Solar Battery Backup in Cyprus: Size kW and kWh

A solar battery backup system needs two separate sizing checks: enough kWh to supply the selected loads for the required duration, and enough kW to run them simultaneously. A large battery does not compensate for an undersized backup output. In Cyprus, the connection design and applicable EAC requirements also need to be established before equipment is ordered.

Storage does not automatically provide backup

Some installations use batteries to increase self-consumption while remaining dependent on the grid for operation. The US Department of Energy's inverter explanation distinguishes solar-plus-storage systems designed to work independently during outages. The capability has to exist in the actual installed configuration.

Obtain a single-line diagram that identifies the battery, inverter, grid connection and backed-up circuits. Ask the designer how the installation isolates itself from the network during an outage. Treat backup operation as a demonstrated function, not a feature inferred from the word “hybrid” in a product name. Electrical alterations and testing belong with the responsible qualified installer.

Build a critical-load schedule

Start with essential equipment, then add optional comfort loads. A refrigerator, router and selected lighting form a different requirement from whole-house cooling, an electric oven or pool equipment. Record actual running power, expected operating time and starting requirements for each appliance.

The following worksheet is an illustrative six-hour outage scenario. Its average powers are assumptions for arithmetic, not measurements of a particular home.

The average load is useful for energy sizing. It does not describe the highest instantaneous demand. Refrigeration and other motors can require greater starting power, while different appliances may overlap in ways that the averaged schedule hides.

Convert load energy into battery capacity

For a preliminary calculation, nominal battery capacity equals required load energy divided by the usable fraction and discharge-path efficiency. In the example, assuming 80% of nominal capacity is available for the planned event and 90% delivery efficiency gives 2.28 / (0.80 × 0.90) = 3.17 kWh approximately.

These percentages are design assumptions, not specifications for every battery. If a manufacturer already states usable capacity, applying a depth-of-discharge reduction again would double-count that restriction. Similarly, round-trip efficiency includes charging losses and is not identical to discharge-path efficiency. Ask which definition the proposal uses.

Allow separately for standby consumption, degradation and any reserve needed after the planned outage. The available state of charge at the moment of failure is crucial. A nominal 10 kWh battery that has already discharged for evening bill savings cannot be assumed to hold 10 kWh when the grid fails.

Check the inverter's backup power

List the largest permitted combination of simultaneous appliances. Compare it with the continuous backup rating, not merely the inverter's grid-connected PV rating. Then compare motor-start requirements with the specified short-duration overload capability and its duration.

A three-phase property adds another question: which phases receive backup and how are loads distributed? A total system rating alone may hide a per-phase limit. The electrical designer should identify any circuits that remain unavailable and any restrictions on large appliances. Medical or other safety-critical equipment needs a dedicated continuity assessment rather than this household worksheet.

Our battery storage guide provides the broader category context. When obtaining proposals, request a load schedule and an explicit backup output specification alongside the battery capacity. Comparing only the advertised kWh leaves half the design unchecked.

Can panels recharge the battery during an outage?

That depends on the inverter, coupling arrangement and control design. Require confirmation that solar production can continue in the proposed islanded mode, including the conditions for restarting after a depleted battery. Do not assume that an AC-coupled existing PV inverter remains operational when the new battery system is backing up the house.

For a conservative overnight calculation, begin with no solar contribution. Add a daylight scenario only after the designer states the operational limits. Clouds, shading and the timing of the outage prevent a daily generation average from serving as a firm recharge promise.

The Australian Government's battery guidance notes the need to manage consumption during an outage and avoid exceeding inverter capability. That operating principle applies beyond Australia; its local installation programmes and incentives do not establish Cyprus eligibility.

What to establish with the Cyprus installer

Ask which current EAC procedure applies to the proposed storage arrangement and obtain the relevant documents. EAC publishes a storage system technical guide; the designer should confirm the applicable version and connection conditions. This article does not prescribe protective-device sizes or replace the electrical design.

The proposal should also locate the battery, record the manufacturer's environmental and clearance requirements, identify monitoring access and explain the warranty's operating limitations. Indoor and outdoor suitability should be checked against the specific product documentation rather than assumed from an enclosure photograph.

Commissioning evidence to request

Have the installer demonstrate a controlled loss-of-grid test using the agreed circuits. Record whether loads stay on, what interruption occurs, whether solar recharge operates as specified and how the installation returns to normal. Test the intended operating mode, not a temporary demonstration configuration that differs from the handover settings.

Keep the diagram, settings, test record and operating instructions together. Identify who can change the reserve setting and how the owner receives fault notifications. A backup system is more useful when household members understand which appliances can run together.

Short answers on battery sizing

How long will a 5 kWh battery last?

If 4 kWh is actually available at the loads, a constant 0.5 kW demand gives approximately eight hours. A 2 kW demand gives approximately two hours. Those examples assume the power rating supports the load.

Can a battery support air conditioning?

Possibly, if the running demand, starting behaviour and circuit configuration fit the backup design. Add the selected AC's measured consumption to the schedule and recalculate duration.

Is whole-home backup necessary?

Not for every brief. A separate essential-load arrangement can make the requirement clearer. The choice follows the outage needs and electrical assessment, not battery capacity alone.