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Charge Controllers 101

Do you need a solar charge controller?

If your solar PV system will require batteries, then YES! If not, you can skip right on by this page. Why? Because solar charge controllers control or regulate the charging of batteries in a battery-based solar PV system. And because most residential solar electric systems are “grid-tied” systems, they do not use batteries and thus have no need for solar panel controllers. But all the off-grid homes and remote equipment power by solar-charged battery systems (lights, sensors, instruments, etc.) need charge controllers to safely and efficiently charge their battery investments.

Victron Charge Controller

What do charge controllers do?

Didn't we just cover this? Kind of. But let's get a little more specific. You may wonder why these devices aren't just called battery chargers? Generally speaking, a battery charger refers to a device that you plug into an AC outlet and then connect to a battery to charge it. You may have one in your garage to charge the car battery when dead. A charge controller is used to regulate the voltage and current coming from a DC energy source like a solar PV array. It sometimes helps to think of these as solar charge controllers or DC charge controllers, especially if your system may also include an inverter/charger (mentioned on our Inverter page). In that case you would still need both the inverter/charger (which involves AC charging of the battery bank) and a DC solar charge controller to regulate the flow of solar DC energy into the batteries.

Charge Controller - Water Faucet Analogy.

The goal in charging a battery is to bring the battery's voltage up to a factory-defined level that represents its full charge. A classic analogy will illustrate how solar charge controllers work. Imagine you want to fill a glass from a water faucet. Think of the faucet as the charge controller and the glass as the battery. The water level in the glass represents the battery's voltage level. The water flow represents the current. As long as the water level is low enough, and the flow of water slow enough, then the glass will accept more water. Just like a low battery will accept DC current. But turning the faucet wide-open will quickly overflow the glass from the force of the water flow. Similarly, without a charge controller, excessive DC current flow can overcharge the battery. But adjusting the faucet, reduces the water flow to more steadily fill the glass without spillage. Likewise, a charge controller controls regulates the DC current flowing into the battery to steadily raise the battery's voltage to effectively and efficiently re-charge the battery without causing damage.

Battery Charging Set points.

More specifically, a charge controller regulates current into the battery by based on charging "set points" for that battery. Battery manufacturers specify certain voltage levels ("set points") for each of the 3 stages of battery charging. There is a set point for the bulk, absorption and float charge stages that solar panel controllers keep track of. So a depleted battery is like that empty glass. The charge controller feeds the the highest current (like the fast water flow of an open faucet into an empty glass) during the bulk stage until the voltage level rises to the bulk stage set point at which point the battery is about 80% recharged. At that point, the charge controller reduces current (or flow) like a slow-running faucet until it reaches the absorption set point. After that the charge controller basically just drips enough current to keep the battery voltage at its float set point (filled to the brim).
What kind do I need?
There are two types of charge controller technology used these days. The cheaper, effective but more limited PWM or pulse width modulation charge controllers are one type. While MPPT or (maximum power point tracking) charge controllers are the more efficient and flexible, but more expensive type. On our website, you'll find PWM charge controllers under the Small Charge Controller page, but you'll find MPPT charge controllers on both the Small Charge Controller and Large Charge Controller pages. We define Small Charge Controllers to generally be those up to 30 Amps, and Large Controllers above that.

PWM Charge Controllers.

In the typical scenario, we look to see if we can simply match the voltage of the controller to your battery bank. So a 12 volt controller matches with a 12 volt battery bank/system. This is the typical situation with an RV or boat. Similarly, if you have a 24 volt battery bank for your off-grid house, you would match it with a 24 volt charge controller. Same for 48 volt systems. In these scenarios, the cheaper and perfectly good choice would be a pulse width modulation (PWM) solar panel controller. Huh? We'll explain in a minute. Contrast the PWM controller with a maximum power point tracking (MPPT) charge controller. The MPPT controllers cost more, but allow you to use a larger voltage solar panel/array with a smaller voltage battery system. So a 60 cell, 30V solar panel can charge a 12 volt battery bank when an MPPT controller is used.

MPPT Charge Controllers.

