L-Kougen Co. Ltd.
Homepage Top(ENG)

 Middle Capa Division



What is the Weather Synchronization System?

The Weather Synchronization System is the control system we use to accurately measure the charge accumulated over the day and adjust the brightness of the LED lights at night. On the days that the battery reaches a full charge, the light will shine at its rated brightness. However, for example, if the battery only charges up to 60% due to inclement weather, the lights will shine at 60% of their rated brightness during the night. By doing this, we are able to keep the charging to discharging ratio close to 1:1, which helps us minimize the size of the battery.
For any solar light, it is necessary to have a countermeasure for inclement weather. Many companies tend to use a large battery to address this problem. This way, on a good day they may charge 7 days' worth of electricity (for example) to compensate for days with bad weather.
However, we believe that the Weather Synchronization System will become the industry standard in the near future. Why is that? Because there is no reason it should not be the industry standard. Already, many other companies are installing solar lights throughout Japan that use the Weather Synchronization System technology.

Below, we will simply explain the Weather Synchronization System. Although we use numbers to make it easier to explain (solar panel electrical output, battery capacity, power used for lighting, etc.), these numbers do not necessarily represent actual values. The actual values will depend on many other factors that we will take into consideration, such as the brightness of the installation site and solar panel size.

Step 1: Tokyo Basic Model

How it was Done Until Now
For a light that consumes 40Wh overnight, the solar light unit must be able to charge seven days' worth of electricity (280Wh), necessitating a huge battery that can store this amount. This way, even if the battery does not charge for six days due to weather conditions, the light will continue to shine for at least 6 nights. As long as there is more than 40Wh of power in the battery, the light will operate as advertised.

However, once the battery passes this threshold, there is no guarantee that the light will stay on throughout the night; an all-or-nothing system. Furthermore, lead acid batteries tend to decrease in capacity after many charge-discharge cycles. In the above example, the battery that could originally store 7 days' worth of charge may only be able to store 3 days' worth of charge after a few years.
Weather Synchronization System
With the Weather Synchronization System, if the light uses 40Wh overnight, then we prepare a battery with the same capacity. Unlike the lead-acid battery, the battery we use is a one that can withstand 10,000 charge-discharge cycles while only losing a small fraction of its battery capacity over its lifespan. For the solar panel, we decide its dimensions based on information about the brightness throughout the year. We choose the smallest size solar panel that will fully charge the battery at least 292 days out of the year (80% of the time). The above example shows data for Tokyo when there is nothing blocking the sunlight. From past weather data, we found that the number of days where the energy is over 4MJ (megajoules) is about 80%, and given a 40Wh battery, we can calculate the size of the solar panel that will yield a fully charged battery 80% of the time (in this case, a 30W solar panel). This completes the Tokyo Basic Weather Synchronization System.
80% of the time, the battery charges fully during the day and is spent over the course of the night. The battery charges fully the next day and the cycle continues. A cycle like this would quickly wear down a lead-acid battery, which would then need to be replaced. However, a high cycle battery will allow this kind of usage. For the days where the energy is below 4MJ due to inclement weather, the battery will not charge fully during the day, so we measure the charge that was accumulated over the course of the day (*1), and adjust the LED brightness accordingly (*2). For example, 30Wh will result in a 75% (30/40) decrease in the LED brightness at night. Even if the battery only charged 10% (for really bad weather), the LED lights will still shine throughout the night without turning off, albeit at 1/10 their normal operating brightness.

