A saved kilowatt-hour and an exported kilowatt-hour can have different values. Keep the two revenue lines separate.
Draw the two flows
Electricity used at home as it is generated reduces some grid purchases. Surplus sent to the grid is a different flow and needs the appropriate arrangements. The national energy mediator’s guide explains self-consumption and the options to examine.
Read the export terms
Ask who buys the surplus, which contract applies, how payment is measured and which conditions determine the rate. Do not copy a tariff from a neighbour’s older installation into your own estimate. Keep connection, commissioning and payment conditions visible in the project documents.
Treat virtual storage as a contract
An offer described as virtual storage does not put the electricity in a physical battery at home. Read the credit rules, charges and exit terms carefully, and check compatibility with support arrangements. Compare the complete annual cost with a straightforward surplus-sale scenario.
Compare the value of each kilowatt-hour
For an example year with 4,000 kWh generated and 1,600 kWh used directly, surplus without storage is 2,400 kWh. At example prices of €0.30/kWh for purchases and €0.08/kWh for sales, direct use avoids €480 of purchases and exports earn €192. Show these separately before subtracting charges. This makes it easier to see how a different household schedule or export offer changes the result.
Read a virtual-storage offer as a complete bill
Write down the subscription, treatment of credited energy, charges on later withdrawals and what happens to unused credit. Ask whether you must also buy electricity from the same company and how the offer ends if you change supplier. Compare the full bill for a year with an ordinary surplus-sale arrangement. A promise to “use your summer electricity in winter” needs contractual quantities and costs behind it.
Make the payment records easy to reconcile
Identify which meter records export, which organisation issues statements and the expected invoicing or payment process. Keep commissioning and contract references with your readings. After the first statement, check the period, quantity and price against the agreed arrangement. If your app and the payment statement differ, first check whether they measure generation or export and whether their dates align; those are not necessarily the same totals.
Your planning checklist
- Separate quantities for direct use, surplus and purchases.
- The buyer, contract, applicable rate and payment process.
- All subscription, withdrawal and exit costs for virtual storage.
- Meter references and records for checking the first statement.
Common questions
Does selling surplus remove the household electricity bill?
No. The home can still import when production is insufficient and may still pay fixed charges. Export income and import costs are separate parts of the annual calculation.
Can I use my neighbour’s export rate?
Use the terms applicable to your own installation and contract. Commissioning circumstances, scheme conditions and the offer selected can differ. Ask the proposed buyer to identify the basis of the rate in writing.