Fundamentals › Electricity demand and load profiles
Next to heat demand, the time profile of electricity demand is the second load-bearing boundary condition. It determines how much photovoltaic electricity is used on site, how high the power-to-heat ratio of a CHP unit turns out and what grid capacity has to be secured. EPOS-Plan works with hourly load profiles for this purpose.
Types of profile
For residential buildings standard load profiles scaled by annual consumption and number of occupants are usually sufficient. For commercial, office and industrial sites they are too coarse: there, operating hours, shift patterns, ventilation and refrigeration shape the profile far more strongly than the weather. EPOS-Plan therefore allows a stored profile, a profile assembled from daily and weekly patterns, or the direct import of metered load data.
Metered load data
Where quarter-hourly values from the grid operator are available they are preferable to any synthetic profile. EPOS-Plan aggregates them to hourly values and checks them for gaps, time zone offsets and daylight saving jumps. A single complete year of measurements makes the assessment of self-consumption and storage considerably more reliable, because it is precisely the midday hours that decide the success of a photovoltaic system.
Splitting demand into components
It is useful to separate base load, operating-hour dependent load and temperature dependent load. Base load runs around the clock and is only partly covered by photovoltaics. Operating-hour dependent load correlates well with solar irradiance and favours self-consumption. Temperature dependent load from refrigeration occurs in summer and likewise matches the photovoltaic yield. Recording these shares separately allows the effect of a battery storage system to be estimated far more accurately.
Additional consumers from the heat side
Heat pumps, immersion heaters, circulation pumps and charging infrastructure create additional electricity demand that need not be contained in a metered load profile if the plant is still being planned. EPOS-Plan derives this demand from the simulation and adds it to the base profile hour by hour. Only this sum forms the basis for grid purchase, load peaks and the self-consumption ratio.
Load peaks and capacity charges
For customers on special contracts the highest quarter-hourly load of the year determines the capacity charge. Heat pumps and charging points can raise this peak; storage and anticipatory management can lower it. EPOS-Plan reports the annual peak load and the time at which it occurs, so that peak shaving measures can be evaluated economically.
Practical notes
Annual electricity consumption from the utility bill should always be reconciled with the sum of the profile used. Deviations of more than five per cent indicate an incorrectly scaled or unsuitable profile. For new buildings without measurements, a sensitivity calculation with demand twenty per cent higher and lower is recommended in order to test the robustness of the design.