in a "bus" -- perhaps it was a 1995 Chrysler TEVan, or maybe one of the pilot electric buses running there in the late 90's. They were probably not in this '79 VW TVA Bus. All mentions of these batteries I can find involve electric vehicles -- it's unusual for them to be used to power a house.

Being vented NiCads probably accounts for these batteries' long useful life -- surely at least 15 years. Still, with only twenty-four good ones left, they are probably toward the end of their lifespan and need to be taken care of in order to last.

Once I realized they were NiCads, I knew the charge controller was charging them wrong. NiCads like to be charged at a higher voltage than the 13 or so volts used for lead acid. I would have liked to charge them at 16 volts, but that would feed back through the house wiring, and could fry 12 volt stuff. Checking ratings, 15 volts seemed the highest voltage I could risk.

Coming back a week later, I found the batteries charged up to 13.4 volts. And they are now working great. Through several cloudy days, we had all the power we needed. And when the sun was out fully, I sometimes saw the solar panels charging the batteries at 125 watts -- fully half of the panels' rated capacity, and much better than before. The batteries start each evening at 13.4 volts, and only drop to 13.3 by morning. We started using electric lights more, and then just leaving them on all evening, and the nslu2 online all night, and the batteries remained at the magic 13.3 in the morning. This is because NiCad batteries have a near-constant voltage until they are perhaps 30% discharged. In other words, I had been charging them less than half full before.

I have figured out how to combine the two banks the batteries are in into one large bank, and once I get the cables to do that, I hope to have battery capacity to get through up to a week of solid clouds in midwinter.

battery box and solar panel
solar charge controller adventure
Xantrex controller, temporarily badly installed

As planned I have installed the Xantrex C-35 charge controller in the offgrid house. This was a bit of an adventure..

First I had to wait around in town all day for the UPS man to deliver the thing. Of course he didn't until 4, so by the time I got over to the house it was almost dusk. Further delayed by necessary visiting with the nearest neighbor (a country thing), who claims there are "panthers" up this holler.. So by the time I was ready to work, it was nearly too dark.

First I checked the battery bank which I had left charging for a week without a controller or backflow diode. It had gained only half a volt (to 10.5v), so now I knew I really did need the controller in order for the sun to work for me while I am away.

Then, barely able to see, I swapped that bank to provide house power. By 10 pm, using just my laptop, I'd drained 1.5 volts from it and it was as low as it should go. I had 4 hours of laptop battery. This was a bit of a problem since I tend to stay up until 3 am on it.

Instead, I spent 2 hours, by kerosine lantern light, exposing, tracing, and testing wiring. I was able to find 2 wires that were clearly going to the battery bank and had current, and 2 others that were labeled as going to the panels, and, in the dead of night, had no current. Great, I thought, that's the wires I need, let's hook up the controller..

And I did, although only to the battery, since after all I couldn't be certain the other two wires were for the panels, without seeing voltage on them in the daytime. (This turned out to be probably wise, because in the morning, when I tried it, the controller reported no PV voltage. They turned out to be mislabled, and actually connected the battery to the breaker box.)

The problem with doing all that stuff at midnight is it took me quite a long time to wind down. I normally start winding down at 10 am and get to sleep at 3. Last night I got to sleep at 5.

My four hours of battery for my laptop were nursed all hours through the night. Mostly thanks to powertop and the improved power saving of the kernel these days. And to not having wifi or anything enabled. I do wonder if my recent use of redshift to redden the screen causes the it to use less power at night, as I have never gotten five hours out of this laptop before.

Anyway, to get the controller hooked up to the PV array and actually charging the batteries, I ended up having to rip lots of wiring out of the wall, until I simplified the mess to something I could understand. And at the moment I've bypassed the PV array's breaker, which is certainly a safety hazard. So more wiring to do, but I did get it working.

Finally, I hooked the house wiring up to the same battery bank that is being charged from the panel. This house had been using a 2 battery bank setup, because without a charge controller to moderate the PV voltage (17-25 volts), you can't also connect a load that expects 12 volts. The charge controller fixes that problem.

The other battery bank is sitting unused for now. Later, I will equalize and connect the two, in order to get one large(ish) battery bank.

Now, during the sunny fall daytime, I can use all the power I want; it's free from the sun. Battery bank shouldn't drain at all when I use power during the day, and the controller should charge them up and keep them topped off, so they'll be there for me at night.

Now to verify that it's working like it's supposed to!

(I posted some documents and more thoughts from this here).

sunny day

I'm back in town. After approximatly 4 full days of use, the first battery bank dropped to 9 volts, my cutoff point for safe use. Which turned out to be below the safe use point of my laptop power adapter, which burnt out while I was busy listening to music and adding power-saving caching stuff to my mpd setup. Irony not appreciated, world.

I decided to come back while the other bank is still relatively full.

my modest PV array

Hurrying downtown to grab lunch in between work on Branchable, I noticed it was a beautiful sunny day, and I realized that this makes such days even better, because besides enjoying them, I know I'll be enjoying the yield on chilly nights sometime later.

Well, in theory. Actually, the very antique charge controller in the house was dead and bypassed, so I removed it. I called its manufacturer wondering if it could be refurbished, but they suggested it belonged in a museum. So I've ordered a new controller, a Xantrex C-35. Until that comes, pretty days like today will charge, or possibly over-charge the batteries, which will then drain back out at night.

solar day 2

End of the second day in the off-grid house. Three things strike me about being here: quiet, rhythm, and awareness.

