Solar Heat Pump and EV on Single Phase: DNO Limits

Picture a family home with an older single-phase supply. The owners add solar, then a heat pump, then an EV charger, and each installer only checks their own equipment. On a cold weekday evening the oven, an electric shower and the charger all run together and the supply fuse opens. Nothing was faulty. The loads were simply never added up. This guide shows how to add them up, and what to do when the total is too high.

Last updated: November 2026

This guide covers the engineering and regulatory decision for running solar, a heat pump and an EV charger behind one single-phase supply, mainly in the UK with notes for Germany, the Netherlands and other European markets. It gives a method for deciding when load management is enough and when a three-phase upgrade is the right call. The worked examples use assumed loads and plain arithmetic, so they are illustrations, not customer data.

In this guide:

• Single-phase service capacity in the UK, Germany and the Netherlands
• The simultaneous load problem and why monthly bills hide it
• DNO application thresholds and the G98 versus G99 split
• The three ways to build dynamic load management
• Priority logic for heat pump, EV and battery
• Three worked examples with stated assumptions
• When a three-phase upgrade is the right answer
• Export limits and the Smart Export Guarantee
• MCS notification and the Smart Charge Points Regulations

Why Single-Phase Constraints Now Dominate Residential Design

For years, residential solar was a single-load problem. The PV system was the only large new electrical item, and the existing supply was ample. That is no longer the case. Heat pumps and EV chargers can each draw several kilowatts for hours, and they often sit behind the same single-phase fuse as the solar system.

Three structural factors drive this:

• Heat pumps run for long periods in cold weather, and their peaks tend to coincide with the evening cooking and lighting load.
• A single-phase EV charger commonly runs at 7.4 kW in the UK, which is 32A at 230V. Higher ratings need more phases or a larger supply.
• A solar system above 3.68 kW on a single phase moves out of the simple notify-after route under ENA EREC G98 and into the G99 process.

The simultaneous load, not the annual kWh, is what trips a fuse. A 100A supply can deliver about 23 kVA. Three or four large loads running at once can reach that ceiling in a home that uses a modest amount of energy over the year. Modelling coincident loads at short intervals is the only way to see the risk before commissioning, and the residential load analysis guide explains how to build that profile.

Single-Phase Service Capacity: UK, Germany and the Netherlands

Supply size is set by the connection agreement with the local network operator, and it differs by country and by age of the property. The figures below are arithmetic from the rated current, not published guarantees, so always confirm the actual rating for the site.

United Kingdom

UK homes have a single-phase cut-out fuse, commonly in the 60A to 100A range. The MCS guidance on notifying DNOs sets different heat pump notification routes for a maximum demand of up to 60A and of 60A to 100A. The capacity follows from the rated current times the nominal voltage:

The kVA figure is a ceiling on the rated current. It ignores power factor, fuse time-current behaviour and the network’s own limits, so treat it as the start of the calculation, not the end.

Germany

Many German homes are supplied on three phases from the meter, but older or very small connections can be single-phase. The limit then comes from the house connection and the local grid operator, whose technical connection rules for low voltage (VDE-AR-N 4100) apply. Heat pumps and chargers above certain sizes must be reported to the grid operator, so ask for the current registration thresholds rather than assuming them. A 22 kW charger needs a three-phase supply in any case.

Netherlands

Dutch homes may have a single-phase or three-phase connection, and the connection size is recorded in the grid operator’s records. A single-phase connection of 35A at 230V gives about 8 kVA, so one 7.4 kW charger could use almost all of it. Ask the grid operator for the registered connection before you design the load stack.

Other European Markets

• France: Residential supplies are set by a contracted power level. Check the subscribed power and whether the meter is single-phase or three-phase.
• Italy: Household supplies are contracted in kW. A charger and heat pump can push a home past its contracted level, so the contract is the first thing to read. See also solar panel ROI in Italy.
• Spain: Contracted power also applies. Charging above the contracted level needs a change with the supplier or distributor. See also Spain net metering.

For market-by-market rules, the Europe solar compliance hub is the place to start.

The Simultaneous Load Problem

The mistake that defines residential electrification is treating each load as independent. A heat pump, a 7.4 kW charger and a PV system each look fine on paper, and each may be sold by a different installer. The problem is the overlap.

