Solar power: we’re getting closer

Most 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. This 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.

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.

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. Commissioning 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.