Micro invertor on a solar PV installation

s2art

zeupater wrote: »

Hi

Then the average failure rate becomes 1 in 30000Hrs v 4 in 30000Hrs ..... the issue of labour and access hasn't been addressed. If the warranty includes all costs, ie labour & access/scaffolding, and is independant insurance backed then I would agree that the option could be competitive with a system inverter made by an established manufacturer ... if not I'd personally prefer to wait and see and I doubt that I'll be waiting 300years either ....

Just looking at comparing costs, a system inverter is likely to cost around £0.35/Wp against duo microinverters at £0.55/Wp and single panel units at £0.80/Wp, so a ratio of 1:1.6:2.3, or alternatively, looking at a 4kWp system, a premium of £800 for duo units or one of £1800 for single panel units .... a cost which is really only justifiable under shade conditions due to improved performance as it would either cover the cost of a repair or a long term warranty, or even pay/part pay for a new inverter at some time ....

HTH
Z

See; enphasenergy.com/downloads/Enphase_WhitePaper_Reliability_of_Enphase_Micro-inverters.pdf


As it says, MTBF is not as useful as wear-out-rate, however the 300 year+ figure is obtained using the same tests as are applied to PV panels.

As for the cost per KW, your figures seem high-ish for the duo, and lowish for the string inverter. Perhaps the quotes I have had for string inverters are on the high side. There does seem to be a big variation in prices from the installers.

zeupater

s2art wrote: »

See; enphasenergy.com/downloads/Enphase_WhitePaper_Reliability_of_Enphase_Micro-inverters.pdf


As it says, MTBF is not as useful as wear-out-rate, however the 300 year+ figure is obtained using the same tests as are applied to PV panels.

As for the cost per KW, your figures seem high-ish for the duo, and lowish for the string inverter. Perhaps the quotes I have had for string inverters are on the high side. There does seem to be a big variation in prices from the installers.

Hi

My point was that most people don't understand what MTBF really means in the real world. I don't even understand why Enecsys would mention a high MTBF in their sales literature and then their CEO publishes this ... http://www.enecsys.com/downloads/UnderstandingMTBF.pdf ... which seems to rubbish anyone in the solar pv industry for doing so by saying "The inference made by suppliers in the solar industry quoting high MTBF numbers attempts to support an expectation of a long life. Such statements are factually wrong" .... perhaps Paul Engle should have a quiet word with his marketing department

Anyway, I have no problem with microinverters ... they seem to be an excellent solution to small systems, multi-faceted roofs and shading ... I just think that they are comparatively expensive if you don't need them and that they are likely to be a more expensive long-term maintenance prospect due to high level access .....


Regarding Cost/Wp for comparison, it was based on ....

4kWp Inverter (SMA/Fronius/Power One etc) - £1400/4000 = £0.35/Wp
Enecsys Duo - (£275x8)/4000 = £0.55/Wp
Enecsys - (£200x16)/4000 = £0.80/Wp

.... and any installer should be able to trade purchase at around/below these prices.

HTH
Z

s2art

OK, we seem to be violently agreeing on MTBF. But I question your figures which assume identical failure rates for string and micro inverters.

WRT prices, where does that figure of £275 for the duo come from? I have been looking for the price of the SMI-D480W-60, but couldnt find it.

Must admit that the Fronius extended warranty (£200??) makes them look a better deal than the micros for the moment.

zeupater

s2art wrote: »

OK, we seem to be violently agreeing on MTBF. But I question your figures which assume identical failure rates for string and micro inverters.

WRT prices, where does that figure of £275 for the duo come from? I have been looking for the price of the SMI-D480W-60, but couldnt find it.

Must admit that the Fronius extended warranty (£200??) makes them look a better deal than the micros for the moment.

Hi

The figures I used assumed a string inverter failure after 30000 run hours (about 10 years) and microinverters after 60000 run hours, so 20 years therefore the failure rates aren't identical ..... the run hours however were standardised on 30000 to compare the failure (1v4 for the duo / 1v8 for standard) against a common measure ... This would assume that the average lifespan of a microinverter would be double that of a string inverter, but because there were more microinverters in a system there is stastically a more likely failure rate within the system.

HTH
Z

RightRevBod

We had a visit from a local installer yesterday. I raised the subject of micro inverters and he was not keen. He agreed that they were a good idea in principle., but that the technology was rather too young. Understandably he was concerned about the cost of any maintenance within the period of the installation warranty he was providing. It would be more expensive for him to have to get scaffolding to remove/replace a micro inverter on the roof than to access a string inverter inside the building.

Bit of a moot point at the moment as Enecsys are not supplying micro inverters at the moment.

However, he was more of a fan of DC optimisers (thanks zeupater), but was not aware of any which had obtained MCS approval. He has gone away to check on this and do some calculations.

Does anybody know of an aproved DC optimiser that could be used in this installation?

He was also suggesting that a Diehl platinum inverter might be suitable (subject to the calculations he is doing now)

Does anybody have experience of Diehl inverters?

Gizmosmum_2

Diehl are good German inverters with a 10 year warranty but I'd still challenge anyone to find better value than the Fronius inverters about the same price as Diehl with the 20 year warranty. Got to be installed before end of October though.

jeff_p

another question.... can you connect into am existing circuit and still get the FIT's