[27/09/2016]. A brand-new Tesla Powerwall storage system has been installed as a retrofit of an exhisting 5,8 kWp residential solar array in Northern Italy.
Before the installation the share of the produced energy directly used by the home (so called self-consumption) was about 30% – which is quite normal for a household. The rest of it used to be fed into into the grid and cashed back at less then half of the purchase tariff thanks to the net-metering program.
The estimated share in the proposal was 65%. The increase in the self-consumption quota was going to decrease the energy bill by almost 2/3 and allow the user to break even from the investment in less than 10 years – also thanks to the tax-break provided for residential installation of energy-saving equipment.
The Powerwall is delivered in a wooden box equipped with a mounting frame and the back steel plate which is going to be bolted into the wall to support the 90 kg weight of the battery.
The picture shows the box as well as the packages of the SMA Sunny Boy Storage (SBS 2.5), the Sunny Home Manager data-logger and the two Energy-meter [pdf] – the Amperometric meters measuring the energy outflowing from the existing inverter (non an SMA in this case) and from/to the grid meter.
Mounting the Powerwall requires no time thanks to the pre-cabled wirings. The battery is fixed in its positions with lateral screws to avoid any movement. The battery is connected to the SBS with energy wires and a LAN data cable, then the lateral and inferior covers has to been clamped with easy-fix. The start-up is immediate, once the lower cover is fixed and you hear a “click” – the cover pushes onto two tiny activation buttons (which they could made more visible actually).
A bit more hassling was the data connections. In our case we had to place a switch to feed the two patch wire purchasing data from the two E-meter and feeding into the Home Manager Box (the box has just one LAN port). The data connection supplied by SMA includes RS485 wires to be connected to the Sunny Home Manager – a more fussy solution.
We believe the installation would be more hassle-free – and “cleaner” – if the Sunny Home Manager was fitted with two LAN ports and the box would come with two pre-assembled patch wires.
The data flow from the SBS starts immediately after the internet connection is activated via wi-fi or LAN, as you may see from the Sunny Portal.
The battery had a 30% charge level as delivered by the factory. The solar array charges the battery as soon as there is enough energy left after having supplied the house loads. The charging priority is given to the loads – due to the high tariffs applied in Italy – then to the battery and anything left is fed into the grid.
The noise level is really low – quite a buzz like a low-power inverter.
The charts from Sunny Portal clearly show the graphics after a few days of operation:  the solar array powers the home loads and feeds what’s left into the gird once the battery is fully charged (upper-left chart),  the house is powered up by the solar PV or storage battery from dawn up to almost midnight (lower-left),  the share of self-consumption during the first days above 75% (lower-left chart).