What is the difference between an on-grid and off-grid system?
In contrast to an on-grid system, which is connected to the public power grid, an off-grid system is completely self-sufficient. In Germany, on-grid systems are predominantly used, as there is a well-developed power grid here. In addition, the surplus electricity generated by on-grid systems is usually fed into the utility grid, which means that the consumer receives a not insignificant payment. A positive factor is also the decentralized generation of electricity directly at the consumer, which avoids high transport losses.
In contrast, off grid systems are mostly used in places where no power supply is available and by not feeding the surplus electricity into the public grid, the consumer does not have the advantage of remuneration and amortization of his solar system. In fact, a very expensive electricity storage system is needed to regulate the surplus of solar electricity generated. With an on-grid system, this is not necessary, which means that the purchase costs are lower.
Another advantage of On Grid systems is the constant possibility to access the public power grid, even in case of insufficient coverage of the own demand by the self-generated electricity.
On the other hand, an off grid system offers complete independence from the public power grid and can therefore be used anywhere. This means that the consumer is not dependent on fluctuating electricity prices, which enables a well calculable cost calculation with a constant power consumption.
How can you recognize good solar panels?
First of all, a distinction is made between polycrystalline and monocrystalline panels. Whereas the somewhat more expensive monocrystalline modules contain pure silicon and achieve a higher efficiency, the less expensive polycrystalline modules consist of less pure silicon crystals. Here it is important to note that the higher the efficiency of the panels, the more electricity can be generated from the incoming solar radiation. Since the amount of electricity generated is crucial for a good solar panel, the quality can also be calculated based on the power density. Here, you divide the power (watts) by the module area and should get a value between 130 watts/m². Another criterion for high quality solar panels is the IEC 61215 standard, which is found on most panels sold in Germany. In this certification, the corresponding module is tested for any defects, efficiency and many more criteria. This certificate is issued by TÜV Rheinland, for example, and consumers can see which solar panels have received it. For many consumers, the economic factor is also important. Here you can assume a useful life of 25 years and you can calculate the electricity produced during this time. If one puts now acquisition costs and current yield in relation, one gets an overview whether a certain model is suitable for the individual consumer. Due to the high exposure to weather, the degradation is also very crucial, because this value indicates how much power loss a solar system has over the years. A low value is therefore better than a high value and should be around 0.1 percent degradation per year.