UK GAS-Prompt prices rise as demand outstrips supply
* Gas system undersupplied by 5.4 mcm
* Friday's demand 14 pct above season norm
* UK carbon tax boosts gas-fired power generation
May 15 (Reuters) - Prompt natural gas prices in Britain rose on Friday morning, as lower imports from Norway and high demand from gas-fired power plants left the system undersupplied.
Prices for within day delivery were 44.55 pence per therm at 0822 GMT, up 0.15 pence since their last settlement. Prices for day-ahead delivery were up 0.85 pence at 45.10 pence per therm.
With supply flows at about 199 million cubic metres (mcm) per day on Friday and demand expected to be about 204.4 mcm, the system was 5.4 mcm undersupplied, National Grid (LSE: NG.L - news) data showed.
Friday's demand was around 14 percent above the seasonal norm of 179 mcm, the data showed.
Traders said demand for gas from gas-fired power generators has risen since Britain's domestic tax on carbon dioxide (CO2) emissions from power plants almost doubled last month to 18 pounds per tonne.
The tax has a bigger impact on coal-fired power plants because they emit almost double the amount of CO2 than efficient gas plants.
Gas-fired power plants contributed 37 percent of Britain's total electricity supply on Friday morning with coal plants contributing 23 percent, National Grid data showed.
Analysts at Thomson Reuters Point Carbon also said prices were rebounding on Friday after slipping on Thursday due to over-supply.
"Prompt prices dropped yesterday on the back of a surge in LNG (liquefied natural gas) send-out that lead to an oversupplied system. The NBP lost value against Continental (Swiss: CONT.SW - news) hubs and prices could adjust upwards today given the tight UK system," the analysts said in a daily research note.
Norwegian imports via the Langeled pipeline were around 25 mcm/d on Friday morning, National Grid data showed, down from around 30 mcm on Friday and much lower than its full capacity of 70 mcm/d.
Langeled is Britain's main sub-sea gas import route. Further along the curve, gas for delivery in June was 0.35 pence higher at 43.00 pence per therm and the Q3 15 contract was up 0.30 pence at 43 pence per therm.
In the Netherlands, the day-ahead gas price at the TTF hub was 0.08 euros lower at 20.65 euros per megawatt-hour (MWh).
The benchmark European Union carbon price dipped 0.05 euros to 7.57 euros a tonne on ICE Futures Europe. (Reporting by Susanna Twidale; Editing by Keith Weir)