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Department for Business, Energy and Industrial Strategy

Saturated Steam to Electricity Conversion Equipment

1.1    Scope

Saturated steam to electricity conversion equipment covers products that are specifically designed to generate electrical power from waste or excess wet or saturated steam by reducing the steam pressure. The categories of product covered under the Energy Technology List (ETL) scheme include:

  1. Screw expanders – as wet steam passes through the product, it turns a screw rotor, which is connected to a generator. Energy is removed from the steam as the pressure reduces, which is converted into rotational shaft energy and then electricity. 
  2. Non-condensing or back pressure turbines – equipment which features rotary turbines where high pressure input steam is allowed to expand as it passes through the turbine. This releases energy and lowers the pressure of the steam at the outlet, without increasing the temperature. 

Products should be sold as packaged units that can be fitted to industrial processes. Products that incorporate any form of combustion equipment, including boost burners, shall be excluded.

1.2    Definitions

Saturated steam to electricity conversion equipment is specifically designed to convert waste or excess saturated steam, from a specific process, into electrical power by means of a closed thermodynamic power cycle that does not involve the internal combustion of fuel. 

1.3    Requirements 

1.3.1    Eligibility requirements  

To be eligible, products shall:

  • Utilise waste or excess steam source from a process (i.e. steam is not produced for the primary purpose of power generation).
  • Use wet or saturated steam at the inlet (i.e. not superheated steam).
  • Be designed to use water or steam as the thermal working fluid (i.e. product shall not use any thermal working fluid applicable to Organic Rankine Cycle).
  • Not be part of a Good Quality CHP scheme, under CHPQA.
  • Not exceed 700kWe power output at standard conditions.
  • Be designed to provide three-phase electricity output.
  • Not incorporate any form of combustion equipment, including boost burners.
  • Be designed and include fittings for permanent installation.
  • Have an appropriate Conformity Assessment mark.

1.3.2    Performance requirements 

Eligible products shall meet or exceed minimum overall efficiencies as set out in Table 1.1. Minimum efficiencies shall be achieved across the specified range of inlet and outlet pressures. Eligible products shall also achieve a net electrical efficiency of at least 4.5%.

Table 1.1    Overall efficiency thresholds for saturated steam to electricity conversion equipment 


1.4    Measurement and calculations

1.4.1    Performance metrics

The Overall Efficiency is defined as:


The Net Electrical Efficiency shall meet or exceed 4.5% and is defined as follows:


Net electrical output is defined as the electrical output minus any electrical input into the product. Actual enthalpy drop is defined as the change in the inlet enthalpy of the steam entering the product minus the outlet enthalpy of the steam. The inlet mass flow rate is the flowrate of the steam as it enters the product.

1.4.2    Measurement Standards and Test Requirements

The required minimum performance shall be determined using Methods A or B, as set in and below.    Method A - Direct measurement

Under this test method, product performance shall be demonstrated by calculating the overall efficiency from measurements of net electrical output, actual enthalpy drop and inlet mass flow rate. Overall efficiencies shall meet or exceed the threshold minimum efficiencies as set out in Table 1.1.

Products can either be tested in an accredited laboratory, or performance may be determined from measurements made during field trials or acceptance tests, provided that the measurements have been made by, or witnessed by, an accredited laboratory or contractor that is accredited to make those measurements. The product’s overall efficiency shall be calculated by an independent body that is competent to verify the measurement data.

The assessment shall be done in accordance with the procedures set out in:

  • EN 306:1997  -   “Heat exchangers – Methods of measuring the parameters necessary for establishing the performance”; or
  • BS EN 60953-2:1996  -  “Rules for steam turbine thermal acceptance tests, Part 2: Method B: Wide range of accuracy for various types and sizes of turbines”

The assessment of electrical output and electrical input shall be done in accordance with the relevant procedures set out in: 

  • BS ISO 8528-6:2005  -  “Reciprocating internal combustion engine driven alternating current generating sets – Test methods”.    Method B - Validated design calculations

Under this test method, product performance shall be demonstrated by calculating overall efficiency and net electrical efficiency from design calculations. The accuracy of these calculations shall be verified by an independent accredited laboratory.

The product shall not exceed the threshold electrical power output of 700kWe at standard conditions.

The test report shall include (or be accompanied by):

a)    Manufacturer’s design data for the product
b)    Details of the methodology (including any standards used) and calculations verified by the independent accredited laboratory, used to determine product performance
c)    A copy of the published performance data for the product

1.5    Verification for ETL Listing 

Any of the following testing routes may be used to demonstrate the conformity of products against the requirements:

  • In-house testing – Self-tested and verified or cross-checked by an independent body
  • Witnessed testing
  • Independent testing
  • Acceptance Tests or Field Trials (must be witnessed by an independent body)

Further information regarding the routes can be found in Guidance Note 5 on the ETL product testing framework1

1.6    Conformity testing

Products listed on the ETL may be subject to the scheme’s conformity testing programme in order to ensure listed models continue to meet the ETL requirements.