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Solar lights need direct sunlight to work at maximum efficiency. 8 hours of full sunshine will allow solar garden light to operate for up to 15 hours. Reduced sunlight due to shade, cloudy days or rain will reduce working time 1 to 5 hours, depending on the reduction in irradiance.
All devices using solar energy for their operation depend on sunshine and the brighter the better. However, that doesn’t mean to say that they stop working in cloudy conditions.
Diffuse sunlight also plays a part and also reflective sunshine helps to charge up the batteries inside solar lights. How do these lights work? Let’s take a look inside:
- How solar garden lights work
- How long do solar garden lights last
- Do solar garden lights need batteries?
- Do solar garden lights affect plants?
- Do solar garden lights work in winter?
How solar garden lights work
There are many types of solar garden lights but they all work in the same way and contain the same basic components:
- A solar cell
- A battery
- An l.e.d. cluster with reflectors
- On/off switch
- Simple circuit board with blocking diode, current limiter and l.e.d. driver
The blocking diode stops current from the battery from feeding back into the solar cell at night-time. The current limiter is hardly necessary as the solar cell output is very low at between 100mA to 400mA, which means a solar charger isn’t needed.
100mA is more than enough to charge the battery. The better quality solar lights have a solar cell with a higher capacity, say, 600mA to 800mA, and these will perform much better in less than full sunlight.
Typical solar cell output voltage is 1.5V and the l.e.d.s require 1.2V.
How long do solar garden lights last
Any device will last as long as it’s weakest component and solar lights are no exception.
The first thing to ‘fail’ will be the battery, which have a life of about 1000 cycles, depending on the charge/discharge rate and depth of discharge.
In general, the battery will need to be changed every 3 or 4 years, depending on the quality.
In theory the solar cell will last 25 years minimum and will probably carry on generating current for some years after that.
Video – can solar work without sunlight?
Why do solar garden lights stop working?
Connections can come loose, particularly if subject to rough handling. If they can’t be re-soldered, then the unit is no good.
It’s very unusual for the l.e.ds to fail. These are basically solid-state diodes and last for over 100 000 hours.
The plastic casing will probably be the first thing to deteriorate, becoming brittle in the sun. All in all, with regular battery changes and care in handling, you can expect a solar garden light to last 10 to 15 years.
Can solar garden lights be repaired?
There are some things that you can do if a solar garden light stops working. If a wire breaks, for example, you can re-connect it with a soldering iron – it’s very easy.
If the switch fails, then this can be by-passed (it’s not really necessary IMO).
The l.e.d.s certainly can’t be repaired or replaced, nor can the circuit-board. However, they are mass-produced for cheapness and almost designed to be thrown away if and when they fail.
Do solar garden lights need batteries?
Batteries are essential for solar garden lights! Solar cells cannot operate at night and they don’t store energy at all, making some form of energy storage vital to successful operation.
Do solar garden lights need rechargeable batteries?
Solar garden light batteries need to be rechargeable so that the solar cell can charge them up during the day when the sun shines.
It’s normal to use a single AA size 1.2 volt Rechargeable Ni-MH (Nickel-metal Hydride) Battery between 600mAh and 1000mAh.
Do solar garden lights affect plants?
Extensive research has been done on night-time lighting effect on plants but no bad effect have been found.
Although the wave-lengths of l.e.d. light is quite narrow and not at all like sunlight, it hasn’t been found to harm plant-life.
There was some concern that a plant’s circadian rhythm could be disturbed by too much light at night but this has been found not to be the case. The strength of an l.e.d. light is tiny compared to the power of the sun.
Do solar garden lights work in winter?
In general, the sun’s power is much less in the winter than in the summer. Normally, this is not a problem with good quality solar garden lights as the solar cell is a little over-sized.
Even if the irradiance is less than optimum, they should work just as well. Depending on the location, a solar garden light may not work for the full 15 hours at night, but less – it all depends on irradiance.
Irradiance is the strength of the sun’s rays and is governed by location and season – see the table below:
Table 1 – Seasonal irradiance San Francisco vs Anvhorage
Seasonal Irradiance for San Francisco by month (Peak-Sun-Hours)
Seasonal Irradiance for Anchorage, Alaska by month
Do solar garden lights work in the shade?
Irradiance is the key. Shade or cloudy days blocks some of the sun’s energy and so reduces the solar light’s efficiency. It may or may not keep alight all the way through the night, but this depends largely on your geographical location.
The table below compare solar garden light performance by irradiance according to location. NOTE: The running times are not definitive but comparative.
Table 2 – solar garden lights running time compared (by location and irradiance)
Peak-sun-hours (Global Solar Atlas)
Estimated running time (hrs)
4 (US average)
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