Testing Mini Grid Tie Inverter + Panels

[cye]

I recently acquired a'secondhand' mastervolt soladin 600 grid tie inverter which needed testing, and I also had purchased earlier in the year some 'new old stock' spanish made 165w mono panels that i had not yet tested. this post describes a very quick combined test of both the panels and the inverter. I connected two panels into a series string and plugged both ends of the string into the inverter.

In theory this setup could deliver a max of 330w if the panels had been inclined and oriented correctly, but for the purposes of a quick test i simply leaned the panels up against whatever was handy in the back garden.




The inverter is from a respected quality dutch designer,very popular with self-installers because the model can handle small panel arrays. This model complies with connection standard G83/1, which until april (?) this year was the GB standard( GB has since moved onto G83/2). NI/Ireland minimum requirement remains G83 part 1 at the time of writing. This model of inverter is also popular with some commercial installers because it has mppt power point tracking and, as several of these inverters can be 'stacked' if required. I.e., several inverters can be used on a single property with a number of small panel strings, and this is a simple way of dealing with an awkward property which has a mix of roof faces with different orientations, inclinations, and/or shading.

Now for a permanent grid-tied setup we would need a DC isolator between the panel string and the inverter, and an AC isolator between the inverter and the 240v mains,etc. But, for a quick test i simply covered the panels whilst i connected them to the inverter (no risk of a shock from the DC when panels covered), and then connected the inverter to a household socket. Between the household socket and the inverter i inserted a plug-in watt meter, in order that i could measure the power output.

(for the record, i recommend that readers do not regard what is described here as good advice or best practice, and a qualified electrician should always be consulted/employed for all matters relating to a grid tied system or indeed any alterations to household mains wiring, that local building control regulations complied with in all respects, etc, etc.....now, moving swiftly on... )

here's a pic or two of the series 'string' of two isofoton IS-165 monocrystalline panels.


(between the two panels you can see the blue inverter)

[cye]

...and here's the result. Given that the panels were not inclined correctly i was pleasantly surpised to see output in excess of 300w, and indeed, just after this photo was taken, the output exceeded 310w. not bad for late afternoon.



(The soladin 600 is rated as being 93% efficient, so 330wp X 93% = 307wp, so with having seen >310w and the panels aren't even inclined correctly, this is a very good result bearing in mind this is an inverter fit for 700wp and won't be working at its greatest efficency with a panel string of only 50% of what it's designed to handle. I think the most likely explanation is that panels are probably doing better than their rating would suggest.)


the above shows that i have actually used two metering devices. the white one is a £10 watt meter purchased from eBay. Accurate as it may be on the wattage reading, the white meter unfortunately does not distinguish between import and export. i therefore also employed the black meter in the pic, which is a salvaged 'old world spinny disc' consumption meter. These meters are useful because the disk not only spins forwards when the house is drawing electricity from the grid, but the disc also spins backwards (and winds back the register) when power is going into the grid. so, using both these meters together, i could see both the direction of the power flow and the exact wattage. i could of course just have used the black meter on its own, but then i would have had to measure the time between clicks on the black meter's register to compute the wattage, whereas the white meter tells me the wattage instantaneously.

and here's the spec of the panels i was using. these were made in circa 2007. At 165w peak per panel, these are much smaller than the those typically used these days on domestic roofs (std now is circa 285-300wp per panel). i deliberately purchased these panels though because they were small enough to transport in an ordinary saloon car (unlike the modern 285-300w panels), because they are good deal easier to man handle on one's own, because they are more robust than larger panels (more frame for the glass area so less), and last but not least because being an older design meant they were available for (almost) a song (at £0.60/wp + delivery).





finally, i should point out that i did not just go and buy any old inverter for these isoforon panels. Every make/model of panel has a different spec, and any proposed string of panels needs to comply with the spec of the proposed inverter. Mastervolt has a design model/spreadsheet available to download for free from the mastervolt website. Before any of the above, I used the design model to first check if was ok to wire two of these specific isofoton panels in series into the soladin 600 inverter. (In fact, a series string of 3 such panels can safely be used with this inverter, but 2 panels were enough for me for this simple test).