Small-scale energy storage systems are a game-changer opportunity for customers, networks and retailers in the space of residential energy provision. The solar PV systems wave has well and truly hit. This has enabled small energy users to take energy pricing into their own hands to some degree.
Residential battery energy storage systems (resi-BESS) offer customers the ability to store their solar PV generation and use it later. There are also a number of home energy management systems (HEMS) coming onto the market that enable customers to view and manage their energy use.
To understand how changes in technology will affect energy usage, Queensland network provider and retailer Ergon Energy is running a trial of 10 customers on a single street connected to the same distribution transformer, with the support of the Queensland Department of Energy and Water Supply.
Each household has solar PV, BESS and HEMS installed on the customer side of the meter. Trials were conducted over 12 months, with a second phase about to commence. In phase one, three cost-reflective tariffs were tested among houses where four different types of storage systems were installed.
The customer circuits were arranged into three groups:
Essential: light and power circuits; power is supplied from grid, solar PV or battery storage.
Non-essential: cooking, shed power; power is supplied from grid only.
Controlled: hot water, air-conditioning, pool pumps, bore pumps; power is supplied from grid only via economy tariff.
The essential circuits could use power from the grid, solar PV or battery storage and this choice was determined by the BESS, which were programmed by Ergon personnel. The BESS control algorithms were proprietary to each vendor, were all very different in setting up and in general all were less sophisticated than desired or expected.
The field trial tested three tariffs with customers in a shadow environment, so actual costs were not incurred and a small financial incentive was provided motivation to change behaviour based on the tariff details. The three tariffs tested were: time of use (TOU), capacity (CAP) and time of use demand (TOUD). Each tariff test was conducted for two weeks and analysed against each other and a control period. Customers were given the specific tariff details the week prior to testing and then notified again on the morning the testing commenced.
Problems along the way
A significant number of challenges and barriers were encountered during the project. Integrating BESS and HEMS technologies into existing electrical installations was problematic. Customers experienced a range of issues that included considerable switchboard modifications, lost HEMS data, power outages, undesirable operational outcomes from the BESS and failure of appliances.
The HEMS was a very good energy monitoring device, providing circuit level data in one-minute intervals. However, issues were encountered when attempting to control loads. The lack of integrated communications between the solar PV and the BESS also caused some issues.
There was a large variation in quality and functionality of the BESS units installed on this project and there were issues with all brands of BESS. Increased cost did not correlate with a decrease in issues. The most expensive unit provided some of the greatest challenges and the least expensive unit was the most reliable but most complex to program. The total house load was not able to be supplied by the BESS and hence only light and power circuits were powered by the BESS, with grid supply the only source for cooking, pumping and cooling loads.
Cost-reflective tariffs can provide more accurate price signals to customers for the delivery of energy. Time of use tariffs are too static and do not always accurately indicate the system or local peak. They also encourage daily cycling of BESS, which reduces life of the batteries when there may not be a need to do so.
Capacity and demand tariffs provide a good signal to customers in regard to household power limits, but without a suitable control system either within the BESS or the HEMS, household load management is almost impossible to achieve. The time of use demand tariff was complex and customers did not understand it or have an energy management system that could avoid costly impacts. A smarter energy management system, either as part of the BESS or as a separate HEMS, is needed for demand tariffs.
Customers, energy retailers and networks have different drivers and incentives with regard to operating a BESS. Energy utopia is when these stakeholders all achieve their desired outcomes through a sustainable and cost-effective model (a win-win-win).
What have we learned?
Customers with multiple sources of energy (grid and solar PV), storage (BESS) and an advanced energy management system (HEMS) have all of the hardware required to provide the best chance of reducing impact from cost-reflective electricity prices.
This project has shown that without an effective integrated control system, negative grid and customer impacts cannot be avoided. The project has also demonstrated the amount of opportunity for further development of BESS and HEMS to provide improved outcomes for the customer while remaining adaptable in the energy market.
The most likely scenario for achieving energy utopia is with a local integrated advanced energy management system that can receive data from local and remote sources, make decisions, and control loads (where desirable), generation and storage to achieve positive outcomes for customers, retailers and networks.
Dean Condon is technology innovation engineer at Ergon Energy, where he leads projects to evaluate grid-connected technology. He has worked in the electricity industry for 25 years and on the Queensland Solar City project since inception in 2007.