In the city, I am constantly annoyed by noise. Here, there's a empty, echoing feeling to the quiet. It's not lack of noise exactly -- I can hear cicadas and birds right now -- but it's still quiet. At first I wanted to fill it, but now I can feel my hearing instead expanding outward. Catching a faint engine noise, or a dog barking in the distance.

Here there's a rhythm to the day driven by the sun. Get up, connect the batteries to the solar panels. (Only necessary because the charge controller is broken.) Check and record the battery levels, make sure the panels are producing well. Think about adjusting them at solar noon. Check the cooler to see how the ice is holding out. Do weekly chores: Refilling the kerosine lanterns and replacing the rock salt used to control the humidity, which is the downside to a earth-sheltered house that stays 70 degrees cool on a 90 degree day. In the evening, watch the sun go down, disconnect the solar panels, record battery levels, and light lanterns. That's the shape of the day.

Besides being aware of distant sounds and time time of day, being here brings to the fore awareness of consumables. Until I get a fridge sorted out, I have a cooler full of ice that I have to monitor. There's propane for the stove, and kerosine for the lanterns. And of course always the state of the batteries. So far, the first battery bank seems likely to last longer than the ice. I'll know better tomorrow.

Unfortunatly I burned out the 5v power supply I was using to run my NSLU2 in a wiring mishap, so I have to run that on an inverter for now, and the batteries, though not low, can barely power both the inverter and my laptop. This has made staying online tricky. But I'm finding dialup surpisingly tolerable, and it helps to generally slow down, too. Despite all the above, I got about as much real work done today as I normally would.

freedombox for a solar powered house

I'm swinging on the front porch shade, with happy wifi bars lit up on my laptop. A good network makes for a happy home, isn't that how the saying goes? (Maybe not yet.)

Typically that's easy to achieve -- here it wasn't. The house is solar powered, the only connection to the outside is a phone line. So I needed a computer that would work in that environment, using minimal (12 volt) power, and getting the most out of the limited bandwidth while providing those happy wifi bars.

At DebConf we learned that the name for these little home servers we have been building for years is "FreedomBox". All right then, here's my latest FreedomBox build.

A typical inexplicable tangle of computer bits.
  • Computer: NSLU2. There are faster choices than the "Slug", but on dialup, speed doesn't much matter, and there are not many lower-powered choices. And with the NSLU2, I can take advantage of years of development and experience, that has resulted in great support for running eg, Debian on it, and deep available knowledge of hardware hacks. It's proven, cheap, highly reliable hardware, and I had it lying around.
  • Power: The NSLU2 is a 5 volt computer. There are some highly (90%) efficient 12 volt to 5 volt converters, which I covet. But the cheap and easy option is a automotive USB power adapter. So power is coming in to the NSLU2 on a USB cable. It's possible to just plug that into its usb port and it will run. But that wastes a port. Instead, I made the other end of the usb cable have a NSLU2 power socket on it. So, no wasted ports. The system has available as many amps as the voltage converter supplies. Not many. Booting it with too many usb gadgets attached could be an issue. (If I need to run an external usb hard drive, it had better have its own power supply.)
  • Wireless: ZyDAS 2501 USB dongle. Not my first choice, just one I had lying around. This device cannot run in AP mode. It is, by the way, possible to use some USB dongles in AP mode with a modified hostapd, but the few I know that work are out of stock. No problem; this house won't have many visitors, and I can tell them the details for connecting using Ad-Hoc wireless mode.
  • Storage: 64 gb thumb drive I had lying around. Hmm, last time I touched a NSLU2, I had only 1 gb drives lying around. Progress.
  • Modem: My NSLU2 is modified to have an external serial port, so I can use an external modem if desired. But I suspect a USB modem will use slightly less power, even though this third USB device means I need a USB hub too. I was doubtful about finding a USB modem dongle that works with Linux, but it was actually no problem, the USR5637 Just Works.
  • Software: Debian Linux of course. For the first time I'm using the polipo web proxy cache, and it works marvelously on dialup and on this low-spec system. Combined with dnsmasq, this makes web browsing over dialup actually not painful.

Since the solar house is in the sticks, the result is a server I call "stick".

old house

An old house, theoretically empty, but still filled with the cruft of its history. Here an old classroom-style pencil sharpener mounted on a wall. In a kitchen cabinet, a plastic bag of dried fish of unknown provenance. Old books. Somewhere, a moldering, out of tune piano. How does this make you feel? Maybe depressed, or urgently needing to wipe it all clean and repaint?

Myself, as long as the previous inhabitants are people whose heads I don't mind getting into, I like this environment. I will carve out my own part of it, clean and reorganise that, but generally leave the rest as-is.

It's weird that, if we were talking not about houses, but software, I'd probably bulldoze it down, compost it, grow trees from it, and start over.

This house has the added complication of a solar power system that has accreted broken parts and workarounds over the years. So far I don't understand the original design, let alone what it developed into!

I'm spending a few days here now just to try to learn how it behaves -- how long can I run my laptop and forgetfully leave lights on before the battery bank reaches unsafe levels? Am I even measuring the level of the right battery bank? (Why does this incoming solar power display still read 21, in the middle of the night?)

I haven't been in this situation since spring of 2001. And then I only had to contend with no running water, and dialup. Now I also have to deal with limited power. Interesting times.