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Choosing a technology for home energy system with storage: DC coupled vs AC coupled

Choosing a technology for home energy system with storage: DC coupled vs AC coupled

What exactly is AC and DC coupling? These are ways that solar panels are coupled or linked to a battery system or energy storage. The connection between the solar panels and the energy storage system can use either alternating current (AC) or direct current (DC)—two types of voltage which transmit and conduct electricity. AC is when the electricity flows back and forth rapidly in both directions, whereas with DC, the electricity flows in one direction only.

The electric grid and most household appliances use AC to operate. Most electronic circuits use DC, solar panels produce DC, and batteries store DC energy. Therefore inverters are installed alongside solar panels, to convert the DC electricity from your panels into AC electricity.

AC-coupled battery storage setups have been more common for residential and commercial solar installations, but as more DC options become available, DC coupling is gaining in popularity.

Pros and cons of AC coupling

AC-coupled battery systems are both easy to design and easy to implement and, because of this, have a lower up-front cost. Another benefit is that AC solar storage solutions allow you to charge your batteries using both your panels and the utility grid. This means if your solar panel system isn’t generating enough electricity to fully charge your battery, you can still rely on the grid to fuel your battery.

The downside, however, is that AC-coupled solar-plus-storage systems use two separate inverters, which makes them less efficient than the DC-coupled systems in terms of power output. The process of inverting electricity from AC to DC, or from DC to AC, results in small efficiency losses, so the more inversions that take place, the larger the overall reduction in system efficiency.

Pros and cons of DC coupling

The major advantage of DC-coupled battery systems is that they are more efficient than AC systems. This is because DC systems only require the use of one inverter. Similar to the AC battery, the DC solar storage system allows you to charge your batteries using your solar panels and the utility grid, the advantage here is that they have a built-in inverter which allows this and has less efficiency losses.

Another advantage of DC coupled is the prevention of “clipping losses” at the point of the inverter. This means when DC energy exceeds inverter nameplate capacity, instead of energy being lost, it gets stored into the battery. Also, the DC coupled battery is designed to be used every day, use the battery when the sun goes down and fill with clean energy when the sun comes up. DC coupled lets you “harvest more energy with the same solar panels”.

The downside is that DC-coupled options are more complicated to install, which can drive up upfront costs and installation time.

AC or DC: Which Should You Choose?

The answer to this question depends on your situation, your need, and whether you have an already installed solar panel system. If you are looking to add battery storage to an already installed solar PV system, then AC would be the better option. This is because you will already have a solar inverter system installed with your panels and rewiring for a DC-coupled system is a complicated process that can increase installation costs. If you’re installing a solar panel system and battery setup at the same time, a DC-coupled system will be the better option because of the higher overall efficiency of DC-coupled setups.

How Can Energy Storage Benefit you?

  • Energy storage provides you with your own power bank- This allows you to have access and complete control over when and how to use the stored energy.
  • Round-the-clock power- Solar panels generate power when the sun shines, but when it is cloudy, and at nighttime, they are not beneficial. A battery allows you to store any electricity you don’t use, so you can tap into it at night or when it’s cloudy.
  • Greater energy independence and security- Storing surplus solar power makes you less reliant on the grid. This gives you the independence to decide on when to use the stored power, save money, avoid sky-rocketing prices, and to keep your power running during emergencies such as storms.

Battery storage systems that store solar energy, whether AC or DC are qualified for 26% fed tax credit for qualified taxpayers.  Our experts here at Valley Solar are knowledgeable on the various programs and what they entail. We will be happy to help you apply for incentives covering up to 70% or more of the cost, and we can discuss how you may qualify for zero percent loans that are available for MA customers.

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