An “off the shelf” kit to convert outdoor light to solar power can save you time and fuss, but doing it yourself will save you money and ensure a system that stands the test of time.
Let’s jump straight in.
Converting Outside Mains Lights to Solar Power – Your Choices
Stand-Alone Solar Light Fixture Replacements
This is probably one of the most technically simple options out there. In many situations, it can be costly and less effective though.
This option involves removing the existing AC light fixture, cables, and switches and replacing them with stand-alone solar lamps or solar lamp kits. The heavy lifting of ripping out all the old equipment is about the hardest part, and replacing the individual lights is relatively simple.
A simple stand-alone solar fitting is illustrated below.
How Do Stand-Alone Solar Lights or Solar Light Kits Work?
Stand-Alone Solar Lights
As their name indicates, stand-alone solar lights are all-in-one solar light solutions. They consist of a light fitting with a stand or mounting plate, solar panels, and battery all in one easy-to-install unit. All you need to do is mount them or stick them in the ground and walk away. Their solar panel and internal circuits charge the battery and switch them on at night and off during the day.
Solar Light Kits
They typically have separate solar panels with the rest of the components mounted in the light fixture. This is a great feature if the location of the light fixture doesn’t get much direct sun. The solar panels can be placed away from the light fitting in a high sunlight area, keeping the battery properly charged.
Now, that sounds like an ideal solution for converting outdoor lights to solar. And it is under specific conditions, particularly for those who don’t want to get involved in the technicalities of the other options. However, they may not be suitable for many users. Here are some of the pros and cons of using stand-alone solar light units.
- Very easy to install.
- Virtually zero maintenance.
- Great aesthetic appeal.
- No cables or extra hardware required.
- Excellent flexibility. You can move ground mount fittings around at will.
- Initially expensive, especially where large layouts are involved.
- Low efficiency and light output. Small battery packs tend to cause the lights to fade long before sun up.
- Although some fittings feature replaceable batteries, many don’t. When the battery dies, you need to go shopping for a new fitting adding to the overall cost.
Converting Existing AC Light Circuits to Accept DC Globes
The second option for converting your outdoor light circuit to solar is a lot more technically challenging than using stand-alone lights. It’s way more effective and efficient in the long run, though.
In straightforward terms, this type of conversion involves installing a standard solar-powered system and feeding its low voltage DC output directly to your existing light fittings. Once your AC globes are replaced with suitable DC LED globes, you are good to go. An example of this type of setup is illustrated in Fig. 1 below.
Now let’s look at this type of conversion in detail.
Rating Your Solar Panels, Charge Controller, and Battery
The first order of business is establishing how large your solar system needs to be. This is fairly straightforward and involves calculating the total wattage of all the LED lamps in the circuit. If you decide to use five 8 watt globes and five 16 watt globes, this is how it would work.
5 x 8 watt = 40 watt
5 x 16 watt = 80 watt
Adding the two values gives you a total circuit power rating of 120 watts. This figure will make sizing your solar panels, charge controller, and the battery or battery bank simple.
Note: It’s wise to add at least 20 percent to your total wattage figure to cover any additional light fixtures you might want to add later. In that case, the figure would be 144 watts.
Once you have the solar system set up and running correctly, it’s time to make the conversion.
Important Safety Notice!
Please note: Some of the steps in this process involve working with high voltage mains power. If you are not qualified to do so, please refer the work to an electrical professional.
Disconnecting the Existing Line Power Feed
In most cases, the AC grid current for outside lighting enters the circuit at an exterior or interior light switch or automatic day/night switch.
Once you have located the entry point, you can isolate the power and disconnect the mains feed. Please note: The disconnected mains wiring must be safely isolated using wiring nuts.
Connecting the DC Solar Power Feed
At this point, you can connect the DC feed from your batteries to the switch. In the case of a conventional light switch, the connection would look similar to the illustration below.
If you are using an automatic day/night switch, the wiring would depend on the type of switch used. However, the theory stays the same, with the positive battery lead being connected to where the AC live lead came in. The same applies to the negative battery lead and the neutral line going to the light fixture.
