How to Balance Solar Import and Export
Author: Steve Fairless
Originally Published: 21st July 2026 · Updated: 3rd September 2026
The best solar strategy is not automatically “never import” or “export as much as possible”. It is to direct each kWh to the route that creates the highest net value after tariff rates, battery losses, power limits, state-of-charge requirements and future demand are considered. Sometimes direct self-consumption is clearly best. At other times, a strong export window can be worth prioritising while the battery is charged cheaply from the grid.
At Sustainable Energy Engineering, we treat import, storage and export as one controlled energy system. The array, battery, meter, inverter and tariff have to work together. A system that generates plenty of electricity can still deliver disappointing savings if the controls repeatedly charge at the wrong time, export at a weak rate or leave the battery empty before the expensive period.
This guide explains the value calculation, the technical constraints and the practical settings we use to build a strategy that can change with season, weather and tariff structure.
Import vs Export: The Short Answer
- Use solar directly where it avoids a higher import cost. Direct use also avoids battery conversion losses.
- Store surplus when later use is more valuable. Battery capacity and charge power determine how much can be shifted.
- Export when the payment is worth more than storing or curtailing. The correct comparison is net value, not the export rate alone.
- Grid-charge when the tariff spread justifies it. Include round-trip loss, standing consumption and battery wear.
- Keep a reserve only for a defined purpose. Backup energy held permanently cannot be used for daily optimisation.
- Review the strategy seasonally. A winter grid-charging plan may be poor in spring when solar surplus is abundant.
Understand the Four Main Energy Flows
A grid-connected solar and battery system can supply the property directly from PV, charge the battery, export to the grid or import from the grid. The inverter and energy-management system decide how those flows are prioritised within their programmed rules.
Our solar battery designs begin with the customer’s actual demand profile. The controls should support that profile rather than forcing every household into one generic “solar first, battery second” schedule.
Three Numbers That Are Commonly Confused
A battery can contain enough kWh for the evening and still import during a short high-power load if its discharge kW is lower than the demand.
Direct Solar Use Is Usually the Cleanest Energy Path
Electricity consumed while the array is generating normally passes through fewer conversion stages than electricity stored and discharged later. It also avoids buying a grid unit at the current import rate. Where import costs materially exceed export payments, direct self-consumption is often the highest-value route.
That does not mean switching on wasteful loads simply to avoid export. The appliance or process should have a genuine purpose. Flexible loads such as hot-water heating, EV charging, dishwashing or commercial processes can be scheduled to coincide with solar where that does not create other costs.
How to Compare Self-Consumption With Export
The avoided import value is the import price that would otherwise have been paid. The export value is the payment received for sending the unit to the grid. If the energy passes through a battery, round-trip losses mean less than one full kWh returns for use or export.
The formula makes the decision transparent. We do not assume that a high export rate automatically wins, because the battery may need to preserve energy for a more expensive import period. Equally, we do not assume that self-consumption always wins if the export rate temporarily exceeds the later avoided import value.
An Illustrative Tariff Comparison
The figures below are an example to show the calculation, not a current tariff quotation. Assume 10 kWh of surplus solar is available and the battery returns 9 kWh after all charge and discharge losses.
| Option | Assumption | Illustrative value |
|---|---|---|
| Export immediately | 10 kWh exported at 15p/kWh. | £1.50. |
| Store and avoid import | 9 kWh later avoids import at 28p/kWh. | £2.52 before any cycling allowance. |
| Store and export later | 9 kWh exported during a 25p/kWh window. | £2.25 before cycling allowance. |
| Curtail | Energy is neither used nor exported. | £0 direct energy value. |
Under those hypothetical rates, later self-use has the highest gross value. Change the tariff spread or battery losses and the result can change. This is why settings copied from another household are not a reliable strategy.
What the Smart Export Guarantee Does
The Smart Export Guarantee requires certain electricity suppliers to offer payment for eligible small-scale low-carbon generation exported to the grid. Solar PV is eligible subject to the scheme conditions, metering and supplier requirements. Ofgem’s generator guidance covers installations up to 5 MW total installed capacity.
SEG does not set one universal export rate. Suppliers choose their tariffs and conditions, so the customer must compare the actual offer, time windows, technology requirements and import-tariff interaction. We separate the scheme’s eligibility rules from the commercial tariff rate.
An Export Tariff Is Not a Guaranteed Lifetime Price
Tariffs and terms can change. We design the system so it remains useful through direct self-consumption and flexible control rather than relying on one temporary price relationship for the entire payback forecast.
How Battery Capacity Changes the Balance
A small battery may fill early on a bright day and leave later solar available for export. A very large battery may absorb more surplus but remain partly empty through winter or require more cheap grid energy to justify its capacity. The right size depends on the amount of energy that can be shifted repeatedly.
