Flexible Tariffs and Battery Charging Automation for Winter

Back Nikola Nedoklanov 8 min read December 4, 2023 1492 words
Simple automation for battery charging and smart use of flexible tariffs for maximum savings using Solar Assistant.
A conceptual and artistic representation of flexible tariff solar battery charging automation for winter in a 16:9 aspect ratio, suitable for a blog post. The image should feature a modern and stylized depiction of a solar panel and a battery, connected and symbolizing the integration of solar energy systems with home automation. The background includes subtle winter elements like snowflakes or frost, and the design should be adaptable to different color backgrounds. The overall feel is futuristic and innovative, focusing on renewable energy and smart technology, in JPEG format.

Winter spells a return to buying electricity from the grid for home solar energy system owners. Nevertheless, we can put our system to work again by leveraging flexible tariffs with our batteries. Charging cheaply overnight and offsetting the expensive hours is excellent. Yet we still want to make the most of the few sunny days. However, a full battery in the morning can get in the way of fully utilising those hours of sunshine.

Simple Battery Charging Automation Based on PV Forecast

An automation can help maximise your savings. But there are many ways to make such an automation, and they all look complicated. Fortunately, I have a simple and powerful way to solve this problem. On top of that, I think many people already have the crucial components required for the solution.

I will focus on solving one specific problem:

How to dynamically adjust the percentage of overnight charge so that it charges to 100% when low solar production is expected on the next day.

This automation is only worthwhile if you have access to a flexible tariff that allows you to charge your battery using cheaper electricity from the grid. There are many ways to achieve some degree of automation.

Keep it Simple: Solar Assistant and Overnight Charging.

A diagram illustrating a smart solar battery charging automation system. It shows an inverter connected to a battery display indicating 95% charge. Two-way communication is depicted between the inverter and a module labeled 'Solar Assistant' via MQTT protocol. 'Solar Assistant' is further connected to 'Home Assistant,' which is linked to 'Forecast.Solar' represented by a solar panel icon with a sun. The diagram visually explains the process of automating solar battery charging based on solar energy production forecasts.
Frecast.Solar provides the estimates and Home Assistant, via Solar Assistant configure the overnight charge percentage.

Energy is cheaper overnight, and complex logic fails more often. Hence, this automation is about simplicity. Here are the key reasons I went for this specific solution.

  • I use an Economy Seven tariff.
  • My system consists of a larger East-facing and smaller West-facing strings. Half a day of rain can have an outsized negative effect. Therefore, overnight charging can bring me benefits through most of the year.
  • My inverter, Sunsynk 3.6, seamlessly integrates with Solar Assistant and offers remote configuration. I already have Solar Assistant set up.

Components of the Solution?

Relative Simplicity of Automating the Battery Charging

The solution’s relative simplicity is why I decided to go for it. I appreciate that this is an entry-level solution, so treat it as a gateway or first step to more sophisticated automation.

Sunsynk 3.6 ECCO Inverter

Sunsynk 3.6 ECCO is thoughtfully built with many configuration points, and so far, I have never failed to find what I need there. The battery State Of Charge (SOC) settings are yet another example of useful configuration. Directly in the inverter, you can configure the time slot you wish to charge from the grid and enable grid charging for this slot only. Then the only thing that remains to do is adjust the SOC percentage with a dynamic configuration that comes from outside. Luckily, the Sunsynk 3.6 ECCO integrates seamlessly with Solar Assistant and exposes all the required configuration points via MQTT.

Interface snapshot of an inverter system settings panel showing options for solar export, grid charge scheduling, and setting night tariff times for efficient energy management.

What is Solar Assistant and Why Use It?

Solar Assistant is a solar energy system monitoring software tool. It is a proprietary software product and you buy it once and own it. The software runs on a Raspberry PI computer.

RS-485 to USB adapter connected to a Raspberry pi picture of a working solution

I use a Raspberry Pi that I keep near the inverter for an easier wired connection between them.

The tool interfaces directly with your inverter. It can also connect directly to the batteries or use the inverter as a proxy. You can choose between a wide selection of supported protocols so chances are high for your specific hardware to find the one it needs.

I value it highly for its real-time monitoring, analytics, and historical data. Solar Assistant connects to the internet for remote monitoring and configuration of the inverter. This is an amazing feature as it offers an easy to integrate with of your inverter and battery via MQTT.

Solar Assistant - Setup and Cost

Solar Assistant is the cornerstone of this automation. It links your inverter and Home Assistant where the forecast and the automation logic reside.

Setting up Solar Assistant is not trivial, regardless of the maturity of the application. It has been built to support many inverters, batteries, and protocols. Hence, it is full of variances, and likely one of them will work for you. However, finding the right configuration and the right communication cables for your inverter can get .

Cost is the other important aspect of this point. Solar Assistant is proprietary software and requires you to purchase a license . Additionally, it takes over an entire Raspberry PI, which means yet another purchase. On the other hand, the price of a Solar Assistant setup is low relative to the cost of a 3.6kW inverter and 4kW of panels.

There additional benefits to having Solar Assistant setup in your home solar energy system. For example, real time monitoring and detailed information about each of my batteries are my favourite metrics I get from having Solar Assistant in my setup. If you are considering buying and setting it up to automate your battery, I recommend you do enough research up-front to be sure that the integration and remote configuration of your inverter is supported.

Home Assistant

Setting up Home Assistant is easier than Solar Assistant. Moreover, you can get it for free and start in minutes. You can run it on a Raspberry PI or in a Docker container on your home computer. The quick setup is valuable when verifying that your home solar energy system works with the automation you will create.

When linked to your Solar Assistant, you will see a list of all data points and configuration points your inverter exposes. Now, you can explore and verify that you can configure your battery SOC remotely and experiment with a manual configuration.

Screenshot of a solar automation interface showing triggers for solar production forecast, with conditions to adjust the State of Charge (SOC) for efficient energy management.

Forecast Solar

Forecast Solar is a service you can add to your Home Assistant setup. You configure it with your location, the PV capacity of your string, direction and tilt angle. Each string is set up individually. You get a PV generation forecast for the remaining kWh today and tomorrow alongside other forecast values.

Screenshot of a solar automation interface showing triggers for solar production forecast, with conditions to adjust the State of Charge (SOC) for efficient energy management.
List of the automations I use. Two by two they react to Forecast.Solar changing the estimate for tomorrow. Additionally, each day after midnight it checks today’s estimate as this may be different closer to the time.

These automations set the SOC to 100% when the PV energy production is too low and reduce the overnight charge to 40% when we expect to see more sun in the next day.

When Is This Automation Not Right For You

There are a few straightforward cases where you can easily decide against this approach:

  • Your tariff is - you get cheap energy time slots based on grid production surpluses, which may happen at various hours. In this case, you want to invest the time and effort in a more sophisticated automation.
  • You are not convinced your inverter and battery are supported by Solar Assistant .
    • If your inverter and battery can integrate, you are not convinced they allow remote configuration via MQTT.
  • You do not want to spend more money on your system.
    • This solution requires the purchase of proprietary software and additional hardware, too.


Leveraging flexible tariffs and smart automation transforms winter’s solar challenge into a triumph. The integration of Solar Assistant with Home Assistant arms us with the foresight to adjust to solar PV energy variability and capitalise on off-peak rates. Thus, ensuring our solar journey is as cost-effective as it is eco-conscious.

Use this guide as a gateway to automation or as all you ever need, if you like me like to keep your setup simple and effective. The possibilities for expansion of this setup are vast and ready to be harnessed.

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