Inverters for solar PV panels: your questions answered
Posted by Chris Rudge on 6 August 2010 at 8:52 am
Q1: I hear that inverters for solar PV systems typically last a maximum of 5 years, (Sunnyboy ones seem to fall over in Cambridge after a year, because of the way the grid is here). At £1,000 a pop, that makes a big difference to the economics of PV/ FITs, so it would be great to have someone blog about how to choose an inverter!.
Q2: On a solar PV system where is the best place to site the inverter? Closest to panels in a loft rather than 10/15 meters away in an attached garage? Are DC losses over the 15 meters significant to system efficiency? Do Electricity Regs cover this?
1. Inverters should last much much longer than 5 years. SMA (Sunny Boy) inverters have a 7 year warranty as standard and you can ask your installer to obtain extended warranties direct from the manufacturer if required. Like most mains connected equipment, inverters will be susceptible to mains borne transients. In rural locations this will more of an issue due to overhead power line lightning impulse pickup, etc. However, to help guard against such situations your installer will easily be able incorporate surge suppression into the PV system at minimal extra cost.
Any G83/1 compliant inverter available in the UK will be suitable, and certainly at the moment, where some smaller installers across the UK are having difficulty obtaining inverters at all, one cannot be too choosy regarding inverter type unless you are prepared for a long wait.
2. Technically, locating the inverter as close to the array to minimise DC losses is the order of the day, but in the real world other conditions prevail. In the main, inverters are large bulky items that are difficult to fit inside a standard domestic layout. For this reason they get relegated to the loft space.
This looks an ideal location, being near to the array on the roof, and in the domestic location, this will probably remain the popular choice.
Interested in a hybrid inverter? Read YouGen's blog on the topic.
There is a drawback with using the loft, it gets hot in bright sunshine which in turn will have the tendancy to prematurely overheat the inverter. Whilst the inverter can kick in its cooling fans to regulate its own temperature, the downside is it will also de-rate the output a little to minimise current throughput (and heating).
Therefore, if there is another room, large cupboard or garage that has space for the inverter, it will be better situated there. Cable losses are simply dealt with by using larger diameter cables if necessary, so no problems there.
More information about inverters and solar PV from YouGen
About the author: Chris Rudge is a qualified electrician who specialises in renewable energy.
If you have a question about anything in the above blog, please ask it in the comments section below.
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