Amortization Period

The period required to get to the point when the capital value of the investment first becomes positive. Amortization periods greater than 40 years are not calculated in the program.

Annual Heating Requirement

The total amount of energy that is required over the year for space heating.
Annual Price Increase Rates
The annual percentage increase in prices compared to the previous year.


A series of equal payments, taking into account the life span and interest rate.

Anti-Legionnaire’s Switch

For systems with the anti-legionnaire’s switch facility the DHW tank is loaded in adjustable intervals.

Auxiliary Heating

Auxiliary heating ensures that, even when there is not enough irradiation, the desired tank temperature is reached and, for systems with space heating, also supplies the heating loop. Auxiliary heating usually refers to the boiler.

Azimuth Angle

See Orientation.

Boiler Efficiency

The boiler efficiency describes the relationship between the primary energy used (relating to the calorific value of the fuel used) and the net energy produced.

Cash Value

The capitalised payments at the time point at the start of the assessment period. A cash value is positive if it represents an income and negative when the amount represents a cost. Investments, subsidies, savings and running costs are calculated.

Circulation, (secondary)

(Secondary) circulation can be used for hot water preparation. This increases comfort (hot water is available straight away even with long piping systems), but it is also coupled with losses.

CO2 Emissions

The CO2 emissions avoided by the use of the solar system are calculated. In addition, emissions factors are used, according to the (savings on) fuels used. See also Fuel Savings.

Collector Array

In T*SOL ®, the collector array consists of the collectors and the piping.
Collector Loop Connection
In T*SOL ®, the collector loop connection represents the connection between the collector array and the storage tank.

Collector Loop Efficiency

Quotient of the energy emitted from the collector loop and the energy irradiated onto the collector area (active solar surface).


Control parameters can be set for different components. For storage tanks, for example, desired temperatures, switching temperatures, etc.

Conversion Factor

The conversion factor indicates the amount of absorption when the irradiation is vertical to the collector surface, when the collector temperature is equal to the ambient temperature.

Cost of Solar Energy

The cost of solar energy is calculated by dividing the solar energy produced in a year by the annual cost of capital investment (less subsidy) plus annual running and service costs (taking account of life span and capital interest).


See Cash Value and Cost of Solar Energy.

Daily Consumption

The average daily DHW consumption. This is usually around 35-45 liters per person per day at a water temperature of 50°C.

Desired Temperature

The minimum temperature of DHW. If the desired temperature in the upper layer of the tank is not reached, the auxiliary heating is switched on.


Abbreviation for domestic hot water.

DHW Requirement

See Daily Consumption.


The collector loop efficiency and the system efficiency are calculated.

Emissions Calculation

See CO2 Emissions.

Energy, generated by the solar system

Comprises of energy transferred to the standby tank from the solar tank, due to consumption and any existing return circulation control in the solar tank.

Energy, released or generated

Released or generated energy is that which is transferred from one component (collector loop, storage tank, etc.) to another.

Energy, supplied or conveyed

Energy supplied to a component, e.g. irradiation, heat transfer at the heat exchanger or heat transfer by mass flow due to consumption or circulation.

Fuel Consumption

The calculation of fuel use is based on the energy transferred to the auxiliary heating heat exchanger, with the heat equivalent and the auxiliary heating efficiency, according to the type of fuel (natural gas, oil, wood pellets, district heating).

Fuel Price

The price for the primary energy selected which is valid at the time of the calculation. The currency used in the program for this entry is dependent on the country settings on your computer (e.g. in Windows under Start/Settings/System Control/Country Settings).

Fuel Savings

The available solar energy is converted, using the respective auxiliary heating efficiency, to give the corresponding primary energy equivalent.

Gross Surface Area

The gross surface area is calculated from the external measurements of the collector. However, the specific collector characteristics are not usually taken from the gross surface area, but from the active solar surface, which is taken from the test report provided by a testing center.

Heat Flow Requirement

See Standard Building Heat Flow Requirement.

Heat Gains

The window area related to the gross floor area and the type of window are entered in the Heat Gains worksheet so that solar heat gains can be calculated. In addition, the Internal heat gains (e.g. heat produced by electrical appliances) should be entered.
Heat gains comprise of the solar heat gains (dependent on the window area and type of window) and the internal heat gains (e.g. produced by electrical appliances).

Heat Requirement

See Standard Building Heat Flow Requirement.

Heating Loop

Two space heating loops can be defined in T*SOL via the flow and return temperatures – a high temperature (HT) heating loop (for radiators) and a low temperature (LT) heating loop (for under floor heating).

Heating Temperature Limit

If the outside temperature falls below the heating temperature limit, the heating is switched on.

Incident Angle Modifier

The additional reflection losses that occur when the sun is not vertical to the collector surface are expressed by the incident angle modifier.

Inclination (Tilt Angle)

Describes the angle between the horizontal and the collector surface. It is 0° if the collectors are flat on the ground and 90° if they are vertical.


For the collector array installation you need to enter parameters for the inclination (tilt angle) and orientation (azimuth angle). The radiation processor uses these two parameters to calculate the irradiation onto the tilted surface.