What Simultaneous Means in Practice

Take a winter evening in a UK home, with these assumed loads:

• Oven at 2.5 kW
• Kettle at 3 kW
• Heat pump at 3.2 kW
• Electric shower at 9 kW
• EV charging at 7.4 kW
• Base load (lights, TV, fridge) at 0.8 kW

The total is 25.9 kW. That is above a 100A supply (23 kVA) and well above an 80A supply (18.4 kVA). The loads are assumed round numbers, not measurements from one home, and nameplate kW is treated as kVA for simplicity.

How quickly a fuse opens depends on its time-current curve. A modest overload can last a while before the fuse operates and a large one clears quickly. Read the curve for the actual fuse, and do not design to the edge of it.

PV changes nothing in this scenario. The worst case is a winter evening with no PV output at all.

Why Monthly Bills Hide the Problem

A home that uses 11,000 kWh a year averages about 1.25 kW over the year (11,000 divided by 8,760 hours). The bill looks ordinary, yet the evening peak can be many times the average. Sizing that starts from monthly bills misses the spike entirely. Interval data from a CT-clamped meter or a smart meter shows it. Designers working on solar EV charging integration should start from interval data, not bills, and the load shifting guide shows how to move flexible loads away from the peak.

A 65% Planning Margin

As a rule of thumb used in this guide, not a standard, keep the simultaneous controlled load under about 65% of the supply rating. The margin leaves headroom for the loads you did not list and reduces nuisance trips. The arithmetic gives these ceilings:

DNO Application Thresholds: G98, G99 and G100

The Energy Networks Association (ENA) publishes the engineering recommendations that govern how small generators connect to UK low-voltage networks. Three matter here. For the wider context, see the glossary entry on distributed generation.

EREC G98: Microgenerators

ENA EREC G98 Issue 1 Amendment 7 (2022), as hosted by Dcode, covers microgenerators of 16 A per phase or less. The document states that 16 A per phase corresponds to 3.68 kW on a single-phase supply and 11.04 kW on a three-phase supply, based on 230 V nominal voltage.

For a G98 installation, the installer must make the DNO aware before commissioning or no later than 28 days after it, counting the day of commissioning as day one. The document also says that where the total aggregate capacity of an installation exceeds 16 A per phase, the G99 process applies and the DNO needs to be consulted before the installation is undertaken.

The MCS guidance on notifying DNOs adds that solar PV up to 16A per phase is notified within 28 days of commissioning using Form B, and that battery storage on G98 follows the same notification route. It also says that an integrated solar PV and battery system should expect G99 to apply, and that a DNO may require a different form from the standard one. Always check with the specific DNO.

EREC G99: Larger Generators

Above the G98 threshold, G99 requires an application and DNO permission before connection. MCS says higher-capacity installations need the appropriate G99 form and that battery storage above 3.68 kW needs its form submitted before installation. Processing times vary by DNO and by network area, and no single timeline applies, so ask the DNO for its current service levels.

EREC G100: Export Limitation

Export-limiting schemes, where a device caps what a system can send to the grid, are covered by a separate ENA recommendation, G100. This guide does not quote its thresholds. Check the current issue, confirm the DNO accepts an export-limited design for your case, and keep the commissioning record of the limit setting.

G99 for Solar Plus Battery Plus EV Charger

When solar, a battery and a charger form a coordinated system, the DNO will usually assess the maximum export the whole assembly can produce. A battery can export when PV is dark, so the design has to constrain battery export through inverter settings and declare that figure on the application. This is where single-phase designs most often meet a DNO objection.

Dynamic Load Management: Three Architectures

Dynamic load management is the technical answer to the simultaneous load problem on a single phase. A measuring device watches the whole-house current, and a controller lowers a flexible load, usually the charger, when the total nears a set limit. There are three common ways to build it. This guide does not publish vendor figures such as response times or prices. Take those from each manufacturer’s own datasheet.

Architecture A: Charger as the Controller

The charger measures the incoming current through a CT clamp on the meter tail and reduces its own rate when the total gets close to the limit you configure. It is a practical default when the home needs one flexible load managed and the heat pump runs independently.

Architecture B: Inverter as the Controller

A hybrid inverter that reads the grid CT can dispatch the battery and set the charger’s limit through a communication link. This suits new builds where the battery is central. The downside is lock-in: changing the charger later may mean losing the managed behaviour, so check compatibility before you sign.