Step 2: Adjustments

One of the only downsides to the Weather Synchronization System is that the brightness of the LED lights decrease on days with bad weather. It goes without saying that some customers do not mind this tradeoff, as long as the light does not turn off during the night. However, for those who think this is still a problem, we will perform the necessary adjustments (Step 2 for the Weather Synchronization System).
Step 2 Adjustments may be necessary when…
  • You do not mind the lights being dimmer on occasion, but you want to guarantee at least 50% brightness at all times.
  • The installation site has low exposure to sunlight and the standard data does not apply, resulting in numerous dim lights in the area.
  • The installation site is surrounded by tall buildings and during the day the solar panel is covered in a shadow.
For reasons like those listed above, we will adjust the solar panel and battery size the minimum required amount to meet performance expectations.
The main adjustments we make are to increase the size of the solar panel or add another high cycle battery. In some cases, we do both. However, to remain cost-effective, we make only the necessary adjustments based on the weather data available. Since commercializing the Weather Synchronization System in 2008, we have installed over 3000 solar lights. We have experimented with many solar panels and battery capacity combinations for over 10 years, and we have collected data about how much the batteries charge under different conditions. As a result, we can predict how the charging behavior will change given energy values (MJ) and solar panel output (W), and using this information we can accurately simulate how the batteries will operate.
If we implemented the Tokyo Basic model in a place like Akita, where the weather conditions are not as favorable as Tokyo, there will be many nights when the Weather Synchronization System activates, and there will be many days where the battery charges less than 50%, especially during the winter. However, with minimal adjustments, the number of times the Weather Synchronization System activates will decrease and even on its worst days the lights will shine a reasonable amount.

In summary, L-Kougen's Weather Synchronization System

How it was Done Until Now
  1. Uses a high cycle battery (over 10,000 charge-discharge cycles, does not require replacement for over 26 years).
  2. Uses minimum size solar panel and high cycle battery to achieve full brightness more than 80% of the time. Decreases the brightness proportionally to battery charge if not fully charged.
  3. Uses a circuit that accurately measures the remaining battery charge.
  4. Can be adjusted (solar panel size and number of high cycle batteries) as needed. Even though a 20% to 30% decrease in brightness is generally acceptable, if not, we will make the necessary adjustments based on the data we have collected over the years.
*1 To accurately measure the remaining battery charge (SOC), the Weather Synchronization System uses a circuit that measures the voltage and current every 5 seconds, and integrates these values.
*2 For days with inclement weather, the LEDs will decrease in brightness. However, it is worth noting that the human eye cannot detect a 30% decrease in brightness (measured in lux). Only after a 50% decrease can some people notice a decrease in brightness. People, unlike luminometers, will adjust their pupils to take in more light in dim environments, which results in this insensitivity. The Weather Synchronization System is a new solar lighting technology based on this human tendency.
  • A simulation of the Tokyo Basic Model in Akita, which is considerably dimmer than Tokyo
  • A simulation after making modifications (50W solar panel and an additional high cycle 96Wh battery)
- Reserve Method (how it was done until now) Weather Synchronization Explanation
Price For the same battery capacity, the lead-acid battery is cheaper than the high cycle battery, but with weather synchronization enabled, the battery capacity is greatly reduced. Because this means you can also make the solar panel smaller, and as a result the pole and foundation smaller as well, the entire construction and installation cost is also significantly cheaper. Furthermore, considering lead-acid batteries have to be replaced in about 5 years, the cost efficacy is very good.
Installation space × Because both the panel and the battery can be smaller, you do not need a maintenance box at the bottom of the pole. You can instead install the battery underneath the solar panel, or install it on an existing pole or wall. See here for examples of maintenance boxes not on the pole.
Lifespan/ maintenance × High cycle batteries are designed to last over 26 years. The first weather synchronization installed in Kiyotake Kindergarten in Miyazaki was installed in 2008, and it goes without saying that after nine years, we have not needed a replacement.
Countermeasures for inclement weather The Weather Synchronization System makes the lights shine dimly on days with bad weather. However, by increasing the panel size and battery capacity, we can adjust how often the lights dim and how much they dim. On the other hand, lights that use the Reserve Method will turn off completely after they have depleted their battery.
Copyright(C) 2005- L-kougen co.,ltd All Rights Reserved.