Solar energy is among the cheapest source of electricity and also the eco-friendliest. It is, therefore, not surprising that many households are keen about installing photovoltaic systems.
However, for many homeowners, technical jargons related to solar power installation can be confusing. Most likely, you’ll hear your installer talk about the solar panel wiring which is an important consideration when it comes to PV installation.
As with any electrical installation, how the solar panels are wired (either series or parallel) is crucial. The wiring design and configuration significantly impacts the performance of the circuit. When wired properly, the solar system performs optimally and guarantees better savings and ROI. The type of connection also determines the appropriate solar panel cable and type of inverter to be used.
Normally, you’ll need multiple solar panels to harness sufficient solar energy that can power up your home. The basic options are parallel and series connection. In advanced setups, these circuit configurations can be combined.
What is series connection?
When wiring solar panels in series, electricity travels through one path. Each solar panel is connected to the next using solar cables. Think of it like the string lights wherein all light bulbs are connected to each other with one wire. It’s the same
with solar panels.
Solar wire runs from one panel’s negative terminal then to the positive terminal of the next panel and so forth until all the units are connected. Series wiring creates a continuous, closed loop.
The main difference between series and parallel connection is the overall voltage and amperage of the circuit. In a series circuit, the voltage of each panel adds up thereby resulting in a higher overall voltage while the amps unchanged.
What is parallel connection?
Connecting solar panels in parallel is a little bit more complicated. Instead a single string of wire, there are two centralized wires: one solar wire connects all wires from the positive terminals and another for wires from the negative terminals. These two centralized wires then run to the charge controller or inverter, depending on the solar system’s design.
In parallel connection, the voltage remains unchanged while the amps of each panel add up resulting in higher total amps.
Solar panels wired in series works just like the conventional Christmas lights. If a bulb is busted, a socket is defective or a portion of the wire is damaged, the entire string will not light up. This is because electricity flows through a single wire. To make the Christmas lights work again, you need to find the problem bulb or defective socket or wire and repair it. However, there are also parallel-wired Christmas lights. The string of lights continues to work even if there is a defective portion.
This is also how series-wired solar panels works. Electricity travels in a single direction through the solar cable. If any of the panels in the series has a problem with the connection, the entire circuit is affected. In contrast, solar panels wired in parallel continue to work even if there are loose connections or a defective panel.
Typically, the type of inverter used by the PV system depends on how the solar panel cables are designed.
How to use string inverter for wiring solar panels?
String inverters can be used to interconnect solar panels. To operate efficiently, these inverters require a certain amount of voltage and current from the solar array. They are also equipped with MPP trackers that alter voltage and current to amplify the power produced. When using string inverters, these rated values need to be considered. You need to ensure that the required voltage and current are adequately supplied by the solar panels.
Typically, for crystalline solar panels the voltage requirement is around 40 volts and for string inverters the voltage window is 300-500 volts. This allows you to connect around 8-12 panels in series. However, if you need to connect more than 12 panels in an array, you can design two strings consisting of 8 panels each plus two panels connected in parallel.
In general, parallel wiring is the preferred wiring option because it allows uninterrupted operation of the solar array even when there is a problematic unit. However, this is not always the case. In some applications, wiring the panels in series is recommended. A reliable installer can help you decide on which wiring configuration is suitable for your application. In some cases, hybrid approach, which combines parallel and series wiring, is recommended.
When it comes to PV installation, it is vital to achieve the recommended voltage and amperage to ensure the circuit’s optimum performance. As mentioned earlier, in series wiring the voltage adds up while the amperage remains unchanged. In parallel wiring, it is the opposite.
So, if you have an array of five panels with 5 amps and 12 volts each, wiring the circuit in series would yield 5 amps and 60 volts. In contrast, if the same array is parallel wired, it would have 25 amps and 12 volts. The recommend set up largely depends on the amperage and volt requirement of the solar inverter, battery, and solar wiring. Pay particular attention to the solar wire and design as it can impact the overall volts and amps.
Is it possible to add another panel in an existing solar system?
Unlike other electrical installations, you cannot just hook additional solar panel cables to an existing PV installation. This makes is vital to consider future expansion when designing solar system. This is also the reason why installers recommend going with full installation. It is important to carefully evaluate your power needs to determine the number of panels to use in your system. Likewise, your budget should also be considered. However, if you face budgetary limitations or have overgrown the estimated power needs, you could consider hooking additional panels to your existing system.