Architecture C: Standalone Controller

A dedicated device monitors all CTs and sends control signals to the heat pump, charger, immersion heater and other switchable loads. It suits installs with three or more controlled loads or equipment from several makers. The cost is install complexity, and the installer owns the configuration.

Priority Logic for Heat Pump, EV and Battery

Once load management is in place, the priority logic decides what gets throttled first. There are two separate decision trees: one for import when the grid is supplying power, and one for export when PV has surplus.

Import-Side Priority

On a constrained single-phase supply, in descending order:

1. Safety circuits and fixed base load. Lights, fridge, alarms and freezer are never throttled.
2. Heat pump for hot water and space heating. Throttling it risks comfort and hot water availability. Many heat pumps can modulate down instead of switching off, and the controller should prefer that.
3. EV charging. Reducing the rate is usually harmless if the car sits overnight, because it still finishes before it is needed.
4. Battery charging from the grid. This is a financial optimisation, not a comfort or safety function, so it is the first thing to drop.

Export-Side Priority (Solar Surplus)

When PV produces more than the base load can absorb:

1. EV charging. A 7.4 kW charger can absorb most of what a small array produces, and an exported kWh is normally worth less than an imported one.
2. Hot water immersion or heat store. Diverting surplus into stored heat avoids buying grid power later for the same job.
3. Battery storage. Fill the battery once the first two are satisfied.
4. Export to the grid. The final destination, paid under whatever export tariff applies.

When Priorities Conflict

A winter morning shows the edge case. The heat pump is running, the owner plugs in the car and PV is weak. A charger set to wait for solar will pause. If the owner needs the car at 10:30, waiting for sun fails them.

The answer is two profiles on the charger: one that waits for solar surplus as the default, and one that forces charging to a set level by a set time as the override. Explain both to the customer at handover.

For installers building these workflows into proposals, solar proposal software can present the design and expected savings together once the load stack has been checked.

Worked Example 1: UK 100A Home with Heat Pump and EV

This is an illustration with assumed loads, not a customer record. A home has a 100A single-phase supply (23 kVA), a 5 kWp PV system, a heat pump drawing 3.2 kW in cold weather and a 7.4 kW charger.

Without load management

The total is 100% of the 23 kVA capacity before the kettle (3 kW) goes on. Adding the kettle gives 26.1 kW, which is 113% of capacity.

With load management

Assume a controller lowers the charger to its minimum setting of 6 A, about 1.4 kW (6 x 230). The stack becomes 3.2 + 1.4 + 2.5 + 9 + 1 + 3 = 20.1 kW, which is 87% of capacity. That is inside the rating, but above the 65% planning margin, so the design relies on the controller working every time. The shower finishes, the kettle clears and the charger returns to full rate.

The honest conclusion is that load management makes this home workable and leaves little spare. If the owner adds another large load later, the answer changes.

Worked Example 2: Netherlands 1x35A Home with Heat Pump and EV

This is another assumed example. A home has a single-phase connection of 35A at 230V, about 8 kVA (35 x 230 = 8,050 VA). It has solar, a 3 kW heat pump and a 1 kW base load, and the owner wants an 11 kW charger.

The problem

The heat pump, charger and base load add up to 3 + 11 + 1 = 15 kW, almost twice the 8.05 kVA capacity. An 11 kW charger cannot work on this connection. Check the grid operator’s connection rules before ordering one.

Two options

Option A: stay single-phase with a 3.6 kW managed charger. The load stack is 3 + 3.6 + 1 = 7.6 kW, which is 94% of capacity. That fits, but only just. The controller has to cut the charger to a lower rate when anything else is switched on.

Option B: ask the grid operator for a three-phase connection and fit an 11 kW charger. At 3 x 25A, capacity is 3 x 25 x 230 = 17,250 VA, or about 17.3 kVA, and an 11 kW charger splits into about 3.7 kW per phase. This allows faster charging but means a connection change and possibly a different heat pump model. Get the grid operator’s quote and the equipment cost before comparing.

The point of the example is the method, not the answer. If the owner’s driving needs are met by a 3.6 kW managed charger overnight, the single-phase route avoids the upgrade. If they need fast charging, the three-phase route is the cleaner fix.

