How accurate is the solar forecast?

Our solar forecasts use Visual Crossing Weather API combined with your specific system configuration (panel capacity, roof angle, location) to provide accurate predictions. The 7-day forecast has an average accuracy of 85-90% for UK and EU locations.

Which solar inverters are supported?

Solar Forecast supports FoxESS, SolarEdge, Fronius, GivEnergy, Sigenergy, Huawei, SMA, and Solax inverters. You can monitor live generation data directly from your inverter through API integration.

Is the app free to use?

Yes! Solar Forecast offers a free tier with 3-day forecasts. Premium users get extended 14-day forecasts, 36-hour detailed predictions, historical analytics, and live inverter monitoring. Premium costs £4.99/month with a 7-day free trial.

Do I need to install any hardware?

No hardware installation required. Solar Forecast is a web-based app that works on any device. Simply enter your location and system details to start receiving forecasts. For live monitoring, you can optionally connect your existing inverter via API.

What countries are supported?

Solar Forecast works across many nations. We provide accurate forecasts for any location with available weather data.

Electric Vehicles & Solar Charging: Why Exporting Sunshine Might Beat Charging Your Car

*Published: October 2026 | Reading Time: 11 minutes*

Introduction

If you own both solar panels and an electric vehicle, the natural assumption is obvious: you should plug your car in during the day and run your daily driving on pure, free sunshine.

It feels intuitively right. Why send your solar electricity back to the grid when you have a 60 kWh battery sitting on your driveway waiting to be filled? Modern smart chargers even have dedicated "eco" or "solar capture" modes designed to do exactly this.

Yet for a growing number of UK homeowners on modern smart energy tariffs, charging your electric car directly from your solar panels is actually a financial mistake. In fact, depending on your tariff arrangement, you could be significantly better off doing the exact opposite: exporting every spare unit of solar generation during the day, and charging your car overnight from the grid.

In this guide, we will examine the counterintuitive mathematics of smart tariffs, explain when solar car charging makes sense (and when it costs you money), look at how to protect your home battery from accidental drainage, and share a practical decision framework for getting the most out of your setup.

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The Tariff Arbitrage Opportunity: Doing the Maths

The reason daytime solar charging is not always the best choice comes down to one development in the UK energy market: the emergence of two-tier smart EV tariffs with high export rates.

Consider the tariffs currently available to many UK households:

**Overnight EV Import Rate:** Suppliers such as Octopus (Intelligent Octopus Go), British Gas (Electric Driver), and OVO (Charge Anytime) offer overnight charging windows at roughly **7p per kWh**.

**Fixed Export Rate:** Under the Smart Export Guarantee (SEG) or supplier-specific export products (such as Octopus Outgoing), homeowners can easily secure a fixed export rate of **15p per kWh**.

Now consider what happens to a single kilowatt-hour (kWh) of solar power generated on your roof at midday.

Scenario A: You Charge Your EV from Solar

You divert that 1 kWh into your car battery. Your car gains 1 kWh of charge.

Cost to charge: £0.00.

Forgone export income: 15p.

**Effective cost of that charge: 15p per kWh.**

Scenario B: You Export Your Solar and Charge Overnight

You let that 1 kWh export to the National Grid at midday. That evening, your smart charger tops up your car during the 7p off-peak window.

Export earnings credited to your bill: +15p.

Cost to import that 1 kWh at night: -7p.

**Net profit in your pocket: +8p per kWh.**

The Numbers Over a Year

An electric vehicle driven 9,000 miles a year consumes roughly 2,500 kWh to 3,000 kWh of electricity.

If you divert 1,500 kWh of solar generation into your car over spring and summer instead of exporting it:

Charging via solar: You save paying 7p overnight, keeping £105 in your bank account, but you surrender £225 in export credits.

Exporting solar and charging off-peak: You pay £105 for night electricity, but collect £225 in daytime export credits, leaving you **£120 better off**.

For two-car households or higher-mileage drivers, this gap widens even further. You are effectively selling electricity to the grid at retail prices and buying it back at wholesale prices overnight.

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When Does Solar EV Charging Still Make Sense?

Tariff arbitrage is brilliant, but it is not universal. Charging your EV directly from your solar panels remains the winning strategy in several specific circumstances:

1. You Are on a Flat-Rate Tariff

If you do not have access to a dedicated EV tariff and pay a standard variable rate of 24p to 28p per kWh around the clock, daytime charging is king. Using your own solar generation saves you the full 25p import cost, which comfortably beats any modest 5p or 15p export rate.

2. You Have Low or Zero Export Remuneration

If your system is not registered for the Smart Export Guarantee, if your export payments are capped at an older 3p to 5p rate, or if you have an uncertified DIY addition, any solar power pushed to the grid is either wasted or poorly rewarded. In this case, capturing every spare electron in your car battery is the sensible move.

3. Your DNO Has Capped Your Export

Under UK grid rules (specifically G98 limitations), single-phase domestic connections are capped at exporting 3.68 kW. If you have an oversized 7 kWp solar array generating 6 kW of power on a clear May afternoon, your inverter must either clip or throttle generation unless that surplus has somewhere local to go. Diverting that excess into an EV allows you to soak up power that the grid would otherwise refuse to accept.

