sonnenFlat delivers $3,400 annual saving, less than 6-year payback


Coupling rooftop PV with battery storage has been attractive to Australian households since its introduction. The ability to have backup power in the event of a power outage plus the ability to use “your own” solar electrons rather than feed them back into the grid has clearly been something that homeowners are interested in.

However, uptake has been somewhat delayed by residential battery costs – which can end up blowing out the payback period for the system when compared to simply installing rooftop solar. Given this, the results achieved by the Fenech family in NSW is pretty remarkable and turns this prevailing logic on its head – with the help of an EV.

Since the installation of a 7.56 kWp rooftop solar system, coupled with 10 kWh sonnenBatterie residential storage system, the Fenech household has saved $3,428.31 on energy bills in twelve months. The savings have been achieved under the sonnenFlat electricity model, which replaces a standard household electricity contract with the utility.

Before installation of the solar+storage system, and signing up to the sonnenFlat, the Fenech household’s monthly electricity bill was $614.39 – for a four bedroom, three bathroom home – or $5.28 per day. Annual petrol costs for the household’s car was estimated to come in at $3,000 – which householder Stephen Fenech replaced with an EV in the past 12 months. With the EV being charged from the solar PV and battery, along with grid power under the sonnenFlat scheme, these were reduced to zero.

The combined electricity and petrol savings result in the annual $3,428 savings figure and the system payback of 5.3 years – not bad going and demonstrative of the increasingly attractive value proposition proposed by solar and storage when EVs come into the picture.

The sonnenFlat operates as a virtual power plant (VPP) of sorts, with sonnen assuming the costs of electricity purchased from the grid, with the company being allowed remote access to the storage system to provide power to the grid when needed. In Germany, sonnen is already providing grid services to grid operators through the sonnenFlat program.

Sonnen reports that some 3,000 sonnenBatteries have been installed in Australia and are participating in its VPP.

Natural Solar partnered with sonnen in mid-2017 to begin rolling out the sonnenFlat model. In November 2017 the first family in New South Wales signed up to the sonnenFlat.

Solar providers are increasingly looking to move into the electricity retailing business, with Hanwha Q Cells announcing its Q Energy and Q Home Cloud for the German market in May this year.

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