we are trying to size a battery system to an existing PV system.  we have put in a load profile and PV system. It has given is a recommendation HTW of 89.5kWh. what does HTW mean

Dear robharris,

Thanks a lot for your question. HTW is stands for the University of Applied Sciences of Berlin ("Hochschule für Technik und Wirtschaft" in German). The research group led by Prof. Dr. Volker Quaschning published a detailed analysis and recommendations for the storage size (both in terms of power and energy):

Parts of the study in English

Website of the research group

Kind regards,

Martin

I'm running simulations where I'm defining a photovoltaic (PV) system paired with a battery energy storage system (BESS) and load profiles. The total annual load consumption is 4,019,704 kWh. When I define the battery system, the software (or methodology) suggests a recommended storage capacity from HTW of 4,019.7 kWh.

I've tested this across several projects with different load profiles, and I consistently get a recommended HTW capacity that matches the annual load, just converted into MWh (e.g., 4,019,704 kWh → 4,019.7 kWh).

This led me to the conclusion that the HTW recommendation is simply based on the total annual load and does not account for the actual PV generation or available excess energy.

I'm wondering if this is actually the case – is the HTW method just giving a baseline recommendation based purely on consumption, without considering PV production and self-consumption dynamics? If so, does that mean it's not appropriate for accurately sizing a battery in a system with solar PV where generation profiles and surplus energy play a critical role?

Has anyone else experienced this or dug deeper into how the HTW battery recommendation is calculated in PV + load setups?

Dear Filly,

Thank you for your inquiry.

The information on the ‘Battery system’ page is a recommendation based on the load profile data and is intended as a rough guide.

The simulation of the battery system only takes place with the simulation of the overall system. The battery system can only be optimised after the overall system has been simulated.

You can find more information in our online help and here.

The HTW recommendation is based on this study (unfortunately only available in German):

Optimale-Dimensionierung-von-PV-Speichersystemen_Quaschning.pdf