Solar home systems with Steca solar charge controllers

A solar home system consists of a Steca solar charge controller, one or more solar modules, a battery and the connected loads.

The solar charge controller is connected directly to the battery using as short a cable as possible, and mounted on the wall near to the battery, so that it can be effectively cooled by the passing air flow.

In principle, the battery is always connected to the charge controller first. Then the solar module field is connected to the solar module input of the charge controller. Only direct current loads are used in solar home systems. They are connected directly to the load output of the charge controller. This means the Steca solar charge controllers always show the exact charge status of the battery, and thus ensure optimal battery maintenance in all situations. Various Steca energysaving lights, Steca solar cooling units, DC-to-DC converters and other appliances can be used.

The Steca solar charge controllers control the energy flow of the entire system. They make sure that the solar module charges the battery quickly and effectively, but they also protect the battery against overcharging. If the loads discharge the battery, the charge controller, thanks to its precision in calculating the charge status, switches off the load at exactly the right moment, thus protecting the battery from the dangers of deep discharge

Furthermore, Steca charge controllers are equipped with an intelligent battery monitoring system. The most effective charging method is selected according to the requirements of the batteries. The charge controller is the central controlling component in solar home systems, since it affects all the functions of the system. For this reason, it is important to choose a reliable and high-efficient charge controller.

NIGHT LIGHT SYSTEMS

An important special application of solar home systems are the so-called night light systems.

These fit with the design of the solar home systems, but are equipped with a special Steca charge controller which automatically turns on the connected lights for a set time after sunset, and turns them off again the next morning. These systems are perfectly suited for street lamps and automatic night-time lighting

Another special model makes these systems into the ideal solution for bus stops and similar applications. Operating in conjunction with a motion detector, the lamp is only turned on at night time when movement is detected in a specified area. After a few minutes, the light is then automatically turned off again. This function can be implemented with any Steca night light charge controller by connecting it to an external motion detector.

Steca‘s Charging Technology

The performance of our products is shown by the accuracy of the state of charge (SOC) measurement, which results in the long lifetime of the battery.

What does SOC mean?

The SOC (State of Charge) indicates the actual charging status of the battery. If the battery is fully charged the SOC is 100 % - if it is completely empty the SOC is 0 %. All values in between are possible, but a lot of battery types should not reach SOC values less than 30 %. It is important not to confuse the SOC with the capacity of the battery. The SOC does not reflect the remaining capacity of the battery. The actual remaining capacity of the battery is influenced by a lot of parameters besides the SOC. Multiplying the SOC with the nominal capacity of the battery results in information about the residual capacity of the battery. This value does still not reflect the remaining capacity accurately due to various other parameters including the age of the battery.

Why is SOC calculation important?

If a battery is charged, the charge controller needs to know if it is full to prevent battery damage due to over charging. While discharging, the controller needs to know if the battery is empty in order to prevent dangerous deep discharging. There are several possibilities to determine if the battery is full or empty. The most common criterion is the voltage of the battery. A certain fixed voltage is set to disconnect the load and protect the battery. Unfortunately this criterion is improper. Especially in solar systems, low discharging currents are common and lead to improper battery maintenance if a fixed voltage for load disconnection is used. Better solutions also take the charging / discharging current into account to determine if the battery has to be disconnected from the load. But also this method does not allow an adequate load disconnection to protect the battery optimally due to a very low accuracy and a high error rate. A lot of additional parameters, like temperature, the age of the battery, the user behaviour and other values, influence the battery. Only an accurately calculated state of charge allows to disconnectthe load correct according to the properties of the battery. This is why Steca developed a powerful and precise algorithm to determine the actual state of charge of a battery

How does the Steca SOC algorithm work?

The Steca state of charge algorithm is a combination of different methods in order to ensure a precise calculation combined with a stable long time performance. Cost optimised product realisation is additionally another important point for Steca. Years of experience in this field and important research activities led to a self learning “fuzzy logic“ algorithm. It takes into account the user behaviour and the ageing of the battery. The voltage of the battery, as well as all battery currents, are watched closely by the charge controller in combination with the temperature. The charger approximates the SOC, during a  learning period which takes place in the first cycles. By monitoring the battery and adapting parameters to the changes, a self learning algorithm results that is also able to take the use of the battery into account. This characteristic makes the Steca SOC algorithm a powerful and reliable function, which will ensure the correct monitoring of the battery. The user benefits from a fast and precise information about the battery status that is displayed on the charge controller. Finally the user benefits from the most important advantage to enlarge the life-time of the battery with the help of an optimised battery maintenance.PV