15.1 Prosumer Terms and Vehicle Storage
Key Takeaways
- Handbook v1.3 outcome 6.1.1 treats a prosumer as a premises that both consumes and produces electricity, and a Prosumer's Electrical Installation (PEI) as the BS 7671 Part 8 picture of that installation.
- An Electrical Energy Management System (EEMS) coordinates generation, storage, loads and grid or supplier signals; it is not another name for the electrical energy storage system (EESS) battery stack.
- Island-mode is designed backup with a changeover that isolates backup circuits from the public network before they are energised; it is not accidental islanding of a dead street.
- Arbitrage is buy or store when energy is cheap and use or export when it is expensive; self-consumption is using PV on site rather than exporting; time shifting is store now, use later.
- V2G is Vehicle to Grid, V2H is Vehicle to Home, and V2X is the generic vehicle-as-storage label; a bidirectional charger's AC rating counts toward the 16 A generation test.
Quick Answer: Handbook v1.3 Learning Outcome 6.1.1 wants a short set of prosumer words used correctly. A prosumer both consumes and produces electricity. A Prosumer's Electrical Installation (PEI) is the BS 7671 Part 8 idea of that installation as a whole — loads, local generation, storage and the grid interface together — not a battery-cabinet brand. An Electrical Energy Management System (EEMS) is the controller that coordinates those parts. Island-mode is designed backup with changeover, not accidental islanding of a dead street. Arbitrage means buy or store when energy is cheap and use or export when it is expensive. Self-consumption means using photovoltaic (PV) generation on site rather than exporting it. Time shifting means store now, use later. Vehicle storage uses V2G (Vehicle to Grid), V2H (Vehicle to Home) and V2X as the generic vehicle-as-storage label. This OpenExamPrep section is independent study material for City & Guilds 2922-34; it is not a City & Guilds publication.
Why a PV award still examines prosumer language
Unit 301 only sets three questions (10 percent) on Learning Outcome 6. That is a small slice of the paper, not a licence to skim. LO6 is how the handbook joins the PV generator you have been designing to storage, electric vehicles used as batteries, export limits, and the fact that the dwelling is no longer a one-way consumer. The neighbouring award 2923-34 is the dedicated small electrical energy storage systems (EESS) qualification. 2922-34 still examines these LO6 ideas on the PV knowledge test. Do not skip this chapter because batteries belong on the other course.
Independent OpenExamPrep teaching uses handbook v1.3 together with BS 7671 Part 8 and the Energy Networks Association (ENA) connection recommendations already taught under design. OpenExamPrep is not a City & Guilds, IET, MCS or ENA partner and does not set wiring or connection policy.
Prosumer and the PEI
A consumer only takes energy from the public supply. A producer only sends energy out. A prosumer does both in the same premises: lights, heat pumps and kettles still import; PV, a battery inverter or a bidirectional vehicle charger can generate or export. The word is about roles at the installation, not about a tariff brand.
Prosumer's Electrical Installations (PEIs) take that idea into BS 7671 Part 8. Part 8 treats the electrical installation as a system that can consume and produce, including local generation, electrical energy storage, controllable loads and a connection to the public network. The PEI is the installation, not a sticker on the inverter. It includes the consumer unit, the PV inverter, any battery conversion equipment, any island-mode changeover, and the point of connection the Distribution Network Operator (DNO) or Distribution System Operator (DSO) sees.
Exam traps: calling the PEI the battery cabinet; calling it the smart meter; calling it MCS registration. Those are components or schemes inside or beside a PEI. Part 8 is the wiring-regulations picture of an installation that is no longer one-directional.
EEMS is the coordinator, not the store
An Electrical Energy Management System (EEMS) decides when generation, storage and loads run, within the limits you are allowed to present at the connection. It is the brain. The EESS is the store — battery modules, a battery management system, conversion. A hybrid inverter may embed EEMS functions; a separate controller and meters may do the same job. The 2922 point is the role: import and export against set-points, charge and discharge decisions, smart-grid or supplier signals, and island-mode switching when that function is designed in.
If there is no EEMS, a simple string inverter still converts DC to AC and still has anti-islanding. It does not automatically arbitrage a half-hourly tariff or soak surplus into a vehicle.
Island-mode is designed backup — not accidental islanding
Accidental islanding is the safety failure already taught with inverter functions: the public feeder is dead, but a generator keeps it live. Loss-of-mains / anti-islanding must stop that.
Island-mode operation is the opposite design intent: a planned backup. A changeover (automatic or manual, to the product and BS 7671) isolates backup circuits from the public network before the inverter or vehicle supply energises them. The fridge on a backup board may live. The street must not. Island-mode is not the hybrid staying in parallel and hoping. It is not a G98 reconnection timer. It is not a brochure word that authorises backfeed.
Arbitrage, self-consumption and time shifting
These three get mixed on sales slides. Keep them as separate 6.1.1 terms.
