Solar hybrid inverter - 3.6kWh or 5kWh?

murmeltier

I have recently started looking into getting quotes for a solar + battery installation and been recommended 10x425W panels giving 4.25kWp (south facing).

The installer recommended a 3.6kWh hybrid inverter and a 9.5kWh battery.

Costwise I've been told there won't be a big difference if opting for a 5kWh inverter, and I've also been told that using a bigger inverter would increase system performance only ever so slightly by 1.2%

What I'm trying to understand:
Does a 3.6kWh hybrid inverter make sense, or should we opt for a bigger size (5kWh)?

Given it looks unlikely we'll be able to increase the solar output beyond 4.25kWp should we stick with 3.6kWh?

We're expecting to switch to EV and possibly ASHP in the next few years, would this make a difference for inverter sizing?

Screwdriva

Would be helpful if you could share the brands of the components and the cost quoted to you:

1) As a general rule of thumb, and especially factoring in an EV/ ASHP, maximizing roof coverage with panels is a wise decision. Are you able to fit more panels across your South/ Western roof aspects? 

2) Depending on your answer to 1), a 5kW inverter with 10 X 425W panels wouldn't make sense. However, 10 X 550W Sharp panels can make optimal use of roof area where two smaller panels won't fit. In this example, a 5kW inverter does make sense. A survey will determine feasibility. 

3) Installers tend to specify the 3.68kW inverter due to the simplicity of the G98 application and the superior efficiency during the cloudy/ overcast days. The number of aspects may also factor in. 

4) If you plan on an EV + ASHP, you really should invest in a modular battery from a quality brand. My top picks are the Powerwall (~£10K installed for 13 kWh) or the Libbi (~£9.5K installed for 10 kWh). Both come with built in inverters and offer excellent aftersales support. 

murmeltier

Thanks.

Quote is for 10x Perlight Delta 425W Total Black Mono panels, GivEnergy 3.6 hybrid inverter and GivEnergy 9.5kWh battery.

Quoted total cost appx 12k.

Small local independent installer, didn't seem to have any issues with G99 when I raised it as a possibility but couldn't see a way of fitting more panels.

DougMLancs

Other aspects of your quote aside, if you go for Givenergy, make sure you get quoted for at least the Gen 2 Hybrid (Gen 3 recently released). You’ll really appreciate the 3.6kW charge/discharge rate from the battery as a pose to 2.6kW from the Gen 1.

murmeltier

DougMLancs said:

Other aspects of your quote aside, if you go for Givenergy, make sure you get at least the Gen 2 (Gen 3 recently released too)

Quote is for GivEnergy Gen 3

DougMLancs

Ideal 👍 it’s a shame you can’t squeeze more panels on though

Exiled_Tyke

The inverter should always be lower capactity than the the peak panel output.  This will produce some clipping at peak times but this is rare.  Most of the time the smaller inverter will be working more effeciently than a larger one.   I read details of a commercial installation (and I wish I could still find it but I seem to have lost it) that suggested inverters should be in the range of 70-80% of the peak panel production.   

Screwdriva

I agree with Doug. I would insist on 

1) Gen 3 GivEnergy battery and inverter as Doug as rightly pointed out AND

2) the longest available extended warranty possible for the inverter / battery (10 years?) AND

3) any one of the following panel brands: Sharp / Hyundai / Solarwatt/ REC / Eurener, all known for offering top quality warranty/ aftersales support years after installation. I would not invest in Perlite on my roof, no matter what any installer said. 

I believe you are being over-quoted. I have seen a recent similar quote for 10 X Sharp 410W Panels + Gen 3 Givenergy battery + inverter for ~£11K. 

paul991

perlight ? or perlite

Johnny_M_P

Hijacking this thread if I may as its a similar query:

I have the folloing set up:

14 panels of Longi 405W panals, SW facing 30deg slope and no obstructions/shadow.

3.6Kwh Lux convertor

2 x 3.2KwH batteries.

The recorded output of the panals, according to the Luxpower tops out at 3.9Kw.  The theorectical output would be 5.67Kw.

Presumably this is limited by the inverter?

Would I have been better with the 4.6Kwh LuxPower, only losing 1Kwh rather than the current 2Kwh.

The panals are maxing out on a sunny day for at least 6 hours.

DougMLancs

@Johnny_M_P I suspect your installer was trying to avoid making the G99 application that would’ve been needed for a larger inverter. 5.67kW of panels on a SW aspect was always going to see a lot of clipping (where the panels produce more than the inverter can handle) in the summer with a standard 3.6kW inverter and your installer should’ve discussed this with you. 

There’s a strategy you can use to soak up some of that lost energy. For sunny days you’ll want to make sure there is spare capacity in your batteries still when you hit that peak generation period. If you change your battery charge settings so that they won’t charge from solar until 1pm (or whenever you normally see generation being throttled) and then limit that charge rate to say 1.5kWh then that’ll give you up to 4 hours where your batteries are charging at 1.5kW AND the house/grid are still getting your max inverter limit of 3.6kW. Others may explain it better but that’s the gist.

Your other option is to pay for a bigger inverter to be fitted and apply to your local DNO with a G99 for a higher export limit. The payback of that option would need some working out though.