This is possible using a laptop and the appropriate software.

The recent reduction in rooftop solar subsidy rates and the prospect of a solar tax are raising concerns among solar users.

In Victoria, the minimum feed-in rate was recently reduced to 3.3 cents per kilowatt-hour. IPART forecasts that in NSW, solar exports will be worth between 4.9 and 6.3 cents per kilowatt-hour in 2024/25, compared with 7.7 to 9.4 cents in 2023/24. These changes make optimising solar at home crucial, especially for charging electric vehicles (EVs).

During months with less sunlight, charging an EV at a steady pace throughout the day is not efficient because the solar system produces more energy around noon than in the morning or afternoon. This means you can export kilowatt-hours at a low electricity price around noon, and then buy energy at a higher price later in the day. Timing your EV charging times to coincide with peak solar production can help avoid this problem.

However, setting up an optimized solar system to charge EVs can be expensive, with the need to purchase special chargers, home batteries, or meters, all from the same manufacturer. And doing it all manually is a huge hassle—who has time to regularly check the sun and adjust the charge throughout the day?

Instead, many homeowners already have all the necessary equipment on their personal computers. The computer could manage and optimize solar energy usage, making additional expensive equipment unnecessary if only it had access to all the devices.

I tried this using Tesla API and Fronius Inverter API on my Mac and managed to get it to “smart charging”. Now, based on solar power (read from Fronius API) and if the battery is below 80%, the Mac tells the Tesla to start charging (via Tesla API).

If the cloud clears, the charging current will decrease, then increase again when the sun returns. This is a very efficient way to charge, and on a typical spring day, it will save you about $5 compared to plugging in overnight. All by making existing equipment smarter.

There are still some limitations: Accessing detailed electricity flow data from smart meters can be difficult because some energy companies only make this data available in CSV files rather than via APIs.

So I can’t easily read the actual, real-world usage of the software at home. It also only works with some manufacturers, I haven’t looked at all of them yet, but from a few checks, many car manufacturers are still in the development stage of such APIs, rather than having them up and running.

These constraints underscore the need for open standards in the energy sector, and some efforts are underway worldwide under the banner of “Open Energy.” Future standards will be helpful if they allow us to seamlessly integrate all our energy devices into a smart and efficient home.

Below I have included links to two APIs from Fronius and Tesla to help you get started. I would also like to invite the community to help see if we can continue to develop such software. It works for me right now, but it would be great if we could make it more robust so that anyone can install it.

This could easily improve home solar systems and make optimised EV charging more accessible. If you are interested, live in VIC Bayside or Glen Eira and have a similar setup to mine (Tesla, Fronius Inverter, Tesla Wall Charger, Apple Mac computer) please contact me at (email protected).

Links to technical documentation: