Here’s the lowdown on the ‘HEMS’
Home energy management systems (HEMS) are rapidly gaining popularity around the world as the technology behind them improves and as small-scale solar power and battery storage become more viable.
But what exactly constitutes a home energy management system? We’ve seen some conflicting descriptions; with this article we aim to bring some clarity to the discussion.
Definition of HEMS
Like anything, the definition for ‘home energy management system’ will differ slightly from source to source, but we believe the below neatly encapsulates the concept without being too broad.
A home energy management system is a technology platform comprised of both hardware and software that allows the user to monitor energy usage and production and to manually control and/or automate the use of energy within a household.
A home energy management system’s hardware usually consists of a ‘hub’ device which relays communications between the goings on inside the house, the user and in some cases the local utility or electricity retailer.
This hub is usually installed on the home’s electrical board, but may also be installed ‘virtually’ in cases where the HEMS operates purely on a wireless network. Other, less essential components may include ‘smart plugs‘, light & temperature sensors, and smart devices within the home.
The software used in a HEMS is what moderates the ingoing and outgoing data and communications. From a user’s perspective, the software is the interface that allows access to monitoring data and control functions of the system. The interface usually takes the form of an app or web portal.
The software for some HEMS has the express goal of increasing the energy effectiveness or efficiency of the household, while the focus of others is simply to control devices remotely or automatically for convenience or security purposes.
As for monitoring, the sophistication of the way in which the data is displayed will vary, but will usually include some variation of the below:
- Device & appliance data — Which devices are on and off? How much energy is each one using?
- Granularity of time data — What is the smallest time increment that the system keeps track of — or that it displays to the viewer?
- Insights delivered — Does the system send notifications to tip off the user to trends and issues that they may not pick up on without parsing through the data themselves?
As for control, a HEMS may allow a user to do a range of things, including:
- Turn devices on and off remotely
- Set devices to operate on schedules
- Set up conditional rules for device operation
- Manage the flow of energy from solar panels (and other generators) through the home or in and out of batteries
- Allow ‘machine learning’ to take over and run the system semi-automatically
What exactly does a HEMS monitor and manage?
Home energy management systems can vary greatly in the breadth of their applications. There are four main aspects of home energy that a home energy management system can be involved in. Some HEMS operate with all four, while others may only work with one or two. We’ve outlined each of them below.
The core functionality of a versatile home energy management system involves the use of electricity within the home. A HEMS should give the user the ability to ‘see’ what devices are doing and to remotely ‘reach in’ and turn them on & off or otherwise modify their operation (e.g. turning down the thermostat temperature on an air conditioning unit).
Provided that the HEMS is geared primarily to save the user money, key considerations in electricity use management will include to grid electricity rates, whether the customer is on time of use billing, and whether there is solar power or batteries available on site.
A HEMS may also be required to operate in an off-grid scenario, in which case its role is even more crucial in ensuring that energy is used effectively so that it is always available when required.
Small-scale solar photovoltaic (PV) power — in the form of solar panels — has become commonplace in many countries, allowing homes to generate a portion of their electricity on-site. Depending on the situation and the incentive structure, a solar system owner may make it a priority to ‘self-consume‘ their solar energy directly or to export it to the grid as much as possible.
The presence of solar battery storage makes the equation even more complex — making a home energy management system an even more attractive option than for a home with no on-site generation.