The inverter transforms solar and battery electricity into usable household electricity. You can think of your inverter as a complex junction box for the solar and battery. As such, it does not create electricity, the solar panels and battery are the energy generators and are the devices supplying electricity to your property.

This depends on many factors; the amount of panels, the maximum output from each panel, the angle they face and any shading they might incur. If your system was installed by an MCS accredited solar installation company, then they will have supplied you with an annual performance estimation with your quotation, and a user manual or handover pack upon completion that will include this information.

One important factor of solar generation is that your inverter is limited to supplying only 3.6kW of household electricity to your property, regardless of the potential maximum output from your solar pv panels. This is a regulation set by your grid operator.

If your panels are producing more than 3.6kW of electricity, any excess will be stored in your battery for later use. If the battery is full and cannot take any more excess solar, the inverter limits the solar pv production to 3.6kW.

Bear in mind that your panels will only achieve maximum output at around noon on clear and sunny days in summer. The rest of the time your solar pv panels will be producing less than maximum and your inverter is sized to be optimal at the lesser, average outputs, rather than for the rarer occasions of maximum solar generation, resulting in a higher overall annual performance.

This depends on many factors and there are several likely causes; the solar pv panels may be experiencing shade from a tree or chimney, the sky may be more overcast than it seems to the human eye, or the panels may be very dirty and require cleaning (most panels are self-cleaning).

Another far less common cause is that your panels are producing more electricity than your inverter and battery can currently accept, in which case your inverter limits the solar generation. Most residential inverters are limited to supplying only 3.6kW of household electricity to your property, regardless of the potential maximum output from your solar pv panels. This is a regulation set by your grid operator.

If you think that your solar pv panels are continually underperforming from something other than these suggested possible causes, you should contact your installer.

A kilowatt (kW) is 1000 watts (W). A kilowatt is a measure of how much power an electric appliance consumes. The higher the kW of a device, the more electrical power is needed to operate it.

A kilowatt-hour (kWh) is a measure of how much power an electrical appliance uses in kilowatts per hour. Some Electric Suppliers call a kilowatt-hour a ‘unit of electricity'. If you use a 2kW appliance for an hour it will consume 2 kilowatt-hours.

Some appliances have varying energy demands, for example a washing machine may be rated as 2kW, but this power is only required when heating the water. It will consume less power at different periods of the washing cycle. Therefore over an hour period a washing machine may only use 1.16 kilowatt-hours, comprised of a 10 minute period of heating water at 2kW, and a 50 minute period of washing the clothes at 1kW.

The value of your Solar generated electricity is calculated from the amount of it you are consuming in the property, the amount of it that is being stored in the battery, and the amount of it that is being exported to the Grid.

Any solar electricity that you are consuming in the property is valued at the rate of your Grid tariff, equal to the price of electricity had you imported it from the Grid.

Any solar electricity that is being stored in the Battery does not yet have a value. It will be valued when the solar stored electricity is discharged and used in the property or exported to the grid.

Any solar electricity that is being exported (supplied) to the Grid is valued at the rate of your Grid Export tariff.

Solar Export occurs when excess solar electricity is supplied (exported) to the Grid. When the Solar PV panels are generating more electricity than your property needs, the excess will be used to charge your battery. If the battery is fully charged and can not accept any more electric, then the excess solar electricity has nowhere else to go and will automatically export on to the grid. Your Electric Supplier will pay you for any electricity you export on to the Grid.

Ideally you want to utilise all of the solar generated electricity either by consuming it in your property or storing it in the battery for later use at times of higher Grid electricity costs, but this is not always possible (your battery may be fully charged, or your property has no immediate requirement for the additional electricity) in which case the Solar will automatically export to the Grid.

You can minimise the amount of Solar PV that exports to the Grid by utilising the excess solar electricity in your property, for example, by running your washing machine or dryer, or by charging your Electric Vehicle. Due to the fluctuation in solar generation, however, this may cause your property to import some Grid electricity to supplement the solar and battery electricity.

The inverter transforms solar and battery electricity into usable household electricity. You can think of your inverter as a complex junction box for the solar and battery. As such, it does not create electricity, the solar panels and battery are the energy generators and are the devices supplying electricity to your property.

Your battery storage capacity is usually 5kWh or 10kWh of electricity for a single battery, although this may vary. Discharge capacity is usually 90% or the total battery capacity to prevent damage from total discharge.

You should refer to your Installation Handover Pack or documents provided by your installer. Some installations have additional batteries. They are usually represented in applications as single larger capacity battery.

That depends on the discharge capacity of your battery and the maximum supply capacity of your inverter. Your battery may be able to quickly discharge a lot of stored energy, but the maximum battery discharge rate may be limited by your inverter. Government regulations limit the maximum supply of inverters to 3.6kW in order to ensure that the Grid is not overloaded when Solar and Battery Systems are exporting excess electricity to the Grid. Visit NIE for more details:

Northern Ireland Electricity Networks - Microgeneration

A kilowatt (kW) is 1000 watts (W). A kilowatt is a measure of how much power an electric appliance consumes. The higher the kW of a device, the more electrical power is needed to operate it.

