not tabletop solar

Borrowed a pickup truck today to fetch my new solar panels. This is 1 kilowatt of power on my picnic table.

solar panels on picnic table

DIY professional grade solar panel installation

I've installed 1 kilowatt of solar panels on my roof, using professional grade eqipment. The four panels are Astronergy 260 watt panels, and they're mounted on IronRidge XR100 rails. Did it all myself, without help.

house with 4 solar panels on roof

I had three goals for this install:

  1. Cheap but sturdy. Total cost will be under $2500. It would probably cost at least twice as much to get a professional install, and the pros might not even want to do such a small install.
  2. Learn the roof mount system. I want to be able to add more panels, remove panels when working on the roof, and understand everything.
  3. Make every day a sunny day. With my current solar panels, I get around 10x as much power on a sunny day as a cloudy day, and I have plenty of power on sunny days. So 10x the PV capacity should be a good amount of power all the time.

My main concerns were, would I be able to find the rafters when installing the rails, and would the 5x3 foot panels be too unweildly to get up on the roof by myself.

I was able to find the rafters, without needing a stud finder, after I removed the roof's vent caps, which exposed the rafters. The shingles were on straight enough that I could follow the lines down and drilled into the rafter on the first try every time. And I got the rails on spaced well and straight, although I could have spaced the FlashFeet out better (oops).

My drill ran out of juice half-way, and I had to hack it to recharge on solar power, but that's another story. Between the learning curve, a lot of careful measurement, not the greatest shoes for roofing, and waiting for recharging, it took two days to get the 8 FlashFeet installed and the rails mounted.

Taking a break from that and swimming in the river, I realized I should have been wearing my water shoes on the roof all along. Super soft and nubbly, they make me feel like a gecko up there! After recovering from an (unrelated) achilles tendon strain, I got the panels installed today.

Turns out they're not hard to handle on the roof by myself. Getting them up a ladder to the roof by yourself would normally be another story, but my house has a 2 foot step up from the back retaining wall to the roof, and even has a handy grip beam as you step up.

roof next to the ground with a couple of cinderblock steps

The last gotcha, which I luckily anticipated, is that panels will slide down off the rails before you can get them bolted down. This is where a second pair of hands would have been most useful. But, I macguyvered a solution, attaching temporary clamps before bringing a panel up, that stopped it sliding down while I was attaching it.

clamp temporarily attached to side of panel

I also finished the outside wiring today. Including the one hack of this install so far. Since the local hardware store didn't have a suitable conduit to bring the cables off the roof, I cobbled one together from pipe, with foam inserts to prevent chafing.

some pipe with 5 wires running
through it, attached to the side of the roof

While I have 1 kilowatt of power on my roof now, I won't be able to use it until next week. After ordering the upgrade, I realized that my old PWM charge controller would be able to handle less than half the power, and to get even that I would have needed to mount the fuse box near the top of the roof and run down a large and expensive low-voltage high-amperage cable, around OO AWG size. Instead, I'll be upgrading to a MPPT controller, and running a single 150 volt cable to it.

Then, since the MPPT controller can only handle 1 kilowatt when it's converting to 24 volts, not 12 volts, I'm gonna have to convert the entire house over from 12V DC to 24V DC, including changing all the light fixtures and rewiring the battery bank...

PV array is hot

Only took a couple hours to wire up and mount the combiner box.

PV combiner box with breakers

Something about larger wiring like this is enjoyable. So much less fiddly than what I'm used to.

PV combiner box wiring

And the new PV array is hot!

multimeter reading 66.8 DVC

Update: The panels have an open circuit voltage of 35.89 and are in strings of 2, so I'd expect to see 71.78 V with only my multimeter connected. So I'm losing 0.07 volts to wiring, which is less than I designed for.

DIY solar upgrade complete-ish

Success! I received the Tracer4215BN charge controller where UPS accidentially-on-purpose delivered it to a neighbor, and got it connected up, and the battery bank rewired to 24V in a couple hours.

charge controller
reading 66.1V at 3.4 amps on panels, charging battery at 29.0V at 7.6A

Here it's charging the batteries at 220 watts, and that picture was taken at 5 pm, when the light hits the panels at nearly a 90 degree angle. Compare with the old panels, where the maximum I ever recorded at high noon was 90 watts. I've made more power since 4:30 pm than I used to be able to make in a day! \o/

12 to 24 volt house conversion

Upgrading my solar panels involved switching the house from 12 volts to 24 volts. No reasonably priced charge controllers can handle 1 KW of PV at 12 volts.

There might not be a lot of people who need to do this; entirely 12 volt offgrid houses are not super common, and most upgrades these days probably involve rooftop microinverters and so would involve a switch from DC to AC. I did not find a lot of references online for converting a whole house's voltage from 12V to 24V.

To prepare, I first checked that all the fuses and breakers were rated for > 24 volts. (Actually, > 30 volts because it will be 26 volts or so when charging.) Also, I checked for any shady wiring, and verified that all the wires I could see in the attic and wiring closet were reasonably sized (10AWG) and in good shape.

Then I:

  1. Turned off every light, unplugged every plug, pulled every fuse and flipped every breaker.
  2. Rewired the battery bank from 12V to 24V.
  3. Connected the battery bank to the new charge controller.
  4. Engaged the main breaker, and waited for anything strange.
  5. Screwed in one fuse at a time.


The house used all fluorescent lights, and they have ballasts rated for only 12V. While they work at 24V, they might blow out sooner or overheat. In fact one died this evening, and while it was flickering before, I suspect the 24V did it in. It makes sense to replace them with more efficient LED lights anyway. I found some 12-24V DC LED lights for regular screw-in (edison) light fixtures. Does not seem very common; Amazon only had a few models and they shipped from China.

Also, I ordered a 15 foot long, 300 LED strip light, which runs on 24V DC and has an adhesive backing. Great stuff -- it can be cut to different lengths and stuck anywhere. I installed some underneath the cook stove hood and the kitchen cabinets, which didn't have lights before.

Similar LED strips are used in some desktop lamps. My lamp was 12V only (barely lit at 24V), but I was able to replace its LED strip, upgrading it to 24V and three times as bright.

(Christmas lights are another option; many LED christmas lights run on 24V.)


My Lenovo laptop's power supply that I use in the house is a vehicle DC-DC converter, and is rated for 12-24V. It seems to be running fine at 26V, did not get warm even when charging the laptop up from empty.

I'm using buck converters to run various USB powered (5V) ARM boxes such as my sheevaplug. They're quarter sized, so fit anywhere, and are very efficient.

My satellite internet receiver is running with a large buck converter, feeding 12V to an inverter, feeding to a 30V DC power supply. That triple conversion is inneficient, but it works for now.

The ceiling fan runs on 24V, and does not seem to run much faster than on 12V. It may be rated for 12-24V. Can't seem to find any info about it.

The radio is a 12V car radio. I used a LM317 to run it on 24V, to avoid the RF interference a buck converter would have produced. This is a very inneficient conversion; half of the power is wasted as heat. But since I can stream internet radio all day now via satellite, I'll not use the FM radio very often.

Fridge... still running on propane for now, but I have an idea for a way to build a cold storage battery that will use excess power from the PV array, and keep a fridge at a constant 34 degrees F. Next home improvement project in the queue.