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jimjames

My question is about the startup voltage. Can anyone explain whether this matters or not.

We had one company that appeared to be trying to pull the wool over our eyes claiming their inverter was better than everyone elses because it had a lower startup voltage. From my experience once the inverter starts it carries on generating till sunset so a lower voltage may give a few more mins morning and evening but unlikely to be significant.

Energetic_2

jimjames wrote: »

My question is about the startup voltage. Can anyone explain whether this matters or not.

We had one company that appeared to be trying to pull the wool over our eyes claiming their inverter was better than everyone elses because it had a lower startup voltage. From my experience once the inverter starts it carries on generating till sunset so a lower voltage may give a few more mins morning and evening but unlikely to be significant.

I have heard this before, i think it's a sales tactic only quite frankly, and here's why. The panel voltage is pretty stable, its the current that varies most, in low light the panel voltage will not be far off what it is in full sun, the power difference is that the current might be 8.5A compared to 0.5A.

So its the POWER that is important. If the inverter is started up by the voltage but the power density isn't there, the inverter will draw from the grid untill it can start generating or the panels can at least cover it.

We've had this with one customer who complained his inverter was consuming (stealing) 60W for about 20min every morning before it was able to generate. (-: Wattmiser is the polite term...

e

John_Pierpoint

Any thoughts on "solar edge" - my brother in law has used that, but I think it is because he has an architect designed house that has a steep roof, facing mostly east and west with dormer windows poking out all over the place.

Dave_Fowler

John_Pierpoint wrote: »

Any thoughts on "solar edge" - my brother in law has used that, but I think it is because he has an architect designed house that has a steep roof, facing mostly east and west with dormer windows poking out all over the place.

I've been very happy with my Solar Edge system. It deals with shadowing very well. As I reported in my post http://forums.moneysavingexpert.com/showpost.php?p=58642349&postcount=2195 the system with a standard inverter lost more 75% of its power when half the panels were covered with snow. At this time of the year System 2 is progressively shaded by the house during the afternoon. The Solar Edge optimisers ensure that the 'off' panels do not detract from the overall output.

Dave F

Energetic_2

TBH i've never used them, the idea seems sound and i'd consider using them in the right situation but so far never needed to.

I see lots of problems witthe monitoring system on another forum but it's usually because it's not been set up correctly by the instaler.

Good to hear that others are finding that they work well, my only concern with them is that of the micro inverters - if you have a problem with a module mounted component at some point, scffolding etc will be required to resolve it. Their warranty is unlikely to cover that so the installer or the owner would be out of pocket. A string inverter is likely to be much more accessible.

Martyn1981

John_Pierpoint wrote: »

Any thoughts on "solar edge" - my brother in law has used that, but I think it is because he has an architect designed house that has a steep roof, facing mostly east and west with dormer windows poking out all over the place.

Hiya John. I'm nearly 6 months in with my SE system. Still too early to 'claim victory' but I'm slowly getting more and more confident that it does what it says.

I think of shading as a disease, and a SE system (or other) as a way of preventing the disease spreading. Our WNW system produced 408kWh's (aug-dec) against a target (PVGIS climate) of 399kWh's (102%). The target is straight off the site without deducting for shading, despite there being quite a lot.

[ESE system is 'normal' with less shading. Same 5 months it hit 98% of target]

Very keen to see what it does in May and June, but slowly coming to the conclusion that it works very well.

Biggest issue though, that everyone says, is access - what if a PO fails! Personally I think they are a great tool, but only in the right situation, so lots of shading, or lots of panels pointing in lots of different directions and pitches, or even a mixture of panel types and sizes.

Mart.

rogerblack

Energetic wrote: »

I have heard this before, i think it's a sales tactic only quite frankly, and here's why. The panel voltage is pretty stable, its the current that varies most, in low light the panel voltage will not be far off what it is in full sun, the power difference is that the current might be 8.5A compared to 0.5A.

There is a grain of truth here.
A series group of ten panels outputting 360V, if eight are shaded totally and they have bypass diodes, would output 70V or so at nearly nominal amps.
An inverter that can run at this voltage will have an output of 20% nominal - one that can't work at all at 70V won't have an output.

Clearly, in some limited cases, a low startup voltage is beneficial.
For the case of unshaded panels in dim light - it's quite, quite useless, for the reasons mentioned above.

rogerblack

jamesingram wrote: »

Strangely UK MCS states(demands?) that installers should size inverter to 80% of total installed panel wattage. Most manifacturers suggest 90-110%.
I believe most other regs. usually defer to manifacturers instructions.

I did some calculations based on a localish sites reported output.
Doubling the panel size is not unreasonable (at least for that site, assuming the reporting was accurate.
https://forums.moneysavingexpert.com/discussion/comment/49694945#Comment_49694945


I came to wondering, after noticing on a local PV installations instantaneous generation graph how little time it's close to its maximum.

 *    orig  new  ideal  %
  1 1911 1911 1911 100
1.2 1911 2285 2293 99
1.4 1911 2628 2675 98
1.6 1911 2932 3057 95
1.8 1911 3200 3440 93
  2 1911 3441 3822 90
  3 1911 4399 5733 76
  4 1911 5102 7644 66

This was a simple calculation based on computing the 10 minute interval instantaneous outputs of a local 4kW installation with larger panels (for about 5 months)

Columns are:
Excess installed capacity - so the '2' row is for 8kW solar with a 4kW inverter.
Original output in kWh over the period.
New output in kWh over the period.
Output if there was a properly sized inverter installed.
Efficiency (how much you get relative to a 'properly' sized system.

If it was legal to install more panels, then for this period, for this system, quite large increments in panel size seem to make sense.
For example, a 7kW set of panels with a 4kW inverter generate 90% the output of a 7kW inverter.

This assumes that the inverter only draws 4kW from the panels, and does not switch off - if the panels voltage is too high, it will switch off - the install would need to be properly designed.

The above calculation could be inaccurate if there are spikes in the data that are not reported - if a lot of the time a 50% reported output is 5 min of sun, and 5 miniutes of deep cloud, then a double sized panel will have half the above expected output.

zeupater

jimjames wrote: »

My question is about the startup voltage. Can anyone explain whether this matters or not.

We had one company that appeared to be trying to pull the wool over our eyes claiming their inverter was better than everyone elses because it had a lower startup voltage. From my experience once the inverter starts it carries on generating till sunset so a lower voltage may give a few more mins morning and evening but unlikely to be significant.

Hi

I too have seen this marketing ploy. A number of inverters have the ability to have a lower start-up threshold than the default shipped parameters .... the issue is that too low a setting will simply result in the unnecessary switching at startup, where the system passes the voltage threshold, starts generating causing the panel voltage to drop under load, so the system shuts down .... voltage rises, delay countdown .... starts-up .... shuts down. All of this just causes unnecessary wear on the switchgear, so there could be a considerable value of inverter deterioration for a just few extra watts/year .... that's why the manufacturers use the defaults they do ....

There were some discussions on there boards on this ploy being used by (Aurora ?) installers a year or two ago ...

HTH
Z

aurion22

I'm not sure if this is the right place to post this but I'm concerned that my elderly neighbours have been approached by a company called RoLEC Electrical from Wakefield and have signed a contract (although they told me it was only a quote) for installing panels on their flat roof. They have 7 days to cancel the contract in writing but a surveyor isn't coming out until Monday. Should I be concerned?
I can't see the firm listed at Companies House but they do seem to be registered with MCS & NIEIC.
Does anyone know anything about them?
Many thanks
Loretta

PS Mods, please move this if it's in the wrong place. Thanks .. couldn't see where to start a new thread.