About Us

Sonnenberg Thermal Batteries was founded to tackle two pressing challenges: energy poverty and climate change. By combining simple materials, solar energy, and thermal storage principles, we create solutions that are low-cost, durable, and locally manufacturable.

We are driven by the vision of a sustainable Southern Africa where everyone has access to reliable heat and hot water, regardless of income. Our work is aligned with global climate action goals and we are actively seeking collaboration with partners, researchers, and funders to scale our impact.

Christoph Sonntag, PhD. - Founder, technology and innovation.

Lezanne Sonntag - Business, strategy, and marketing.

Etienne van Achterberg - Technical expert, manufacturing, consultant.

Clinton McLellan - Technical expert, architectural technologist, consultant.

Energy Solutions

Solar Heat Storage Solutions That Work Where Electricity Doesn’t

At Sonnenberg Thermal Batteries, we focus on practical thermal energy solutions that solve real problems for people who live off the grid or cannot afford electric heating. Our systems use solar energy to heat sand during the day, and store that heat for use long after sunset — for hot water, warm air, or even cooking support.

Key Use Cases:

1. Solar-Heated Hot Water

Our sand batteries store solar heat and transfer it to water through embedded metal piping. This allows households, clinics, and schools to access warm water even after the sun has set — without relying on electrical geysers or gas.

• Ideal for rural homes, informal settlements, or container-based housing
• Can integrate with existing water tanks
• Zero operational cost after setup

2. Passive Space Heating

We design modular boxes that blow warm air into living or working spaces using small fans or natural convection. Heated air flows from sand that’s been warmed during the day — even in winter or at night.

• Perfect for small offices, clinics, or classrooms
• Uses existing plastic ducting or metal piping
• Reduces indoor cold stress in uninsulated buildings

3. Daytime Air Heaters with Heat Retention

In sunny but cold regions, we also build solar air collectors paired with sand-based thermal mass. This creates a hybrid solution where warm air is delivered during the day and some of that heat is retained in the sand for slow release after sunset.

• Modular collectors can be wall- or roof-mounted
• Enhances comfort and reduces energy needs

4. Modular Thermal Storage Blocks

We are developing scalable “heat battery” modules that can be placed side-by-side depending on the user’s needs. These can serve single rooms or small buildings, and be expanded over time.

• Built from simple materials (sand, metal, insulation)
• Can be made locally using low-tech tools
• Low maintenance, no moving parts inside the core

Whether you need hot water, warm air, or basic heating, our systems are designed to be affordable, durable, and adaptable to local conditions. Sonnenberg Thermal Batteries is committed to energy solutions that make a real-world difference.

The Sand Battery

Thermal Energy Storage — Made from Sand

A sand battery is a low-cost, passive energy storage system that captures and holds heat from the sun. At Sonnenberg Thermal Batteries, we use sand — an abundant and stable material — to store solar thermal energy during the day and release it later when it’s needed. It’s simple, durable, and doesn’t rely on electricity or chemical reactions like traditional batteries.

How it works

1. Solar Heat Capture

Sunlight enters through a transparent cover and heats the sand inside a highly insulated container — similar to how a greenhouse traps heat.

2. Heat Storage:

Dry sand has a high thermal mass, meaning it can store a large amount of heat without breaking down. Our systems are designed to retain this heat for many hours — even overnight.

3. Heat Delivery:

We embed metal tubing or air channels inside the sand. When water or air flows through these channels, it absorbs the stored heat and carries it into homes, taps, or enclosed spaces.

 

Design Features

• Modular Units — Can be scaled up or down depending on the use-case
• No Moving Parts in Core — Simple, long-lasting design
• No Need for Electricity — Operates with solar heat and passive transfer
• Locally Available Materials — Sand, metal pipe, insulation, and clear covers

Use Cases

• Heating water for bathing, washing, or cooking
• Space heating in small homes, clinics, or offices
• Integration into off-grid solar energy systems
• Daytime air heating with nighttime heat retention

 

 

Why Sand

Sand is non-toxic, abundant, and thermally stable up to hundreds of degrees Celsius. It also doesn’t degrade over time, making it ideal for storing heat in low-income or rural settings where long-term reliability matters.

R&D in Progress

We are actively testing various sand types, container materials, pipe configurations, and insulation strategies to optimize:

• Heat absorption and retention
• Output temperature stability
• Cost and ease of manufacturing
• Durability in outdoor environments

Our goal is to create a solution that’s simple enough to be made anywhere, but effective enough to make a real impact.

 

Contact

Are you interested in partnering, funding, testing, or co-developing our solutions?

We’re currently building pilot projects and welcome inquiries from collaborators, researchers, and humanitarian organizations.