Get more energy with the same size residential battery

Post by Nitsana Bellehsen, Senior Content Manager for EMEA, SolarEdge Technologies | 08/02/2024 6-minute read When your customers are looking to purchase residential batteries, the most important question is how it will help them to have energy to store and use when they need it. One of the parameters that determines this is the actual size of the battery. But there are other elements that significantly contribute to the amount of energy a homeowner will be able to store, even with the same size battery. The most significant of these elements is if it is an AC or DC-coupled battery.

What does AC or DC-coupled mean?

Energy from the sun is harvested in direct current - DC. Our home electricity architecture is alternating current, or AC. In order to use solar energy in our homes, the inverter converts the DC energy to AC for use. The choice of an AC or DC coupled battery affects where the battery fits in to the architecture of the PV system. Does energy go directly from the sun to the battery or does it need to be converted into AC before storage in the battery?  This may sound like a petty discussion – who cares at what point the energy transfer is affected? What difference does it make? But this one choice can make a significant difference in how much energy your customer will have to use in their home.

How to avoid the triple conversion penalty

If you have an AC-coupled battery, the energy is harvested in DC, converted by an inverter to AC and stored in the battery. However, when this energy is needed for the home, it must be converted back to DC AGAIN and then back AGAIN to AC in order to be used in the home. With each conversion, some energy goes to waste. With a DC-coupled battery, the energy is stored as DC – so it goes directly from harvest to the battery for storage, without requiring a conversion. And then, only when it is needed for use in the home, will the energy go through one conversion to AC. Easy. So, with DC-coupling you don’t have to pay the triple conversion penalty – and more energy can be stored in the battery (no conversion – it is all retained) and then more of that energy can be used in the home (only one conversion, instead of two). [embed]https://www.youtube.com/watch?v=x9eTtV4sgVU[/embed]

DC-coupled lets you benefit from oversizing

That’s not all. With a DC-coupled system, more of the energy that is harvested can actually be saved to the battery – and not “clipped”. Or, in plain English, wasted. How does it work? Oversizing a system means that you can produce more than the inverter rating. For example, if you install a 5kW inverter, you can add a certain percentage of additional panels in order to get more energy out of the system. With SolarEdge Home inverters this can be up to 200% more. You may be thinking – why would I add more panels than the inverter rating? It’s to harvest more energy. A system only produces at its peak at midday. Earlier – and later – when the sun is not at its height, the system could conceivably produce more if there were more panels. So, by oversizing, homeowners can add panels and produce more energy throughout the day. With our, dare I say, less than sun-soaked British skies, the ability to oversize can be significant to enabling homeowners to take full advantage of their systems. This is where DC-coupled can make a huge impact. You’ve added up to 200% more panels. At the middle of the day – and even for much longer during our few but welcome sunny days when the system is producing the most it can, you will be able to harvest more energy than the inverter rating. When you’re DC-coupling, that energy goes directly to the battery and can be used in the home whenever it’s needed. With an AC-coupled system that energy is lost. How much more energy are we talking about? When you add in all the benefits of a SolarEdge system (Power Optimizers that mitigate module mismatch, as well as the benefits we spoke about here) a homeowner can benefit from 20 to 50 days more energy than comparable sized traditional string and AC coupled systems. (You can read more details on this here). *

Additional DC-coupled Advantage – no work on the AC distribution board!

DC-coupled enables an easy connection of the battery. When you select this type of battery, there is no extra work needed on the AC distribution board. So, now, if a homeowner asks, “Should I DC-couple my batteries?” you will have practical information and benefits of DC-coupling to offer.

Managing the battery can save even more money

Once a system provides all this stored energy, the trick is taking best advantage of it to save money. Knowing when to store energy, when to use energy from the battery or when to maintain battery power and, instead, draw energy from the grid, can have a great impact on an energy bill. But it is also could be a very time-consuming endeavour to try and oversee. And that’s where SolarEdge Home ONE comes in. As a personal energy assistant, SolarEdge ONE helps make the most of the home's energy while adapting to individual preferences. It makes real-time decisions like storing energy in the battery for forecasted weather events and selling energy to the grid at the right times when it’s possible to earn more. Equipped with manual controls as well as automated, SolarEdge ONE helps to take best advantage of the additional energy available with DC-coupling.​

The value of batteries

Batteries can undoubtedly be a valuable addition to a home PV system, enabling families to use more green energy as they reduce energy spending. Similarly, programs from local electricity providers like the DFS scheme allow certain battery owners to take part in stabilizing the grid and earn financial rewards without having to reduce energy use. It’s critical to select a battery that can assist homeowners to maximize the energy they have.

One final note for installers from Great Britain:

The G100 Issue 2 Amendment 2 regulations add new requirements that we will have to take into consideration when selecting PV components for customers. While it was less optimal to mix and match components from different manufacturers when building a PV system, it is now required to add a G100 controlling device for each component from a different manufacturer, making integration of components all the more complicated. So, when selecting a PV system for your customers, please take into consideration the importance of providing a full system from the same manufacturer.

Do you want to know more about SolarEdge Home Batteries? Click here to see our full range of SolarEdge products.

*Based on simulation performed by SolarEdge during 2023