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A Solar-Powered Lighting System

Need lighting away from a power source? Try this one: it's ideal for your garden, shed or even a camp site. With a 5W solar panel, a 12V SLA battery and a smart controller, it has 3-stage charging for the battery and Maximum Power Point Tracking (MPPT) for the solar panel.

Part 1 - By John Clarke

Features

112V SLA battery operation

1 Ideal for LED lighting

1 Constant current LED
 driver option

1 PIR, switch or ambient
 light turn-on

1 Lamp timer included

1 5W solar panel with
3-stage battery
charging

No, it’s not the old Irish joke about the bloke who invented the solar-powered torch!

Solar-powered lighting is ideal where it is impractical or unsafe to install mains-powered lighting. It can be installed just about anywhere and best of all, running costs are zero because it uses energy from the sun.

Click for larger image
Fig.1: this shows the arrangement of our Solar Lighting Controller. The solar panel, SLA battery and the lamps connect to the Controller. Optional inputs to the controller include a light sensor to monitor the ambient light, a PIR detector and a timer.

In its simplest form, solar powered lighting comprises a solar panel, a battery and a lamp that can be switched on and off. But you do need to ensure that the battery is not over-charged during the day or over-discharged at night; so you need some sort of charge and discharge controller.

Fig.1 shows the arrangement of our Solar Lighting Controller. The solar panel, the battery and the lamps connect to the Controller, allowing full management of charging and lighting. Additional inputs to the Controller include a light sensor to monitor the ambient light, a Passive Infra- Red (PIR) detector and a timer.

For use in garden lighting, the light sensor allows the lights to switch on at dusk and they can remain lit for a preset period of up to eight hours, as set by the timer. Alternatively, you may wish to have the lights lit for the entire night and to switch off automatically at sunrise (subject, of course, to sufficient battery charge).

For security or pathway lighting, the lights can be set to switch on after dusk but only when someone approaches the area.

In this case, a PIR movement detector switches on the lights while the timer switches off the lights after a predetermined period, typically about one to two minutes but settable up to the 8-hour timer limit.

For shed lighting, you may opt to switch the lights on and off using a remote pushbutton switch. They can remain on until they are switched off again or they can switch automatically after a preset period, or at sunrise.

Normally the Controller would be set so that the lights can only come on when it is dark. However, you might want the lights on during day in a shed and this is also possible.

Table 1 shows a summary of all the lighting options which are selected using jumper links. We’ll look at these various options later.

Types of lighting

The Solar Lighting Controller can power 12V compact fluorescent lamps (CFL), halogen lamps and 12V LED lighting. In addition, the Controller can directly drive LEDs using a constant current driver. Best efficiency is obtained with three 1W or 3W white LEDs in series.

The actual total wattage of the lights depends on the application. We recommend that the Solar Lighting Controller be used with up to 10W of lighting when the lights are used for a maximum of 2.5 hours each day.

Lower wattage lighting can give longer lighting periods. For example, 3W of lighting can be used for around seven hours per day.

The restriction on the lighting wattage and usage depends mainly upon the solar panels and their ability to recharge the battery each day. The specified 5W solar panel is ideally suited for recharging a partially discharged 3.3AH battery during the day, assuming at least six hours of winter sunlight is available.

Summer time will obviously provide more hours of sunlight for charging but then there will usually be less need to use the lights because of the reduced night period.

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