An MPPT charge controller feeds the maximum amount of energy produced by the solar array to the battery bank. Voltage may vary from the solar array depending on the sun's intensity. But despite that, an MPPT charge controller can use all of the available energy to charge the batteries Why? Since watts = voltage x current, an MPPT controller can adjust the voltage to match the battery by adjusting the current. This also allows an MPPT controller to use a larger voltage solar array than the battery bank uses. So while the MPPT controllers cost more, they get more charging bang, for the solar array buck. Conversely, a PWM charge controller can only use the voltage supplied by the solar array that matches the battery bank voltage to charge the battery bank . So when panels produce more voltage in better sun and/or cooler temps, the PWM controller can only use up to its rated voltage to charge the batteries--which may mean energy wasted. Similarly, a PWM controller cannot use a higher voltage solar array (say 30 volts) to charge a 12 volt battery bank. But a PWM does a very nice job charging batteries if its voltage is in sync with the battery bank. In the same way pulsing a faucet on and off in quick small bursts get a glass of water nicely full, a PWM controller charges a battery by pulsing quick small bursts of solar energy.

Click here to see our charge controller product lines or drill down into specific types in the menu above.

Dec 29, 2018
Thomas Lindberg
Tags: charge controllers Solar Basics

Inverters 101

Solar Inverters.

If you're exploring the idea of going solar, no doubt you've heard that solar inverters are essential components for most solar electric systems. Buy why is that? Why are solar inverters so important? And what does a solar inverter do anyway? Are all inverters the same? This page’s focus is to layout some of the basics involved with the different types of inverters and try to answer some of these questions along the way.

What is an inverter?

As you probably know, there are two forms of electricity commonly used today. Solar panels produce the form known as direct current (or DC) electricity. DC is also the form of electricity most batteries store. On the other hand most homes and businesses use alternating current (AC). AC faces less voltage drop over long distances, making it a convenient form to move from power plants to end users. An inverter's main function is to invert DC electricity into AC electricity. Inverters span a range of sizes, from small ones that allow you to run your laptop off your car's cigarette lighter, to larger and more robust inverters designed to work with home or industrial solar electric systems. But there really isn't a generic solar inverter. Why? Because there are different types of solar electric systems, which require different types of solar inverters.

Grid-direct inverter.

A grid-tied or grid-interactive solar electric system is the simplest solar system and requires a specific grid-direct inverter. In a typical residential grid-tied system, the solar PV modules send DC current to the grid-direct inverter, which inverts the DC electricity to AC and then sends the AC to home's electric service panel to feed any electricity demand in the house. If the current house loads are less than the AC output from the inverter (like in the daytime when no one is home), the grid-direct inverter routes the electricity back to the utility (causing the meter to run backwards).A grid-direct inverter must produce a clean, pure "sine-wave" of AC electricity that matches the utility grid's wave form. What's a sine wave? An alternating current electrical wave has the shape of a sine wave. If you see an inverter spec sheet that says "modified sine wave," then you know that inverter cannot replicate the utility's form of electrical wave. That means that some devices will not function (or at least not as well as they could) on electricity from a modified sine wave inverter. Today, essentially all grid-direct inverter replicate's the grid's sine wave shape.Grid-direct inverters must also comply with UL-1741 anti-islanding safety requirements of the NEC (National Electric Code). "UL" means Underwriters' Laboratories. The applicable NEC provision requires that when the utility grid goes down, a grid-direct inverter must automatically disconnect the PV array from the electrical system. This is a safety requirement to help ensure electricity from the PV array doesn't flow back onto the utility lines and injure any utility workers repairing the lines during a power outage. This also means that while the solar panels may be producing power during a day-time power outage, the inverter stops the supply of electricity to the house.

Stand-alone, off-grid inverter.

A stand-alone inverter need not concern itself with the grid because it is only used in solar electric systems where there is no grid electricity present. In this situation, the PV array supplies DC electricity to a DC charge controller that charges a battery bank. When the house demands electricity while the sun is shining and the battery bank is full, the stand-alone inverter tells the charge controller to skip the battery bank and route the DC electricity from the solar panels straight to the inverter which then supplies AC electricity to the house loads. When the array isn't producing (at night), the inverter inverts DC to AC electricity that is stored in the battery bank via the charge controller. Today, most off-grid inverters are really "inverter/chargers" because they also include the functionality to allow charging of the battery bank from an AC source (usually a generator). Why? Because unfortunately, the sun doesn't shine all day, every day in most places. After more than a few days without good sun (clouds, rain, snow), the batteries discharge to their limits and can't be fully charged by the solar panels. Connecting a propane or gas generator to the inverter/charger inputs allows for convenient recharging of the batteries. Some inverter/chargers even automatically start the generator when the inverter senses the need.In the past it wasn't uncommon for off-grid inverters to produce a lower quality wave like a "modified sine wave" or a "square wave" since there was no need to match the utility's wave form. But technology has improved and to ensure AC loads in the house or business are appropriately powered (especially today's sensitive electronics), off-grid inverter/chargers commonly produce clean sine-wave electricity.

