The role of converters is often overlooked in photovoltaic systems. Stored in an attic or closet, it may not be the most visible part of the system, but it plays an important role and accounts for a large percentage of the cost of the equipment. A converter is a hub that converts the direct current produced by solar panels into alternating current suitable for the grid.
In a typical residential solar system, solar panels are connected in ‘strings’. That is, they are connected in series so that the voltages on each module are summed. The positive and negative ends of the string are connected to converters a transducer to perform two main tasks:
First, the converter applies the optimal voltage to all solar panels in the string. To extract maximum energy from a solar panel, a specific voltage must be applied across the panel. An easy way to understand this is to remember that power equals current multiplied by voltage. If there is no voltage across it, current will still flow out of the solar panel, but it will not be able to supply energy. If too much voltage is applied to the solar panel, the current from the solar panel is lost, so the optimal voltage is somewhere in between. It is the converter’s job to keep the solar panel at this optimum voltage. This is very tricky because the optimal voltage changes with the temperature of the solar panel. To cope with this, there is a special algorithm built into the converter called ‘Maximum Power Point Tracking’. This algorithm continuously adjusts the voltage to get the most energy out of the system.
The second important task of the converter is to convert the direct current generated by the solar panels into alternating current suitable for the main power grid. In the mains frequency is 50 Hz, so the converter must make sure that the electricity it supplies matches this frequency so it can be used by other appliances in the house or sold to the energy provider.
Converters are very common. Laptop chargers, for example, use a converter to convert mains 50Hz electricity into direct current for your computer (this partially explains why laptop chargers are so expensive, although I still consider them a scam).
One issue is efficiency. Most commercial converters are pretty good at around 97% efficiency, but that means you lose 3% of all the energy you produce when converting from DC to AC. Increasing efficiency to 99% can increase the return on your solar system’s investment and give you a real competitive advantage. A few manufacturers claim to offer almost new ultra-efficient products.
The next issue is reliability. Most converters are warranted for 10 years, which isn’t bad, but it’s only half the guaranteed life of a solar panel. This means consumers must allow at least one converter replacement when financing a solar project. If a converter can be warranted for 20 years, consumers can feel comfortable knowing that the system will operate under warranty for its entire lifetime, until the entire system needs to be replaced.
Transducer manufacturers have been working to improve the reliability of their systems, and products guaranteed for 20 years will soon hit the market. as a side point; Proving 20-year reliability is very difficult to do without waiting 20 years. And there is an entire field of research dedicated to the ‘accelerated stress testing’ of these products.
Another set of new features is the way information is presented. Many converters come with an optional WebBox that allows you to view your solar system’s performance online. Some converters now come with an iPhone app so you can watch your solar power production on the go and, importantly, show your friends at the bar. These types of innovations will keep coming, so keep an eye out to see if this interests you.
Perhaps the most radical development in transducers is the ‘micro transducer’. This means that instead of one large converter, there are many smaller converters attached to each solar panel. There are several advantages to this. First, it can significantly improve system performance. Going back to the max power point tracking feature mentioned above, if not all solar panels perform the same, a generic converter is in trouble. Solar panels may perform differently at different temperatures or due to factory errors.