Worked Example 3: Germany 1x25A Rural Home with Heat Pump and EV

This is a third assumed case. A rural home has a single-phase connection of 25A at 230V, which is 25 x 230 = 5,750 VA. It has a PV system, a heat pump that peaks at 5.2 kVA and a wish to add an 11 kW charger.

The constraint

The heat pump alone is 5.2 / 5.75 = 90% of the connection. An 11 kW charger cannot be added to this supply, with or without load management, because the heat pump already uses most of it. Ask the grid operator what its connection rules allow.

The decision

A three-phase upgrade is the realistic route. At 3 x 35A, the aggregate capacity is 3 x 35 x 230 = 24,150 VA, about 24.2 kVA, or about 8.05 kVA per phase. An 11 kW charger then spreads to about 3.7 kW per phase, and the heat pump could move to a three-phase model. Costs depend on the grid operator and the equipment chosen, so get written quotes for both.

When to Insist on a Three-Phase Upgrade

The answer to whether you need three-phase should come from the numbers. Use these four factors on every electrification quote.

Factor 1: Simultaneous Controlled Load

Add up the nameplate kW of every controlled load: heat pump peak, charger maximum, shower, oven and hob. These bands are working rules for this guide, not standards.

• Under about 65% of capacity: single-phase with load management.
• About 65% to 85%: single-phase only with firm load management, and warn the customer about edge cases.
• Over about 85%: a three-phase upgrade is strongly indicated.

Factor 2: Export Cap

Total export from PV plus battery on one phase has to respect the G98 limit of 3.68 kW or obtain G99 consent for more. Where the DNO will not consent to the export the design needs, three-phase is often the practical way out.

Factor 3: EV Charging Pattern

The charging speed the customer needs matters on its own. A 3.6 kW to 7.4 kW rate is often acceptable on a single phase. A charger of 11 kW or 22 kW needs three phases.

Factor 4: Customer Tolerance

Some owners accept the charger slowing for 20 minutes while the shower runs. Others see it as the system failing. Ask before you quote, and write the accepted behaviour into the proposal.

What Drives the Cost of an Upgrade

This guide does not publish UK upgrade prices, because DNO charges depend on the network, the works needed and the date of the quote. The table lists the drivers instead. Ask the DNO for a written quote and compare it with the cost of load management.

Modelling Single-Phase Sites in Solar Design Software

Designing for a single-phase constrained site means looking at generation and load together. The coincident-load check in this guide is a spreadsheet or load-profile exercise. It sits alongside the solar design, not inside it.

SurgePV’s solar design software covers 3D roof modeling, array layout, shading analysis and energy-yield modeling, and its generation and financial tool covers financial modeling. SurgePV does not publish interval load-profile, heat pump or EV charger dispatch modeling among its capabilities, so run the simultaneous-load check separately and use the design tool for yield, layout and the proposal.

For shaded sites such as terraced roofs or roofs with chimneys and dormers, shadow analysis helps decide the array size. A smaller array may suit a 3.68 kW export limit, because a shaded layout can produce less peak output than its nameplate suggests. Check the modelled peak before you assume it.

For small commercial sites on a single-phase supply, see the companion guide on commercial export limitation design.

Export Limits and the Smart Export Guarantee

The export limit and the simultaneous load are separate questions, but they interact. A single phase with a 3.68 kW G98 limit is fine for PV alone and gets harder once a battery can export too.

Smart Export Guarantee

The Ofgem SEG page says the scheme requires some electricity suppliers, called SEG Licensees, to pay for low-carbon electricity exported to the grid. Eligible installations are in Great Britain and are up to 5 MW, or up to 50 kW for micro-CHP. Licensees set the rate, contract length and other terms, and rates must always be above zero.

The page does not publish tariff rates, and it does not mention batteries. Compare current offers from each licensee, and check each tariff’s terms on smart meters and battery exports before you recommend one.

Why Self-Consumption Usually Wins

An exported kWh is paid at an export tariff, which the licensee sets, while an imported kWh is charged at the customer’s retail price. When the import price is higher, using solar in the home is worth more than exporting it. A heat pump and a charger that absorb midday surplus therefore raise the value of each PV kWh. The size of the gap depends on the customer’s tariffs, so use the actual import and export prices from their bills.