4. Grid Voltage Rise Issues

In rural or suburban areas with older local substations, high solar generation on sunny days can push neighbourhood grid voltages above the statutory 253V limit, causing inverters to trip offline to protect the grid. Putting a 3 kW or 7 kW car load on your domestic supply pulls the voltage back down, keeping your solar system generating reliably.

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The Technical Reality: How Solar EV Charging Works

If you decide that charging directly from solar suits your situation, there are practical technical realities you need to plan around.

The 1.4 kW Minimum Threshold

Under the international charging standard used by all modern electric cars (IEC 61851 / Type 2), the absolute minimum current an EV can accept on a single-phase supply is **6 amps**.

At UK mains voltage (230V), 6 amps equals **1.38 kW** (roughly 1.4 kW).

This means your smart solar charger (such as a Myenergi Zappi, Ohme ePod, or Hypervolt) cannot trickle-charge your car with 300W or 500W of surplus sunshine. Unless your roof is producing at least 1.4 kW *above* your normal household baseload, the charger cannot start in pure solar mode.

When passing clouds cause generation to dip below 1.4 kW, your charger faces a choice based on your settings:

**Pure Solar Mode (e.g. Zappi 'Eco+'):** The charger pauses and waits for the sun to return. If clouds pass frequently, charging starts and stops repeatedly.

**Solar Assist Mode (e.g. Zappi 'Eco'):** The charger maintains the minimum 1.4 kW rate by topping up the deficit from the grid or your home storage battery.

The Home Battery Cannibalisation Trap

This brings us to the biggest pitfall facing owners with solar, a home storage battery, and an EV: **accidental battery cannibalisation**.

A typical domestic battery storage system holds between 5 kWh and 10 kWh. An electric car battery, by comparison, holds between 50 kWh and 90 kWh; roughly seven to ten times the capacity of your house battery.

If your EV charger initiates a 7 kW charge while your home battery is full, your house battery will attempt to satisfy that demand. Left unconfigured, your car will drain your entire home battery flat in less than 75 minutes. You then head into the evening peak with an empty home battery, forcing your house to import expensive grid electricity while you cook dinner.

To prevent this, you must configure your system correctly:

1. **CT Clamp Hierarchy:** Ensure your EV charger's Current Transformer (CT) clamp is positioned upstream of the home battery monitor, so the charger knows not to treat home battery discharge as surplus solar.

2. **Scheduled Charging Lockouts:** If your charger and home battery communicate (or if you use an energy automation platform), set your home battery to pause discharge whenever the EV is actively charging.

3. **Reserve Limits:** Keep a minimum 20% to 30% state of charge reserved exclusively for household lighting and appliances.

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Summary Decision Matrix: What Should You Do?

To help cut through the confusion, use this straightforward guide to match your tariffs to the optimal charging habit:

|---|---|---|---|

| **Cheap night EV rate (e.g. 7p) + Good export rate (15p+)** | Export all surplus solar to the grid | Charge exclusively overnight during the cheap window | **Optimal:** You earn 15p on export and buy back at 7p, profiting 8p per unit. |

| **Flat-rate import (24p-28p) + Modest export (5p-15p)** | Divert surplus solar straight into the car | Supplement with grid only when necessary | **Optimal:** Every unit stored in the car avoids a 25p import purchase. |

| **Dynamic / Agile tariff (Octopus Agile)** | Monitor day-ahead rates; export when prices peak | Charge during negative or ultra-cheap plunge hours | **Optimal:** Flexible arbitrage; charge when grid prices drop below export value. |

| **Strict G98 export cap (3.68 kW) with large array** | Export up to 3.68 kW; divert remainder to EV | Top up remainder overnight | **Optimal:** Prevents inverter throttling while capturing maximum export revenue. |

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How Solar Forecast Helps You Plan

Whether your goal is to export for maximum revenue or soak up every photon into your vehicle, timing is everything.

Solar Forecast gives you the clarity you need the evening before:

**Surplus Predictions:** See your anticipated generation hour-by-hour alongside your typical household baseload, showing exactly how many kilowatt-hours will be available for export or vehicle charging.

**Weather-Informed Planning:** If tomorrow's forecast predicts heavy overcast skies and only 4 kWh of total generation, you know immediately not to rely on daytime charging; schedule a full overnight grid charge instead.

**Tariff Calculations:** Input your specific import and export unit rates in your settings to view projected financial returns and choose the most profitable strategy for your household.

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The Verdict

The idea of running your car on 100% home-grown solar power is undeniably appealing, but in the modern UK energy market, smart economics often points in the opposite direction.

If you have access to a 7p overnight rate and a 15p export tariff, treating your solar array and your electric vehicle as two independent financial assets will leave you comfortably ahead. Let your panels earn high-value export credits by feeding clean energy into the neighbourhood grid when demand is high, and charge your car with cheap, abundant off-peak power whilst you sleep.

Good energy management is not about dogma; it is about using the rules of the system to minimise your running costs and make renewable energy work for you.

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*Curious how much surplus power your roof will generate this week? [Configure your system on Solar Forecast](https://solarforecast.co.uk/) and start planning your charging schedules with confidence.*