Unfortunately, most existing PV systems are not capable of taking in new solar panels. Usually, solar systems are equipped with inverters designed to accommodate the estimated load. But in case the power inverter is oversized, then you can possibly hook additional panels. The only caveat is that you may need to upgrade the solar wire and other components to comply with the current NEC standards.
You’d also consider whether the new panels will match with the old ones. If the existing circuit is wired in series, it might not allow additional panels. Typically, the maximum circuit voltage restricts the type of panels that can be wired to it. For example, older models would come with 12V, 800W capacity, while newer solar panels now come with comparatively higher capacity ranging from 30V-60V and up to 200W. If you need to add a panel with the same amps and voltage, it might be best to just install a separate array.
Using micro-inverters or optimizers in the PV circuit allows you to expand one panel at a time. Micro-inverters prevent limitations related to string inverters. This gadget allows you to add new solar panels in an existing string inverter even if they are maxed out. However, the additional panels must be hooked to its AC side.
How to reduce voltage drop?
As electrical current travels over a long distance, the electrons face friction thereby reducing its voltage. This phenomenon is known as voltage drop and can cause the solar PV system to perform poorly. Proper wiring design is crucial to reduce voltage drop.
In solar PV systems, the acceptable voltage drop is less than 3%. A solar array with massive voltage drop might be unable to power the inverters and be inefficient. There are four strategies employed to minimize losses.
1. Increase the wire diameter
Solar cables come in a wide range of sizes, such as solar cable 4mm and solar cable 6mm. Wire size significantly impacts voltage loss. If it is possible to use bigger size wire, it can help minimize voltage drop across the wires. The only problem is that bigger size wires are costlier.
Wide diameter wires provide electrons with more space to travel per square inch. As a result, there is less friction and less voltage loss as compared with small-diameter wires.
If the system design allows bigger solar wires, it is a good investment in the long run, considering the efficiency of the PV system.
2. Optimize placement of inverter within the loop
Compared to the DC voltage wires, there is higher voltage drop as electricity passes through the AC wires from the inverter to the service panel. Although, in some systems, it’s the opposite that happens.
The wire that provides higher voltage pushes more current thereby causing voltage drop. To optimize the inverter, it should be placed close to the low voltage-end.
3. Decrease wire length
The shorter the solar wire used, the better. For every inch travelled, electrons face more surface area for contact and friction; and therefore more heat loss. By using shorter wire length, there is less running and surface area. It is crucial for installers to consider this while designing the system.
The goal is to keep solar cable length under 100 inches lengthwise to keep the voltage drop within the acceptable 3% range. To achieve this, components should be situated close to each other to reduce wire length.
4. Use of high-voltage products
Installers often use overly long wires to reduce resistance. Alternatively, products that require high voltage to function can cut resistance.
Power optimizers, when used in conjunction with inverters, result in a fixed voltage regardless of the number of solar panels in the circuit. For instance, a circuit with 340/390V will constantly maintains this output when power optimizers are installed. Without power optimizer, solar inverters give fluctuating voltages ranging between 200 to 480 volts. They fluctuate around 240 volts, either dropping or shooting up. There is a direct relation between the number of string panels and the resultant voltage. Using larger strings can keep the voltage drop in check.
In PV system design, voltage drop is a major consideration because it can greatly affect the efficiency of the circuit. Installers must employ a holistic approach when planning the complex wiring system of a solar PV installation. Components, solar wire, and equipment used in the system should be carefully selected, with efficiency as top priority.
Why is wire management important?
Wire management is another important, yet often overlooked aspect of PV wiring design. More than aesthetics, proper wire management is vital for the longevity of the installation. It ensures safety and minimizes maintenance.
When solar cable and wires are not managed properly, numerous potential issues could arise. Since they are installed outdoors, these components are exposed to extreme temperatures as well as wind, rain, and snow. Rodents might chew on dangling wires. The cables might be abraded by sharp edges of roofing or mounting system. These damages can potentially jeopardize the reliability and safety of the solar system.
Wire management involves proper support, protection and routing of solar wire and cable. Latest standards and regulations should be followed. Proper wire management will prove vital later as it makes maintenance and troubleshooting a lot easier. So, during the installation process make sure that the contractor follows the standards to keep your PV system’s wiring neat and manageable.