What Is A Solar Charge Controller?

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Alongside hydro and wind power, the sun is no doubt the answer to our existential energy emergency, providing both individuals and businesses alike with free, clean energy, day after day.

However, although we can rely on the sun to rise each morning, the level of sunshine is a lot less predictable.

What Is A Solar Charge Controller?

This poses quite the problem to a battery designed to receive a fixed rate of energy, but a solar charge controller can help to smooth out the flow of power to our solar batteries in order to keep them safe and optimize our yield.

Let’s put these wonderful contraptions under the microscope!

What Does A Solar Charge Controller Do?

In a nutshell, a solar charge controller offers two forms of protection to the user, both of which are related to our solar batteries.

The first of these securities is known as “overcharge protection”, meaning it prevents any voltage in excess of the battery spec from reaching the battery.

Why Is Overcharge Protection Important?

There’s no avoiding general thermal issues with batteries — They get warm when used, and that warmth triggers a steady rate of decay.

Luckily, modern solar batteries are built to survive normal running temperatures for impressively long periods of time as long as they get plenty of breaks to cool down.

What these batteries aren’t as capable of handling are temperatures exceeding those generated during normal use, and what causes temperatures to get so out of control?

Overcharge, that’s what!

As overcharge warms the cells of a battery, it leads to a process known as thermal runaway in which the battery reaches a state of self-heating that continues until the battery gives up the ghost or overcharge stops.

A solar charge controller prevents this from ever happening by acting as a middleman between your panel array and your solar battery.

It takes in the variable voltage from the panels, tempers it, then passes it on to your battery in a digestible form.

Charge Controllers Vs. Vampiric Panels

The second form of protection a solar charge controller prevents is something known as back-feeding, a process involving the draining of a battery during your panel’s inactive periods.

Although it seems like it, back-feeding isn’t evidence of your panels using power when inactive; it’s simply an example of electricity following the path of least resistance.

As the panels are not collecting energy and forcing it towards your battery, your battery has the lion’s share of the power, and thus, a portion of your energy threads back towards the panels and leaks out into the night.

Charge controllers stop back-feeding dead in its tracks, ensuring all that hard work your panels put into building up your solar yield wasn’t for naught!

My Solar Battery Is Rated To Handle My Panels. Will I Need A Solar Charge Controller?

My Solar Battery Is Rated To Handle My Panels. Will I Need A Solar Charge Controller?

You wouldn’t be the first to think that if you match your battery with your solar panels perfectly, there will be no risk of overcharge, and thus, you can save a few bucks by forgoing the charge controller, but I’d highly recommend rethinking your approach.

Here’s the thing… The advertised voltage output of solar panels isn’t always spot on.

In fact, because of the variable nature of sunlight, their actual spec is more of a range than a fixed number, so even though a manufacturer may claim a panel is rated for 12 volts, it might actually be capable of pushing out something to the tune of 16 or perhaps even 20.

Now, let’s say you purchased a battery that handles that 12 V without breaking a sweat; that’s all good if your panel puts out a stable 12 V, but it’s simply not going to, and when it exceeds this rate, your battery will take on damage, and some of your stored energy will be siphoned by back-feeding.

Will I Always Need A Solar Charge Controller?

There are a few instances where a solar charge controller isn’t strictly necessary. For example, if you’re using a zero-maintenance 1–5 V solar panel, you probably don’t need a controller.

The general rule of thumb is that if your panel is putting out about 2 V per 50 battery amp-hours, you’re good to go green sans the solar charge controller.

Types Of Solar Charge Controllers

Solar charge controllers are a varied bunch; you can find them in various shapes and sizes, and, of course, price points.

Those at the lower end of the market are rated for 4–6 amps, such as this Sunguard unit, while on the other end of the spectrum, you’ll get full-blown MPPT units capable of handling 60 amps and beyond, like this one from Victron.

That said, when dealing with really advanced solar panel systems, many prefer wiring two smaller charge controllers in parallel to spending big bucks on an all-singing-all-dancing mega unit.

Ultimately, you have three choices when it comes to charge controllers:

  • Simple 1- to 2-stage controllers — These will disconnect your panels if voltage gets out of hand… they’re not very efficient and are considered fairly outdated.
  • 3-stage and/or PWM — These controllers essentially have an auto on/off switch that regulates battery voltage. They’re far more efficient yet still quite affordable. Take a look at this fantastic Renogy unit, for example.
  • MPPT (Maximum Power Point Tracking) — MPPT charge controllers are the crème de la crème. They increase efficiency to the 94–98% range, ensuring your solar yield remains largely uncompromised. They also tend to come with flash extras such as onboard computer control systems.

Final Thoughts: Which Type Of Solar Charge Controller Is Right For You?

My first recommendation here is to forget all about 1- 2-stage controllers, as they’re basically fossils now, but choosing between PWM and MPPT is a little more complicated.

If you’re running a pretty small system, and you’re not all that worried about maximizing efficiency, a PWM controller will suit you fine.

On the other hand, if you’ve got a sizable panel array, and you want to take the sun for all it’s got, it’s definitely an MPPT solar charge controller that you need!