New install design question
Hi, I have just had installed 14 x 430w panels + Fox ESS H1-5.0-E-G2 inverter. When I ordered the system I understood the max output of the system would be 6.02 kW. When I received the MCS certificate the total installed capacity was given as 5.0 kW. I presume this is because the inverter is rated at 5.0kW. If my assumption is correct the output from my system will be truncated at 5.0 kW on a sunny day (It has already peaked at 4.8kW in February sun). Do you think this is a sensible system design or should I have been offered the option of the 6.0-E inverter when I placed the order?
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Dave Foster
- Posts: 1662
- Joined: Thu Oct 13, 2022 7:21 pm
You system is capable of producing ~6 kWp in ideal conditions but that will derate with hot weather and light cloud so it's always useful to have a little more on your roof than your inverter output is rated for.
The inverter is limited to 5kW on it's ac output, but as you are capable of generating 6kW it could be sending 5kW to your house and export (ac output) whilst charging the batteries at 1kW (dc) so it shouldn't clip unless your batteries are fully charged (you haven't mentioned batteries or sizing but I assume you have them?).
Your DNO will sometimes specify an output limit so that could be why you only have a 5kW inverter but as already said it won't really affect you that much in normal operation.
The inverter is limited to 5kW on it's ac output, but as you are capable of generating 6kW it could be sending 5kW to your house and export (ac output) whilst charging the batteries at 1kW (dc) so it shouldn't clip unless your batteries are fully charged (you haven't mentioned batteries or sizing but I assume you have them?).
Your DNO will sometimes specify an output limit so that could be why you only have a 5kW inverter but as already said it won't really affect you that much in normal operation.
Thanks for reply. No I don't have a battery at present, but may consider upgrading in future. When I looked at the battery option it seemed to push back the break even point by several years. I can see the prices of batteries online seem to be about half the price that the installer was quoting as part of the pv installation, so I will see if I can get a more competitive price to upgrade.
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WyndStryke
- Posts: 44
- Joined: Mon Nov 18, 2024 9:16 pm
Batteries actually can pay back quite quickly, but you need to be on the right tariff etc.Parkview wrote: Thu Feb 20, 2025 7:06 pm Thanks for reply. No I don't have a battery at present, but may consider upgrading in future. When I looked at the battery option it seemed to push back the break even point by several years. I can see the prices of batteries online seem to be about half the price that the installer was quoting as part of the pv installation, so I will see if I can get a more competitive price to upgrade.
For example, with my tariff (E-on Next Drive)
* 00:00-07:00 charge up battery at 6.7p/kWh ('force charge')
* 00:00-20:00 Run home off battery (effective cost 7.3p/kWh after considering round-trip losses) & solar, and export any surplus solar to the grid at 16.5p/kWh ('feed-in first')
* 20:00-24:00 Gradually export any surplus battery capacity at 16.5p/kWh (worth about 9p/kwh), leaving just enough to last until midnight ('force discharge')
For this to work, the battery needs to be just big enough to last from 7am to midnight on the heavier usage winter days. The biggest return is from running your home on cheap overnight power and exporting solar, the arbitrage in the evening is just a small bonus since the return is less.