DIY Solar Energy System, Part 1: Basic Theory and Charge Controllers

Author: oakwhiz (33 Articles)

I run things around here at Minousoft Software. I enjoy developing games and building DIY electronics.

For a while, I’ve been looking into building my own solar power system. I have experimented with tiny solar cells before, but this is different – I’m looking for enough power to run an appliance. This would be very useful for charging things like cell phones, media players, etc. without wasting energy off the grid. Additionally, I could power an always-on outdoor microcontroller project for free, without changing any batteries. And, if I was in an area with no power connections, I could bring a solar panel and battery, and have electricity. I could even mount the panel on an electric vehicle and have it recharge itself for free!

(Much more important information after the jump!)

But first, before I start: How do solar panels (aka photovoltaic modules) actually generate free electricity?»

In my quest for more information, I discovered several important concepts which I will discuss in this series of articles:

• Charge controllers
• Batteries
• Sun tracking
• Maximum power point tracking
• Energy losses and inefficiencies
• Assembling photovoltaic (PV) cells into panels
• Mixing-and-matching different photovoltaic panels
• Choosing used, broken, and cheap parts
• Buying cheap parts versus buying quality parts

First up is charge controllers. What’s a charge controller, you may ask? A charge controller is a device which goes in between your PV panels, your batteries, and your loads (aka appliances.) The charge controller mainly charges the batteries, but many different types exist. Some of them have extra features to intelligently handle the electrical power in different ways, and some of them are simplistic and just shut off the electricity flow from the PV panels when the batteries are finished charging. Some things to watch for when looking for charge controllers:

• The voltage and current input/output ratings of the controller must match your PV panels and your battery bank.
• The charge current(s) must be sufficient to charge the number and size of your battery bank.
• The maximum ratings should be picked with respect to future expansion, i.e. if you are adding more solar panels later.
• The controller must be designed to charge your exact, specific type of battery. You can’t use the wrong type of charger, or the batteries will explode. More on this later.
• The controller should have fuses/circuit breakers, over/undervoltage protection, and some switches to control everything.
• If using lead-acid battery types, it may be useful to consider a charge controller that does simultaneous desulfation. If a lead-acid battery is pushed hard, mistreated, or not charged for a long time, a layer of deposit (sulfation) begins to form on the surface of the internal battery plates, which prevents electricity from moving through the battery. A desulfation system sends a specially-tuned high frequency pulse through the battery which will actually cause sulfation to flake off and dissolve back into the battery acid, essentially breathing renewed life into a poorly-performing battery. If the battery is desulfated while it is float charged, any sulfation that forms during normal use will be dissolved soon after.
• Lead-acid batteries should be charged with a 3-stage microcontroller-based charger. This maximizes battery life and efficiency.
• A large PV system may require battery equalization features in order to balance any cells which are underperforming.
• Controllers with battery monitors built-in can make life easier if you don’t want to manually check the battery condition with a multimeter.

It’s important to select the right charge controller.

You can buy charge controllers, but as with just about every other part of a PV system, they tend to be expensive, and cheap units can have questionable manufacturing quality. Almost all of them are at least $100, and most are more than $250. The advantage here is that someone else has already done the math for you, and you usually get some type of warranty or guarantee for component failure. It can be well worth buying a good charge controller, especially for large PV systems.

You can also build your own charge controller. This is not for the faint of heart. You will require intermediate DIY electrical engineering skills. The advantages to this method are that it can be cheaper, easy to repair, and more customizable to your needs. If you are inexperienced, you might be able to get away with copying someone else’s circuit design, but you risk dealing with unknown ‘glitches’ in the circuit when it is actually built.

Next time, I will be talking about batteries and how they are important for your PV system! If you enjoy these articles, show your support by subscribing to our blog, bookmarking us, sharing this article with your friends, or donating. Any comments, questions, or suggestions you have would be greatly appreciated.

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