Wednesday, February 3, 2010

Solar power: we’re getting closer

The solar panels installedMost of the snow melted off the porch roof yesterday. So, today, once I got a few things done inside the house, I worked on installing the rest of the solar panels. This job went quite well and didn’t take too long. Before lunch I started wiring them together. I finished after lunch.

There are 15 panels in all. There are three sets of five panels which are each wired in series. That means they are connected positive to negative. Another view of the installed panelsThis multiplies the voltage while the current stays the same. So, once five panels with a voltage of 17.4 volts each and an amp rating of 5.75 amps are wired in series, the voltage is 87 volts and the amperage is 5.75 amps.

Each of these three five-panel strings is then wired in parallel – connected positive to positive and negative to negative. Wiring in parallel multiplies the current while the voltage stays the same. So, three strings of 87 volts and 5.75 amps wired together in parallel yields 87 volts with 17.25 amps.View of the panels showing how they are mounted to the roof

There are of course variations in the voltage and amps coming off of the panels depending on different factors like how direct the sun light is and the temperature of the panels. Increasing the voltage by wiring in series allows smaller gauge wire to be used to bring the power from the panels to the solar charge controller since the wire gauge required is based upon the amperage and the length of the wire.

The solar charge controller I purchased will take the 87 volts (with variations) and convert it to the appropriate voltage for charging my battery bank. The battery bank is nominally 24 volts, but it will be charged closer to 29 volts. The controller is rated to handle up to 150 volts, but I’m happy with 87.

The three strings of series-wired panels are combined in a combiner box. The negative leads are attached to one bus bar, and the positive leads are attached to another bus bar. This combines the positives and the negatives from the panels allowing only one wire for postive and one for negative to be sent into the house to the charge controller.Combiner box

After installing and wiring the panels, I hooked up the negative and positive battery cables which lead to the disconnect box and from there to the other components of the system. I had them disconnected so that nothing would accidentally become powered inside before I wanted it to. After connecting them, I flipped the circuit breaker for the charge controller, and it woke up ready to be commissioned. The solar charge controllerCommissioning just meant I needed to verify the battery bank information for the controller.

It was late enough in the afternoon that the sun wasn’t shining directly enough on the panels for them to be producing power. So, I wasn’t able to determine for sure that everything is operational as it should be. I believe I wired them correctly, but I’ve made mistakes on other things before. Hopefully, we’ll have some sunlight tomorrow so that I can verify that things are working correctly and let the sun charge the batteries completely.

There are six tasks left to do before we flip the switch and go off the grid:

1.  Run the 12-2 wire from the inverter through the floor into the kitchen.
2.  Connect the wire from the inverter to the existing wiring in the outlet for the electric stove.
3.  Disconnect the mains from the AC circuit breaker box in our home.
4.  Connect the wire leading to the electric stove outlet to as the mains.
5.  Run the wires and connect the Bogart Engineering Trimetric 2020 battery monitor.
6.  Flip the switch to turn on the inverter.

At that point, we’ll be off the grid and on solar power. Don’t worry, I’ll disconnect the power from the utility company outside at the disconnect box before doing the wiring in the house. I have no desire to let electricity course through my body.



I saw you write previously about the thought of the wind catching the panels like a sail. There likely is a way to measure the potential wind load on a structure, but I don't know off hand.

I don't know how wind flows around your house and area. The danger would be in a thunder storm, or time of un-natural high wind.

You don't want these blowing off, as it would likely shatter the panels to fall from the roof...

It will be interesting to see how these produce for you.


I believe it would take some unusual winds to move the frames. The panels won't come off of the frames, and I don't think the frames can come off of the roof. I'm still going to add some guy wires, but based upon the usual wind patterns, they will be just fine.

I'm also curious how they will produce. Their current location isn't ideal, but it should work fine (there are a couple trees that can shade the panels somewhat at certain times of the year). On the new house they will have unobstructed access to the sun. I'll update when we get some good sun on them (mostly cloudy tomorrow and rain possible the next two days after that).


That was my thought about the wind also. We are also in a Mobile Home, so your story is something I find very interesting, since "solar" is one of future projects.My question is how do you think you will fair with no AC. This place is like a sardine can in the summer, with the metal roof and all. That's one of my biggest concerns. Thanks! I <3 your blog!



Hey, M! So far wind has not been a problem. The panels and their frames are quite sturdy.

Regarding no AC, we haven't used it the last two years. Our mobile home is partly shaded by a couple oak trees on the south side (they'll also shade the panels some, but not enough to be a problem, I believe). Also, it was built in MI, so it has a bit more insulation than some southern built mobile homes. We have also set up a summer kitchen on the back porch which will keep a lot of heat out of the house. It's amazing how much heat is generated by a stove inside.

I'm glad you like my blog! :)


It is super windy here. Last year we had a tornado and we lost our greenhouse. Our house is only a little shaded, because we had to take our tree down over the house because of during a Hurricane a few years back. We are talking about installing a solar whole house fan, and some kind of grate system to help with taking the heat out of the house. We put up a solar shower/sink outside, and are in the process of making an outdoor oven/stove. It gets very hot in here when cooking! I could probably bake things by setting them on the table ! LOL Thanks for the info!

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