If you have a yard and have ever thought about lighting it at night, then you have probably heard about solar yard lights. They are still pretty expensive, but their advantage is that you don't have to run any wiring for them. As long as a location gets direct sunlight, you can put a light there in about 15 seconds.
These lights are extremely interesting because they are almost like mini-satellites. They generate and store their own power during the day and then release it at night. This is just like a satellite that stores solar energy while it is on the sunny side of the planet and then uses that energy when it's on the dark side. In this article, you will learn exactly how it happens!
The Basics
A solar light consists of the following components:
If you pop off the cover, you will find that all of the working components are mounted as a single unit. On the back side you see this:
Next, we'll take a closer look at some of these components.
Producing Light
If you have read the article How Solar Cells Work, you have a basic understanding of solar-cell technology. A solar yard light uses standard solar cells in a very straightforward application.
A single solar cell produces a maximum of 0.45 volts and a varying amount of current depending on the size of the cell and the amount of light striking the surface. In a typical yard light, therefore, you need four cells wired in series (see How Batteries Work for a discussion on series wiring). In this yard light, the four cells will produce 1.8 volts and a maximum of about 100 milliamps in full, bright sunlight.
The solar cells are wired directly to the battery through a diode (which prevents the battery's current from flowing back through the solar cell at night). The battery is a completely standard AA Nicad battery. A battery like this produces about 1.2 volts and can store a maximum of approximately 700 milliamp-hours. During the day, the battery charges, reaching maximum charge except on shorter winter days or days when there is heavy overcast.
At night, the solar cells stop producing power. The photoresistor turns on the LED. How do the streetlights turn on automatically at night? shows you a very simple circuit using a transistor and a relay to control a light using a photoresistor. In the case of this light, the relay is replaced by two other transistors.
The controller board accepts power from the solar cell and battery, as well as input from the photoresistor. It has a three-transistor circuit that turns on the LED when the photoresistor indicates darkness.
The LED draws about 45 milliamps with the battery producing about 1.23 volts (0.055 watts). It produces about half of the light that a candle would. The Nicad battery, when fully charged, can operate the LED for about 15 hours.
Half of a candle's light is not very much, and if you have ever purchased one of these yard lights you know that it really is not enough to provide illumination. You use them more for marking a trail -- they are bright enough to see, but not really bright enough to illuminate the ground to any great degree.
The reason why these lights are so expensive right now is because of the solar cells and, to a lesser degree, the Nicad battery. Solar cells remain expensive because they are manufactured from silicon crystals in cleanroom conditions. They are much less expensive than they were 10 or 20 years ago, but still fairly pricey. As a result, solar yard lights cost $10 to $20 per light.
The yard light shown here uses a single LED. More expensive lights may offer a combination of an LED and a small halogen flashlight bulb. The LED is on all the time, and the light bulb turns on for a minute or two when a motion sensor detects movement.
Solar powered lights add a lot of features to outdoor landscaping, giving you more flexibility when designing your garden. To get the most out of your solar outdoor lights, you still need to maintain and use them properly. Outdoor solar landscape lightscan last for many years of continuous operation if well cared for. Of course, choosing a high quality brand is also important. In this learning article, we present some tips for improving the lifespan and performance of solar powered lights.
You have just installed solar lamp post lights or hanging solar lanterns and you are now illuminating your garden at night. These solar garden lights work simply by using power from solar panels and one or more rechargeable batteries. Through the PV effect, the solar panels generate electricity from sunlight and thus charge the batteries during the day. When it gets dark, the energy stored in the batteries powers an LED light.
Siting and panel tilt angle
Solar panels are found on top of solar garden lights. Although geographic location and weather conditions strongly affect solar panels' output, you can always follow a few simple steps to optimize your lights' performance. In order to fully charge the panels, you should put the solar lights in an outdoor space where there are 6-8 hours of direct sunlight per day.
Pay attention to trees, walls or roofs that could shade the solar panels and lower their output during the day. Also, the panel tilt angle of some garden solar lights, like security solar lights or solar power spotlights, can be adjusted to make the most of the sun. In the United States, for example, you should set the panels' tilt angle to about 30 degrees in summer and 45 degrees in winter. Naturally the panels should also be facing south.
Charging before use
You may be excited after purchasing a set of solar path lights and eager to install them. However, don't immediately put them to use. First allow the lights to be exposed to direct sunlight for about 5-10 cycles (charging at day and discharging at night) in order for the battery to charge to its full capacity. Afterward you will find that the lights can last at least 8 hours in dark, almost from dusk to dawn.
Avoid street lighting
Most solar garden lights are automatically turned on and off by a light sensor that detects surrounding light levels. At night, when light levels are below a value in the sensor's memory, the light is activated. Similarly, the light will automatically turn off at dawn when it detects more light. In order for it to work properly, the sensor needs to be sited properly. When choosing a spot for your solar light, ensure that the device is not placed near night-time light sources such as porch lighting or street lighting.
If it is poorly located near a light source, the solar light sensor will react to ambient light as well as artificial light source simultaneously. The high powered porch or street light (compared to solar landscape lights) will thus decrease the sensitivity of the solar light sensor and could even eliminate the solar light's automatic activation capability.
Cleaning solar panels
It is important that dirt and debris is kept off of the solar panel to the greatest extent possible. A dirty solar panel will not fully charge the battery and thus shorten the battery life. Operating solar lights covered with dirt and debris may cause the light to malfunction. To maintain high performance make sure to clean the panel regularly with a dry cloth and warm soapy water. Also, remember to clean snow off the panel in winter.
Battery replacement
Generally speaking, the rechargeable battery can be replaced every two years in order to maintain the maximum capacity. If you have a long winter or extreme weather conditions in your area, it would be better to change the battery every year.
Storing solar lights
Solar lights for garden can be left outside year round, even in cold weather. However, if you wish to store your light indoors for more than three days, follow these steps to prevent damage to the light's rechargeable batteries:
- Store lights at room temperature in a dry location.
- Store the solar light where it can receive some sunlight or artificial light each day. The battery needs light to maintain a charge during storage.
- During prolonged storage, units must be fully discharged and charged once every month. Otherwise you can also remove the batteries and replace them when ready for use.
- Do not store solar lights in a box or a dark room without a source of light on the solar panel. This will damage the batteries and deteriorate their ability to hold a charge.
- For best performance, do not store for prolonged periods.
Using these basic and simple tips, you should get years of use out of your solar landscape lights, solar patio lights and other solar lights you use outdoors.
