The conversation around solar panel batteries in Portugal has become noisy because a lot of people try to sell the wrong idea: that a battery “multiplies” savings just by existing. It does not. A battery does one very concrete thing: it shifts energy in time. It stores part of the solar energy produced during the day so you can use it later, especially in the late afternoon and at night. If you do not have surplus during the day, the battery has little to store. If you do not have meaningful consumption at night, the battery can fill up and just sit there, underused. That is why there is no universal answer. There is a right answer for your consumption profile.
The most honest way to look at this is simple: without a battery, you save with the energy you manage to consume at the moment it is produced. With a battery, you save with that direct energy and also with an extra portion you manage to “pull” into the night period. The rest may go to the grid as surplus, with or without being sold, but that does not automatically replace a battery and it should not be used as an easy argument, because it depends on contracts, conditions, and your own situation.
To frame this with real numbers from the Portuguese market, self consumption already has a relevant scale: in the self consumption report for 2024, ERSE estimates that around 73% of the energy produced by self consumption units was effectively self consumed. The total surplus energy injected into the grid that year was 536 GWh and, of that surplus, ERSE indicates that 43% was traded on the wholesale market, with the remaining share not being valued in the market. This matters because it confirms two things: on average, self consumption is relatively well sized, but there is still meaningful surplus, and not all of that surplus turns into revenue. It is precisely in that space that a battery may or may not make sense, depending on your case.
Self consumption without a battery: when it is enough and when it leaves money on the table
Without a battery, the solar system works like a tap that only gives water when the sun is present. Everything that is switched on at home during that time window “drinks” solar energy and reduces purchases from the grid. When the house is practically empty during the day, what stays on is the basics: fridge, standby loads, router, and little else. In this scenario, a relevant part of the production can become surplus because there is not enough consumption to absorb the energy at that moment.
That explains why two homes with the same system get very different results. A home with remote work, with meals prepared at home, with a heat pump or water heater programmed to heat water during solar hours, with machines running in the afternoon, achieves a much higher direct self consumption rate. The difference is not “luck” or “the panel brand”. It is the hourly consumption profile and load management.
Here is the simple calculation that cuts through the noise. Imagine a home that, on a typical day, can consume 60% of the system’s production directly. The other 40% is surplus. Without a battery, the savings come essentially from those 60%, because that is kilowatt hours you did not buy from the grid. If the 40% surplus is sold, it can bring some additional return, but it should not be confused with bill savings, because it is a separate revenue stream and it may have rules and associated implications. If it is not sold, that energy still “exists” in the electricity system, but for you, in practice, it does not reduce your bill any further.
The big truth is this: before you talk about a battery, you have to squeeze direct self consumption. Scheduling hot water for solar hours, concentrating laundry and dishwashing in solar hours, bringing forward oven use, adjusting heating or cooling to pre heat or pre cool when there is production, or scheduling electric vehicle charging around midday, often delivers more value than buying storage blindly. It is zero investment in hardware and it immediately increases the energy you stop buying.
Self consumption with a battery: what really changes and how to do the maths without being misled
With a battery, your goal is to turn part of the daytime surplus into nighttime self consumption. And here it is worth being direct: a battery is only “worth it” if it increases your self consumption in a material way. If your system is already being almost fully consumed during the day, the battery has little to store. If you have surplus but your nighttime consumption is low, the battery also does not do magic, because it will fill up and you will not use it.
The right question is not “how many panels do I have” or “how many kilowatt hours do I produce per year”. The right question is “how much energy do I buy from the grid after the sun goes down and how much energy do I have left over during the day”. The marriage of those two curves is the battery.
Make a practical estimate of your consumption between late afternoon and midnight on a normal day. If your consumption in that period is, for example, 4 to 6 kWh consistently and you have daytime surplus to charge, a battery with usable capacity around that range can make sense because it will be used almost every day. If your typical nighttime consumption is 1 to 2 kWh, it is very easy to end up with too much capacity, and then you are paying for a battery just to watch it sit there. If your nighttime consumption is very high, for example 10 kWh or more, a battery can help, but it already requires more serious sizing and analysis, because charging and discharging power, habits, seasonality, and even your contracted power come into play.
It is also important to say the part that generates criticism on social media: no battery system should be sold as a “promise of total independence” for a normal home connected to the grid. The battery reduces purchases from the grid, especially at night, and increases self consumption. But in winter there are days with low production and you remain dependent on the grid. That is not a defect, it is the physical reality of solar.
And watch out for another recurring confusion: having a battery does not automatically mean having electricity when there is a grid outage. In grid connected installations, there are safety rules and protections that prevent the system from continuing to feed the grid when there is an outage. To have real backup, the installation has to be prepared to operate in off grid mode and it usually includes specific configuration and, often, a critical loads panel. This is the kind of detail that separates a serious project from a rushed sale.
As for technology, it makes sense to mention concrete examples because people search for brands. The Huawei LUNA line, for example, is modular, with 5 kWh modules and the possibility of expansion up to 30 kWh, depending on the configuration. The manufacturer indicates technical specifications such as IP66 classification in the modules and in the control module, and clearly describes the logic for expanding capacity. This is useful because, in practical terms, it allows you to start with a smaller storage size and grow later, instead of trying to guess the perfect size from day one.
The Portuguese framework and what you cannot ignore in a well done project
A self consumption project is not only about hardware. It also needs to be properly regularised and aligned with what you want to do with surplus. In Portugal, there are thresholds and prior control procedures associated with power and with the intention to inject surplus. For self consumption above 700 W and up to 30 kW, the legal framework provides for prior communication. And from an operational point of view, E Redes clearly indicates that if you intend to inject or sell surplus to the grid, or if installed power is above 700 W, registration in the DGEG self consumption portal is required. This is not bureaucracy to scare anyone. It is simply the correct path so you can be confident and have the installation properly framed.
This detail also helps answer the stigma of “this is all a mess”. It is not a mess when it is done by people who know what they are doing. What is messy is when someone tries to sell quick solutions without explaining what changes when you start injecting surplus, what the steps are, and what the responsibilities are. If the goal is a serious investment, the project should start from real consumption, move through real sizing, and end with installation and registration done properly. And this is where a competent installer stands out: they do not just sell you equipment, they deliver a system that works in your day to day life and within the rules.
In the end, the choice between self consumption with a battery or without a battery is not ideological, it is maths and habit. If you have meaningful daytime consumption and you can shift loads to the day, a system without a battery often already gives you excellent savings and a very strong return. If you have regular daytime surplus and consistent nighttime consumption, the battery makes sense because it increases your self consumption and reduces purchases from the grid when electricity is more needed. If you sit between these two worlds, the best advice is simple: start by measuring and optimising consumption, then size storage based on what actually happens in your home, not based on “internet averages”.
Conclusion: is it worth it or not?
A battery is worth it when it does work. Work means turning daytime surplus into nighttime consumption, frequently, and with a size adjusted to your real consumption. If your home has little daytime use and a lot of late day consumption, the battery tends to be an excellent complement to self consumption because it attacks your biggest point of grid purchases. If you already consume a lot during the day, the battery can still make sense, but the additional gain is smaller and you have to be more demanding in sizing so you do not pay for capacity you will not use.
If you want a practical criterion, without promises and without talk: the battery pays off when you can identify, with some consistency, daytime surplus and meaningful night purchases. If one of those sides fails, the battery stops being an obvious decision and becomes a comfort, optimisation, or backup decision, as long as the system is prepared for it. This is the opposite of easy marketing, but it is exactly the stance that avoids regrets and reduces the “stigma” on social media, because it is based on facts, not slogans.
