Does a weather-dependent heat-pump COP change the sand-store versus heat-pump verdict?

What it found

The earlier cost comparisons charge the air-source heat pump a flat November–March price divided by one table COP of 3.6. Here the pump's electricity cost is the heat-weighted mean of price / COP(T) over every hour, with hourly temperatures from the ERA5 reanalysis (five German cities, population-weighted, 2015–2019) and the Staffell et al. (2012) COP fit used by when2heat and PyPSA-Eur. The table's 3.6 is what a 35 °C floor-heating sink gives (seasonal COP 3.52–3.67); a 45 °C sink gives 2.79–2.91 and a 55 °C radiator sink 2.18–2.28. The store's weekly-cycling flip multiplier rises from 1.16/1.20/1.20/0.59/1.02 (table) to 1.25/1.29/1.33/0.71/1.15 at 45 °C and 1.37/1.40/1.48/0.86/1.30 at 55 °C, so a realistic COP widens the store's margin in four years but 2018 still favours the pump. Daily cycling stays robust (flip 2.4–4.1×). The heating base temperature (12–18 °C) moves the flip by at most 0.06. Inputs not from a source: the 15 °C base, city weights and the sink temperatures, which are swept; the COP fit is a published regression, not a measurement of a specific unit.

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More in Energy supply and dense energy storage

• How far must capital costs move to flip the sand-store versus heat-pump verdict, and is that more than the price year moves it?How far must capex move to flip the sand-store vs heat-pump verdict? Weekly cycling flips on a 2 to 40% store-capex change (the cost table's own vintage step is 26%); daily cycling holds to 2 to 3.5 times.
• How much can the sand store's heat exchanger cost before a heat pump wins again?How much can the sand store's heat exchanger cost? Weekly cycling survives about 120 to 270 EUR per kW in four of five price years; daily cycling survives 460 to 900; 2018 never wins.
• Does the sand-store versus heat-pump verdict survive a modelled electricity price instead of the real one?Does the sand-store vs heat-pump verdict survive a modelled price? Mostly: 32 of 40 cells agree with real prices (21 for the flat merit-order price), but weekly cycling, whose margin is under EUR 0.011/kWh, is wrong in sign in 5 of 5 years; as a charge scheduler the model costs under EUR 0.0011/kWh.
• How much cheaper must a store's electricity be than a heat pump's for a sand heat store to deliver heat for less?How much cheaper must electricity be for a sand heat store to beat a heat pump? Sourced costs (PyPSA technology-data) on the energy-thermal model: a daily-cycled store needs the pump's electricity about 2 times dearer, weekly 5, monthly 16, seasonal 120 (house); the heat lost in standby, not the sand, rules out seasonal storage.
• If a sand heat store buys electricity only in the cheap hours of a German price series, when does it beat a heat pump?When does a sand heat store beat a heat pump on hourly prices? With 189 GW solar and 137 GW wind and a modelled German price series, a daily or weekly store wins in all 5 years (EUR 0.027/kWh against 0.071); a levy of 0.10/kWh or a surplus-hour price above about 20–35 EUR/MWh removes the win.
• On real German day-ahead prices, does a sand heat store beat a heat pump, and was the modelled price right?On real German day-ahead prices, does a sand heat store beat a heat pump? Yes at wholesale: daily cycling wins in all 5 years (EUR 0.045–0.062/kWh against 0.070–0.074) and weekly in 4; the earlier merit-order model was flat at EUR 54.6/MWh and wrong; a EUR 0.10/kWh levy removes the win.

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Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.