Battery Export Considerations

A battery that exports counts toward the G98 aggregate limit. MCS notes that storage above 3.68 kW needs its G99 form submitted before installation. If the battery can discharge faster than the export limit, set the inverter to cap grid export and document the setting at commissioning.

G99 for Battery Export Above 3.68 kW

A homeowner who wants a large battery to discharge into the grid during a high-price window needs G99 consent. This is the area where a DNO is most likely to refuse single-phase, and the answer varies by network. For homes that genuinely need battery export above the single-phase limit, three-phase is often the only way.

MCS, Notification and Smart Charge Points

Three UK requirements touch a solar, heat pump and EV package.

MCS and DNO Notification

MCS tells installers that if they plan to install heat pumps, solar PV, wind or battery storage, they are required to notify the relevant network operator. It sets different routes for heat pumps by supply size. For a maximum demand of 60A to 100A, apply before installing, and the DNO assesses supply capacity within 10 working days. For a maximum demand up to 60A, you may connect and then notify within 28 days. If the installation does not meet the notification criteria, apply before connecting.

Identify the DNO with the ENA postcode tool or the first two digits of the MPAN, and check whether that DNO wants a different form.

Heat Pump Grants

The government’s Boiler Upgrade Scheme page lists a £7,500 grant towards an air source heat pump, with extra money for some off-gas homes until March 2027. The page says the system must meet certain standards. Check the scheme’s eligibility rules for installer and product requirements before you promise a customer the grant.

Smart Charge Points Regulations

The Electric Vehicles (Smart Charge Points) Regulations 2021 require a relevant charge point to have smart functionality, meaning it can send and receive information over a communications network and respond by changing the rate or timing of charging. They also require pre-set default charging hours outside peak hours, defined as 8am to 11am and 4pm to 10pm on weekdays, which the owner can change. A charge point must also support a randomised delay.

The Regulations set smart functionality. They do not set a maximum-load rule, and they do not make a CT-based load controller mandatory on a constrained supply. Treat load management as a design decision.

Wiring Rules

The wiring rules for EV charging installations are in section 722 of BS 7671, which the IET maintains and amends. This guide does not quote clause numbers, because the amendments change. Use the current edition and the manufacturer’s installation instructions for the cable, protection and earthing design of each charger.

Common Mistakes Installers Make

Six mistakes recur, and each has a clean fix.

Mistake 1: Selling an EV Charger Without Checking the Service Fuse

The surveyor never checked the cut-out and the install goes ahead. Months later, a heat pump is added and the fuse opens. The fix is to put the service fuse rating on the first survey checklist.

Mistake 2: Choosing the Wrong Connection Route

An installer applies for G99 when the export could be limited, or notifies under G98 when the combined PV and battery exceed the limit. The fix is to add up the aggregate capacity, including the battery, and ask the DNO which route applies.

Mistake 3: Treating Each Load Designer Independently

The PV installer, heat pump installer and charger installer often work in sequence and none of them sees the whole load. The fix is one single-line diagram showing the service fuse, every controlled load and the controller, shared with all three.

Mistake 4: Ignoring the Smart Grid Ready Input on the Heat Pump

Many heat pumps offer an input that lets a controller request different operating modes. Most installers wire only the normal mode. If the model has the input, wire it to the controller and set the logic.

Mistake 5: Leaving the Export Limit at the Inverter Rating

A G98 install is limited to 16A per phase, which the ENA document equates to 3.68 kW on a single phase. Installers sometimes leave the inverter’s export limit at its rating. Check the setting in the inverter interface and record it on the commissioning paperwork.

Mistake 6: Skipping the Load Test

After install, test the worst-case coincident load: oven, kettle, shower, charger and heat pump all running. Include the test in the commissioning checklist and record how the controller responds.

Three-Phase Versus Single-Phase Heat Pumps

The heat pump model affects the whole conversation. Many installers pick the single-phase variant because it is simpler to specify. Three-phase models exist to spread the load across phases.

When a Three-Phase Heat Pump Makes Sense

These are working rules of thumb, not standards.

• The property already has a three-phase supply.
• The heat pump is large enough that one phase carries a heavy share of the stack.
• The customer plans a charger above 7.4 kW.
• The property has a high, sustained heating demand.

