Earth Notes: 16WW Energy Systems Diagrams

Updated 2026-09-09.

Energy subsystem diagrams including microgeneration and storage at 16WW. #energy #microgen #storage

A central location for schematics of current (and former) energy systems at EOU Towers.

Not in this page:

Data collected by these systems: see the energy series dataset.
Devices run off these systems, eg see: On Setting Up a Raspberry Pi 3 Off-grid Server.

Note that extensive logging and processing of real-time and historic data from all energy subsystems is performed on Raspberry Pis.

Some current energy system settings are made available automatically.

Overview of Grid-connected Heat Systems

One of the biggest consumers of energy at 16WW is heat, both space heat and DHW (Domestic Hot Water).

This is view of subsystems that help achieve Net Zero while supporting heat provision amongst other services.

202608 grid connected — Outline schematic of all grid-connected (heat-related) systems at 16WW in 2026. These collectively and separately provide demand response services to reduce carbon emissions and grid strain.

Grid-tie Solar PV System

Summary: current capacity ~5kWp(e) (Sanyo HIT) PV, ~4.5kWp(e) (SMA SunnyBoy 1100/1200) G83 inverters, AC-coupled, half east-facing, half west-facing, slope ~23° in each case.

Read more on the (first round of the) installation.

The electrical schematic (circuit diagram) for first 1.29kWp (2008).

The electrical schematic (circuit diagram) at expansion to 3.87kWp (2009).

The electrical schematic (circuit diagram) at expansion to 5.16kWp (2010).

20100415 3rd round schematic 5p16kWp excerpt — Solar PV 5.16kWp generation system as of 2010-04-15.

As of 2025-05-19 since 2018 Enphase monitoring reports 25.2MWh generated, 7.7MWh imported, 13.3MWh exported, 18.3MWh consumed, so grid dependence 42%.

Note that although the DNO did not require limiting to 16A (~3.7kWh), the split east- and west- facing arrangement means that output is rarely above. During 1136549 minutes (~18942h) of monitored non-zero generation from 2020-08-15 to 2025-05-19 inclusive, about 3794 minutes (63h, 0.3%) have been above 3700W. About 20 minutes (all near solar noon) have been at or above 4.5kW (~20A), with a maximum of 4567W at 2023-06-05T11:57Z.

See the 'merit order' of grid-tied PV generation use.

Enphase Storage System

Summary: current capacity ~6kWh(e)/~1.3kW(e), AC-coupled.

Read about the Enphase AC Battery Grid-connected Storage in Our UK Home (2018-08-06) then Enphase AC Battery #2 (2021-09-15) then #3 and #4 (2021-11-01) and Enphase AC Battery #5 (2025-04-17).

Enphase Energy Storage Diagram — Generic Enphase (UK) installation schematic, courtesy of Enphase via Eco Partners. Note that 16WW for example has two separate PV subsystems with their own meters for separate Feed-in-Tariffs; the Enphase solar monitoring clamp fits on after the circuits merge after the meters to be able to measure aggregate generation. As of the end of 2021, 4x AC Batteries to ~1kW/5kWh are installed on the storage branch.

See also PDF original, courtesy of Enphase via Eco Partners.

As of 2025-05-19 since 2018 Enphase monitoring reports 3.5MWh discharged and 4.5MWh 'charged' (so ~78% round-trip efficiency).

Heat-pump, Eddi PV Diverter and Thermino Heat Battery

Summary: Thermino 150ePV (MPN SKP-BAW-ATZ-1) capacity ~7kWh(h) down to 50°C, ~10kWh(h) total to cold ~10°C, heat pump Secon 180l (MPN TRSMVH-0180SFC) DHW cylinder capacity likely ~6kWh, 3kW(e) peak charge rate via myenergi Eddi (MPN MYEN-EDDI-16A1P01).

See the heat pump configuration.

Note that the demands on the heat pump for DHW and space heat are reduced by the low-flow shower head, internal wall insulation, smart TRVs and the MHRV.

