In short…

I want to build a home battery from reclaimed lithium ion cells. By using this battery to store solar energy, I aim to demonstrate off-grid electrical self-sufficiency.

Motivation

Electricity is expensive in Australia, and the Australian government is woefully unexcited about the renewable-energy future. For a country with so much sunlight, it is hard to believe how reticent we’ve been to embrace solar power. On top of this, lithium batteries are shipped overseas for non-trivial recycling. Extending their utility lifespan just makes sense!

Goals

The ultimate goal is to demonstrate off-grid self sufficiency, but this home-brewed project will have to start small and pull itself up by its bootstraps. Some of the important steps include:

1. Build a modular home battery from cells reclaimed from waste laptop batteries.
2. Usefully power some appliances in the house from the battery.
3. Charge the battery using electricity from on-site roof-top solar panels.

Other less tangible goals include keeping costs at a minimum and learning more about the various technologies required for an off-grid solar-powered home.

Feasibility

The sun delivers about 1000W per square metre to the Earth’s surface. My house has a roof area of about 100 square metres, and Sydney gets about 6 effective solar hours per day.  This means that my house is delivered 600 kWh of energy per day!

It’s not so easy to capture all of this energy. Let’s assume that only a quarter of my roof is angled appropriately (towards North), and that I could cover this area with solar panels which are about 15% efficient. I would produce 22.5 kWh of electricity per day.  My household consumption over the last 12 months has averaged about 13.5 kWh per day, and so it should be possible for my small suburban home to be electrically self-sufficient.

Clouds and nighttime make it necessary to store energy, and batteries do this for us all the time (phones, laptops, watches, etc). Lithium ion chemistry has become widespread due to its high energy density, and it is this density that is important in many applications – we want portable devices to be small and light! As batteries age they lose some of their capacity, and they usually lose utility before they are fully “dead”. A home battery is stationary and has space, so does not require high density. It is the ideal way to make further use of aged cells.  Laptops are ubiquitous, and discarded laptop batteries must be plentiful.