Sizing and Optimisation of a Photovoltaic Project for Self-Consumption

What is self-consumption?

Self-consumption means directly consuming all or part of the energy that you produce yourself. This can be done in several ways:

Total self-consumption – a site connected to the public grid that consumes everything it produces, but can also consume from the public grid.

Self-consumption + Feed-in – a site connected to the public grid that consumes part of its production and sells the rest (feed-in). It can also consume from the grid.

We can also mention:

Standalone systems – a site disconnected from the grid and 100% powered by its own production.

Collective self-consumption – also known as “energy communities” – involves sharing production with different nearby sites, for financial and/or social reasons. This format is still evolving and depends on country-specific regulations.

Under what conditions is a self-consumption project interesting?

In 2010, in France, the electricity produced by a PV installation could be sold at a very attractive rate, up to 58c€/kWh. It was therefore more advantageous to sell the entire production than to consume it on-site because electricity was much cheaper to buy, around 12c€/kWh.

Today, the feed-in tariff (price of the produced electricity) is much lower, around 10c€/kWh. Since this price is lower than the purchase price of electricity from the public grid (~20c€/kWh in 2024), the owner has more interest in self-consuming directly, as the savings are more valuable than the feed-in tariff.

However, the technical and economic study of a PV installation for self-consumption is a little more complex, since it requires a constant comparison of electricity flows, which can vary greatly during the same day and over the year, as well as their associated valuations. For this reason, it is strongly recommended to study the installation on a dedicated software, capable of managing not only the yield calculation, including the influence of the near shading, horizon profiles and all the losses of the system, but also all the considerations for consumption, storage and sale of the surplus energy. Without taking all these elements into account, it is impossible to know if your project will be profitable and meet the energy requirements.

Calculate a consumption profile

While self-consumption is now a powerful lever for adding value to one’s production and increasing the return on investment, the simulation has an added layer of complexity. Knowing how to optimise a PV study for the site’s consumption profile is the key to getting the best results.

The load curve (of the consumption profile) can typically be obtained in digital format from the electricity supplier, the consumer can download it from his customer area.

In the event that the load curve is not available, or is incomplete, archelios PRO provides alternative solutions:

A full-year load curve can be created from incomplete data,

Typical profiles provided by BDEW (Germany) are available and can be a first step in creating a relevant profile,

Finally, the user has the option to select specific devices and define their usage periods, and can do the same for electric vehicles.

Sizing of a self-consumption PV installation

In general, a south-facing photovoltaic system receives more irradiation annually and can produce more electricity per module thanks to its adapted tilt and orientation. For self-consumption, other configurations such as ‘East-West’ installations should also be considered, since the two orientations make it possible to produce more at the beginning and end of the day, at the cost of reduced production when the sun reaches its peak.

The study must clarify the technical and economic performance of a proposal, something archelios PRO does intuitively. On the technical side, it calculates the energy yield and on-site consumption at each time step. From an economic point of view, a precise profitability analysis is made by taking into account the hourly feed-in tariffs and electricity purchase price. This level of technical and economic precision makes the study 100% bankable, making it easier to finance a project if needed.

A powerful software feature allows the plant size to be optimised according to the desired self-consumption and self-generation rates, thus avoiding oversizing the installation. Based on a technical and economic analysis, archelios PRO can also compare different variants to identify which one gives the best results.

How can I optimise the self-consumption rate for my customer?

To increase the self-consumption rate, a simple option is to shift your consumption to the production period to take better advantage of the energy produced and save money. Some controllable devices such as heat pumps and hot water tanks can be used to ‘store’ energy in the form of heat, for later consumption.

In some cases, the consumption period doesn’t coincide with the production period, drastically reducing the self-consumption rate and thus the savings. Battery storage enables users to respond to this problem but requires the purchase of additional equipment at a significant price. Nevertheless, storage is a valuable tool for powering devices outside the solar production period: charging an electric vehicle at night, cooking, lighting in the evening…

archelios PRO offers users the possibility to simulate a storage system and optimise its capacity to achieve the desired autonomy. It is also possible to monitor the battery’s state of charge at any time of the year to check the correct application of the charge/discharge strategy.