Grid-Tied with Battery Back-up.

A grid-tied with battery back-up solar electric system combines components and functionality of a grid-tied system and a stand-alone battery-based system. As a "hybrid" system, it is the most complex system with the most components. The inverter for this system is also more accurately called an inverter/charger because it can connect with an AC source to charge the battery bank when the sun can't do the job. But in the case of a hybrid system, the utility grid is present so the primary AC source used to charge the batteries is the grid. Some models allow a secondary AC source (a generator) to be connected as well. Like a grid-tied inverter, this hybrid inverter also sends excess solar-produced electricity back to the grid (as long as the batteries are fully charged). And when the grid goes down, the hybrid inverter disconnects from the utility grid (like a grid-tied inverter does) and pulls DC electricity from the battery bank, inverts it to AC and sends to a special "emergency" or "back-up" load center or panel. To avoid excessively large and expensive battery banks, a home owner must be selective and only choose important loads to be backed up.

String vs Module level inverters.

For grid-tied solar electric systems, there is another choice to be made. Do you want a single "central" inverter to which all strings of solar panels connect? Of do you want to attach an individual "micro inverter" behind each solar panel that inverts DC to AC at the panel? Or do you want a hybrid style central inverter connected to DC optimizers attached to each solar panel? How to choose?

String inverters.

String inverters are the original workhorse style of the solar grid-tied inverter. These types of inverters are tried and true. And today, they are generally cheaper than module-level micro inverters or DC optimizers. They do lack the ability to optimize and "maximize" the power produced from each solar panel. And they also can't reduce the impact one shaded or impaired panel may have on the array's production. For example, shade on one panel may reduce the production of the entire string of panels in that array. A string inverter can maximize power production of an individual string but not at the module level.

Microinverters.

These devices are little mini inverters that attach behind the module and invert from DC to AC at the module level. This means that that AC wiring connects the solar array to the house, which is cheaper and less subject to voltage drop than DC wiring. But more importantly, having a mini inverter connected to each module means that each module can be adjusted to produce the maximum amount of power possible (called maximum power point tracking or MPPT). So if one panel is shaded, it does not reduce the power produced by the string In general, microinverters should produce a bit more power than string inverters, which is a good thing! Finally, for some of us, our inner geek appreciates the ability to monitor individual panel production on our home laptop or phone. But beyond satisfying our curiosity, monitoring also makes it possible to quickly fix or replace any components minimize downtime.

DC Optimizers.

These types of inverters are a bit of a hybrid. Like a microinverter, a DC optimizer attaches to the rear of each solar panel. And they enable maximum power point tracking (MPPT) for each panel as well. But the module-level optimizer doesn't invert to AC at the panel. Instead each optimizer connects back to a central inverter where AC electricity is actually produced. These devices can be a bit cheaper than a true microinverter while providing similar benefits.

Solar Inverter Pages.

Hopefully this introduction has helped you become a bit more familiar with the terminology and the choices available for solar inverters. Check out here or drill down in the menu above. Give us a call so we can help get you the right inverter for your project

Dec 29, 2018
Thomas Lindberg
Tags: Inverters Solar Basics

Module Versatility – 72 Cell Solar Panels

Why choose a 72 cell solar panel?

Oct 23, 2018
Thomas Lindberg
Tags: 72 cell Solar Panels

SPS Project Spotlight – Small Hunting Cabin Solar System

SPS Project Spotlight - Small Hunting Cabin Off-Grid Solar System

Yesterday a customer came into our office looking for a nice power solution for his hunting cabin. Initially, he had some questions about a pre-configured portable solar kit that he had noticed online. These plug and play solar kits can be a great choice for particular applications, but after speaking with him for a few minutes, the custom design wheels started to turn in our heads!