20250121 plumbing schematic hand drawn on whiteboard — Plumbing schematic hand-drawn by engineer (thank you!) TRV = temperature relief valve, PRV = pressure relief value, CYL = DHW cylinder, vertical dotted black line is the corner at back right of cupboard, ABY = automatic bypass, AAV is automatic air valve, C (black) and H (red) are cold from mains and hot to taps (DHW), green is radiator loop cold/return side and red is warm/flow, Rad F and Rad R are radiator flow and return to upstairs, Ra F and Ra R are radiator flow and return downstairs, Pri F and Pri R are primary flow and return from external unit, Volu is volumiser, Exp V is expansion vessel, Mag Filter is the magnetic debris filter in the radiator circuit. Click to expand image.

20250121 radiator circuit isolator valve 1 at back of cupboard — Images in order (click to expand): (1) first radiator circuit isolator valve (back); (2) second radiator circuit isolator valve (right).

20250121 radiator circuit isolator valve 2 at right of cupboard — Images in order (click to expand): (1) first radiator circuit isolator valve (back); (2) second radiator circuit isolator valve (right).

DHW schematic v3 — Heat-pump and heat-battery integration (v3). The thin pipes are the vanilla heat-pump only DHW system before the heat battery is re-integrated. X is a closed valve, O is an open valve. I1 is the immersion heater driven from the Eddi output 1 (connected as of 2024-11-27), I2 from Eddi output 2, and HP is the heat input coil from the heat pump. Non-return valves, expansion vessels, etc, omitted for simplicity. As of 2024-11-28 the Thermino/Intasol is not reconnected.

20250226 Thermino pipework landscape DM — Thermino 150ePV heat battery DHW pipework schematic (by DM 2025-02-26). Bottom left box is the Thermino. Tall DHW cylinder on the right. Mini expansion vessel (and pressure relief valve, not shown) top middle. Intasol in the middle half-way up. See original PDF. Also see the Thermino and heat pump systems diagrams.

The Eddi has an external current clamp deployed at our meter tails to measure total flow in and out of the building, connected to CT1 terminals. As of 2024-09-27 the CT2 clamp is on the heat pump supply.

Read more on the Thermino heat battery installation including the older DHW system schematic.

See the Eddi Solar PV Diverter Top-up Dataset.

Note that the Eddi and Thermino are partly managed remotely as of 2022-08 to 2024-11 via Raspberry Pis to:

Provide overnight boost to the Thermino when grid intensity is low.
Pause diversion/boost in any minute when grid frequency is low.

As of 2025-11 the Eddi controls the DHW cylinder immersion heater to perform pasteurisation cycles.

2025-02-21: see Reconnecting the Heat Battery.

Off-grid Solar PV System

Summary: current capacity ~1kWh(e) usable, ~0.7kWp(e) PV, DC-coupled.

20260829 T8 — Off-grid PV system as of 2026-08-29. The `LS2024RP` (`U2`) solar controller is PWM (Pulse Width Modulating) and has as input a heterogeneous parallel mix of nominal 12V panels though with varying Vmpp and orientations. `U1` is a more sophisticated MPPT (Maximum Power Point Tracking) solar controller and its primary array provides the bulk of generation (`geno`) to the system, though nominally with less than half the panel power. `U1` is monitored over serial `MODBUS` by the server. The `Load` output from `U1` is used for the server, laptop, etc (`cono`). The direct output from the battery is also brought to the house and is used for AA battery charging and similar intermittent bulk loads, and is unmonitored. [As PDF]

Off-grid system notes:

The top set of panels (PWM) is 2Wp (amorphous) + 40Wp (amorphous) + 60Wp (multijunction) on the west of the house, 2x20Wp (amorphous) + 100Wp on the east, via blocking diodes where not built-in.
The RPi2 is powered via an efficient hard-wired car USB adaptor (previously a stand-alone switching regulator), stepping the 12V down to 5V, with short leads to help handle demand spikes.
2021-09-03: the battery was replaced with a 220Ah Victron.

Note that the Internet router is powered from the mains via a (12V) adaptor, which also has a 5V USB output. The adaptor also has a 12V-nominal input from the off-grid system, but preferentially uses 240V mains. When the off-grid system is in a good state, a 'dump' signal from the RPi disconnects mains from the adaptor with a relay, forcing the adaptor to draw from off-grid and act as a dump load. Thus the off-grid system acts as a huge UPS for the router too. The adaptor has at times driven more/other loads than the router. All recent 16WW routers have been 12V supply at ~1A; far more power-hungry than my MacBook Air as of 2023.

See Expanding and Optimising Off-grid PV for Mid-winter.