When all the preceding steps have been completed, you could theoretically replace all the high voltage AC globes with DC LED globes and you’re all set. Unfortunately, it’s not that simple, and this is where one of the biggest potential headaches, when you convert outdoor light setups to DC solar, comes into play.
Light Circuit Cable Rating
When you were running your lighting on 120-volt using 60-watt globes, the current or amperage system would have looked like this.
- 10 x 60-watt globes = 600 watts total
- Circuit volatage = 120 volt
- Total circuit current – 600/120 = 5 amps
Now that you have converted to lower voltage DC the results look like this, taking into account that an 8 watt LED lamp produces the same light output as a 60-watt incandescent lamp:
- 10 x 8-watt globes = 80 watts total
- Circuit volatage = 12 volt
- Total circuit current – 80/12 = 7 amps
An electric cable gauge, or the thickness of the cable, is determined by the amount of current the cable will handle. If your light circuit cables were correctly rated for 120 volt AC, they might be too light to manage the increase in DC amperage. And this would certainly require you to replace all the cables in your outdoor light setup.
It is possible to offset this problem by choosing a higher battery voltage for the solar component of the conversion. For example, a 24-volt system’s amperage would be 3.3 amps, and a 48-volt system with 1.7 amps, both well within spec.
The takeaway from this example is careful planning and sensible battery choices can mean the difference between a slick installation and an expensive mess. For instance, if you decided to up the system’s light output using 20 watts LED globes, the amperage jumps to a whopping 17 amps!
Here are the pros and cons if you convert DC outdoor light to solar.
- Lower system costs: This setup doesn’t require an inverter making the solar system cheaper and easier to install.
- Lower operating costs: Overall, this type of conversion delivers the best energy consumption figures.
- Safety: Running lower voltage DC in your garden is a lot safer in terms of electrocution and fire risks than using high voltage AC.
- Cable rating: This can be a biggie. If you are installing a new DC system, it’s not an issue, but it can become a major problem if you convert an existing AC circuit. If you get it wrong, any savings you make on an inverter will likely be eaten alive by the cost of upgrading the cables.
Converting Outdoor Lighting to a Solar High Voltage AC System
This option is probably the best overall choice for using solar energy to drive your outside light circuit. It allows you to seamlessly integrate the existing fittings and cables with the new solar component. Outside of the solar installation, the only real change will be ditching the AC globes to favor high-efficiency LED lamps. For these reasons, we’ll cover this option in more detail.
In short, an AC solar lighting system is similar to the DC example mentioned earlier. The only difference is the inclusion of an inverter. An inverter takes the lower voltage DC input from the solar battery and turns it into the same high voltage AC power on your present light circuit. An example of this type of installation is illustrated in Fig. 2.
Sizing Your Solar System
Getting a firm idea of your lighting setup specs is the first step in sizing your solar components. To kick the process off, you must decide on the number of LED lamps you’ll use and what their combined wattage will be.
Let’s assume you’ve been using 15 lights in your circuit with 60-watt conventional bulbs. To get the same light output, you’ll need to use 8 watts LED bulbs.
You’ll use the same equation as we’ve used earlier – 10 x 8-watt bulbs = 80 watts total to get to your total power figure. If you add a 25 percent safety margin, you’ll end with a total demand of 100 watts.
Doing the Math
We now know that the maximum power load of the system with a safety margin is 100 watts. Using that figure, we can calculate the average continuous running current of the circuit. As there are no startup spikes, the average figure will be just fine. Our voltage is 120 v, and the power requirement is 100 watts. To get our AC amperage, we divide the figure by the voltage, 100/120, to get o.833 or 1 amp rounded up.
Using standard calculations, you can now work out the capacities of the rest of your solar components. Working backward, let’s start with our inverter.
Inverter and Battery Rating
A one amp current draw is really insignificant, and it’s going to be hard to find an inverter rated that low. A modest 1,500 watt, 24 volt DC to 120-volt inverter will deliver a continuous current of 12.5 amps and run your lights without breaking a sweat. With electrical components, bigger is always better. Over-rating the inverter will lengthen its life and leave you with excess power to expand your circuit or add other elements later.
Before you can decide which battery to buy, you’ll have to make a call on what your battery voltage is going to be. Common solar battery voltages are 12 volts, 24 volts, 36 volts, and 48 volts.
