Photovoltaic metering configurations, feed-in tariffs and the variable effective electricity prices that result

Occupants of dwellings with photovoltaic (PV) systems can often benefit financially by time-shifting their use of electricity in relation to the times when the PV is generating. This financial benefit is owing to differences between the import and export prices, which in some cases can be a factor of four or more. Quantifying the exact financial benefit in terms of the dwelling´s effective electricity prices is, however, not trivial; it depends on the physical meter arrangement, the dwelling´s electricity tariffs (including any feed-in-tariff), the instantaneous levels of PV generation and household demand. This study reviews typical metering and tariff configurations for the UK, and Germany, and systematically considers how the effective price may be calculated. This study reviews and expands upon general advice for occupants aiming to reduce electricity bills: demand should be kept below generation; external irradiance is a useful proxy for determining effective electricity prices. Furthermore, designers of feed-in tariffs should consider that focusing on generation payments encourages consumption typically around mid-day, which may be counterproductive from a grid-balancing and environmental perspective. Conversely, a focus on export payments discourages mid-day consumption but may increase the risk of over-voltages in local networks.