Let’s Widen Our Idea of Energy Storage

We are backing ourselves into a very one-dimensional view of energy storage when there are so many other viable options to achieve the same benefits.

Article from | Chris Sparkes

There’s no doubt that the meteoric rise of residential battery storage 2016 has completely transformed the solar model. Between 2016 and 2020, for example, the residential battery storage capacity in the UK increased by 324%, with price decreases and energy tariff concerns creating perfect conditions for this trend to accelerate.

The result is that solar has become a much more compelling prospect to the average 9-5 worker, who cannot use most of their generation whilst the sun is shining. They can now save it for later to make the most out of their system. Not only that, but they are also reducing peak demand on the grid for the potential to reduce wholesale electricity prices and reduce the carbon intensity of the grid.

But this is flogging a dead horse. Even in 2020, 40% of new solar installations included battery storage. Our client base is well-aware of the benefits of battery storage. However, it may be a victim of its own success: we are backing ourselves into a very one-dimensional view of energy storage when there are so many other viable options to achieve the same benefits.

The reason for this exclusivity is that battery storage is compatible with any electrical device. Post-inverter, it is simply AC electricity, just like from the grid. It’s like receiving money for your birthday instead of a voucher; you can use it anywhere. As such, it is easily understood by the end-user: Your excess solar will go in the battery and then you can get it out again later.

As a result, its disadvantages and limitations are often overlooked. One of the most obvious of these is cost. Although the price of a lithium ion cell per kWh has reduced below $181, the consumer price tag of a battery module is still between £750 and £900 per kWh. Therefore, a 5 kWh battery module could still cost around £4,500 before installation. If a customer’s tariff remained at 36p/kWh, this would take almost 7 years to pay back, assuming one full charge cycle per day.

The second major drawback is efficiency. Unlike other energy storage solutions, a battery is not the endpoint for the electrical energy and so it is subject to a more convoluted journey. In other words, the energy goes from panels to DC/DC converter, to battery, to DC/AC inverter and finally to the load. Each part of this journey is subject to its own inefficiencies, so heavy reliance on battery storage will inevitably result significant losses.

For example, imagine an inverter with 97% efficiency is coupled to a 5 kWh battery with 95% round trip efficiency. That energy is subject to three lots of inefficiency as it cycles through the inverter twice. The result is an efficiency of 89% before any other losses are accounted for, resulting in a loss of 550 Wh a day, as a minimum.

A final issue with relying on battery storage is their output limitation. Generally, a domestic battery module will have a maximum discharge rate of around 4 kW and will always be limited by the inverter to which it is coupled. This means a high risk of clogging-up the system and diluting those well-documented battery benefits.

I am not arguing that we should stop selling battery storage whatsoever. It is a powerful and highly beneficial resource. We simply need to expand to current and potential alternatives to increase the scope of the benefits. The chemical potential energy of a battery is simply one axis on a plethora of eligible energy forms, which also includes radiant, elastic potential and mechanical energy.

The good news is that alternative energy storage solutions already exist; we just need improve their uptake and find ways to increase their scope. Perhaps the most effective current solution is a solar diverter for hot water heating. Similar to a hybrid inverter, they use a current transformer around the live incomer to monitor when excess solar is being exported and they divert this energy to the immersion heater, instead.

Such a system addresses many of the issues associated with battery storage. Even a 150 litre water cylinder can store around 7 kWh of energy, with a solar diverter costing around a quarter of amount of a battery with such a capacity. It also reduces the inefficiency as the immersion coil is the endpoint for the electrical energy, so requires much less inversion and conversion.

My question is: Why stop there? Energy storage systems can simply be loads which meet the following conditions:

They are a resistive load or can otherwise operate within a wide power range.

They can either store energy to be used later or can be used effectively at the time that excess solar is produced.

Their cost allows for a reasonable payback period for the end user.

Our common quest to create a net zero power grid and reduce wholesale energy costs means that there should be huge, vested interest from many stakeholders to make this a priority and find as many ways as possible to meet these criteria and reduce peak electricity demand.

We should start to incorporate energy storage into the design of everyday appliances as solar conquers more and more of the general population. For instance, what about storage-heating ovens that can be set to preheat with excess generation? Or lighting that can charge up during the day to be used in the evening? We could even have automated vacuum cleaners that use excess solar to keep your house squeaky clean while you’re at work.

I’m just spit balling here, but the potential is there. Here’s to hoping manufacturers and solar installers heed my call.

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