June 15 (Reuters) - * California's wholesale electric costs rose 25 percent in 2017 due to higher natural gas prices, according to a report by the market monitor for the state's power grid operator on Thursday.
* Gas supplies are expected to be tight in California this summer and winter due to continued reduced availability of the Southern California Gas' (SoCalGas) Aliso Canyon storage facility in Los Angeles, following a massive leak between October 2015 and February 2016, and the ongoing shutdown of several pipelines.
* The average total cost of electricity and reserves in the state's power grid run by the California Independent System Operator (ISO) rose to $41.77 per megawatt hour (MWh) in 2017 from $33.52 in 2016, the market monitor said.
* Power prices in 2015 and 2016 were both at record lows for the biggest trading hubs in the West with SP-15 EL-PK-SP15-SNL in Southern California averaging just $34.16/MWh in 2015 and $30.96/MWh in 2016, according to Thomson Reuters data going back to 2001.
* Gas prices at the SoCal Citygate rose to $3.41 per million British thermal units (mmBtu) in 2017 from $2.55 in 2016 and $2.78 in 2015, the market monitor said. The average in 2016 was the lowest for the SoCal CityGate NG-SCL-CGT-SNL on record, according to Thomson Reuters data going back to 2011.
* SoCalGas, a unit of Sempra Energy, is only expected to be able to deliver about 3.6 billion cubic feet per day (bcfd) of gas from non Aliso storage fields and pipelines this summer. That is 0.2 bcfd less than last summer due to increased pipeline outages, according to federal and state agencies.
* If gas demand exceeds 3.6 bcfd, which is common in the winter but has only occurred once in the past five summers, some gas deliveries to power generators may be curtailed, the agencies warned.
* After the leak, state regulators reduced Aliso Canyon's capacity from 86 billion cubic feet (bcf) to about 25 bcf. The total capacity of SoCalGas' four storage facilities, including Aliso, declined from 136 bcf to 74 bcf now.
* SoCalGas now has about 60.8 bcf of gas in storage and is hoping to have stocks full before the winter when homes use much of the region's fuel for heating.
* The market monitor said peak demand in the ISO rose in 2017 to 50,116 MW from 46,232 in 2016. The all-time peak was 50,270 MW in 2006.
Reporting by Scott DiSavino; Editing by Bernadette Baum