Excess photovoltaic production - how to manage

From Electrical Installation Guide

When the locally produced power exceeds the loads consumption, there are several possible options for managing the excess power:

Fig. P50 – Photovoltaic production versus power consumption

Inject excess PV production to the grid

Grid injection is one of the simplest ways to manage photovoltaic excess. When photovoltaic production is higher than the loads consumption, the excess power will naturally go to the grid.

Although simple, this solution is usually not the most profitable. The injected photovoltaic electricity is bought at a lower price than the wholesale price, or not paid at all.

Fig. P51 – Photovoltaic excess can be injected to the grid

Limit the photovoltaic production

Limiting the photovoltaic produced power is used in particular when the injection to the grid is not allowed. The power limitation is done by controlling the photovoltaic inverters, so that they reduce the DC voltage reference of the solar panels, to reduce the photovoltaic power output.

Fig. P52 – PV excess can be avoided by limiting the photovoltaic produced power

Store the photovoltaic excess for later use

Storage systems provide a very effective solution: they can store the excess of the solar production and make this energy available for later use. Today, however, this option is costly and often has a long payback period.

To improve the return on investment, storage can be associated with other use cases, such as providing a backup power supply, improving demand response, and avoiding peak power usage to reduce the power of the subscribed contract.

Fig. P53 – Photovoltaic excess can be stored for later use

Shift some loads to the period of photovoltaic production

Load management is a very attractive option which consists of simply making some loads operate during the period of photovoltaic production, as much as possible. These loads must be flexible and manageable through a control system. Examples of such loads include electrical vehicle charging, water heating, and to a certain extent, HVAC (heating, ventilating, and air conditioning).

Fig. P54 – Shift loads to consume more during the periods of PV production, in order to maximize the usage of PV produced power

The load management strategy has obvious advantages: it is cost effective, easy to implement, and guarantees a quick payback. Unlike storage, it does not require the installation of additional equipment and thus presents a better profitability.

When a load shifting strategy is not enough to absorb the total excess photovoltaic production, it can be used in association with a storage system. In that case, load shifting offers the additional benefit of reducing the size—and optimizing the use—of the storage system.