Self-consumption means using PV on site rather than exporting it. Lunchtime washing while the array is producing is self-consumption. Charging a battery from the array so the house uses that energy after sunset is self-consumption achieved by storage. Exporting surplus and buying it back later is not self-consumption; it is using the network as a buffer.
Time shifting is the physical move: store now, use later. The energy might be midday PV, or cheap-rate grid energy stored in a battery or vehicle. Time shifting is how you move kilowatt-hours through time. It does not by itself say whether you are avoiding export, avoiding a peak import rate, or preparing a later export.
Arbitrage is the price strategy: buy or store when energy is cheap, use or export when it is expensive. Overnight cheap-rate charging of a battery, then running the house at the evening peak instead of importing, is arbitrage. Holding battery energy to export when an outgoing tariff spikes is also arbitrage. Arbitrage can use PV or grid energy. It is not a synonym for having a battery.
A competent 2922 answer can stack them: the EEMS time-shifts midday PV into the evening (self-consumption) and may also arbitrage a cheap overnight window, without breaking the DNO export cap.
V2G, V2H and V2X
A vehicle battery is storage on wheels if the charger is bidirectional.
- V2G — Vehicle to Grid: the vehicle can discharge to the public network (or provide grid-support services through that connection). That discharge is generation at the point of connection.
- V2H — Vehicle to Home: the vehicle can supply the dwelling. That may be grid-parallel (offsetting import) or, if designed, island-mode backup. V2H is not automatically a licence to export, and it is not a one-way 7 kW charge point.
- V2X: the generic label for the vehicle as storage — V2G, V2H and related building-supply patterns under one umbrella. If the paper says V2X, do not invent a fourth physics; say the vehicle is being used as a store.
A unidirectional EV charger is a load. It does not add to aggregated generation under G98/G99. A bidirectional V2H/V2G unit does, because discharging presents AC generation. The AC rating of that conversion path counts toward the 16 A per phase generation test, together with PV and any battery inverter.
Term versus 2922 meaning versus trap
| Term | 2922 meaning | Trap |
|---|---|---|
| Prosumer | Premises that both consume and produce electricity | Thinking it is only a supplier brand or an old feed-in tariff name |
| PEI | BS 7671 Part 8 installation that consumes and produces, including generation, storage, loads and the grid interface | Calling the PEI the battery box, the app, or the MCS certificate |
| EEMS | Controller that coordinates generation, storage, loads and grid or supplier signals | Treating EEMS as another name for the EESS battery stack |
| Island-mode | Designed backup with changeover so backup circuits are isolated from the public network before they are energised | Accidental islanding, or backup that keeps a dead street live |
| Arbitrage | Buy or store cheap, use or export expensive | Any battery movement, even at a flat tariff |
| Self-consumption | Use PV on site rather than export it | Exporting kWh and buying them back, then calling that self-use |
| Time shifting | Store now, use later | Assuming time shift only applies to PV, or that it always means export |
| V2G | Vehicle discharges to the grid or provides grid services | A one-way charge point |
| V2H | Vehicle supplies the home | A marketing sticker that skips G99 and changeover |
| V2X | Generic vehicle-as-storage umbrella | A separate inverter family on the LO3 type list |
Scenario: EV charger marketed as V2H on a G98 house
A house already has a fully type-tested PV inverter at 3.68 kW (16 A on 230 V single-phase), notified under G98. A salesperson offers a wall unit marketed as V2H. The datasheet shows 7 kW bidirectional conversion: it can charge the car and discharge into the house.
Walk the conversation in this order.
- Name the function. If the unit can discharge, it is vehicle storage (V2H, and V2X as the generic). If it can export through the meter to the feeder, it is also V2G. A one-way charger is not V2H just because the brochure used the letters.
- Count generation. 7 kW / 230 V ≈ 30 A. That conversion path alone is above 16 A per phase. It is not a G98 accessory. Add the existing 3.68 kW PV and aggregated AC generation is about 10.7 kW. G99 applies. Permission is required before you connect the bidirectional unit. G100 sits on top if the DNO caps export.
- Do not hide behind it only being V2H, not V2G. Supplying the home in parallel still presents generation at the installation. Island-mode V2H still needs a changeover so a power cut does not backfeed the street. Anti-islanding on the PV inverter does not turn an unisolated 7 kW vehicle inverter into a legal backup.
- Honest options: a unidirectional charger (a load) if the customer only wanted charging; a bidirectional product only after a G99 (and G100 if required) assessment; island-mode only with a designed changeover and manufacturer backup instructions.
The 2922 skill is to refuse a marketing name as a connection route. V2H on a G98 house is a generation and PEI problem, not a weekend add-on.
Which statement matches handbook outcome 6.1.1 and BS 7671 Part 8 on a Prosumer's Electrical Installation?
How should a 2922-34 candidate separate island-mode operation from accidental islanding?
A G98 house with a 3.68 kW PV inverter is offered a 7 kW wall unit marketed as V2H that can discharge into the house. What is the honest 6.1.1 reading?