Your browser is not supported. Please update it.

4 October 2019

Centrica tries to spice up water-tanks-as-storage with Mixergy

Startup Mixergy has caught a significant break this week, as Centrica has announced it will be using the firm’s platform to control residential hot water tanks as part of a Firm Frequency Response (FFR) project in the UK. This is another wrinkle in the tale of using water tanks as battery capacity, but one that might finally have the proper legs to take off.

The water tanks are being aggregated as part of a larger Virtual Power Plant (VPP), which is the term used to describe a collection of assets that are treated like a grid-scale power generation appliance. In this case, it’s actually a bunch of hot water tanks in homes, which can fire up their heating elements as needed, but these VPPs can be constructed out of all manner of things.

In FFR, these tanks will be used to help balance the frequency that the electrical grid is operating at, as keeping it within half a Hz is vital to operation. Firing up the tanks will put a draw on the grid, and so bring the frequency down – from a level it reached via an oversupply of renewable energy, most likely. The inverse is also true, so you could stop the draw to raise the frequency. FFR is different from capacity storage, where you are storing energy for use at a later time, although you can perform both functions with the same asset.

Of course, 100 tanks don’t make much of a difference, but the VPP will total 2.5 GW of capacity, which is rather sizeable – with much of the portfolio comprising industrial DR assets. Centrica says this is the first instance where residential and industrial assets are being aggregated in the same pool. Centrica’s Business Solutions wing offers its Flexpond DR platform to other companies, and announced that Tepco was a customer in June.

Thousands of water tanks will be added in time. In the UK, however, water tanks are something of a dying breed, thanks to the popularity of gas boilers that power both the home’s instant hot water and central heating systems. To this end, water tanks are something of a relic from a time where these combination boilers didn’t exist, and where system boilers filled the hot water tanks to serve as the instant supply.

However, water tanks could make a resurgence, as new homes move towards using electricity for hot water and central heating. This shift could take decades, but removing the natural gas supply from homes is a key step towards the UK’s decarbonization targets.

If that shift is going to take place, the user experience has to be exceedingly good. Should VPP tinkering mean that a household has no hot water ready for the morning ablutions, there will be hell to pay with the utility – irate customers canceling, threatening to sue, and tarnishing the brand name. To this end, scheduling is key, or perhaps just sufficient advances in the capabilities of electric boilers so that tanks don’t have to be relied on to such an extent. As lack of gas central heating will adversely affect the valuation of a house, this is as much a cultural shift as a technical one.

Charles Cameron, chairman of Centrica Innovations, said “the first batch of 100 hot water tanks, which are now in homes in the UK will, at times of stress, be capable of capturing energy at low market prices on sunny or windy days when there is an abundance of renewables on the network, all whilst maintaining efficiency, cost and comfort for our customers.

Mixergy itself is an Oxford University spinout that has received investment from Centrica Innovations, a unit set up in 2017 to target new technology opportunities. As well as Mixergy, Centrica Innovations has also invested in GreenCom Networks, a startup focused on home energy management systems (HEMS).

Centrica and Mixergy believe that the tanks will help reduce heat losses, and cut the demand for water and energy by up to 40% annually. IoT-based sensing technology is key to this, where the fill-level and household usage data are used as the inputs for the calculations that determine when to set the tank in motion. The idea here is to only heat what is needed, rather than heat a full tank that never gets below half-capacity.

Mixergy CEO Pete Armstrong said the firm is “very excited to be at the heart of Centrica’s mission” to add additional flexibility to the energy system. Together with Centrica, we are paving the way for smart tariffs which will reduce energy consumption and carbon emissions by storing excess renewable energy on the grid.”