The way to get the most energy into, and pull the most energy out of your batteries is to charge them the way they want to be charged. This can change depending on the technology of the battery you’re trying to charge, the conditions of the environment your battery is in, the health of your battery, and how much energy is already in your battery.
A charge controller’s job is to know the best way to charge the battery technology you’re using, as well as to monitor the environment and the health of the battery and modify how it charges your battery accordingly.
That depends on where you’re getting your energy to charge your batteries, what kind of batteries you have, how long you need them to last, and what kind of performance you want to get out of your system.
The Smartest Solar MPPT 5010 is one of the best controllers you can buy. It combines a solar MPPT device and a charge controller that knows a broad range of battery technologies to give you the best of both worlds – higher solar panel efficiency and higher battery life.
MPPT stands for Maximum Power Point Tracking.
A MPPT device is one which is designed to pull the maximum amount of energy available from a solar panel at any given moment.
Solar panels generate different amounts of energy from moment to moment, depending on how much sunlight is hitting the panel, how direct that sunlight is, and how much energy you’re trying to pull. If you pull too little energy, you’re not getting the full potential out of your solar panel, but if you try to pull too much the voltage collapses and you get very little energy.
MPPT technology is designed to scan solar panels and determine the maximum amount of energy that can be pulled from a solar panel at any moment, then draw just under that level so that the voltage doesn’t collapse. This way, the efficiency of the solar panel can be maximized under a variety of environmental conditions.
Our system uses a 3-stage charging method, with optional correction for environmental temperature. The three stages are bulk, absorption and float.
The maximum power output from the solar panel changes anywhere from 3-10% depending on the temperature. The rating is calculated at an ideal temperature of 25C (77F). Higher temperatures result in lower maximum power, lower temperatures result in higher maximum power.
The short answer is that the MPPT function is used only when the battery is hungry enough to take on a lot of energy all at once.
Charge controllers only invoke a MPPT function when there’s enough of a difference between the voltage of the solar panel and the voltage of the battery (usually at least 1V) and when the rate at which you can charge the battery safely is high enough to take advantage of the output from the MPPT function (bulk-stage charging).
MPPT stands for “Maximum Power Point Tracking,” and “PWM” stands for “Pulse Width Modulation.”
MPPT and PWM represent two methods for controlling how power is drawn from the power source (such as a solar panel) and fed to the battery or battery pack. MPPTs are by far more efficient, but PWMs cost less. Both technologies can be used together in the same controller, but since doing so will increase your cost, the idea is to choose the technology which best fits your performance needs and budget.
Charge Controllers using MPPT automatically adjust to allow your solar panels to run at peak voltage in different lighting and seasonal conditions. It then takes the power collected from your solar panels, calculates the best voltage for charging your batteries, and then converts the power to that voltage with minimal power loss. v
For example, say that your solar panel generates 20V @ 5A (or 100W), and your battery charges at 10V. Without MPPT, you’d charge your battery at 10V @ 5A (50W), only half the power available from the panel. With MPPT, you’d charge your battery at 10V @ 10A – the same 100W generated by the solar panel, but shifted to a voltage your battery can charge at with minimal power loss.
In this example, MPPT potentially doubles the efficiency of the system. Many Charge Controllers with MPPT can accept high input voltages, and then convert that voltage down to a level your system and batteries can handle comfortably without throwing power away.
In order to decide which technology is best for you, you’ll need to look at several things:
A Charge Controller using MPPT technology can collect and store enough energy to offset the price difference over one using PWM. A Charge Controller using PWM, if you carefully match it to your power requirements, can be a cost-effective solution, especially for smaller systems. There are also more Charge Controllers on the market using PWM, since they’re less expensive to make.
It’s important to remember that your Charge Controller is the heart of your energy generation system. Understanding what kind of devices your system will need to power, what kind of batteries you will be using, and what kind of environmental conditions you can expect will go a long way towards helping you make the right choice.
To get an idea of how an MPPT can benefit you, it’s time for a little rough math. Take the voltage your solar panel is rated at. Divide that number by the voltage of your battery or battery pack. That’s the approximate gain you can expect in a system that uses an MPPT over a system that doesn’t.
In other words, in a system that uses a 24V panel and a 12V battery, you can expect to collect twice the energy if you use an MPPT versus if you don’t.
For example, a rating of 100W and 20V in 25C means that, at 25C (77F) you could potentially get 20V @ 5A out of your panel. These are the numbers that describe the kind of power that the manufacturer wants you to expect to get out of your solar panel.
Solar panel ratings are always ideal-world numbers. They assume a particular temperature and a sun that beams directly onto your panel at all times. This, of course, isn’t how things work in the real world. These ratings also assume that you will be able to use every scrap of energy that the panel collects for you, and that simply isn’t true either.
You might be running a substandard controller that isn’t efficient and thus loses power. You might be trying to charge batteries that are almost fully charged, which means that they’ll absorb less energy per second than a very hungry battery will.
A good rule of thumb, if you’re using a quality controller, is to just throw 10% of the rated power out the window when you’re figuring out how much you can expect to collect. You will also need to keep in mind that even this number is optimistic when your batteries have a good charge or when the weather is bad.
Irradiance is a measurement of the raw power hitting the surface of the solar panel. With clear skies and a good angle on your panel, your panel will see a higher level of irradiance than on a cloudy day with a poorly angled panel.
A solar panel’s irradiance is usually measured in watts per square meter, and is sort of like the miles-per-gallon rating on your car – it assumes ideal conditions, just like your panel’s overall wattage rating.
Whereas the overall wattage rating for your solar panel is designed to help you dream about how much power you can get with that one solar panel, the irradiance rating is designed to help you dream about how much power you can get by buying a whole bunch of solar panels, since it’s power over a unit of area instead of power per panel.
The best-case is 1000W per square meter. A more realistic number would be 800W per square meter. Most solar panels have specification sheets that will show you this is the more reasonable number.
Note: All specific numbers mentioned above are approximate, ideal-world numbers. Real-world results will vary based (in part) on environmental conditions and the condition of the equipment being used.
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