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Welcome to electriciansjournal.com. My name is Jim Bernth, founder of Electrician’s Journal. I’ve been an Electrical Engineer for 36 years, and really enjoy writing condensed technical articles about topics that can benefit others in the Electrical industry. My goal is to summarize and condense potentially complex topics that are most important to Electricians as well as Electrical Engineers into a “take-away” format, and also share application-specific insight and experience. Every topic posted will likely be important to most people in the electrical industry at every level. Each post should take the average reader no more than 15 to 30 minutes to read. The number of topics posted are growing every day. If you have any questions or have interest in a particular topic and would like to see it posted, send all inquiries to: jimbernth@gmail.com.

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Jim Bernth, EE

NOTE: The author, James Bernth, assumes NO liability for the misapplication or inaccuracy of any information found herein. All published information on this site is for the sole purpose of personal and professional enrichment and is never intended to be the sole resource. All critical information should be thoroughly researched by multiple resources to confirm its validity before being applied.

Solar Power Systems Explained

Solar Power Systems Explained

James Bernth
Renewable Energy

Introduction

Solar power is likely the most common form of renewable energy today and has been for many years. Perhaps the reason why most people have not taken advantage of this power source for their home or business is because of its high initial cost. However, the cost has come down considerably in recent years and there are ways to make solar power even more affordable if you are handy with tools and have a basic understanding of electricity. In this post, we will discuss the building blocks of a solar power system and ESS (Energy Storage System) in detail.

Solar power systems are found in residential, commercial, and industrial applications and are rapidly gaining traction as cost savings and off-grid power availability become increasingly important in every market sector. Thus, solar power systems are installed in diverse environments and geographic locations. Due to the overall simplicity, availability of components, and adaptability to various applications, solar is likely to be the most common power installation in the future of renewable energy.

Two types of ESS’s (Energy Storage Systems):

  • AC-coupled: The DC power goes to the inverter first before it gets to any battery banks. Before this energy is stored, it has to pass through the inverter a second time, which result in small losses. These systems are most common in older installations because of their simplicity in being added to an existing power system.

  • DC-coupled: The DC goes through a charge controller (often called an MPPT - Maximum Power Point Tracker) directly to the battery bank. Power does not pass through any inverters before being stored, which is much more efficient. Furthermore, the MPPT maximizes the efficiency of the solar panels by allow them to operate at their maximum potential and still converting their total DC voltage output to a safer, useable level for the DC bus.

DC-coupled ESS (Energy Storage System) major components:

  • Renewable energy source - solar, also called PV(Photo-Voltaic) cells

  • Charge controller (MPPT) - for DC-coupled systems only.

  • Inverter - converts DC to AC and AC to DC depending on mode of operation. Many inverters are bidirectional. Multiple inverters can be used for modular power capacity expansion.

  • Transfer switch - can be used between grid and inverter(s), between grid and emergency generator, or both.

  • Battery set(s) for energy storage.

AC-coupled ESS (Energy Storage System) major components:

  • Renewable energy source - solar, also called PV(Photo-Voltaic) cells

  • Inverter - converts DC to AC and AC to DC depending on mode of operation. Many inverters are bidirectional. Multiple inverters can be used for modular power capacity expansion.

  • Transfer switch - can be used between grid and inverter(s), between grid and emergency generator, or both.

  • Battery set(s) for energy storage.

Notice in an AC-coupled system, there is no charge controller such as an MPPT (Maximum Power Point Tracker) because the DC power produced by the solar (PV) cells goes straight through the inverter, is immediately converted to DC, stored in the battery bank, then converted back to AC for use at the load distribution panel. That’s three (3) conversions, DC to AC, AC to DC, and DC to AC, each having a small power loss. Although an AC-coupled system is easier to install into an existing traditional AC electrical system and are less expensive, the DC-coupled systems are far more efficient and more cost effective in the long run.

Solar Panels

Solar panels are made up of five basic components:

  • Solar photovoltaic cells

  • Toughened glass: 3 to 3.5mm thick

  • Extruded aluminum frame

  • Encapsulation: EVA film layers

  • Polymer rear back-sheet

NEC Article 690 requires the wiring for the PV (photovoltaic) arrays to be tied together in a junction box called a combiner box and also pass through a DC-rated safety disconnect.

Charge Controller

The charge controller, often called an MPPT (Maximum Power Point Tracking), is used only in a DC-coupled ESS (Energy Storage System) to directly connect the PV array DC output to the battery bank for storage.

Battery Bank

Battery banks can be in the form of individual conventional size batteries or rack-mounted battery packs in a fairly wide range of sizes (rated in kwh). These batteries are typically wired in series to increase the voltage.

Inverter

Inverters are designed to convert DC power to AC power, and in reverse mode will convert it back again for storage in a battery bank or DC utilization. Solar power systems can be configured with a single inverter or multiple inverters. They can also be configured in 240VAC single-phase, 120/240VAC split-phase, 120/208VAC 3-phase, 480VAC 3-phase, or 277/480VAC 3-phase. Inverters can be configured in AC or DC coupled systems and can operate in several different modes of operation: such as grid-coupled, off-grid, grid-interactive, or stand-alone.

Generator

Generators are designed to convert mechanical energy to AC electrical energy and are rated in KW (kilo-watts). They are available in a wide range a package sizes for use in residential, commercial, and industrial applications. Some are intended for stationary use, others for mobile use. Sizes range from < 1 KW to several 100’s of Giga Watts. They can be driven by gas-powered or diesel engines. For more information on generators, please refer to our other post on generators.

Main Circuit Breaker Panel

The main CB (circuit breaker) panel is the central location for the incoming electrical service to the main CB and related branch CB’s. This box and associated wiring distributes power to the AC loads.

Codes Applying to Solar PV (Photovoltaic Systems)

  • NFPA 70 - National Electrical Code

    • Article 690 - Solar PV (Photovoltaic) Systems

      • Also contains information on Grounding & Bonding of PV systems.

    • Article 705 - Interconnected Electric Power Production Sources

  • NFPA 855 - Standard for the Installation of ESS (Energy Storage Systems).

  • UL 9540 - Standards for ESS System Safety.

  • UL 9540A - Standards for Testing of ESS System Safety.

We hope you have enjoyed reading this post and found it helpful. Please feel free to visit Electrician’s Journal often to further expand your skillset and share this resource with others.

 
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