Support cost savings calculation with solar panels, battery storage, and dynamic electricity pricing

[vostring]

Describe your core improvement

I would like Home Assistant’s core energy management to support cost savings calculations that combine: solar production, battery storage behavior, and dynamic electricity prices (time-of-use tariffs).

Specifically, the system should calculate the monetary savings when:

• A battery is charged with solar energy (or during low-price hours).
• That stored energy is later used during expensive hours instead of buying from the grid.

Currently, the Energy Dashboard shows consumption, production, and export, but it does not calculate what the actual monetary savings are when using a battery to shift load between expensive and cheap hours.

The enhancement would allow Home Assistant to:

• Combine real (or simulated) solar generation and battery usage with dynamic hourly prices.
• Calculate “with battery” vs. “without battery” cost scenarios.
• Show potential or actual savings directly in the Energy Dashboard.

This would make Home Assistant much more useful for households with solar panels, storage batteries, and hourly electricity pricing models (like Nord Pool in Europe), by clearly showing the financial benefits of optimizing battery usage.

Current limitations

The current Energy Dashboard provides insights into energy flows (consumption, production, export, and battery usage), but it has several key limitations:

• It does not calculate the monetary savings of charging a battery with solar energy (or during low-price hours) and using it during high-price hours.
• Users cannot compare “with battery” vs. “without battery” cost scenarios directly in the dashboard.
• There is no native support for simulating or forecasting cost optimization based on dynamic electricity pricing.
• To calculate actual savings, users currently need to create complex template sensors or use external tools, which is not user-friendly.

These limitations prevent Home Assistant from showing the full financial impact of battery and solar optimization for households with time-of-use electricity tariffs.

Technical benefits

Implementing this feature would enhance Home Assistant’s core capabilities by:

• Allowing the Energy Dashboard to natively calculate monetary savings based on real or simulated battery usage and solar generation combined with dynamic electricity prices.
• Enabling “what-if” scenarios, such as comparing costs with and without battery storage, without requiring complex templates or external tools.
• Providing a foundation for automated energy optimization, such as recommending or controlling battery charging/discharging to maximize savings.

This improvement would strengthen the core energy management functionality, making it more useful for households with solar panels, storage batteries, and time-of-use electricity tariffs.

Additional context

No response

[vincedarley]

I think a pre-requisite of this would be for home assistant to understand the changing "cost" of electricity, taking account of what fraction of the electricity being produced and consumed (in a given time period) is from grid vs solar vs battery, and understanding the varying costs for each (grid costs vary depending on your electricity tariffs by time of day, solar is approximately zero cost, battery costs depend on the cost of electricity used to charge the battery,...)

I wrote up an approach which I think would work for this here: https://community.home-assistant.io/t/energy-cost-for-the-individual-devices/334932/183?u=vincedd (in the "Energy: cost for individual devices" feature request thread with 1143 votes over there!), reposted below for clarity:

If I understand correctly, one of the challenges with this request is that while it seems straightforward. It is only straightforward for those without solar or home-batteries. If you have solar and/or batteries then the cost of electricity in any time period is more difficult to determine - when an individual device consumes electricity, what is the cost of that combination of grid/solar/battery at that moment?

However, “difficult” is not the same as “impossible”. Having thought this through, here’s how it can be done.

3 sources of electricity:

Grid (cost given by electrical supplier - can often change every half hour)
Solar (cost is “free”, similarly for Wind, etc)
Battery storage (cost depends on the cost of electricity used to charge the battery, with a round-trip efficiency factor applied).
For any short period of time (e.g. every 5 minutes), we can observe and measure:

EP_grid (the kWh provided by the grid) (zero if off-grid or exporting…)
EP_solar (the kWh provided by solar) (zero at night, etc)
EP_battery (the kWh provided by the battery) (zero if we are charging the battery)
Here ‘EP’ = Energy Provided. And then EP_total is the sum of all 3: EP_grid + EP_solar + EP_battery

And similarly when charging the battery, there is a

EP_solar_charging (the kWh used from solar to charge the battery)
EP_grid_charging (the kWh used from the grid to charge the battery).
At any moment in time we have electricity being consumed and electricity being provided. Grid can provide and consume (if you are exporting). Solar panels only provide. Battery can provide and consume.

The cost of electricity in any interval of time is the weighted cost of the electricity from each provider. So the real-time cost per kWh for any device consuming electricity then, is:

Cost of electricity in any interval ‘C_elec’ = C_grid * EP_grid/EP_total + C_solar * EP_solar/EP_total + C_battery * EP_battery/EP_total. (where, as above, EP_xxx is zero if that provider is not currently providing electricity, so if the battery is not discharging, EP_battery is zero).

How do we calculate each of C_grid, C_solar, C_battery? C_solar is easy (it is zero). C_grid is also easy - it is the cost per kWh charged by the grid in that time period. C_battery needs to be calculated.

To do that we must maintain a total cost (money) that has been stored in the battery. This is updated any time that the grid is used to charge the battery at all:

Total_cost_in_battery = Last_period_total_cost_in_battery + EP_grid_charging * C_grid + EP_solar_charging * C_solar.
Again C_solar is zero.
C_battery is then Total_cost_in_battery/Total_kWh_in_battery - in units of money/kWh obviously. Note that the kWh in battery is required here - it will presumably be slightly less than the kWh used to charge the battery (since that process is not 100% efficient). So need to have battery monitoring to tell you the kWh stored. If the battery has been mostly charged with solar and/or cheap overnight electricity, then the C_battery will be low. We may also need to directly apply an inefficiency factor to C_battery to account for the outbound inefficiency. i.e. when our battery drops from 20kWh to 15kWh, we may only have consumer 4.95kWh of electricity - the final 0.05kWh is lost. We should account for that by adjusting C_battery. Or we could separately measure accumulated “battery losses” and attribute a cost to that. But I think better to adjust C_battery so that the consumers of the electricity are more accurately costed.

So, using the above we can calculate ‘C_elec’, and hence know the cost of electricity in our system in the current time interval. That is the cost that should be applied to any consumer of electricity in this time interval: mostly that is all of your household devices. If you are exporting to the grid, then it is also your supply cost for that export (so the grid should be paying you more than C_elec if you are choosing to export!).

[sambillings2]

This is a very well-explained feature request, and it highlights a real gap in Home Assistant’s current Energy Dashboard. For households using solar panels, battery storage, and dynamic electricity tariffs, the financial impact of smart energy shifting is just as important as the energy-flow data. Being able to compare “with battery” vs. “without battery” cost scenarios directly in the dashboard would make the system far more practical, especially for users who rely on hourly pricing models like Nord Pool.

Integrating these calculations natively—rather than requiring custom templates or external tools—would give people a much clearer view of how much they’re actually saving by charging batteries with solar or during off-peak hours. It’s a feature many solar-powered homes could benefit from, similar to how advanced monitoring tools are used in commercial solar brisbane setups to showcase real-time cost optimization and load shifting. Adding this capability would definitely make Home Assistant’s energy management more powerful, transparent, and user-friendly.

[vish022091]

I support this feature too and just in case anyone isn't aware, this feature received over 1140 upvotes on the Home Assistant community forum