Quick answer
A built-in schedule can be enough when the site uses electricity in a steady pattern, tariff prices change at set times and solar output is fairly predictable. If the battery can charge, discharge and keep its reserve at the right times without regular changes, a separate EMS may not save enough extra money to pay for itself.
A client may not need a separate energy management system, or EMS, when their electricity use follows a predictable pattern, their tariff prices change at set times, and their solar panels regularly produce a similar amount of spare electricity.
In that case, the installer can program the inverter controls to:
- Charge the battery during the same low-rate period each day
- Discharge the battery during the same higher-rate period
- Store spare solar electricity for the client to use later
- Keep a fixed minimum amount of charge in the battery
- Reduce the amount of electricity the client buys from the grid during a peak that usually occurs at the same time
Before recommending this approach, check the client’s recent interval data. The client’s meter records how much electricity they use during each half-hour or 15-minute period. You can use these records to check whether the client follows a reliable pattern from one day to the next.
Do not assume that the client uses the most electricity at the same time every day simply because the business keeps regular opening hours. Staff, machinery, heating, cooling, or vehicle charging may cause the client’s highest demand at different times on different days.
You also need to calculate how much the client will save. Compare the low-rate and high-rate tariff prices, then allow for the cost of charging and discharging the battery and the electricity lost during the process.
For example, the client might pay 15p per kilowatt-hour to charge the battery and then use that electricity instead of buying power at 20p per kilowatt-hour. The client will receive less than one kilowatt-hour back from the battery for every kilowatt-hour they buy to charge it. The price difference may therefore leave them with very little saving.
When the client’s electricity use does not follow a reliable pattern, or fixed charging and discharging times do not save enough money, a forecast-led EMS may produce a better result. The supplier can program the EMS to calculate the charging and discharging times from forecasts of the client’s electricity demand and solar generation.
What should you check before recommending a separate EMS?
Before adding a separate EMS to a proposal, check whether the installer can use the client’s existing inverter controls to do everything the client needs.
Review the client’s electricity data and check whether:
- The client uses the most electricity during the planned discharge period
- Weekends and seasonal changes affect when the client uses electricity
- The client uses electricity differently on unusually busy, quiet, or lightly staffed days
- The usable battery capacity matches the amount of electricity the client expects to need during the planned period
- You can see the same pattern of electricity use in the half-hourly or 15-minute records
Next, ask the installer or inverter supplier whether they have connected the inverter controller to the grid meter and configured it to change the battery output in response to live meter readings.
The client may not benefit from paying for another EMS when the installer has already configured the existing controls so that:
- The battery charges and discharges at times that match the client’s usual pattern of electricity use
- The battery output changes in response to live grid-meter readings
- The battery discharges during the client’s usual period of highest demand
- The battery does not charge or discharge when the likely saving would not justify the additional wear
In that situation, the client may pay for a separate EMS without gaining much extra control or saving.
You may have a stronger reason to recommend a forecast-led EMS when you can see from the client’s electricity records that they currently:
- Buy high-rate electricity during demand peaks even though the battery has enough charge to reduce those grid imports
- Export spare solar electricity while the battery still has room to store it
- Charge or discharge the battery at less favourable tariff times
Before recommending the extra controller, software, and support, calculate the additional saving in your model and compare it with the additional costs that the client will pay.
Related questions
Does a client need a separate EMS if the inverter already controls the battery?
When is it worth adding a separate EMS to a commercial battery?