The 2nd most expensive part of your home solar system is the solar power inverter. These devices are the heart of your intertie system. They convert the solar panel’s low voltage, high current electrical signals and turn them into something we are all very familiar with – good ole 120AC. The AC of course is compatible to tie into the power grid – hence the term “intertie”. See you getting smarter by the sentence!
Inverters range from $.70 – $1.00 per watt so in a typical home you can expect to pay about $2500-$3000 for a good solar power inverter. It’s important to get a quality inverter since this is the weakest solar link in your home solar system.
The cool thing about inverters is that if you get an oversized one you can add more solar panels later for more power. So here’s a suggestion. As long as the price-point’s not crazy, why not get two small inverters that are equal to your solar needs? This way if you have an inverter problem you’ll only lose half your system until you can get the bad one replaced. Yes these things break down – no system is perfect!
There are two different types of inverters: string inverters and micro-inverters . We’ll be discussing only string inverters here since the micros are kind of a new product and we want to stick to the tried and true. String inverters are just large boxes that are typically mounted near your circuit box or the electric company’s meter. If you’re using two inverters they can be mounted “in parallel” to each other.
Your solar panels will be grouped into “strings” so that they match up with your inverter’s specs-more on that in a bit. It’s probably best to let an electrician design and perform this tying in. You must keep your panel in evenly grouped multiples so you don’t overload your inverter. For example, let’s say you have a 12 panel array with four series of three panels that are connected in parallel.
This is fine but you can’t have 11 panels because there are no grouping multiples that equal 11. Another important panel consideration is that you should use identical panels. Do not cheap out and buy mixed panels and expect to tie them all in together. It’ll ruin your system’s efficiency.
String inverters are the cheapest type of inverters (compared to micro-inverters) with a wide variety of reliable manufactures to choose from. Here are some articles with more detail on five of the most well known inverter manufacturers:
Solectria Inverters
Xantrex Inverters
Fronius Inverters
SMA Sunny and Windy Boy Inverters
Pv Powered Inverters
Since string inverters are easily mounted in convenient locations they are easy to maintain. But it’s not all peaches and cream with string inverters. When you group the ‘strings’ of solar panels they will need to be laid out in the sun but if one or more of the panels gets “shaded” the entire string pays the price. The total inverter energy output will start to degrade. Similarly if one of the panels goes bad or breaks the system output is cut considerably.
Look for these solar power inverter specifications:
PV Start Voltage: Tells you when the inverter starts to convert the power from your solar arrays. This gives the true inverter efficiency since all inverters need a minimum power input before they can start to convert into AC. The stronger the required sun-rays need to start converting the less efficient your inverter will be.
CEC Rated Power output: This is the max output wattage the inverter delivers over different operating temperatures.
Maximum recommended PV input power: This tells you what the inverter’s max input power should be from your solar panel array. You need this spec to help you size your system. If you exceed your inverter’s capabilities you’ll get a really inefficient inverter.
Solar power inverter features to look for.
You’re looking to get the most efficient inverter you can afford. Manufacturers love to cite peak efficiency as a selling point for their inverters. Don’t be fooled. This peak is only reached at max load when the sun is strongest. You want to see the efficiency over a variety of conditions such as: input power, temperature and output load. So inverters that only show high efficiency for one number are not giving you the whole story.
