Maybe it would be possible to bin the 15min electricity price data in hourly averages or two hour averages to extend the work time of HP? This is something that electricity providers still do in the transition period, when the actual 15 min periods are combined in hourly averages to calculate the final electricity price in the energy bills. The option could be to combine average prices in one, two, etc. hourly blocks and the end user could chose how many of these blocks the HP should be off or at lower operational power.