Source
https://www.energytrust.org/wp-content/uploads/2017/11/Water_Heater_Energy_Storage_wStaffResponse.pdf — original source (opens in a new tab; the file is not redistributed)
Summary
A first-level technical “paper study” by Flink Energy Consulting (Ken Dragoon) for Energy Trust of Oregon, assessing whether electric water heaters can serve as grid energy storage / load-control. It finds that the existing fleet of electric water heaters is a very large, low-cost thermal-storage and demand-response resource — a typical tank already stores several kWh and could be controlled to shift load — but warns that adding storage by running tanks hotter increases standby losses and on-site energy use, so the grid captures the benefit while the household bears the extra consumption. It is US-context and order-of-magnitude (no lab work). For Neobiome Intelligence it is the international technical case for treating hot-water cylinders as cheap thermal storage — the resource NZ already exploits through ripple control — rather than a NZ cost source.
Key claims
- claim: "The study (Flink Energy Consulting / Ken Dragoon, June 2017, commissioned by Energy Trust of Oregon) is a first-level 'paper study' — order-of-magnitude, no lab work — assessing the grid energy-storage and load-control potential of electric water heaters, in the context of Oregon investor-owned utilities (Portland General Electric, Pacific Power) considering controlling water-heater operating hours to reduce peak loads."
source_location: "Introduction; Staff memo (6 Oct 2017)"
- claim: "A typical 50-gallon (~190 L) electric resistance water heater stores about 6 kWh of heat energy at a 4.5 kW power rating; water heaters have demonstrated 1–20 kWh of storage capability; a typical 50-gallon tank can provide about 73% of the 8.3 kWh average daily hot-water demand (it stored ~50% of daily usage in 1990)."
source_location: "§1 Overview (p.~5–6)"
- claim: "Water-heater thermal storage is potentially far cheaper than batteries: the report cites a 2015 installed lithium-ion cost of just over US$700/kWh for comparison, suggesting the cost of accessing water-heater storage could be much lower."
source_location: "§1 Overview (Handmer 2015 comparison)"
- claim: "Scale: there are roughly 39–50 million electric water heaters in US homes (about 39% of ~100 million residential water heaters) — a large aggregate demand-response/storage resource; average per-heater consumption fell from 4,700 kWh (1990) to 3,000 kWh (2012)."
source_location: "§1 Overview"
- claim: "Key trade-off: using water heaters for grid storage — especially by raising tank temperature to store more energy — increases thermal standby losses and on-site energy consumption; the benefits largely accrue to utilities/grid operators while the household bears the increased at-site consumption. Control strategies that do not change tank temperature avoid this penalty."
source_location: "§1 Summary of Findings; §2 Standby Energy Losses"
- claim: "Heat-pump water heaters deliver substantially more heat per kWh of electrical input than resistance heaters, but as a result have lower electrical storage capacity per gallon (less electrical energy is involved) — a complication for using them as grid storage."
source_location: "§4 Heat Pump Water Heaters for Energy Storage"Neobiome Intelligence relevance
- D01 — hot-water cylinders as cheap thermal storage / demand response. Electric hot-water cylinders are a large, very low-cost thermal-storage resource (potentially far below Li-ion $/kWh) already present in most homes — a ~190 L cylinder ≈ ~6 kWh storage / ~73% of daily DHW. This is the international technical basis for the NZ ripple-control practice the wiki already notes (OT_041: ripple control sheds ~15% of NZ peak, ~half of households) and complements
battery_lfpin the model as a “free” pre-installed storage asset OT_052. - ⚠ It is load-shifting, not net storage. The value is shifting when water is heated (e.g. heat with daytime PV surplus) — not adding storage by overheating tanks, which raises standby losses and on-site consumption. For a self-sufficient community the win is PV self-consumption via a hot-water diverter/timer at normal temperature, corroborating the solar-direct-PV water-heating case (solar_direct_pv_water_heating) OT_052.
- Corroborates LIT_006. The 6 kWh / ~73%-of-8.3-kWh figures match the thermal-storage figures in LIT_006 OT_052.
- ⚠ Scope: US-context, order-of-magnitude paper study; not a NZ tank-CAPEX source (that gap stays RT_003).
Research targets
Research gaps
- NZ hot-water-cylinder CAPEX (300–800 L) — not covered by this source; tracked as RT_003.
- NZ-specific ripple-control / PV-diverter demand-response value for hot-water cylinders (the load-shifting potential at community scale), to size cylinders as dispatchable thermal storage in the model.
Connections
Links to
Technologies (1): Solar-Direct PV Water Heating
Referenced by
Sources (1): RD_028
EDT domains (1): D01: Renewable Energy & Storage Systems