Why your battery is not fully charged - and you are better for it.

Sunny days and a well-stocked home battery seem like a perfect combination at first glance. But sometimes you notice that your battery was not fully charged while the sun was shining brightly. Logical? No. Desirable? Absolutely.

Thanks to FlexiO's smart control, your battery is purposefully not always filled to 100%. Why that is, we are happy to explain. Spoiler: it's all about smart choices, better yields and a healthier power grid.

One example: Negative prices, smart choices

On May 1, 2025, it was a very sunny day. It was predicted to be. You would expect your battery to be fully charged all day. That would make sense because there was a lot of sunshine. Yet that wasn't true at any time of day. That's because of grid balancing.

What is net balancing and why is it important on sunny days?

Grid balancing is all about balancing supply and demand on the electricity grid. On days with lots of sunshine and little consumption, the grid gets out of balance. We want to prevent that, of course. On such days, grid balancing has extra value.

In such situations, power prices drop, sometimes to below zero. Injecting extra solar production that you don't consume or that you don't store when your battery would already be fully charged, then just works counterproductively and can cost you money.

On extremely sunny days, like May 1, 2025, that sometimes means: deliberately not charging to 100% or even limiting your solar panels for a while, aka curtailing.

How does your battery help the grid?

In situations like this, it is important that your battery remains flexible: it must be able to store energy when there is too much. And you need to be able to release energy when there is a sudden shortage, even on extremely sunny days. That's why FlexiO deliberately keeps a portion of your battery capacity free at certain times. This is necessary to be able to charge or discharge your battery at any time as a function of the grid.

For shortest term balancing (such as FCR - Frequency Containment Reserve), this is crucial. With FCR, the grid must be able to recover in seconds to minutes. For that, it is ideal if your battery remains partially free so that it can quickly replenish in either direction.

FlexiO balances the net for you

What was FlexiO doing on May 1, 2025? Thanks to the weather forecast and day-ahead prices, FlexiO knew it was going to be a sunny day.

• Between 8am and 11am, energy was actively taken from your battery and put on the grid. At this time, your generated power still had value. This freed up space on your battery for the afternoon. We do this for PV plants that we cannot curtail, but not necessarily if we can. For plants that can curtail, it may be more efficient to leave the power in the battery.
• Between noon and 4 p.m., your solar production was then stored in the battery as much as possible, without additional injection into the grid and with maximum efficiency. Injection at this time would mean unbalancing the already overcrowded grid and paying for your injection.

A smart buffer for maximum yield

Even though the injection price is negative, there may still be a shortage on the grid. If your facility is currently participating in FCR (or Frequency Containment Reserve) then you will still be injecting at negative prices. These costs are reimbursed by LIFEPOWR. More than that, you generate income by making your battery capacity available to Elia. So you are not left with a loss.

LIFEPOWR only leases your battery capacity to Elia (the grid operator) for FCR when it offers more revenue than savings. So the system always keeps your benefit in mind.

Expectation: your battery will be filled with solar energy.

Reality: it happens, but always with a smart buffer and maximum return.

Why net balancing is good for you and the net

What does this give you as a user now?

• A higher return on your battery
• A fee for balancing the grid
• Smart deployment of your installation, tailored to your energy rate

And for the grid? Less pressure at peak times, less waste of solar energy and more stability.

In short: your battery is more active and valuable than you think, even (or just) when it is not fully charged. So a win-win situation!

Trust the system, FlexiO works for you

It may seem counterintuitive that your battery won't be full on a sunny day. But with smart control through FlexiO, that just means the system is proactively working in your favor. Not just financially, but also for the broader energy system!

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