BESS and renewable energy: How to get more out of solar and wind on your site

Many industrial companies already have solar on the roof or a wind turbine on the grounds. The installation produces renewable electricity, but production follows the weather, not the company's consumption. The sun shines most in the middle of the day, the wind often blows when the factory is running at reduced capacity, and in those hours the question arises: what happens to the electricity that is produced but not used right now?

An industrial BESS system (Battery Energy Storage System) can help shift that electricity in time, so more of it is used on site rather than sent out onto the grid in the wrong hours. But a battery is not always the answer, and sometimes it is the grid connection, not storage, that is the real constraint. This article explains the three ways of handling solar and wind, when storage improves utilisation, when the grid connection is the bottleneck, what you own versus what we optimise, and which data are needed to assess a match.

The three ways to use solar and wind

When a solar or wind installation produces electricity, the energy can fundamentally end up in three places. The three paths are not mutually exclusive, but the balance between them determines how much value the installation creates.

Self-consumption: The electricity is used directly on site in the same moment it is produced. This is typically the most valuable use, because the company then avoids buying the corresponding amount from the grid. When a company uses more of its own-produced electricity, it draws less from the grid and therefore pays less in energy tariff. Self-consumption does, however, require that there is consumption to cover precisely in the hours when the installation is producing.

Export: The electricity that is not used on site is sent out onto the public electricity grid. Production and consumption are settled by the grid company, and surplus production is settled at the market price, which is set hour by hour as the day-ahead price. The problem is that the surplus often arises precisely when many others are also producing. On sunny days with low or even negative electricity prices, solar panels undercut their own business case, because the value of the exported electricity falls.

Storage: A battery absorbs the surplus when production exceeds consumption, and releases it again later, when the installation is not producing, or when electricity is more expensive. Storage does not change how much energy the installation produces. It changes when the energy is used, so a larger share can be applied on site instead of being exported in the least valuable hours.

When a battery improves utilisation of solar and wind

The value of storage depends on how well production and consumption already fit together. If a company already uses most of its solar electricity during production hours, there is little surplus left to store. The self-consumption share always depends on the relationship between the production and consumption profiles, and the gain from a battery is lower when self-consumption is already high. Conversely, there is more to gain when production and consumption are offset, for example when the sun produces during the day while heavy consumption falls in the evening or at night.

Solar and wind also complement each other over the year, because solar panels produce most during the day and in summer, while wind turbines in Northern Europe often produce more at night and in winter. That makes the timing between production and consumption more complex, and it is precisely here that storage can smooth out the differences. With joint control of production and storage it becomes possible to utilise a given grid connection better, so there is room for more within the same capacity.

The mechanism behind this is that a battery is a short-term flexibility tool. Battery storage is well suited to delivering flexibility over hours, typically in the range from one to eight hours. That fits well with shifting solar electricity from midday to evening, but it does not solve seasonal variation. A battery cannot store summer's solar energy until December.

When the grid connection is the real bottleneck

Storage helps with timing, but it does not expand the physical capacity in the company's grid connection. And it is precisely the grid that in many places has become the scarce resource. The electricity grid has in several places reached its limit, and it is a clear barrier to both the expansion of renewable energy and electrification, at the same time as there is limited spare capacity for new grid connections. The pressure is significant: applications for new electricity consumption correspond to a potential eightfold increase of Denmark's current peak demand, and the transmission grid is not built for that rise.

That has two specific consequences for a company with solar or wind. First, there can be limits on how much surplus can be sent out onto the grid in the most congested hours, because the cables locally may already be full. We explain this phenomenon further in our article on grid congestion. Second, an existing connection is not automatically a guarantee that there is room for more: for larger customers in the distribution grid, clarification must be sought with Energinet (Denmark's national transmission system operator) about remaining capacity in the transmission grid, and the particular assessment depends on the available capacity in the relevant area.

In that situation the logic is reversed. A battery can make it possible to use more of the renewable energy locally, so the load on the connection falls instead of rising. Solar and wind without storage are, as we describe elsewhere, a bit like a tank without an engine: the energy is there, but without something to shift it in time it becomes hard to utilise fully. If the grid connection, by contrast, does not even cover the company's base consumption, a battery does not solve that problem, because the battery itself needs spare capacity to charge into.

ZynexGroup's approach to system assessment

Here it is important to be clear about the division of roles. The system is the customer's. That applies to both the battery and any solar panels or wind turbines that the company owns or has built. Our contribution is the hardware, the ongoing commercial optimisation of the system's flexibility, and access to operational data. We do not prepare sustainability reports and we do not advise on ESG or CSRD. That part belongs with the company and its own advisers, who can use the operational data in their own documentation.

The optimisation is about controlling when the battery charges and discharges, so more of the renewable energy is used on site, and so the system utilises differences in the electricity price over the day. Because a battery can respond quickly, it can also take part in the flexibility markets, where it relieves the electricity grid. The same flexibility that at system level can reduce the load on the grid benefits the company locally, but the gain for the individual installation depends on the specific conditions.

We offer a 6-year payback guarantee on BESS systems. We go into the economics behind that calculation in the financial case for BESS, so we do not repeat the figures here.

Realistic expectations and assumptions

A battery does not make a company CO₂-neutral, and it does not in itself make the company green. What it can do is support better utilisation of the solar and wind the company already has, and provide flexibility that can shift consumption and production in time. That is a real but bounded benefit, and the size depends on assumptions that vary from site to site.

The most important assumptions are the consumption profile, the production profile, the grid connection and the price structure. If the difference between cheap and expensive hours is small, there is less to gain from shifting consumption. If consumption already coincides with production, there is less surplus to store. And if the grid in the area is full, the options both to export and to expand can be limited. That is why we refrain from promising specific percentages for how much more solar and wind a system will utilise. That figure can only be qualified once we have looked at the company's own data.

At system level the picture is the same. When the grid or the market cannot take all the production, some of it can be curtailed, and the risk of that rises when the expansion of the grid and market design does not keep pace with the growth in solar and wind. Storage is one of the tools that can reduce that waste, but it is not the only one. Variable production from solar and wind requires more flexibility across the whole system, through grid expansion, storage and more flexible consumption, and flexibility can postpone or in some cases reduce the need for grid expansion, but it does not replace it.

The data basis: production, consumption and meter

An assessment of whether a battery improves utilisation of solar and wind on a specific site rests on three types of data. The first is production data from the solar or wind installation: when and how much the installation produces over the day and the year. The second is consumption data: the company's consumption profile, that is when heavy consumption occurs. The third is metering data from the electricity meter, which ties the two together and shows how much is actually drawn from and sent out onto the grid. Production and consumption are settled by the grid company, and the company can gain access to its own metering data via Eloverblik, Denmark's portal for electricity metering data.

With those three data sources it is possible to see how large the surplus is, when it arises, and how much of it can realistically be shifted to better hours. That is the basis a grounded assessment builds on, rather than general assumptions.

Overall perspective

Solar and wind on site produce renewable electricity, but the value depends on whether the energy is used when it is produced. Self-consumption is typically worth the most, export depends on the market price in the hours when many others are also producing, and storage can shift the surplus to better hours. A battery improves utilisation when production and consumption are offset, and when there is room in the grid connection to charge. Where the grid is already a bottleneck, storage can help use more locally, but it cannot create capacity that is not there.

For a company, the useful point is that a BESS system can form part of an energy strategy and support better utilisation of solar and wind, but that it does not in itself make the company CO₂-neutral, and that the effect depends on specific assumptions. That is an assessment that should build on the company's own data, not on promises of specific results.

Have the potential for your site assessed

If you want clarity on whether a battery can improve utilisation of your solar or wind, we start from your own data: production profile, consumption profile and metering data as well as your grid connection. On that basis we can have a data-based conversation about whether there is a match, and what the next step could then be. You are welcome to contact us.