Capacity should be considered as usable kWh after reserve and operating limits. A nominal 10 kWh product with energy held for backup does not provide the full figure for daily tariff optimisation.
Charge and Discharge Power Matter as Much as Capacity
If the array produces a short high surplus above the battery’s charge limit, the remainder will be exported or curtailed. If the property later uses more power than the battery can discharge, the grid supplies the difference even when stored energy remains.
We therefore compare PV power, battery power, inverter power and household peaks. A strategy that looks strong in an annual spreadsheet can fail in real time if the equipment cannot move energy at the required rate.
When Grid Charging Can Make Sense
Charging at a low overnight price can reduce imports during an expensive peak period, preserve solar for export or provide a winter reserve when daily PV generation is limited. The decision should include the energy lost during charging and discharge, the battery’s standing consumption and any warranty or cycle implications.
Our grid-charging guidance focuses on measured value. If the cheap-to-expensive spread is narrow, the battery may move energy without creating enough saving to justify the cycle.
Forecast-Based Charging
Some systems use weather forecasts, expected solar generation and learned demand to decide how much overnight energy to buy. This can be effective, but forecast error matters. A predicted sunny day that becomes overcast can leave the battery short, while overcharging before a bright day can force valuable solar to export early.
We prefer controls that can be reviewed and overridden. The customer should understand the reserve, charging window and priority order rather than being dependent on an unexplained cloud algorithm.
Seasonal Strategies
In winter, the battery may rely more on off-peak grid charging because solar surplus is limited. In spring, the same overnight charge could occupy capacity that the array would otherwise fill. In summer, export windows and EV charging may dominate.
| Season | Likely issue | Control question |
|---|---|---|
| Winter | Low solar energy and high evening demand. | Is off-peak grid charging cheaper than peak import after losses? |
| Spring | Rapid increase in daytime surplus. | Should overnight charging be reduced to leave capacity for solar? |
| Summer | Frequent full battery and high export. | Can flexible loads or a better export window increase value? |
| Autumn | Falling generation and changing load. | When should the winter schedule resume? |
Backup Reserve Has an Opportunity Cost
A 20% reserve protects energy for an outage but reduces the amount available for daily load shifting. The reserve may be entirely justified for medical equipment, communications, refrigeration or business continuity. It should be a deliberate resilience decision.
We distinguish the financial case from the resilience case. Backup can have value even if it does not shorten payback, but customers should know how much usable daily capacity they are giving up.
Export Limits and Network Requirements
The DNO connection considers the aggregate generation and storage arrangement. Systems up to 16 A per phase can follow the G98 route when all conditions are met; larger generation generally follows G99. Where export must be limited, G100-compliant control may be part of the approved design.
Export limiting is not the same as limiting the DC array to the export figure. A larger array can serve local loads and batteries while controls prevent the agreed maximum from reaching the network. The system must be engineered and commissioned as a complete arrangement.
Smart Metering and Data Quality
Export payment normally requires an appropriate meter and supplier account. Battery and inverter apps may also estimate flows, but their sensors must be installed in the correct direction and position. A reversed current transformer can make import appear as export and cause the control system to behave incorrectly.
We verify the energy-flow diagram during commissioning and compare app readings with the electricity meter. Reliable data is essential for both tariff control and performance diagnosis.
Common Control Mistakes
Settings We Check When Savings Look Wrong
- overnight charging continues into bright solar days;
- backup reserve is higher than the customer intended;
- time zone or daylight-saving settings shift tariff windows;
- current transformers are reversed or assigned to the wrong phase;
- export priority conflicts with battery self-consumption mode;
- charge or discharge power is capped below the design value;
- an EV or hot-water load runs during the most expensive import period;
- firmware or tariff changes have altered behaviour.
How We Build a Practical Strategy
We begin with half-hourly consumption, expected solar generation, actual tariff terms and the battery’s usable capacity and power. We then model direct use, charge windows, expected export, reserve and seasonal changes. The result is a control plan with measurable objectives.
Our energy tariff guidance helps customers understand the structure, but we avoid treating any named tariff as permanent. The system needs to remain adaptable as rates and products change.
Judge the Strategy by Net Grid Cost and Service
A high export total is not automatically success if the household later imports more expensive electricity. A low import total is not automatically success if the battery has been cycled aggressively for a negligible saving. We assess net cost, battery behaviour, comfort and resilience together.
Monitoring should show generation, consumption, import, export, state of charge and tariff periods. That lets us revise the schedule based on evidence rather than intuition.
Need Your Solar, Battery and Tariff Controls Aligned?
Provide your half-hourly usage, tariff details, inverter and battery model. We can assess the energy flow and recommend a strategy based on real net value.
