DIY Easy Home Battery for Solar Energy (on Grid)

I have been looking for my own Home Battery System for a few years now. The reason being that I want to move some of the excess PV-generated power during the day to the night and thus save cost.

The ones commercially available were expensive, complicated to install and many of them depend on the brand of the inverter.

When I searched YouTube videos and instructables on how to build one, I found most of them complex and often off-grid. So I decided to make one myself and so simple that anyone (including me -:) can do it.

And I wrote this instructable so that everyone can do the same. The requirements it meets are:

• On Grid
• Place it anywhere in/near my house
• Independent of the current PV installation
• Only standard, off the shelf products
• Expandable for more capacity or power
• Cheaper than commercial solutions

I built earlier versions, but they were without a proper automation and not so good that I wanted to share it.

This instructable describes how I created or should I say assembled a 2kWh Home Battery System for less than € 800, which is easily adaptable. Hope it inspire you to build the same or a variation of it.

List of items (it is very straight forward - see picture)

• 1x HomeWizard P1 meter https://www.homewizard.com/p1-meter/
• 2x HomeWizard Energy Socket https://www.homewizard.com/energy-socket/
• 1x Subscribtion to 'HomeWizard Energy+' (1 euro/month)
• 1x 24V LifePO4 Battery 100Ah e.g. https://www.aliexpress.com/item/1005003742224306.html
• 1x 24V LifePO4 Battery Charger 20A e.g. https://www.aliexpress.com/item/1005006132204880.html
• 1x 30A Fuse/Switch (optional) e.g. https://www.aliexpress.com/item/1005006161099930.html
• 1x Enphase MicroInverter IQ7+ https://enphase.com/store/microinverters/iq7-series/iq7plus-microinverter
• 1x enphase IQ cable (portrait) https://enphase.com/store/cables-and-connectors/iq-cable-portrait
• 1x set of MC4-connectors (1 Male, 1 Female) and some cables (4mm2)

Important note: This setup requires your home to have a smart meter, with a P1 port. This is required to use the HomeWizard P1 meter product. See their product page for more information.

In the picture you can see all products I used (except the P1 meter, which was already installed)

The system has the IQ7+ micro Inverter which delivers close to 300W of energy during the night. For me that is fine, because it matches my nightly 'standard' usage, but for someone else it might be too much or too little. So before ordering the micro Inverter it is important that we understand the energy usage during the night, so you can tailor it a little whithin boundaries.

Now the first thing is to order and install the HomeWizard P1 meter on your smart meter and let running for a couple of days. The installation is straight forward: you download the HomeWizard app from the App Store or Google Play. The app will guide you through the whole set up and installation process.

After a couple of days you will collected some data you can analyse. The picture comes straight from app and is showing the basic energy needed during the night which is around 300W in my case. Hence the choice for the IQ7+, which delivers that Energy, whereas the IQ7 will deliver around 250W and the IQ7A around 350W. So select the one which is the best match in your situation.

A similar sizing check can be done for the charger. The LifePO4 charger actually uses 29,2V x 20 A is around 600W. So it is important that you have that level of PV excess power available. If lower you could try 10A version, which only uses around 300W. If you look at the picture it was a very sunny day, but also check for a more clouded day to see how much you have spare.

Wiring it up is straight forward, just connect the battery charger to the battery and to the mains and simular for the inverter. Note: the inverter cable comes without a plug, so you will need to add that first, add the plus and minus wire and the MC4 connectors. Also there is a short 230V cable (used to put inverters in parallel), which we don't need and the wires should be isolated well.

Now you basically can run the system 'manually' to test it. E.g. when the sun shines well and you have surplus energy, plug in the charger and load the battery till it is full. Then when the sun is gone or in the evening, plug the inverter in and you can see in the HomeWizard app how much energy is being produced.

Now that we have a functioning system, the next step is to automate it according to your home's energy requirements.

Firstly, install the two Energy Sockets. This can be done easily through the HomeWizard app by following the provided instructions. During installation, you'll have the chance to name them something meaningful. For example, I named mine 'Battery (Charger)' and 'Battery (Inverter)'. It's useful to label the sockets with these names for easy identification when monitoring the system later.

To automate effectively, you should subscribe to 'HomeWizard Energy+', which is approximately 1 euro per month. This subscription unlocks all necessary automation features. Once you've installed the Energy Sockets and subscribed, you can begin automation by navigating to 'EnergySaver' in the app menu. There, you can define the criteria for when to turn the charger and micro-inverter on and off based on the power flow from or to the grid, simply by setting the appropriate parameters for the Energy Sockets.

For Batter (Charger), add the following tasks (also see picture for the end result).

1. First we want the Battery Charger - which takes about 600W - to turn itself on if we deliver over 600 W to the grid (for some time, e.g. 5 minutes):
2. Add task: Measurement Task
3. When Usage of Main(Grid) (note: this is the P1 meter)
4. Drops below -650W
5. for 5 minutes.
6. Turn Battery (Charger) On
7. Secondly we want to turn if off again, when there is no more surplus power delivered to the grid:
8. Add task: Measurement Task
9. When Usage of Main(Grid)
10. Rises above 0W
11. for 2 minutes.
12. Turn Battery (Charger) Off

For the Battery (Inverter) we can do the opposite and add the following tasks (also see picture for the result).

1. First we want the Battery Inverter - which delivers around 300W - to turn itself on if your home uses more than about 300W from the grid (for some time, e.g. 5minutes):
2. Add task: Measurement Task
3. When Usage of Main(Grid) (note: this is the P1 meter)
4. Rises above 260W
5. for 5 minutes.
6. Turn Battery (Inverter) On
7. Secondly we want to turn if off again, when there is no need for extra energy anymore:
8. Add task: Measurement Task
9. When Usage of Main(Grid)
10. Drops below -50W
11. for 3 minutes.
12. Turn Battery (Inverter) Off

Simply connect the sockets to your charger and inverter to complete the automation. Your battery will charge when there is enough surplus energy, and the inverter will begin to supply power from the battery when necessary.

That's all. Allow it to run for a few days and adjust the automation as needed. I hope this inspires you to undertake a similar project.

The Battery.

The inverter will continue to operate until the battery is completely depleted. However, for Lithium Batteries, the Battery Management System (BMS) will cut off the power supply once the battery reaches a nearly empty state. Consequently, this system is not applicable for batteries lacking a BMS, such as Lead Acid batteries.

You might discover that the battery's capacity is inadequate to last the entire night (like shown in the picture). A simple solution is to connect an identical battery in parallel, which effectively doubles the capacity..

Placing the system

The entire system can be connected through any socket to the mains, allowing you to place it anywhere within or around your house where your WiFi signal reaches. However, it is advisable not to charge or discharge LiFePO4 batteries at temperatures below 0°C or above 45°C for optimal performance and longevity.

Special thanks to VoiceToScript for assisting in the formulation and writing of this instructable.