One Solar Panel To Rule All My Landscape Lighting

For under $100, I installed a smart solar controller. It grabs excess energy from an existing panel and applies it to a single deep-cycle marine battery, powering about 20 LED landscape fixtures.

I recently wrote about the dire e-waste mess being created by the proliferation of short-lived standalone solar landscape lighting. They tend to have short lifespans, for a number of reasons.

In that article, I suggested taking a different approach: Tap into energy created with professional, glass-faced solar panels to run a 12-volt low-voltage system instead. 

I just put my own advice to work, so I’m eager to share the outcome with you. Hint: It’s all good, and might give you the confidence to try it yourself.

The Right Controller

I researched a lot of solar charge controllers before settling on this model. Along the way, I learned some important technical details. First, in most cases a “PGM” controller won’t work because it can’t transform higher voltages to the necessary 12 volts (or thereabouts). 

You need what’s called an MPPT controller. They cost more, but they perform multiple functions, as I’ll explain. Mine was about $89 bucks on Amazon.

Let me just list some of the super cool stuff about this controller.

• It recognizes your battery. Seconds after I hooked it up, it guessed correctly that mine was a 12-volt lead acid gel battery, although I later had to change that setting to get the timer to work properly (see below).
• It converts multiple voltages of PV into 12 volts. In my case, the combination of two 36-volt panels in series was delivering up to 72 volts in bright sun. The OOYCYOO (catchy, huh?) dropped that down to 13.8 volts, the optimal charging level for my battery type.
• The circuits include a multi-option timer. You might wonder how this timer will work since the controller has no clock and no photocell. Simple. It measures “dusk” from the moment it receives the last trace of power from the panel. So if you set the run time for 3 hours, your lights run 120 minutes beginning at dusk. Note that you must set the battery type to USE for some reason, to get the timer to work. 
• It won’t let your battery explode (in theory). The controller has multiple safety switches, including overload protection, and underload shutdown. So it helps protect your battery and the lights.

Connecting Lamps: What Gauge Wire?

I wondered if my existing 18 gauge AC extension cord wire (used for the existing 12-volt transformer) would be sufficient to power the low-voltage lamps. 

DC doesn’t like to travel, and the first lamp was 50 ft. from the battery. I checked the math and found I could deliver 120 watts safely to the lamp with my wire. To give myself lots of buffer load, I purchased LED path lights and deck lights with very low loads, about 2 watts each, so my overall power demand was under 50 watts.

I disconnected the transformer and snipped off the female end, then the male end, of the extension cord. I thought about selling or giving away the transformer, but then I’d just be encouraging someone else to waste grid energy. So I mothballed it in a dark corner of my shop.

By switching my landscape lighting over from individual solar posts to one central panel and low-voltage lamps like this, I greatly increased the likely lifespan of my system, made it more reliable, and reduced my future e-waste footprint.

Performance and Return on Investment

I’ve been using my centralized solar lighting for a few weeks now without a hitch. I’ve found that if I run the lights for about five hours in the evening, my deep cycle battery drops to about 80 percent capacity. On a sunny day, it’s back up to 100% by midday. 

I guess you’re wondering, was the outlay of time and gear well spent versus just buying a bunch of cheap solar yard lights for $5 each? 

I spent between $8 and $14.95 per low-solar fixture, saving money by picking up various discount lamps at Lowes each week for a few weeks. Let’s round up and say I spent $15 per fixture, or $300 (including wire). My deep cycle lead-acid battery cost about $150 bucks, so the total outlay was a little under $500.

By comparison, for solar one-off fixtures, I would have spent $100. But let’s assume that those solar lamps would last only 2 or 3 years. The low-voltage ones could, in theory, last 10 or even 15 years. Granted, that’s a rosy estimate, but even if the lights (and battery) only last 10 years, they reach parity in terms of cost with replacing cheap solar lights every 2.5 years. 

A Couple of Caveats

I have “embedded” a few additional costs in this analysis. My solar panel and controller, for example, cost me nothing extra on this project, because I had already installed them to power a DC pool pump. I simply “borrowed” the excess power from the panels to charge up my 12 volt battery and run the lighting.

Note also that I upgraded some of the lamps in the low-voltage fixtures with 2-watt, long-lasting LEDs, at additional cost. 

All that being said, it’s not just the dollar value that makes this project worthwhile. It’s the reduction in e-waste. Instead of replacing dozens of plastic solar lights and their batteries over the years, I can enjoy thousands of hours of net-zero lighting from a renewable source, and recycle the battery at end of life.