What it is: The heat rate measures the efficiency of a power plant by calculating how many British Thermal Units (Btu) of fuel are needed to produce one kilowatt-hour (kWh) of electricity. The spark spread takes the electricity price minus the cost of fuel (natural gas) times the heat rate — a key profitability metric for gas-fired generation.
Why it matters: Lower heat rates indicate more efficient plants and lower production costs. A positive spark spread means generators can profitably sell power relative to their fuel costs, while a narrow or negative spread signals margin compression and potential plant dispatch reductions. Monitoring these metrics helps market participants assess generation economics and expected dispatch.
How to read the signal:
- Green – Healthy spread / Low heat rate: Spark spreads are comfortably positive and heat rates are low or improving. Indicates efficient generation and supportive margins for gas plants.
- Yellow – Margins tightening: Spark spreads are narrowing or heat rates creeping higher. Suggests profitability is declining; watch for potential shifts in dispatch or hedging opportunities.
- Red – Negative spread / High heat rate: Spark spreads are negative or heat rates are elevated, meaning gas plants may be running at a loss. Signals high risk of curtailed generation and potential upward pressure on power prices if supply tightens.
Sources: ISO day-ahead and real-time power prices, natural gas prices (Henry Hub or regional basis) and plant efficiency data from market operators or independent analysts.