When a Single-Phase Heat Pump Is Fine

• The property has a single-phase supply only.
• The heat pump is small enough to leave room for a charger within the 65% margin.
• The customer is happy with charging at 7.4 kW or below.

What to Check on the Datasheet

Use the manufacturer’s own datasheet for each figure. For wider heat pump sizing, see the air source heat pump and solar PV sizing guide and the MCS heat pump and solar UK guide.

What to Watch Next

Three developments will affect this design problem, and none is settled enough to design around today.

Smart Charging Rules

The 2021 Regulations already require smart functionality and default off-peak hours. Any change to what chargepoints must do is a matter for government, so check the current text before you rely on a particular behaviour.

Connection Thresholds

The G98 threshold is 16A per phase in the current ENA document. Any future change would come from an ENA process, so check the version in force at the date of your application.

Network Flexibility

Network operators are looking at paying customers to shift demand during local constraints. A home with a controller that can throttle the heat pump and charger could take part. Check each operator’s published schemes for eligibility and terms before you promise a customer income.

Vehicle-to-Home and Vehicle-to-Grid

Bidirectional charging could one day cover evening loads from the car battery. It adds a new export path and a new application to the DNO, so it changes the connection conversation. See the vehicle-to-grid glossary entry for the basics.

Conclusion: How to Decide on Your Project

Three actions for this week:

• Confirm the service fuse rating on every electrification quote. Read the cut-out label, not the consumer unit. If you cannot read it, ask the DNO.
• Build the simultaneous load table for the property: heat pump peak, charger maximum, shower, oven, hob, kettle and base load. Add them up. If the total is above about 65% of the supply, specify load management. If it is above about 85%, quote three-phase as the main option.
• Add up the aggregate PV and battery capacity and ask the DNO which connection route applies. Keep the record of the export limit you set.

For installers, putting this analysis into the proposal is easier when the design and the money are in one place. See the page for solar installers or book a SurgePV demo to see the workflow on a real roof.

Single-phase supply capacity is the binding constraint on a lot of residential electrification. Designs that respect it deliver predictable comfort. Designs that ignore it deliver tripped fuses and callbacks.

Frequently Asked Questions

Can I run solar, a heat pump and an EV charger on a single-phase supply?

Yes, often, if the loads that can run together stay inside the supply rating. A 100A single-phase supply is about 23 kVA at 230V (100 x 230), so a 5 kW heat pump, a 7.4 kW charger and normal household load can fit when a controller throttles the charger. Add up the real coincident load before you promise it.

What is the maximum load on a single-phase house supply in the UK?

It is set by the cut-out fuse rating times the supply voltage, so a 60A, 80A or 100A fuse at 230V gives roughly 13.8, 18.4 or 23 kVA. Those figures are arithmetic, not a guarantee of usable continuous power. Read the rating on the cut-out, not the consumer unit, or ask the DNO.

What is G98 and G99 for solar export?

G98 covers microgenerators up to 16 A per phase, which the ENA document equates to 3.68 kW on a single-phase supply, connected first and notified to the DNO within 28 days of commissioning. Above 16 A per phase, G99 applies and the DNO must be consulted before the installation. Batteries count toward the total, so check the combined figure.

Do I need a 3-phase supply for solar plus heat pump plus EV?

Not always. The deciding numbers are the simultaneous load against the fuse rating, the export figure the DNO will accept and the EV charging speed the customer wants. Three-phase is usually the answer when the load stack still does not fit after load management, or when a charger above 7.4 kW is required.

How does dynamic load management work for heat pump and EV charging?

A current transformer (CT) clamp on the incoming supply measures whole-house demand and a controller lowers the EV charge rate when demand nears a set limit. It then raises the rate again when demand falls. Check the vendor datasheet for the response time and for which loads the controller can actually switch.

Does the Smart Export Guarantee apply to single-phase solar?

Yes, as far as Ofgem’s SEG page shows, eligibility turns on the type and size of the installation, not the number of phases. The SEG covers installations in Great Britain up to 5 MW, and each licensed supplier sets its own rate and terms. Rates must always be above zero, so compare tariffs.

What is the priority order for solar, heat pump and EV charging?

On a constrained supply, keep safety circuits and base load first, then the heat pump, then EV charging, and charge the battery from the grid last. For solar surplus the order reverses: EV charging first, then hot water or battery, then export. The order is a design choice, so agree it with the customer.