COGIX

The COGIX (COGeneration IndeX) is a profitability indicator for CHP systems that operate on the electricity market. Similar to the Spark Spread or the Green Spark Spread including CO ₂ emission costs, a contribution margin is calculated from electricity revenues and costs for fuel including CO ₂ emissions. In addition, the COGIX also takes into account the heat revenue from the CHP plant.

Calculation formula for determining the index

The COGIX is calculated from generalized assumptions about the CHP system and the current reference prices for input and output variables such as fuel, greenhouse gases, electrical and thermal energy.

${\displaystyle COGIX=p_{el}^{KWK}-{\frac {p_{bs}^{KWK}+e^{KWK}\cdot p_{CO_{2}}}{\eta _{el}^{KWK}}}+{\frac {p_{th}^{KWK}}{\sigma _{A}^{KWK}}}}$

Here mean

COGIX: contribution margin for CHP electricity in € / MWh _el
p _el ^KWK  : achievable electricity price in € / MWh _el
p _th ^KWK  : achievable heat price free CHP system in € / MWh _th
p _bs ^CHP  : fuel price free CHP system in € / MWh _bs
p _{CO 2}  : rate for CO ₂ - emission allowances in € / t _{CO 2 e}
e ^CHP  : specific fuel-related CO ₂ emissions in t _{CO 2 e} / MWh _bs
η _el ^CHP  : electrical efficiency of the CHP plant
σ _A ^CHP  : work-related power figure of the CHP system

application

For the applicable heat price ex power plant, 1.3 times the price for power plant gas has proven to be useful. This means that large industrial customers can be offered an attractive individual district heating price, and higher sales costs for businesses and households can be represented with a district heating tariff that is based on heating costs with natural gas or heating oil.

Since the power index does not significantly influence the COGIX, a power index of σ = 1 is normatively assumed, as found in small CCGT systems and large combined heat and power plants. A value of 85% is assumed as the overall efficiency, so that the electrical and thermal efficiencies of η _el = η _th = 42.5% result with the above current index .

The emission factor for natural gas is 0.2 t per MWh of fuel.

The COGIX is an index that is intended to assess the general profitability of (gas-powered) CHP systems that operate on the electricity market. It is not intended to be used to assess any particular investment project. Since the long-term marketing of power plant capacity usually takes place on the futures market, the variable COGIX reference prices (baseload price, natural gas price, CO ₂ certificate price ) are also taken from the futures market with delivery in the following calendar year (future Y + 1). To the wholesale price of natural gas, 4 € / MWh (based on H _s ) for transport and structuring are added.

${\displaystyle COGIX_{gas}=p_{el}^{KWK}-1,053\cdot p_{gas}^{KWK}-0,47{\frac {t_{CO2e}}{MWh}}\cdot p_{CO_{2}}}$

Note: A COGIX can also be set up for CHP coal-fired power plants by adjusting the emission factor, efficiency and fuel price reference accordingly. The emission factor of coal is 0.34 t per MWh of fuel. In the case of a coal-fired power station, an electricity index of 0.7 is assumed, i.e. H. η _el = 35% and η _th = 50%. The transport costs for coal are estimated at just under € 2 / MWh _fuel .

${\displaystyle COGIX_{coal}=p_{el}^{KWK}-2,857\cdot p_{coal}^{KWK}+1,857\cdot p_{gas}^{KWK}-0,97{\frac {t_{CO2e}}{MWh}}\cdot p_{CO_{2}}}$

Web links

• Felix Christian Matthes, Hans-Joachim Ziesing: Economic efficiency of combined heat and power plants, study for the Association of Municipal Enterprises (VKU), Volume 1: The CHP economic efficiency indicator COGIX - method volume , Berlin, January 2011.
• Felix Christian Matthes: CHP in (and on the way to) the new electricity system, lecture at the 14th CHP Symposium, Duisburg, 2016-06-14.