What Size Solar Inverter Do I Need?<\/strong><\/h2>\n\n\n\nAs you've probably guessed, solar inverter sizing isn't about the physical dimensions. What we really mean is the capacity <\/em>in kilowatts, just like your solar panels.<\/p>\n\n\n\nThere's a bewildering range of solar inverters out there, but most of them are built with similar key characteristics:<\/p>\n\n\n\n
\nMaximum Power Point Tracking (MPPT) - <\/strong>a handy feature that ensures the system operates between a range of voltages for maximum efficiency. The average inverter efficiency is between 90 and 96%, which is a pretty good figure.<\/li>\n\n\n\nInitial Input Voltage - <\/strong>the absolute minimum voltage the panels need to produce for the inverter to start working.<\/li>\n\n\n\nMaximum Input Voltage - <\/strong>the upper limit of voltage that the inverter can handle without sustaining damage.<\/li>\n\n\n\nMaximum DC electricity conversion - <\/strong>the maximum DC power (in watts) that the inverter was designed to handle.<\/li>\n<\/ul>\n\n\n\nSo, how do you know which inverter capacity is right for your solar system?<\/p>\n\n\n\n
To find the right size solar inverter, we need to look at the following factors:<\/p>\n\n\n\n
<\/div>\n\n\n\n
Solar Array Size<\/strong><\/h3>\n\n\n\nThis is probably the most important aspect when choosing the right size solar inverter, as the general rule is to go for one that roughly matches the DC rating of your solar array in watts (or kilowatts).<\/p>\n\n\n\n
For example, if you have a 4kW solar panel array, your proposed inverter capacity should be around 4000w. The main thing is to keep in mind that your inverter has to be able to handle all the power that the solar panel array produces.<\/p>\n\n\n\n
However, it's not as simple as this and we'll need to check a few other details.<\/p>\n\n\n\n
<\/p>\n\n\n
\n
<\/figure><\/div>\n\n\n<\/div>\n\n\n\n
Your Electricity Usage<\/strong><\/h3>\n\n\n\nWe also need to take into account the energy yields required to power the appliances in your home or business. And while this would have been explored when choosing your solar panel capacity, it's helpful to understand how this AC output will be used.<\/p>\n\n\n\n
Don't forget, the inverter will determine the AC power that's sent through to the appliances, and this will have been converted from DC power generated by the solar panel array. You'll see why this is important further along.<\/p>\n\n\n\n
<\/div>\n\n\n\n
Physical Location Of The Solar Panels<\/strong><\/h3>\n\n\n\nThis includes things like the tilt or angle of the roof, the amount of shading and the orientation of the panels. Ideally, your solar array should be installed on a south-facing roof, but they can still deliver when placed on an east or west-facing slope. Even a northerly slope would work, although with reduced efficiency.<\/p>\n\n\n\n
<\/div>\n\n\n\n
Local Climate<\/strong><\/h3>\n\n\n\nThe geography of your property will affect the maximum power output of your solar energy system, as the amount of sunlight differs according to where you are in the country.<\/p>\n\n\n\n
Admittedly, this isn't a major issue, as most good-quality solar systems work efficiently whether they're in Scotland or on the south coast. Any difference in the amount of electricity generated would be fairly minimal as it's all about solar radiation (daylight) rather than sunny days.<\/p>\n\n\n\n
Even so, when combined with other factors, it can make a difference and has to be considered.<\/p>\n\n\n\n
<\/div>\n\n\n\n
Solar Array-To-Inverter Ratio<\/strong><\/h3>\n\n\n\nThis figure compares your solar array relative to the inverter capacity to find the best match.<\/p>\n\n\n\n
You can calculate this by dividing the nominal DC rating of your solar array by the maximum AC output of your inverter.<\/p>\n\n\n\n
<\/div>\n\n\n\n
Domestic Or Industrial?<\/strong><\/h3>\n\n\n\nAC electricity differs depending on whether it's in the home or a business. Residential properties in the UK are generally supplied with single-phase<\/em> 230v AC power, while industrial properties often have three-phase<\/em> power (greater power density at the same amperage) from the electric grid. This makes a difference in the type and size of the inverter.<\/p>\n\n\n\n<\/div>\n\n\n\n
