# Connecting a 48 V battery to a grid tie inverter

I am working on a grid tied wind system project. I am planning to use a battery in the system which will be the source to the grid-tie inverter. Also the battery will be used only as a source to the grid-tie inverter and will not be used for back-up. So, the connection is as follows:

Wind generator (2 kW AC) ----> Rectifier/charge controller ----> 48 V, 5 kWh Battery ----> Grid-tie inverter ----> Grid

• Will a grid tie inverter be able to take input from a 48 V battery?
• Is this type of connection feasible?

Any guidance is much appreciated. Thanks

• Is the inverter you intend to use designed for 48 volt DC input? Commented Sep 11, 2018 at 0:04
• Thanks for reply, Yes, I found a couple of manufacturers in Alibaba who said this will work. But I was not able to find many grid- tie inverters with this type of connection which made me wonder if there inverters to do this, because this type of connection is mostly used in off grid system. Commented Sep 11, 2018 at 0:16
• A low ESR DC node is critical to a good inverter output with unity power factor. This does not necessary need to be a battery as the xx kilofarad capacity is not needed for energy storage for more than 10 cycles or so for x % ripple voltage, but ESR must be considered. Define your dynamic load impedance at this DC voltage to both the rectifier and inverter and method of current limiting. I would prefer you define your solution in terms of impedance ratios, in order to determine load regulation error. Commented Sep 11, 2018 at 0:23
• Can you compute this using Z ratio from V ratios? Then estimate cost of IGBT’s per Amp and VI rating to determine optimum DC value. Commented Sep 11, 2018 at 0:25
• Thanks for your input Mr. @TonyEErocketscientist. My connection is not that complicated as I am using off the shelf components, and battery I am using is also designed for home battery back up which provides continuous 48V output. My actual question is will a grid-tie inverter be able to run from this battery. Thanks. Correct me if I am missing something. Commented Sep 11, 2018 at 0:35

48V x 45A might yield 2kW output if the panel is rated for 2500~3000 W max. But if yours is 2kW max take 2/3 or these values. Solar Panels might be rated for best case Solar Power input which rarely occurs due to latitude, season, elevation angle and daily aiming error.

Low V battery causes higher transistor current losses to boost to 120Vac and 2x more to 4x for same kW rating. e.g. 600Vbat @800V can be 98% efficient at 3kW out but only 94% efficient at 400V while 80V bat.will be much worse but unknown.

It is far more cost effective and efficient to have DC current <10A which implies A much higher battery voltage.

e.g. 2kw/10A=200V and 120Vrms is 340 Vpp or 170Vp so high Vbat runs in buck mode while low Vbat must boost and amplify voltage and this draws more driver current.

The optimum Vbat is the one recommend by your choice of GTI and matching array of PV voltage.

Battery LG Chem RESU 7H_R / 10H_R Voltage range 350 -450 V CC Max. current 10 A Communication RS485

In spite of others named in top 10 Consumer grade GTI’s I think the single phase 2 or 3 kW version is what I might choose for best MTTP and GTI effectiveness with smart monitor remote features . https://www.vpsolar.com/en/prodotto/huawei-sun2000l-2-3-3-68-4-4-6-5ktl/

You do not need a Hybrid GTI from battery since you do not want UPS features.

• Thank you very much for your answer @Tony EE rocketscientist., This was really helpful! Commented Sep 22, 2018 at 23:20
• @TheElectrician glad someone appreciates my efforts Commented Sep 22, 2018 at 23:24