Primary Energy, Efficiency & More...
The aim of this calculator is to perform some very simple calculations in particular around primary energy and efficiency; but also including capacity factor and some simple economic outcomes (costs & revenues).
There are two columns side-by-side.
The one on the left is relevant to a thermal, fuelled power plant - for example gas power generation. The one on the right represents a solar farm, so no primary fuel costs but with the primary energy resource dependent on climate. You can change the names if you wish!
In both cases, inputs are in green and calculated figures in yellow. Pressing "reset" at the bottom will return the calculator to its initial input values.
Common to both are:
1.  An energy output target which, in combination with the various energy resource and efficiency inputs, is used to calculate the required primary energy requirements (how much fuel or - for solar - what size area needed to collect sufficient sunlight).
2.  A $-per-Watt investment cost for the power plant and a conversion efficiency (fuel-to-power or solar-energy-to-power)
3.  An electricity price (multiplied by the target energy output to give revenue). Note that a 1-year period is assumed throughout; i.e. for the energy output, revenue, capacity factor and so on.
4.  Required plant capacity (MW) to meet the energy output target is calculated using the capacity factor (see below!).
The key differences are:
1.  For the fuelled plant on the left, a cost of fuel is input. The input units are $/MMBtu, with a conversion to $/MWh calculated and shown. Of course you could use the calculator for something like a coal or biomass plant, where fuel is more typically quoted in $/ton, by converting that into $/MMBtu. You'd need to know the energy density (how many MMBtu per ton) in order to do that.
2.  For the fuelled plant, capacity factor is an input value - it will depend how often the plant chooses to operate based on its operational flexibility and economics (whether it prefers only to operate at peak times when they price of electricity is high, for example).
3.  By contrast, for the solar plant, capacity factor is not a choice but is limited by the available solar resource, which is an input. The input units here are in energy terms: kWh per square metre per year, referring to the amount of solar energy falling on a square metre of the solar collectors (i.e. panels/modules), taking into account any tracking or optimum positioning they may have. For reference, this is also expressed in average power terms for the year (W per square metre).
4.  Capacity factors for solar are sometimes quoted based on capacity figures in DC (direct current) terms, in other words by adding up the power ratings of all the installed modules. Since the maximum DC output of solar modules is measured against a standardised 1000 W/m2 maximum solar input, you could calculate maximum potential capacity factor here by dividing the actual average solar input by this number. However for an apples-to-apples comparison with other power sources it's always better to express solar farm capacity in AC terms, after DC-to-AC conversion and various other plant losses. The assumption here is that our solar farm's AC output is 85% of that in DC (module) terms. When reading about solar power, you may hear this referred to as a "performance ratio".
5.  For the fuelled plant, lower efficiency will mean more fuel is needed to achieve the target energy output, so fuel costs will rise. For the solar farm, lower efficiency will mean a larger area of solar collectors is needed to gather enough primary solar energy to generate the target energy output. They aren't included here, but in practice this would likely result in higher land lease and maintenance costs, such as panel cleaning. Note that in either case, efficiency does not change the capacity required to meet the target energy output! It just changes the energy input required (fuel or land). It is capacity factor that relates capacity to energy output.
6.  At the bottom of both columns is calculated a simplistic capital investment / annual revenue ratio; to give a very (!) simple measure of how quickly energy sales will pay back the plant cost. In the fuelled plant case, fuel costs are naturally deducted from revenues before calculating this ratio.
Electricity Out Target/requirement (MWh)
Energy Resource Primary Fuel Cost ($/MMBtu)  
Primary Fuel Cost ($/MWh)  
Solar resource (kWh/m2/yr)  
Solar resource (Av. W/m2)  
Power Plant Investment cost ($/W)
Conversion efficiency
Capacity Factor (annual)
Energy Input Primary Fuel required  
Solar energy collection required (MWh)  
Solar collector area (m2)  
Capacity Required (MW)
Sales & Costs Electricity Price ($/MWh)
Electricity Revenue (annual)
Investment required (m$)
Primary Fuel cost (annual)  
Fuel cost as % of annual revenue  
Simple investment/(sales-fuel) ratio