Tuesday, March 31, 2009

MPPT Solar Controller Double Plus Good Good!

This MPPT solar controller is totally amazing. I love this thing. Between this controller, and my new low-power EEE netbook, I just don't worry about electricity anymore.

Tonight I parked underneath a couple streetlamps. And as I sat down to do some computer work, I saw my MPPT controller's charge light blinking. WTF? It's 11PM. No... no way... it can't be... it is! The thing is actually trickle-charging my batteries overnight, using the energy of a City of San Francisco halogen streetlamp!

Probably not a huge amount of electricity there, but it's non-zero. I still have to hack up a USB-to-MODBUS interface to plug my computer into the thing and get more detailed data from it. But, no matter what, the old PWM controller wasn't capable of boosting the tiny voltages from a streetlamp up to a level where it could actually charge the battery. MPPT controllers can.

I'm putting the MPPT controller on the (very short) list of things I'm very, very glad to have bought.

Friday, March 20, 2009

MPPT controller in!

After 3 months of procrastinating, I finally installed the new MPPT solar controller. It is fantastic! I had very little sunlight this afternoon (more rain coming this weekend!), but I had to charge up my electric bike. Batteries were down in the critical zone, 12.4V. As soon as I hooked up the new controller, within a few minutes it rescued my batteries back up to 12.6V! I can't wait to see how it does tomorrow.

The long delay was due to my trying to find the "right" way to terminate the huge #8 wire I'm using. The problem was that the new MPPT controller has screw posts, like a terminal block, not holes with screw-downs. And nobody seems to make screw lugs that'll fit #8 wire! The closest I can find are Kragen ones for #10 wire. I decided to blow off the right way and just do whatever worked, which meant prying open the #10 lugs, shoving the #8 wire in, and then clamping it down. Not the ideal solution, but it works.

I tried to solder the lugs on, for more security, but neither my battery-powered soldering iron nor my 110V iron could get the huge wire hot enough to melt solder. I guess that's why I chose that wire in the first place-- it won't get hot!

But I'm happy the thing is working now. Next step is to build the RS485 ModBus to USB interface I've been pulling together a schematic for, so I can get all the huge reams of data off of this controller and really study how my solar electrical system is working out.

Monday, March 9, 2009

Spring has sprung!

Almost exactly a year ago, I first hooked up my solar electrical system and started drawing power from the sun.

I can tell spring has come now, because I looked over at my solar controller and saw it pulling in 10 amps! That's something I haven't seen in a long, long time, probably not since September.

I'm stunned at the tremendous variability in sunshine here in the northern latitudes of California. It's a huge difference: from 10 amps a lot of the day in the summer, to maybe 1-2 amps for a few hours of the day on rainy days in the winter.

There are several problems. First, San Francisco is in the upper latitudes, so the angle of the sun is lower, especially in winter. So my flat-mounted panels just won't pull in during the winter. Secondly, and also because of the high latitude, the hours of sunshine varies a lot between winter and summer. And, finally, California has a wet season and a dry season. It does not rain all spring, all summer, and all fall! Then we get all our rain in the winter... and then it's over.

Which means: LOTS of rainy days in wintertime, combined with few hours of sunshine, and a very low angle of the sun. So the factor of sunshine between winter and summer is like 10-to-1.

I installed my system in the springtime and started designing my usage based on that type of constant availability of sunshine. As I've blogged before, the end of October was a disaster for me: the rainy season startd, and my electricity usage suddenly way outstripped availability. I recovered by buying a small, low-power netbook. But still, that cost me a lot of money.

Now that spring has come, I can relax a bit more and be somewhat more lavish with electricity. But I've learned just how seasonal this type of thing is.

If anyone is designing a solar electrical system for their van (or for anything), my advice would be: design your system so that it provides enough power for all your uses, in the dead of winter with next to no sunlight. That will be expensive, but not as expensive as having to purchase new, more energy-efficient gear to cope with the lack of sunlight in wintertime.

Monday, March 2, 2009


I went down to the junkyard and bought myself a set of 18 small lockers, 18"x12"x18" each. This is wonderful. They look awful (I need to paint them!) but they are much sturdier and roomy than that awful cheap Costco plastic shelving I was using.

I couldn't get them into the van standing up, so I laid them down on their side. makes a nice shelf, but this position is temporary. I want to mount two of them on the wall, at head-height, one on either side of the van, and one standing up in the corner. That'll free up a lot of space.

For now, though, I'm just happy to have them and all my stuff a lot more organized.