is capable of powering 15,000 homes for over four hours. BYD proposes to use conventional consumer battery technologies such as lithium iron phosphate (LiFePO4) battery, connecting many batteries in parallel. The largest grid storage batteries in the United States include the 31.5 MW battery at Grand Ridge Power plant in Illinois and the 31.5 MW battery at Beech Ridge, West Virginia. Two batteries under construction in 2015 include the 400 MWh (100 MW for 4 hours) Southern California Edison project and the 52 MWh project on Kauai, Hawaii to entirely time shift a 13MW solar farm's output to the evening. Two batteries are in Fairbanks, Alaska (40 MW for 7 minutes using Ni-Cd cells), and in Notrees, Texas (36 MW for 40 minutes using lead–acid batteries). A 13 MWh battery made of used batteries from Daimler's Smart electric drive cars is being constructed in Lünen, Germany, with an expected second life of 10 years. In 2015, a 221 MW battery storage was installed in the US, with total capacity expected to reach 1.7 GW in 2020. The UK had a 50 MW lithium-ion grid-battery installed in Hertfordshire in 2018. In February 2021, construction began on a 50 MW battery storage development in Burwell, Cambridgeshire and a 40 MW site in Barnsley, South Yorkshire. In November 2017 Tesla installed a 100 MW, 129 MWh battery system in South Australia. The Australian Energy Market Operator stated that this "is both rapid and precise, compared to the service typically provided by a conventional synchronous generation unit". Electric vehicles Companies are researching the possible use of electric vehicles to meet peak demand. A parked and plugged-in electric vehicle could sell the electricity from the battery during peak loads and charge either during night (at home) or during off-peak. Plug-in hybrid or electric cars could be used for their energy storage capabilities. Vehicle-to-grid technology can be employed, turning each vehicle with its 20 to 50 kWh battery pack into a distributed load-balancing device or emergency power source. This represents two to five days per vehicle of average household requirements of 10 kWh per day, assuming annual consumption of 3,650 kWh. This quantity of energy is equivalent to between of range in such vehicles consuming . These figures can be achieved even in home-made electric vehicle conversions. Some electric utilities plan to use old plug-in vehicle batteries (sometimes resulting in a giant battery) to store electricity