Chapter 6 Electricity
6.1 Solar power
We have 6.4 kW of LG NeON2 solar panels (320W) and SolarEdge DC optimisers with a Solar Edge 5k inverter. This system provides far more electricity than we require on a typical summers’ day, and around a third of what we require in winter.
6.1.1 Oversizing
The panels are oversized relative to the inverter (i.e. 6.4 kW of panels on a 5 kW inverter). This results in some clipping in the summer, but only reduces generation by around 1.3% per year. Most grid operators, including ours, limit exports to 5 kW. However, for the vast majority of the time the panels are not operating anywhere near their rated capacity. Moreover, the cost of panels is comparatively cheap so it makes sense to oversize in order to generate as much power across the year as possible; the only limitation being that the CEC restrict oversizing to 133% of the rated inverter capacity.
6.1.2 Panel orientation and shading
We suffer from some panel shading during the morning in particular, plus we had to orient the panels across two directions (north and west). A conventional string inverter would struggle to perform well under these conditions. Instead, we used SolarEdge DC optimisers on each panel. This setup allows each panel to operate to their optimum efficiency unaffected by shading on adjacent panels. Doing so is slightly more expensive than a string inverter, but in our case was essential. Another bonus is that this way we can monitor the performance of each individual panel, so it is easy to verify all panels are performing adequately.
6.2 Typical electricity consumption
Compared to many homes we have comparatively high electricity consumption (15 - 20 kWh/day in summer and closer to 30 kWh in winter). This is in part due to the sole use of electricity for providing hot water and heating and the electric car. The latter explains around a third of our winter consumption and half of our summer consumption. Moreover, car charging tends to happen in the evenings when the solar power is not generating (Figure 14: ).
Figure 14: Electricity profiles for typical summer and winter weekdays
The solar PV was only fully metered in late February 2017. Over March and April we tended to export around twice the electricity that we imported from the grid (Figure 15: ). This situation was reversed in the winter months such that so far we have imported -6% more electricity than we have exported. We hope over the full 12 month cycle we will be energy positive, or close to it.
Figure 15: Daily electricity import and export
| Total import: | 7,593 kWh |
| Total export: | 8,042 kWh |
| Total generation: | 10,643 kWh |
| Total consumption: | 10,193 kWh |
| Solar self-consumption: | 24.0% |