After reviewing the customer's expected loads (what he planned to power), showing the customer some solar system components and examples of a few of our off-grid solar charging systems in our warehouse, we were able to get a great idea of exactly what he needed. Keeping low cost and high reliability in mind, our first system design ended up being a 540 Watt pole-mounted system with a 1000W 24VDC - 120VAC inverter. After providing him a quick quote and basic custom wiring diagram, we look forward to the next step with this customer and his installer to see if he would like to look into other options, such as using a larger inverter or possibly an inverter/charger for automated generator use.

As with many off-grid systems, there will probably be a few tweaks to our first design, but we are more than happy to work with our customers until they get exactly what they need and leave with a smile on their face and an extremely reliable system that won't leave them in the dark!

Here's the skinny on what we quoted for this customer, and some notes on what the customer can expect from the system.

Small Hunting Cabin Off-Grid Solar System - Parts List:

QTY: 2 - Peimar 270W 60 Cell Poly Solar Panel SG270P
QTY: 1 - Side-Of-Pole Solar Mount 2X 60-Cell Panel (SOP-Y)
QTY: 3 - HelioLug U Lug PV Lug with Hardware UL 2703
QTY: 1 - 50 ft MC-4 PV Cable Extensions
QTY: 1 - MidNite Solar 3 Circuit Combiner
QTY: 1 - MNEPV 20A PV Breaker
QTY: 1 - MidNite Baby Box
QTY: 2 - MNEPV 30A PV Breaker
QTY: 3 - Two Wire Cable Grip 6mm
QTY: 1 - MidNite Kid 30A MPPT Charge Controller Black MNKID
QTY: 1 - Samlex PST-1000-24 1000W 24V Inverter
QTY: 1 - 2-0 Inverter Cable 48in Red
QTY: 1 - 2-0 Inverter Cable 48in Black
QTY: 1 - Samlex DC-FA-200 Battery Post Fuse Block

Off-Grid Solar System Description.

This is a pretty straight forward 540 Watt 24 Volt system. The two solar panels will be mounted on a side of pole mount from our friends at General Specialties, one of the top-notch U.S. made racking companies we've happily worked with for a number of years. The panels are wired in series, so only a single solar panel extension wire will be required and the panels are fused at the array inside a Midnite Combiner box. The 20A PV breaker is intentionally oversized, the solar panels do have a max series fuse rating of 15A, but here in CO we have seen odd breaker issues in the winter time on pole mounted systems due to the high irradiance and an anomaly we call snow bounce. This 20A breaker is installed inside the Midnite Combiner. Not included in this parts list or wiring diagram, but something that we will also recommend is a lightning suppressor, which would also be installed at the combiner. Our favorite lighting arrester or surge suppressor for this is also made by Midnite Solar, the MNSPD-300-DC.

Wires from the pole will land in the Midnite Baby Box, a handy indoor breaker enclosure, which holds the two 30A breakers for the solar input and output from the MPPT Charge controller. An MPPT charge controller was used not only to step down the voltage from the panels wired in series, but will be better for wintertime production, which is generally when these small hunting cabins are utilized the most. This will feed a 24V battery bank, which the customer currently has but may be interested in upgrading, I'll make some notes below on a couple battery banks that would pair up nicely with the kit.

A 1000 Watt 24V - 120VAC Pure Sine solar inverter from Samlex can power their AC loads, and can either be hardwired to their electrical panel or used standalone with its two standard GFCI receptacles.

A system like this should charge around 1500 - 2700 Watt Hours into the battery each day in the winter time, this is assuming proper panel orientation and 3-5 hours of good sunlight.

We recommended a nice starter battery bank for this cabin solar system that includes four Trojan T105 225Ah 6V batteries. These would be wired in series for a 225 Amp Hour 24 Volt bank, with a total storage capacity of 5,400 Watt Hours.

Off-Grid Solar System - Wiring Diagram

Here's the wiring diagram we worked up for them to give them an idea of how all of the parts work together, we like to keep our parts list in basically the order you see them in our diagrams to make things as easy as possible!

We hope that this customer project spotlight will help inspire your own solar project! Give us a call to explore what kind of custom solution we can provide for you!

Thanks for reading!

Sep 26, 2018
Dan Baldwin
Tags: Cabin Solar Off-grid Solar