Solar Charge Controller : 71/100

The Roger bikes solar series comes to its 5th part today: the solar charge controller. So far we have covered grid-tie vs off-grid, AC vs DC, Batteries, and Solar Panels. In the cabin we are building our solar system will be 100% off grid, it will have a mixture of AC and DC power, there will be 832amp hours/10kW of battery power, and 1.3kW of solar panels.

Once you collect energy from the sun it needs to pass through a solar charge controller before going to the batteries. This is done for 2 purposes:

  1. The solar charge controller regulates the voltage coming from the panels. Since the sun rises and sets, and there are clouds the energy produced from it varies. Electronics however do not like variety in their power source. Once the power is regulated to a consistent voltage it is sent to the batteries.
  2. Charging a battery requires controlling the voltage based on how much energy is in the battery. Once the State Of Charge (SOC) reaches 80% in a lead acid battery the voltage is lowered to prevent damaging the lead plates. This process is handled by the solar charge controller. We will program in the type of batteries we have to the solar charge controller and it will then adjust how it charges to ensure the batteries last as long as possible.

Now that we have the need for the solar charge controller established we need to consider the types and sizes. There are 2 types of solar charge controllers from what I have learned: Maximum Power Point Tracking (MPPT) and not-MPPT. Basically an MPPT solar charge controller is the latest and greatest and ensures you are getting the most out of your panels. It also helps your batteries last longer. MPPT controllers are more expensive than not-MPPT but the price is worth it.

Sizing the controller is a little more involved. First of all you want to make sure the controller works with your battery voltage. We are putting 2 6volt batteries in series to create a 12v battery, so we need the controller to be able to handle 12v, which is pretty much all of them.

The next sizing consideration is based on how much energy your solar panels produce in Volts. You want to have a controller that can handle the voltage your panels produce. If it cannot then you are wasting energy produced by the panels, and overheating your controller.

The final sizing consideration is the output current in Amps. As the controller converts the power from the panels into consistent and usable energy you want to make sure it is all getting converted and sent to the batteries.

For our cabin we have 4 325Watt solar panels for 1300Watts of energy. If we look at the Victron MPPT calculator and enter all the values of our panels they recommend a 150 volt / 85 Amp controller. Currently that controller lists for $680. For $100 more you can get a 150/100 controller and have some overhead if we ever want to expand the system with more panels.

Also when you look at the solar kits at Arizona Sun and Solar that is the charge controller they recommend for the 1300 watt kit.

Workout detail

Got up and walked around on my trails for about 2 hours listening to Botany of Desire by Michael Pollen. Its a fun book about plants and how we have co-adapted with them. He covers the apple, tulip, cannabis, and the potato. So far I am through the apple and tulip and have enjoyed them both. At some point I will write a review but don’t hold your breath, just get the book.


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