When is it worth adding a separate EMS to a commercial battery?

Recommend a separate energy management system, or EMS, when your figures show that the client will save or earn comfortably more each year than they will pay for:

• The controller
• Any extra meters or current transformer clamps
• Integration
• Software
• Support
• Any share of trading income that the EMS provider keeps

Compare the separate EMS with the inverter manufacturer’s best available controls, not with a basic timer.

First, ask the installer or inverter supplier to confirm that they have connected the correct grid meter, installed the right firmware, entered the tariff times, and selected the right battery operating mode and reserve settings.

Then check whether the installer can use the existing inverter controls to cover the client’s main needs, such as:

• Storing spare solar electricity
• Reducing peak grid use
• Charging during cheaper tariff periods
• Keeping a minimum amount of charge in reserve

Most commercial inverter manufacturers already give installers controls that let them adjust battery output using live import and export readings, reduce grid use during periods of high demand, store spare solar electricity, and charge the battery during cheaper tariff periods.

You therefore need to show how much more the client will save or earn with the separate EMS after paying all its extra costs.

What controls does a commercial battery inverter already include?

Most commercial battery inverters now do a lot more than charge and discharge at fixed times. Their built-in controls usually cover:

• Solar self-consumption
• Peak shaving against site demand
• Time-of-use charging
• Minimum state-of-charge reserves
• Control across several inverters
• Combine more than one operating mode

So, before you propose adding a separate EMS to your client proposal, check their current setup. Then calculate how much extra the client could save or earn each year after adding the separate EMS and paying all its costs.

How do I work out the extra saving or income from adding our EMS?

Calculate the extra saving or income from the EMS, not the battery project’s total saving.

Model the same battery twice:

1. With the inverter manufacturer’s best available controls
2. With the separate EMS

Use the same information in both models:

• Half-hourly or 15-minute electricity-use data
• Import tariff and export prices
• Solar generation
• Usable battery capacity
• Charging and discharging power
• Import and export limits
• Efficiency and battery degradation assumptions

Use the site data, battery details, and current performance information that the client can provide. When the client already has an EMS, ask them for any reports or portal data they can access. Check the assumptions behind the figures before using them in your comparison.

Show the client:

• The annual saving or income with the inverter’s best controls
• The annual saving or income with the EMS after all extra costs
• A cautious result based on lower tariff differences, less favourable solar or demand forecasts, or lower trading income

Subtract the cost of the controller, extra meters or current transformer clamps, integration, commissioning, communications, software, maintenance, and any share of the trading income that the EMS provider keeps.

Present the result as a like-for-like comparison. Show the extra annual saving or income from the EMS after all added costs.

You can use GridVolt’s simulator to compare battery performance under different control assumptions. Show the client the additional annual saving they could receive from Energy Manager after deducting all added costs, rather than the battery project’s total saving.

Related questions

Does a client need a separate EMS if the inverter already controls the battery?

How much more can a commercial battery save with optimisation software than with fixed inverter schedules?

How do I size a commercial battery for the best payback?