Expert Talk: A Battery in Every Home?


How realistic is it to have a battery in every home in the near future? I don’t mean like the ones in your laptop, tablet, smartphone, electric bicycle or wireless vacuum cleaner. We’re talking about a static unity, directly connected to your home electricity grid. In this new expert talk, Johan Driesen explains why home batteries have an important role to play in the energy transition.

Written by Prof. Johan Driesen. Johan Driesen is an expert energy systems at EnergyVille and professor at KU Leuven. He conducts research on distributed energy sources, including renewable energy systems, power electronics and their applications, for example in renewable energy, storage and electric vehicles.

How realistic is it to have a battery in every home in the near future? I don’t mean like the ones in your laptop, tablet, smartphone, electric bicycle or wireless vacuum cleaner. We’re talking about a static unity, directly connected to your home electricity grid. This seemed like a crazy idea for a very long time, only affordable for specific applications, e.g. back-up for critical ICT systems such as the server of a local computer network.

However, the situation rapidly changes. Batteries are technologically improved: rechargeable lead-acid or nickel cadmium cells, which used to break down fast or had low efficiency, seem like something from a distance past. Nevertheless, don’t forget that just a decade ago, the first modern electric and hybrid cars were based on these exact cells. Today the focus is on lithium technology. The lithium ion battery was such a breakthrough that the 2019 Nobel Prize in Chemistry was awarded to three scientists, each responsible for an essential part of the basic lithium cells, developed in the last century. The modern Li battery has evolved significantly: it for example contains only a minimum of, or even no contested cobalt anymore. The number of cycles these batteries can handle, easily runs over thousands and are much more tolerant towards differences in usage. The power and energy density rose spectacularly, which achieved an acceptable driving range for electric cars. Even electric planes have come into the picture. Because of mass production and globalisation, the price has dropped spectacularly: in ten years’ time, the price has gone down with factor ten. No one is concerned about safety issues anymore as they were in the first years of portable phones. That means we have varieties of lithium batteries everywhere today, even in the pockets of our pants. At the same time, the sales of new plug-in cars, and by extension battery-driven cars, is becoming substantial as time goes on.

The last domain within which batteries haven’t broken through as a mass product yet, is static storage which is different from mobile, autonomous applications such as in smartphones, laptops and electric cars. These static batteries were initially large-scale, e.g. for the provision of valuable critical reserves, which support the high voltage network. It might seem strange at first sight, because wasn’t buffering non-controllable solar and wind energy one of the biggest concerns of the energy transition? And what can we do about windless, dark nights? For years, it was suggested that batteries could help in these scenarios, but nothing seemed to come of it. There are several explanations for that. To start with, our electricity network was ‘too good’: the reserve available was both large and cheap enough, coming from controllable sources. This is changing as battery prices decrease and the demand for reserves increases. Locally, there is another bottleneck: for years, the distribution network could seemingly pick up the locally produced photovoltaic (PV) energy coming from solar panels, without problems. Of course there were evident peaks of injection around noon, when the sun is strongest and peak demand in the morning and evening when the sun is not yet providing much energy. Because of the net-metering principle, prosumers can draw power back later again, almost free of charge. The electricity grid was double loaded and prosumers only paid a limited prosumer fee to use the electricity grid as a mega battery. This situation is unsustainable today because of the increase of PV capacity and new usage peaks, connected to e.g. charging electric cars or heat pumps.

Installing the digital metre allows for a revision of the electricity tariffs, and a more correct and honest calculation of the impact. Applying a measured (average) capacity component instead of a prosumer fee, creates a financial encouragement to control these peaks, should they be excessive. A battery is the perfect instrument for this task. Additionally, the market has ensured an offer of appropriate units. Wherever in the building, separate units can be placed, equipped with their own alternating current converter, possibly as a retrofit. Another option is to connect the battery directly to appropriate photovoltaic converters directly. This would be both financially and energetically interesting and will become almost a standard option for new installations. A storage unit can be installed immediately or added to the battery-ready converter later on. The size of the battery required to control the local energy (im)balance, is usually not too large: a limited unit of a couple of kWh is often enough. The rule of thumb of 1 to 2 kWh per kWp solar panels seems like a good start.

One could wonder whether this would mean optimal use on a larger scale. Wouldn’t a larger battery, on district level, be a better investment for the local residents, instead of a separate battery for everyone? There are scaling advantages we could think of, but for now, we’re lacking regulations for these types of ‘energy communities’: you can’t simply buy electricity from your neighbours or sell it to them yourself. However, this would definitely be a possibility further on in time, just like a plural use of batteries, the so called ‘value-stacking’. When there are a bunch of those units installed and controllable from afar, a part of the capacity can be aggregated for example, and be offered, for a fee, as a virtual battery for net support.

In short, it seems that batteries will shortly be as self-evident in a home as solar panels on the roof. This trend has been deployed already in our neighbouring countries. The technology is mature, prices are decreasing and the investment can be recovered within a reasonable amount of time, thanks to reforms of the tariff structure. That way, more possibilities are created where revenue can be generated in the future. Balancing solar energy to achieve a higher self-consumption is only the start, limiting peak consumption the next step. Batteries will continue to play an increasingly important technical and economical role for everyone involved within the energy transition.

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