A kilowatt-hour (kWh) is a measure of how much power an electrical appliance uses in kilowatts per hour. Some Electric Suppliers call a kilowatt-hour a ‘unit of electricity'. If you use a 2kW appliance for an hour it will consume 2 kilowatt-hours.

Some appliances have varying energy demands, for example a washing machine may be rated as 2kW, but this power is only required when heating the water. It will consume less power at different periods of the washing cycle. Therefore over an hour period a washing machine may only use 1.16 kilowatt-hours, comprised of a 10 minute period of heating water at 2kW, and a 50 minute period of washing the clothes at 1kW.

If you have excess energy stored in your battery but are still importing electricity from the grid, there could be a few causes.

Battery capacity: Your battery may not have enough capacity to power your entire home during peak demand periods. Depending on the size of your battery, it may only be able to supply a portion of your home's energy needs.

Time-of-use rates: Some utility companies have time-of-use (TOU) rates, which means that the cost of electricity changes throughout the day. If your battery is fully charged during off-peak hours when electricity is cheaper, you may still choose to import electricity from the grid during peak hours when rates are higher.

System limitations: There may be limitations to your solar PV system or battery that prevent you from fully utilising the stored energy. For example, your system may not be designed to handle large loads, or your battery may be experiencing issues that prevent it from functioning at full capacity.

If you want to keep your battery stored electricity until later, you can use the application to control when the battery is charged and discharged. This can help you maximise the amount of electricity you use from your battery when grid costs are high.

Further information on battery scheduling is contained in the user guide.

The value of your Battery stored electricity depends on what source the electricity came from (solar or grid), when it is being used and whether it is supplying your house or being exported to the grid.

Battery stored electricity is first valued when it is transferred into the battery (stored, battery is charging), and then re-valued when it is transferred out of the battery (used, battery is discharging).

THE VALUE OF STORED SOLAR ELECTRICITY

Any solar electricity being stored in the battery is free and does not have a value until it is discharged from the battery.

When stored solar electricity is discharged and supplied to your house, it is valued as a saving that is equivalent to your current Grid tariff rate, equal to the price of electricity had you imported it from the Grid.

When stored solar electricity is discharged and exported to the Grid, it is valued as an income based on your Grid Export Tariff.

While it may seem profitable to export stored solar electricity to the grid, you may find that later that day, when you run out of battery stored electricity, you will need to import high-peak grid electricity which could negate any income earned from exporting the stored solar electricity earlier that day.

THE VALUE OF STORED GRID ELECTRICITY

Any Grid electricity being stored in the battery is valued at the cost of your current Grid import tariff rate.

When stored Grid electricity is discharged and supplied to your house, its is valued as the difference between the cost of the electricity when you stored it and the cost of the current Grid tariff.

For example, if you charged your battery from the grid at a low-peak time and later used the stored grid electricity at a time of high-peak grid, you have saved money by not importing the high-peak electricity.

If in the unlikely event that you stored Grid electricity at a time of high-peak grid, and then discharged it at a time of low-peak grid, then you will have incurred unnecessary costs. Make sure to avoid setting battery charge schedules at times of high-peak electricity.

If stored grid electricity is being discharged and exported (supplied) to the Grid, it is valued at the rate of your Grid Export tariff. It is unlikely that your Grid Export Tariff will ever be greater than any of your Grid Import Tariffs so you should avoid battery electricity being supplied to the grid.

Even if your Grid Export Tariff was, at times, greater that the Grid Import Tariff, it does not make long term economic sense to export battery electricity to the grid. Every full charge and discharge of your battery is termed as a battery cycle, and your battery has a finite amount of them. Any income you would make from repeatedly selling your grid stored electricity back to the grid is unlikely to cover the cost of replacing a battery due to it being overworked (repeatedly cycled).

This is a decision that depends on your Grid Tariff rates, the time of year (summer or winter) and the weather prediction for the following day.

In general, if you have a multiple Grid Tariff rate, where the cost of electricity is cheaper during certain periods (usually at night), and more expensive at other periods (peak hours, usually during the day), then it is potentially advantageous to charge your battery from low cost Grid electricity (at night), storing it for later use at times of high Grid costs (during the day).

Solar PV electricity, however, makes this more complicated. If you fully charge your Battery at night from the Grid (during times of low Grid costs), then later on any excess Solar PV generated electricity can not be stored in the battery (because the battery is full) and it will have nowhere to go but export to the Grid.

If your Grid Export rate is similar or greater to your low peak Grid import rate, then yes, you should fully charge your battery from the grid at low peak times and let the excess Solar export to the Grid. Financially it works out the same or better.

If your Grid Export rate is less than your low peak Grid Import Rate, then you want to ensure there is remaining space in your battery to store any excess Solar electricity.