Quick answer
Not always. If the inverter already follows the right tariff times, stores spare solar, controls peaks and keeps the needed reserve, another EMS may add little. A separate EMS makes more sense when the site changes through the day and the battery needs its schedule updated using live data and forecasts.
An energy management system, or EMS, controls when a battery charges and discharges. Many commercial inverters already include some of these controls, so your client will not always need a separate EMS.
When a client buys a separate EMS, the installer connects it to the inverter. The EMS supplier then sets the software to calculate when the battery should charge or discharge using information such as:
- How much electricity the client’s premises use
- How much electricity the solar panels produce
- What the client pays to import electricity and receives for exporting it
- The import and export limits that apply to the premises
- How much charge the client needs to keep in reserve
The EMS sends its instructions to the inverter. The inverter then charges or discharges the battery.
Before recommending a separate EMS, check what the inverter’s existing controls can already do. The installer may first need to connect the site meter and enter the client’s tariff times, battery reserve, and import or export limits.
Some inverter controls only follow set charging and discharging times. Others also keep exports below a fixed limit or reduce grid use when the client’s demand passes a set level.
A client may find the extra cost of a separate EMS worthwhile when they need the installer or supplier to adjust the battery schedule as electricity use, solar generation, tariff prices, or grid limits change.
What can the client’s existing inverter controls do?
The inverter converts electricity from the solar panels or battery into electricity that the client can use on site. Most commercial inverter packages also include controls that may cover:
- Charging and discharging the battery at set times
- Storing spare solar electricity for the client to use later
- Keeping a minimum amount of charge in the battery
- Limiting how much electricity the client exports to the grid
- Reducing grid imports when the client’s demand passes a fixed level
These controls may cover everything the client needs when their electricity use follows a simple and predictable pattern.
For example, a small warehouse may use a similar amount of electricity each weekday and pay one rate during the day and a cheaper rate at night. The installer could set the battery to:
- Charge during the same cheaper period each night
- Discharge during the same higher-priced period each day
- Keep a fixed amount of charge in reserve
When the inverter controls already cover these needs, the client may not save enough money by adding a separate EMS to recover the extra controller, software, and support costs.
When should you recommend a separate EMS?
Your client may benefit from a separate EMS when their electricity use, solar production, or tariff prices change throughout the day and the existing controls cannot adjust the battery schedule.
The EMS supplier sets the software to calculate when the battery should charge or discharge. The EMS sends those instructions to the inverter. The inverter follows them within the safety limits that the battery management system sets.
The battery management system, or BMS, protects the battery by controlling matters such as temperature, charging rate, and minimum charge level.
A separate EMS may help the client save more when the software can:
- Measure the electricity entering and leaving the premises at the grid connection point
- Use the prices and time periods in the client’s actual tariff
- Forecast the client’s electricity demand and solar generation
- Keep enough charge for a later period of high demand
- Recalculate the battery schedule when actual demand or the forecast changes
For example, an installer may set a battery to start discharging at 4pm every day. However, the client’s highest demand may not occur until 6pm.
A separate EMS could use the demand forecast to keep some charge for that later peak. It could also schedule more overnight charging at the cheaper rate when the solar forecast shows that the panels will probably produce less electricity the following day.
A client with steady daytime electricity use, predictable solar production, and a simple tariff may gain little from this extra control. A client may have a stronger case for it when they have:
- Large or unpredictable peaks in electricity use
- Solar output that changes considerably from one day to the next
- Tariff prices that change at different times
- Import or export limits that affect when they can charge or discharge the battery
- A need to charge and discharge the battery several times during the day
Before including a separate EMS in a proposal, check whether the inverter’s existing controller can:
- Measure all electricity entering and leaving the premises
- Use all the rates and time periods in the client’s tariff
- Forecast electricity demand and solar production
- Change the battery schedule when the forecast or actual demand changes
- Receive charging and discharging instructions from a separate EMS
- Follow a backup schedule if the EMS loses its internet connection or cannot communicate with the inverter
When the existing controller cannot carry out the work the client needs, a separate EMS may justify its additional cost.
GridVolt’s Energy Manager provides one example. It forecasts the client’s electricity demand and solar production for the next 48 hours and recalculates the battery schedule every 15 minutes.
At one commercial site, the client recorded a 41% increase in battery savings during the first 70 days. This result shows what the revised scheduling achieved at that site. Sales reps should not present it as the saving every client will receive.