Home » Learn About Solar Lighting » The science of sizing: How we engineer our solar lights for ultimate reliability

When it comes to solar lighting, size matters. And we’re not saying bigger is better—because often, it isn’t. A well-sized solar lighting system balances efficiency, reliability, and cost-effectiveness, ensuring that it works as expected every night, all year round. Get it wrong, and you might end up with a light that flickers out in bad weather—or an oversized system that needlessly drives up costs.

At Sol, we’ve spent years perfecting the science of solar lighting, designing systems that perform dependably without going overboard. Unfortunately, many companies don’t share our level of experience or attention to detail. They undersize their systems, leading to disappointment when the lights don’t work as promised. So, how do we get it right? Let’s get into it!

The Goldilocks principle (AKA the ‘just-right’ size)

A properly sized solar light strikes the perfect balance: enough solar collection, battery capacity, and LED efficiency to keep the light running as expected without adding unnecessary costs. We like to say it’s the Goldilocks solution: not too little, not too much—just right. To achieve this balance, three key factors come into play:

1. Array-to-load ratio (ALR) – Ensuring enough solar energy is collected to sustain the light’s operation.
2. Battery capacity and backup power – Providing sufficient energy storage to power the lights at night and through periods of bad weather.
3. Efficient LED fixtures and smart operating profiles – Maximizing light output when necessary while minimizing energy draw when it isn’t.

Seems simple enough, right? Let’s dive deeper.

The array-to-load ratio: Energy in vs. energy out

The foundation of a reliable solar light is the array-to-load ratio: the balance between the energy collected by the solar panels (the array) and the energy used by the light fixture (the load). If a light consumes more energy than it collects, it will fail—no exceptions.

One of the biggest factors affecting ALR is location. Different regions receive different amounts of sunlight, known as solar insolation. A solar light in Phoenix will need a much smaller panel than one in Seattle to achieve the same operation. When a system isn’t sized correctly for its location, it either underperforms or becomes unnecessarily expensive.

Some manufacturers attempt to compensate for poor energy management by adding larger panels, but that isn’t the best solution. Larger panels add cost, increase wind load (requiring sturdier, pricier poles), and can create bulky, unappealing designs.

Instead of throwing more panels at the problem, we focus on efficiency—ensuring each system collects and stores the right amount of energy for its specific needs.

Batteries & backup power: Storing energy for when it’s needed most

Solar lighting systems rely on batteries to store the energy generated during the day so lights can operate at night. But not all batteries are created equal, and choosing the right one affects everything from performance to cost.

We use three main types of batteries in our systems:

• Lead-Acid – Proven and reliable, but heavier and more expensive than alternatives.
• Nickel-Metal Hydride (NiMH) – Long-lasting and capable of deep cycling, suitable for a wide variety of climates.
• Lithium-Ion (Li-ion) – Lightweight with high energy density, but sensitive to extreme cold.

One of the most crucial battery considerations is depth of discharge (DOD), or the percentage of capacity used each night. A battery that regularly depletes too much of its charge will degrade faster, shortening its lifespan. Adequately sized systems consider this and build in enough capacity to extend battery life while maintaining reliable operation.

And what about extended periods of cloudy or stormy weather? That’s where backup power comes in. A well-designed solar lighting system includes enough capacity to maintain operation for several days without sun. Our systems are tailored to local conditions, providing reliable performance regardless of weather.

Fixture efficiency & smart operating profiles

Solar lights and LEDs are a perfect match—LEDs are the most energy-efficient lighting technology available, and their ongoing advancements allow for brighter illumination with less power.

Today’s high-efficacy LEDs can deliver over 170 lumens per watt, producing more light using less energy. This is crucial in solar lighting because a lower power draw means smaller solar panels and batteries, reducing costs and improving aesthetics.

Another key to proper sizing? Optimized operating profiles. Instead of running at full brightness all night (we call this dusk-to-dawn operation), many projects use adaptive lighting to conserve energy while maintaining safety and visibility. Examples include:

• Dimmed off-peak hours: The light runs at full brightness in the early evening, dims overnight, and brightens again before dawn.
• Motion-activated lighting: The light dims or turns off at inactive times and brightens when movement is detected.

Choosing the right profile for your application can reduce power requirements significantly, making a solar system more compact and cost-effective while still meeting lighting needs.

Why proper sizing matters

A well-sized solar light ensures reliability, longevity, and cost-efficiency. Here’s what that means for you:

✔ Lights that stay on: No dimming or failures, even in poor weather.

✔ Cost savings: No oversized panels, batteries, or poles

✔ Longer lifespan: Optimized energy management extends battery and component life

✔ Sleek, efficient designs: No bulky installations or unnecessary add-ons

At the end of the day, the best solar light is the one that works as expected every night and in every season. That’s why we take sizing seriously, ensuring each system is built to perform reliably for years to come.

Need help designing the right solar lighting solution for your project? Get in touch with our team!