Your choice of charge, or battery, voltage is really subjective. However, most industry experts agree that a 24-volt system is probably the best choice. This will directly affect your choice of battery and play a role in your solar panel, charge controller, and inverter choice. Here is how all the pieces fit together.
According to standard calculations, a 24-volt inverter requires 1 amp of DC input for every 20 watts of AC output. If you use the power rating of your lights alone, this works out like this: 100 watts/20 = 5 amp DC input. Now, in this case, that’s an hourly rating, i.e., your batteries will have to deliver 5 amps per hour.
Battery Amp Hour Rating
Batteries are rated according to an amp hour (Ah) requirement. For example, a 150 Ah battery will deliver 150 amps continuously for one hour, 15 amps for 10 hours, and 300 amps for 30 minutes.
The length of time your lights will be on will differ according to the season. The longest period would be around 12 hours, and that would be the safe general figure to use. Theoretically, then, if your inverter demand is around 5 amps per hour, you will need a battery or battery bank capable of delivering at least 60 Ah (5 amps x 12 hours).
Rating batteries isn’t quite that simple, though; you must include the equation’s discharge cycle and inefficiency factors. At the end of the day, a battery rating of 120 amp-hours should be a safe bet.
Solar Panel and Charge Controller Rating
This is the last step in the process of getting your outdoor lights running on solar power. It’s also the easiest one to work out. Let’s start with the solar panel set.
A solar panel array of four x 20 volt, 250-watt panels would be a good choice for this project. Wired in series, the solar panel output would be 80 volts (20 x 4) and 1,000 watts (250 x 4). Now 80 volts is way higher than your 24-volt battery rating, and that’s where the charge controller comes in.
There are two charge controller types in general use, namely PWM and MPPT controllers. For this project, an MPPT controller would be the best choice. This charge controller can accept input voltages from solar panels higher than the battery requirements and feed the batteries exactly what they need to charge efficiently. That functionality will give you exact charge control and extra output power if you choose to upgrade the system.
To size your MPPT charge controller, you can use this equation to find its required charge output.
Solar panel power output/battery voltage – 1,000/24 = 41.66 amps charge output. In other words, you’ll need a charge controller that can deliver a charge output of 42 amps to the batteries and accept an 80-volt input from the solar panel. Considering these figures, a 120 volt, 60 amp charge controller would be a perfect match for the solar panel example we’ve used.
Of course, there is a heap of solar panel models out there. The examples here are simply for reference, and it’s not hard to find better suite solar panels.
Let’s consider the pros and cons if you convert outdoor light to AC solar;
- Power consumption cost savings.
- The easiest conversion to implement. Does not require any cable changes.
- Flexibility. A solar-driven AC power grid outdoors can be used for more than just lighting.
- Higher initial cost due to the inclusion of an inverter.
- Higher AC voltages are not as safe as the DC options.
Why Would You Convert Outdoor Light to Solar?
There are a couple of good reasons to convert outdoor lighting or even a single light to solar.
Running Cost Savings
This is a no-brainer. Once the initial roll-out cost of a solar-powered system is covered, the lighting is essentially free.
Maintenance Cost Savings
Solar-powered outside lighting generally costs less to maintain over its lifespan than AC setups.
If you choose stand-alone lights or a DC setup, your outside lighting is far safer due to the low voltages used.
The Green Factor
Using solar power to light your outside space is by far the more environmentally responsible choice.
If you decide to convert your existing AC lighting, there are several solar light choices available to you. Each of these options offers different benefits, and your specific needs would dictate which you choose. However, one thing is certain: you will definitely save a significant amount of money over time.
It’s a Wrap
So, what have we learned from all this? We’ve learned that converting AC outside lights to a DC solar system is a good call. We’ve also established that not all the options will suit your purpose.
Let’s lay those options out in point form.
- Stand-alone or kit-type solar lights are great when you only need a couple of lamps and don’t require powerful illumination throughout the night.
- Low voltage DC installations are excellent options where the system specifics don’t require re-cabling.
- High voltage AC solar options are the easiest to set up and offer great flexibility.
Hopefully, the information in this article will help to make sound choices.
If you have any ideas or experiences you’d like to share, let us know in the comments section below.
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