Interest on Capital

This is the interest on capital borrowed from the bank for the investment or the interest that could otherwise be gained on the capital used.


Investment costs relate to the system costs, less any subsidies kA Value
The product of the thermal transmittance coefficient and heat exchanger area. The value equals the quotients of transferred power and mean logarithmic temperature difference at the heat exchanger.

Life Span

This is the period given by the manufacturer as the expected life of the system in years. For solar water heating systems this is usually set between 10 and 20 years.

Load / Load Profile

Hot water consumption dependent on time. The calculation is based on the definition of different daily, weekly and annual profiles.

Loading Time

Describes the period required for the storage tank to be loaded fully.


A part of the investment that is not covered by the (own) capital available, but is covered by arranging a credit. If the loan interest rate is higher than the capital interest rate, the credit results in extra costs.

Loan Capital

The amount of credit that is arranged.

Loan Interest

The amount of interest that has to be paid on a loan. If the loan interest rate is lower than the capital interest rate taking out a loan works like a subsidy, if the rate is higher, the total costs increase. When interest rates are equal there is no difference.
MeteoSyn Weather Generator (not available with all versions of T*SOL ®)
With MeteoSyn you can generate data for any location you like. Options/MeteoSyn menu.

Measurement Data Import

The data import function incorporates measurement values on DHW consumption, heating, and climate data for use as system simulation data. This kind of simulation can be used for qualitative comparison with the system. For example, considerably higher yield values in the simulation could indicate errors in the system.

Net Present Value

The total Cash Values for investments, subsidies, savings, running costs and loan costs (each has an appropriate sign, e.g. + or -).

Nominal Width

DIN piping widths are used to calculate the collector loop piping widths. Changes can be made by entering new values.

Operating Period

Each respective component is active during the operating period,. A component is not active during the specific time periods (hours, days or months) that have been switched off.

Orientation (Azimuth Angle)

The orientation or azimuth angle describes the angle of deviation of the collector-surface from the south in the northern hemisphere (and from the north in the southern hemisphere). It is 0° when the surface is facing due south. The azimuth is positive when facing west and negative when facing east. An orientation due west corresponds to a value of +90° and an orientation due east is -90°.


The period that has been agreed for paying back the loan.

Price Increase Rate

See annual price increase rates.

Radiation Model

The parameters for global horizontal radiation contained in the weather data are split, according to the model from Reindl, into diffuse and direct parts.

Radiation Processor

Calculates the irradiation onto the tilted surface from the inclination and orientation of the collector array.

Running Costs

The costs arising from operating the system, e.g. maintenance and electricity costs. The running costs’ cash value and annuity are calculated from the interest on capital, the price increase rate and the life span.


The simulation results include the reference fuel savings made during the simulation period due to the use of the solar system.


Investigation of the influence of the ambient environment, consumption and the different components on the operating conditions of the solar system.

Simulation Interval

Time period between two consecutive steps in the calculation. It varies, depending on the system, between 1 and 6 minutes, and is set automatically.

Simulation Period

The total period to be simulated. Simulation periods from one day to one year are possible.

Solar Fraction

The proportion of energy transmitted by the solar system to the standby tank against the total amount of energy transmitted to the standby tank (from the solar system and auxiliary heating).

Solar Tank

The solar tank is the tank or part of a tank that is loaded from the collector array.

Specific Heat Capacity

This gives the amount of heat per m² of active solar surface that the collector, including its heat medium, can store at a temperature increase of 1 Kelvin.

Standard Building Heat Flow Requirement

The heating capacity required, at standard outside temperature conditions, to maintain the room temperature of the building at the desired temperature.

Standard Outside Temperature

Design temperature for the heating capacity.

Standby Tank

A system storage tank which is used exclusively for storing DHW pre-heated to the desired temperature (e.g. System A2).


This enables the water entering the storage tank to flow directly into the tank layer of the corresponding temperature.

Swimming Pool Heating Requirement

The total amount of energy generated by the solar system and auxiliary heating for the swimming pool.

System Efficiency

Quotient of the energy generated by the solar system and the energy irradiated onto the collector surface (active solar surface).

Tank Destratification

With activated tank stratification, in the case that the upper solar tank reaches a higher temperature than the upper standby tank, destratification is carried out.

Tank Model

The stratified tank model works with variable tank layers. The number of layers is not constant, but is adapted during simulation.

Thermal Conductivity Coefficient

This gives the specific insulation losses (e.g. of piping).

Thermal Transmittance Coefficient

The thermal transmittance coefficient (heat loss coefficient) indicates the amount of heat that the collector loses to its environment per m² of active solar surface and degrees Kelvin temperature difference between the average collector temperature and the surrounding temperature.

Tilt Angle

See Inclination.

Volumetric Flow Rate

The volumetric flow rate for the collector array is given in l/h and can either be entered as an absolute figure or is related to the collector area.

Weather Data

The weather data delivered with the program (for a wide range of European and international locations) contains hourly average values for global horizontal radiation, outside temperature and wind speed.

Weather Generator

See MeteoSyn.

Yield, solar

The energy produced by the collector loop.

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