Learning about solar systems and the different units of measurement used to gauge a solar system’s performance can be very confusing. Understanding the optimum method of wiring solar panels can be equally bewildering. Is it better to install the solar panels in series or parallel?
Panels are connected in series when using an MPPT controller. When not using an MPPT controller, connect them in parallel. This method aggregates the voltage while maintaining the amperage. MPPT controllers adjust the higher voltage and modify it for the system’s requirements.
To understand how a solar system is wired, let’s first refresh our understanding of how electricity is measured. By the end of the article, you will understand these, how they relate to solar systems, the options available to wire your solar installation, and which method will be optimum for your application.
You Can Wire Solar Panels In Series Or Parallel
How the system is wired depends mainly on the inverter you are using. If it is in an MPPT enabled inverter, the solar panels will be wired in series.
A typical solar system consists of the following components:
- Solar panels
- An MPPT (maximum power point tracking) enabled inverter acts as the junction between the solar panels, the battery, and the AC DV board. MPPT is explained further in this article.
- The battery is connected to the inverter. The inverter draws energy from the battery or sends excess (unneeded) power for storage and later use.
- The home DB Board connects to the inverter, which converts the DC from the panels and the battery to AC. It distributes this to the electrical devices in the home.
How Is Electricity Measured?
The three primary measurements of electricity that are relevant to a solar system are voltage, amps, and watts. Before we continue, let’s quickly refresh what these are.
When you get your energy bill, it shows the power you used listed as kilowatt-hours. But at the store, you’ll see things like 12-watt light bulbs, 9-volt batteries, and vacuum cleaners with 15-amps of sucking power. Why are there so many measures of electricity?
Several things must happen in an electrical circuit for electricity to flow and work to be done. The most straightforward analogy is to think of an electrical circuit as the tap on your kitchen sink. To make the tap work, you need three things to happen:
- You need to turn the tap on – switch
- You need water to be available in the pipe
- You need sufficient pressure to make the water flow
How does this apply to how solar panels are connected and our electrical terms?
The Role Of Voltage In Solar Panels
An electrical circuit (the water pipes) uses electrons to carry the electricity (like the water in our example).
The electrons need something to push them along in the same manner the water pressure moves the water. The “pressure” in an electrical circuit is called VOLTAGE. The voltage is provided by a positive and a negative terminal. Electrical current moves from a negative terminal to the positive terminal through whatever device you want to power. Voltage is, therefore, the measure of how strong the available electrical current is.
Measuring this is important as most electrical equipment is designed to work within a specific voltage range. Too much voltage and the device will emit a burning smell, and the inside bits will melt in a puff of smoke. Too little voltage and the device won’t work.
How Amps Affect Solar Panels
Not only do we need to know the available pressure of our electrical system, but we must also measure the speed at which the electricity flows. We do this by measuring the amount of electricity that passes a given point in one second. This is recorded as the amperes of the circuit.
In the “tap” example, amps refer to the speed of water flowing out of the tap.
How Are Watts Calculated?
Let’s go back to our water analogy. Instead of just filling the sink, we will put the water to work by spinning a turbine or wheel.
In the first example, we will attach a thin pipe to the tap. By reducing the diameter, the water travels through; we reduce the amount that flows through the system (amperes); simultaneously, we increase the pressure of the water (voltage), and the wheel turns.
Now let’s take the pipe off the tap and use the water, with no adjustment, as it flows out of the tap. Although the pressure is now less (voltage), the speed of the water (amperes) is increased. The result is that the wheel still turns.
If we compare the tap and the pipe, even though the volume and pressures are different, they both deliver power, which in electricity is called Watts. We can control the power (watts) the system produces by controlling the voltage and amps.
If you multiply the voltage and the amps, you can calculate the power (watts).
How Does This Impact In The Solar Panels Are Connected?
You would only use a series connection on your solar panels if you have an MPPT controller. So firstly, let’s look at what an MPPT controller is.
What Is An MPPT Enabled Inverter?
MPPT stands for “Maximum Power Point Tracking.” Solar panels are sized by the maximum number of watts they can produce from the sun’s energy.
In theory, a 130-watt panel will generate 130 watts of electricity – simple, huh!! Unfortunately, as Solar panels and batteries are not intelligent devices, it’s a little complicated.
If you connect a 130-watt solar panel through a conventional charge controller (that is not MPPT enabled), it will not generate 130-watts.
Let’s explain that. Although the solar panels packaging shows, it generates 12 volts at 6 amps. To compensate for the different intensities of the sun at other times of the day and in varying weather conditions, the panels will generate between 50% – 75% more voltage than stated. The problem is exacerbated if the temperature changes the panel’s voltage fluctuates. A lower temperature produces a higher voltage and visa-versa.
Although batteries require a higher voltage than their nominal voltage to charge, they only run at a fixed voltage. If the battery is a 12-volt unit, multiplying the voltage (12v) by the amps (6a), the resulting watts are only 72w. In this example, we lost over 58 watts.
An MPPT controller ensures that the watts produced by the solar panels are always optimal and fully available. The unit will increase the amperage and reduce the voltage (remember our tap and pipe) to match the battery’s requirement to achieve the required watts. Our example will reduce the voltage to 12volts and increase the amps to 10.84. By multiplying the voltage (12v) * the amps (10.84a), we get 130 watts.
The battery now receives 10.84 amps at 12 volts; this results in almost 130 watts, and the system will run optimally.
Which Is The Best Method To Connect Solar Panels?
How does a series or parallel connection affect a solar system?
The Advantages Of Solar Panels Connected In Series
The voltage produced by panels connected in series (negative terminals connected to positive) is aggregated.
Using an MPPT controller means that the highest voltage possible (within a permissible range defined by the controller) is reduced. At the same time, the amperes are adjusted to maximize the power over the whole system.
Using a lithium battery (which requires 14.4 volts) attached to three panels (each producing 17 volts), the total output would be 51volts. As the system only needs 14.4-volts, the MPPT system will only need to operate at 28% capacity in a low light situation to produce 14.4-volts.
Solar Panels Connected In Series Seem Less Efficient
If you don’t have an MPPT charge controller, you will connect the panels in parallel (where positive terminals are connected to positive terminals). Irrespective of the number of panels, the voltage produced will be no higher than each battery individually.
In theory, parallel-connected panels are more efficient. The system will still work if a panel is not working or installed in partially shaded conditions.
If the solar panels are connected in series, the power from the whole array will be compromised.
The downside is that using the example of panels operating in partial light, irrespective of the number of panels connected collectively, they would still only produce 14.4 volts. To reach the 14.4 volts required to charge the batteries, solar panels in parallel need to be operating at 84% capacity.
The 28% capacity series connection is more attainable in low light conditions than the 84% parallel connections. The real-life benefit of panels connected in series is that they will start producing power earlier at the beginning of the day and later in the evening than panels connected in parallel.
Although not optimal, connecting solar panels in parallel to cater to specific circumstances is possible.
With an MPPT controller, the standard protocol is that solar panels are connected in series; this means that, even in lower light situations, the solar panels will produce significantly more electricity than their parallel-connected cousins.