The ultimate guide to interpreting solar lighting spec sheets

 

So, you've decided to use solar lighting for your next project. That's a smart move! But now comes the tricky part—choosing the right product and manufacturer.

 

Shopping for solar lighting isn't like buying an air fryer or a smartwatch. There's no one go-to source like Wirecutter or CNET to guide you. Instead, you'll be looking at spec sheets—those detailed documents that hold all the info you need to compare products and make the best choice for your project.

 

But what exactly is a spec sheet? It's a document that provides all the technical details of a product. It helps you see how different manufacturers stack up against each other, especially when it comes to warranties, certifications, and testing standards.

 

Spec sheets are essential for anyone shopping for solar lighting, but they can be confusing if you don't know what to look for. What do those numbers mean? Which ones are important? How can you tell if a product is truly reliable? We're here to help you decode it all!

 

The information you actually need

 

Here’s the good news: You don’t need to understand everything on a spec sheet to make an informed decision. They’re full of technical details, but not all of them matter for your specific project.

 

Your main goal should be to ensure the product will work for your needs over time. To do that, you need four key pieces of information:

 

1. The size of the solar panel (in watt-peak – Wp)
2. The output of the fixture (in watts – W)
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3. The battery capacity (in watt-hours – Wh)
4. The operating profile or run-time (how long the system needs to run at a certain light level)

 

This data is usually included in most spec sheets. However, some manufacturers may leave out key details to hide weaknesses. If a manufacturer doesn’t provide this information, it could be a red flag about the quality of their product.

 

Here’s an example of a well-documented spec sheet with the relevant details highlighted:

 

 

With these numbers, you can do some simple calculations to determine if the system will meet your requirements.

 

Solar panel collection

 

How big should the solar panel be? Start by finding the average number of peak sun hours in your location during the worst month. The NREL’s PVWatts Calculator is a great tool for this.

 

Let’s say your project is in Charlotte, NC, where peak sun hours in December are 3.73. Multiply that by the panel size (in Wp) to get the daily charging capacity.

 

3.73 x 110Wp = 410 Wh

 

But remember, 3.73 is the average, not the minimum. Some days will have less sunlight. That’s why it’s important to factor in an array-to-load ratio (ALR) to account for low solar days.

 

We recommend an ALR of 1.2:1. Using that:

 

410 / 1.2 = 341 Wh

 

If you skip this step, your system might work fine in summer but fail in winter when solar collection drops.

 

Pro tip: Reputable manufacturers apply derating factors to their calculations to account for dust, snow, shade, and temperature changes. These aren’t always listed on spec sheets, so it’s worth asking about them. If a company doesn’t consider deratings, the system’s performance may fall short of expectations.

 

Fixture output and operating profile

 

You now know how much energy is available, but you also need to calculate how much is needed to power the fixture for the required duration. For that, you’ll need the length of the longest night, which you can find using NOAA’s Solar Calculator.

 

For our Charlotte example, it’s 14 hours. Next, check the fixture’s output (usually given as a range). If you have a lumen requirement, use the fixture’s efficacy to determine the appropriate wattage.

 

For instance, if you need 4,500 lumens and the fixture has an efficacy of 150LPW, you’ll need at least a 30W fixture. Multiply that by the longest night to get the daily load:

 

30W x 14 = 420Wh

 

If your solar panel can only provide 341Wh, the system won’t be sufficient. You may need to reduce the load by using a lower wattage fixture or adjusting the operating profile.

 

A 4D1 profile, for example, would reduce the output in the middle of the night, lowering the overall load:

 

30W x 5 = 150Wh
30W x 50% x 9 = 135Wh
Total = 285Wh

 

This is well within the 341Wh capacity, making the system viable.

 

Battery capacity and chemistry

 

Batteries are crucial for ensuring your solar lighting system runs reliably. A poor battery choice can lead to frequent failures, while a good one can last years without issues.

 

There are different types of batteries—lead acid, lithium, and more. Each has its own recommended depth of discharge (DOD), which affects how much of the battery’s capacity you can safely use.

 

For example, a lithium battery can be discharged to 70%, while lead acid is limited to 25%. This means you need to adjust your battery size accordingly:

 

285Wh x 2 = 570Wh (for two nights)
570Wh / 0.7 = 814Wh (adjusted for DOD)

 

If the spec sheet shows a single battery with 460.8Wh, you’ll need two to meet the requirement.

 

Warning: Some manufacturers ignore DOD recommendations, resulting in undersized systems. Smaller batteries may seem cheaper, but they often fail quickly under real-world conditions.

 

Other considerations

 

Now that you understand how to size a solar lighting system, you can better assess whether a product will work for your project. But there are a few other things to look for on spec sheets.

 

Warranty

 

Even with grants and funding, solar lighting is a significant investment. A good warranty gives you peace of mind and ensures you can return, replace, or repair the system if something goes wrong.

 

Most spec sheets include warranty details, such as “5-year limited warranty” or “10-year warranty (excluding battery).” Be sure to check what’s covered and what’s not. Some companies offer full coverage on the system but only partial on the battery.

 

>>Sol offers a 10-year warranty on all its solar lighting systems, including the battery.

 

Certifications and testing standards

 

Certifications from independent bodies like IEC and IEEE are a great way to verify a manufacturer’s claims. They ensure safety, compliance, and reliability.

 

Another important test is LM-79, which measures the optical and electrical characteristics of LED fixtures. It’s the only standardized test that provides verifiable data on the complete fixture, not just the LED chip.

 

>>Learn more about LM-79 and efficacy

 

Fixture characteristics

 

When evaluating a fixture, ask where it comes from. Some manufacturers build their own, while others use third-party components. Both approaches have pros and cons.

 

Our solution is to partner with top-tier manufacturers like Acuity Brands, known for high-quality, durable fixtures that deliver even light distribution, minimal glare, and long-lasting performance—up to 100,000 hours (over 11 years).

 

Wrapping up

 

Reading and comparing solar lighting spec sheets might feel overwhelming at first, but with the right knowledge, it becomes manageable. We hope this guide has helped you navigate the process with more confidence and made it easier to choose the best product for your needs.

 

Have any questions about spec sheets or anything else? Our team of solar lighting experts is here to help. Contact us today!