BalkonPV mit Speicher. Eine gute Idee?

BalconyPV with storage. A good idea?

The quick answer: It depends. In detail, the reason for memory quickly becomes the reason against memory. Whether it is worth it depends on many factors.

Both in product development and in technology, we have been dealing very intensively with the question of whether we should offer a solution for our balcony power plants with storage in a bundle. So far we have not done this and only sell the components individually, but this may change in the future when we have gained enough experience ourselves so that we can competently advise interested parties.

To get in the mood for the problem with the storage for balcony power plants, the recommendation of two videos in the channel "Schau Energy Saving" Part 1 deals with the planning and considerations for an architecture and Part 2 the DIY proof that it can be worthwhile.

In our planning, we also considered option 2, which is used in the videos, to be the only feasible solution. The reason for this is that the installation of the superstructure does not require any intervention in the heart of the house electrical system. The meter cabinet remains untouched, but part of its possible savings are forgone.

Why are you giving up savings?

In the second option, the memory is loaded using the charge controller. This storage is then discharged by a commercially available inverter with constant power. But that's where the problem lies...

If the battery is full and has a capacity of 1 kWh, it can be "discharged" over 10 hours with a constant 100 watts. The same size of memory with a discharge of 50 watts gives a duration of 20 hours.

Which value is the right one to set as the discharge?

Diagram of a typical load profile

The so-called load profile provides information about this. Only most electricity customers do not know this. The load profile shows when and how much electricity was required. If you really don't want anything to be "wasted", the optimal value is the minimum (yellow line), which is around 50 watts. Of course, this is only valid for this one household and on this day, but the data from our customers shows that this value hardly varies up or down.

If you calculate with 50 watts, then under really optimal conditions the storage can cover this load with solar power for about 7000 hours of 8760 hours a year. In other words: 50W * 7000 hours = 350 kWh / year are avoided by storing electricity.

However, these 350 kWh are more or less additional - and this is where it gets complicated, because the charging control of the storage system will always try to provide the 50 watts and as soon as the storage system is charged, make the entire power available to the inverter as generation (note: I think the circuit shown in the videos cannot do this yet). As a first approximation, one can assume that a balcony power plant with "normal" orientation brings in around 900 full-load hours per year. This means that the PV panels (2* 400W) have an annual production of 720 kWh. From this, the 350 kWh must be deducted from the storage usage, so that 370 kWh are still available as "surplus". As a result, with storage there are fewer hours a year to run the washing machine to ensure no power is 'lost'.

Conclusion: A piece of simplicity is lost

Complexities such as an active energy management system are not actually known in balcony power plants. It should be simple so that the dissemination remains comfortable. How this could be arranged will also be a topic at the online regulars' table of the balcony power plants on April 26th - 8:00 p.m. ( free registration required ).

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