top of page

Fully Charged April 2022

This was the third Fully Charged Live I’ve attended and the second I’ve spoken at. I was invited to talk about energy disruption and what’s coming next so chose to focus on storage.



Storage is going to become important because our energy generation is becoming more intermittent and geographically highly distributed which means we’ll either need appliances to be far more dynamic reacting to that or storage soaking up the rises and falls, or most likely a mix of both. On average around 40% of our generation is from renewable sources and on good days surpasses 60%. But being weather dependent means that generation is highly variable - if you watch the live output of a solar system as clouds go over the output will swing more than 50% and quite rapidly. Wind and solar generation is also spread out across the country which just adds to the challenge. This combined intermittency and distributed generation is very different from the output of a few large scale coal, gas and nuclear power stations providing a steady flat output that we’re historically used to. Hence the role of storage to assist the grid.


Hot water tanks and night storage heaters are forms of storage that have been around for decades and hence also Eco7 tariffs as one method to encourage using energy overnight. This started from the days when coal formed a very high portion of our electricity generation and as overnight consumption can be as much as 40% below the peak period the grid often had surplus energy available overnight. So the core idea and tech of storage helping the grid has been around for ages.


A hot water tank is one-way as it stores energy which can’t be shared back to the grid. A home solar system can send excess energy to the grid and combined with a home battery system can be used to both soak up that excess (grid or home solar) to use later or even export to the grid when needed. Similarly electric cars are evolving from one-way to being able to supply energy back to our homes and the grid too. As more of these systems go online then either a time-of-use (ToU) tariff or other industry signal (something called a flexibility market) can control the charge/discharge cycles to support the grid instead of a very static Eco7 system.


Each of these are different mediums of storage; electric cars and home batteries are an electrical store, a hot water tank holds hot water or systems such as Tepeo and Sunamp can store heat. The Electric Mountain at Dinorwig pumps a lake up and down the mountain to store and release energy at a very large scale. Other futuristic ideas under test are cranes lifting and dropping massive concrete bricks or gigantic flywheels spun up to extreme speeds to store and release energy. The holy grail is looking for long-term storage that will span the seasons. Compressed air in old mines or shipping containers for example could achieve this - more economical as the medium, air, is free compared to the lithium-ion in a battery or the need for exceedingly high insulation for long term heat storage. In the future we could see other storage mediums too.


Domestic storage should play a large part in supporting the grid due to two economic benefits:

  • Participation in the future domestic flexibility markets - i.e. you’ll get paid (or have a beneficial tariff) for helping balance the grid.

  • Type and efficiency of energy production of the system - i.e. electricity, hot water or heat for your home.

Grid-scale storage is already used for balancing the grid but the domestic investment for these two main benefits may result in domestic storage reaching a higher total capacity to balance the grid. The type of energy provided to the home has more benefit than just the electricity, hot water and heat produced - a solar home battery system is soaking up your own energy which is then free to use later (in terms of marginal cost to produce) or a heat pump with it’s multiplier effect (more energy is produced than the grid kWh it consumes) means more efficient production of hot water and heating. And it's possible for a heat pump to charge energy storage devices - either a hot water tank or something like a Sunamp with phase change material. Even your home is a thermal store albeit very temporary compared to an electrical battery or a hot water tank. It’s unfortunate that so many hot water tanks were removed due to the popularity of gas combi-boilers.


A heat pump is actually an energy generator as it produces 3 to 5 times the amount of energy that it consumes (referred to as the coefficient of performance) which is magical. This isn’t breaking the laws of physics though; that energy has to come from somewhere which is either the air or the ground. The airflow exiting the heat pump is several degrees cooler demonstrating energy has been removed from the air. Similarly the ground around a ground array becomes cooler - in the winter you’ll often get frost on the heat exchanger of an air source heat pump or frozen ground above a horizontal ground array. The sun warms the air and the ground so the energy actually originates from sunlight.


My message at Fully Charged Live was therefore that we should be paying a lot more attention to domestic storage. There's going to be a financial benefit by making storage available to the grid and there's a lot of tech coming in this space. Each type of storage is relevant to the generation source (grid v solar v heat pump, etc) and consumption and we shouldn't just think in terms of an electric battery. It's the combined benefit of how and where energy is generated, how it's stored, how you consume it and the potential to do that with the domestic flexibility market that's exciting.


Always look carefully at the type of storage you set up in any home renewable energy projects!

bottom of page