Why Is Solar Inverter Size Important?<\/strong><\/h2>\n\n\n\nQuite simply, it's because inverter size directly affects solar panel efficiency!<\/p>\n\n\n\n
Many solar panel installers recommend that you have an undersized inverter, i.e. one that has a slightly lower capacity than your panels. This means that your maximum power output will be dictated by the inverter capacity rather than your solar panel capacity.<\/p>\n\n\n\n
But why would this be a good thing? Remember the section above that mentioned the orientation and location of your solar panels? Well, if the installer suspects that your property will experience a low level of incident solar irradiation <\/em>(most people know this as sunlight!).<\/p>\n\n\n\nThis means that your solar system won't be operating at its rated maximum efficiency for extended periods throughout the day. As a result, it won't reach the initial input voltage or maximum power output voltage as frequently as it might.<\/p>\n\n\n\n
By using a lower capacity, you will ensure even, consistent and efficient energy production all day. However, while inverter manufacturers design them to handle lower power inputs, it's best not to go much lower than the nominal capacity listed. Remember, your solar inverter will dictate the maximum power output, not your solar panels! Flooding it with DC electricity will eventually damage the capacitors and you'll need to replace your inverter much sooner.<\/p>\n\n\n\n
<\/p>\n\n\n
\n
<\/figure><\/div>\n\n\n<\/div>\n\n\n\n
Lab Conditions Vs Reality<\/strong><\/h3>\n\n\n\nAlso, solar system designers typically use figures obtained in laboratory conditions. This means that solar systems rarely reach peak performance as listed in the product specifications. For example, the datasheet might state that the maximum output of the panels is 4kW at a constant temperature of 25\u00bac. However, solar cells become less efficient as the panels get hotter, so you're unlikely to reach or exceed the inverter's rated capacity on exceptionally sunny days.<\/p>\n\n\n\n
While it's possible to have an oversized solar inverter, it's rarely recommended unless you are planning to upgrade your solar array in the near future and add more panels. Solar inverters work best when they're at or close to maximum capacity. Installing one that exceeds the array-to-inverter ratio will eventually compromise the unit's efficiency.<\/p>\n\n\n\n
<\/div>\n\n\n\n
String Inverters Vs Micro-Inverters<\/strong><\/h2>\n\n\n\nSo far, we've assumed that you'll be investing in a solar system with a string inverter<\/em>, as these are the most widely used units.<\/p>\n\n\n\nString inverters are those that connect a whole solar array, consisting of up to fourteen panels. Each one is joined together, sending the DC electricity through to the inverter as if it were from a single panel.<\/p>\n\n\n\n
These are the cheapest option and they are pretty efficient (provided you pick a good brand). Even so, they have an in-built disadvantage: maximum DC output is capped by the lowest-performing panel, meaning that overall electricity production will be limited. So, if one of your panels is partially shaded or is underperforming in any way, it will affect the efficiency of the entire solar array.<\/p>\n\n\n\n
This shouldn't be an issue if your solar panels are all facing the same direction and aren't affected by shading.<\/p>\n\n\n\n
Micro-inverters, on the other hand, bypass this problem as each solar panel has its own mini inverter. If a single panel is affected by shading or any other problem, the system isn't affected as a whole as each inverter operates independently.<\/p>\n\n\n\n
String inverters typically cost between \u00a3500 and \u00a31000, while micro-inverters cost around \u00a3100-\u00a3150 per unit, bearing in mind that you need one for each solar panel.<\/strong><\/p>\n\n\n\nIt's worth noting that a micro-inverter will boost efficiency<\/p>\n\n\n\n