This paper investigates the impact of non-ideal transceiver hardware impairments on massive multiple-input multiple-output (MIMO) systems, focusing on energy efficiency, channel estimation accuracy, and capacity limits. The authors introduce a new system model that incorporates general transceiver hardware impairments at both base stations (BSs) and single-antenna user equipments (UEs). Unlike conventional models with ideal hardware, they show that hardware impairments introduce finite ceilings on channel estimation accuracy and downlink/uplink capacity. Surprisingly, the capacity is primarily limited by the UE's hardware, while the impact of impairments in large-scale arrays vanishes asymptotically, and inter-user interference becomes negligible. The paper also demonstrates that the degrees of freedom in massive MIMO can be used to reduce transmit power and tolerate larger hardware impairments, allowing for the use of inexpensive and energy-efficient antenna elements. The analysis is supported by theoretical derivations and numerical simulations, providing insights into the trade-offs between hardware quality, spectral efficiency, and energy efficiency in massive MIMO systems.This paper investigates the impact of non-ideal transceiver hardware impairments on massive multiple-input multiple-output (MIMO) systems, focusing on energy efficiency, channel estimation accuracy, and capacity limits. The authors introduce a new system model that incorporates general transceiver hardware impairments at both base stations (BSs) and single-antenna user equipments (UEs). Unlike conventional models with ideal hardware, they show that hardware impairments introduce finite ceilings on channel estimation accuracy and downlink/uplink capacity. Surprisingly, the capacity is primarily limited by the UE's hardware, while the impact of impairments in large-scale arrays vanishes asymptotically, and inter-user interference becomes negligible. The paper also demonstrates that the degrees of freedom in massive MIMO can be used to reduce transmit power and tolerate larger hardware impairments, allowing for the use of inexpensive and energy-efficient antenna elements. The analysis is supported by theoretical derivations and numerical simulations, providing insights into the trade-offs between hardware quality, spectral efficiency, and energy efficiency in massive MIMO systems.