FoxESS Community - Owners & Installers Forum

My S Series1500 was installed a couple of days ago.

I was advised that the house load power should be distributed for my use before any export of excess to the Grid.
It was explained the feed in power and output power, which appear to be an equally shared distribution of power, meant that the house was receiving solar energy power..

Having now watched a user guide video, it becomes clear that the 'load power' in the graph which is the indicator that the house is benefitting from solar energy... has now been zero for over 48hours.. clearly something is not quite right.

I was also advised a 1500 inverter would capture all the energy produced by my 2Kw solar PV array... However the graphs have indicated a clear cut off and dips at 1500 notwithstanding the power generated by the solar panel is more.

Now I am concerned I was wrongly advised could you please assist with my understanding.

Hi there. The S1500 is only able to output up to 1.5kW AC power, so it cannot produce more than this, which is the reason you see the graph peak at this value. How many panels do you have, and do they all face the same way?

I would agree that you should be seeing your house load being supported by the solar panels when the sun is up, I would call your installer and ask them to come back to look at it, it may be one of the clamps that should have been installed to monitor this has not been properly connected.

Do you have an smart meter IHD that you can use to check how much power your house is drawing from the grid? If so when the sun is up and the solar is generating you should be able to see that you are only drawing what you need on top of the 1500W from the S1500, or if you are using less than 1500W, it should show an export value.

Thanks for your reply which is appreciated.

I have 5 panels. I do not yet have a smart metre awaiting an install

Is there a good reason why an installer would undersize the inverter? I can now see what the disadvantages are.

Any thoughts on the dip in solar generation - the panels are all facing the same way.

Thank you..

Sizing inverters vs arrays is a compromise of various things, especially in a place like the UK where the generation can vary widely depending on the season.

Larger inverters do cost a little more, but the main reason tends to be to do with efficiency, because inverters convert power into 'mains' (220V AC) most efficiently towards the top end of their capacity. If you size an inverter for peak loads, you can lose out in efficiency the rest of the time when there is less solar power available. Be aware that the 2kWp rating of your array (presumably 5x 400W panels) is a peak power rating, ie that 400W per panel is what it could generate when brand new, perfectly clean, and in perfect generating conditions. Most of the time it will not be delivering that peak power - and may never do so in fact, depending on the angle and direction.

In the best case, I presume the installer decided that the extra power that could be harvested at peak times by fitting a larger inverter was not worth the tradeoff in efficiency the rest of the year. If one was being suspicious of mind, you might wonder if they had had this inverter in their warehouse for a while and just decided "it'll do". Normally I would expect the installer to provide you with some documentation explaining (mathematically at least) the reason for the decision to specify that particular size of inverter.

Any thoughts on the dip in solar generation

By "dip" do you mean the fact that the generation trace flatlines at 1.5kW?

Thanks for your response...

You can see from the graph, it appears the inverter is unable to hold its own peak of managing solar energy at 2500.

Panels are 415kw (=2.07kw) I am told annual est. Solar generation 1848kw ..If the decision to undersize was based on efficiency would we not consider maximising the energy we could capture ?

You can see from the graph, it appears the inverter is unable to hold its own peak of managing solar energy at 2500.

I'm sorry, I'm not sure where you're seeing this on the graphs you've posted. The first graph shows the output from your inverter which basically flatlines at 1.5kW in line with the maximum output of the inverter.

The second graph shows the voltage of the panel string, which is around 200V.

If the decision to undersize was based on efficiency would we not consider maximising the energy we could capture ?

As I explained above, I don't know exactly why the decision was taken to employ the S1500 for your system. The general tradeoff is to with how efficiently the inverter converts the output of the panels into usable 220V AC power at say, 30% or 50%, vs when it's getting the maximum output of the panels. This comes into play during the day as well as at different times of year - smaller inverters can start working at lower levels of solar input vs bigger ones. Given that you don't get full output from the panels for much of the year in the UK, it's possible for an apparently undersized inverter to give you more usable energy across the year. This article explains in more detail why this can be the case.

From where I'm standing, I'd agree that it appears that your inverter might be a bit undersized, but I'm not a solar installer, and I don't know what other factors your installer might have been taking into account (including, unfortunately, the "I've had this in the warehouse for ages, it'll do for this even if ideally it'd be a bit bigger" one).

I appreciate your input. Since I have no response from my installers, I am now writing to Fox. I need to establish cause, as one week letter and still no graph indication that solar energy is being used by the home! In the absence of a response I think it is the installers. I am sure there must be a governing body I should lodge a complaint with...

Were your installers registered with MCS? You could contact them if you don't have any joy otherwise