Everyone knows the output of a typical rooftop solar system does not match the energy load of a typical household. For some reason, however, most systems are oriented north for peak generation at noon while the residents draw power in the morning and evening. This means most solar energy from rooftop systems is sent to the grid.
It doesn’t make a lot of sense.
If owners had the chance to think again and have their solar arrays rearranged, which ways should they face them?
This is the sort of problem research teams devour as essential sustenance, and a recent paper out of the University of South Australia has delivered a result that could turn the residential solar industry on its axis.
For their research Kirrilie Rowe, at the Research Node for Low Carbon Living, and Peter Pudney, from the Centre of Industrial and Applied Mathematics and the Future Industries Institute, designed an optimisation problem that sought to identify the best directions to face panels to maximise the amount of solar matched to load, rather than simply maximise energy output.
Using data for 29 dwellings in Lochiel Park, Adelaide, and 42 apartments in Bowden, their model imagined system sizes between about three and more than 20 panels to see what difference that would make to choices about layout, where the five options for orientation are east, north-east, north, north-west and west.
The results are surprising and also very obvious. Smaller systems should face north-west, to match afternoon output with load as best as possible. As systems were dialled larger, it’s better to face panels north-east and west, with some north-west. Very large systems are best facing east and west.
EcoGeneration turned the data into charts, to give you an idea of which way to face panels for certain system sizes and array sizes – based on average load profiles for houses and apartments.
It turns out it is generally only best to face arrays due north when a system is smaller than 1.4kW, when there is no surplus energy to export to the grid. “The best thing is to self-consume, in order to reap the benefits [of solar],” Rowe says. Once generation from a system is greater than the load at any time, that’s when it’s best to start pointing panels north-east and north-west.
The Lochiel Park research relied on minute-by-minute load data for one year which were matched to corresponding solar irradiation data and aggregated to half-hourly numbers for convenience sake. About half the kilowatt-hour load for the houses and apartments was outside daylight hours.
Solar feed-in tariffs will one day disappear, so the name of the game is to use as much of your solar energy as possible. As more households with PV upgrade to smart meters and are included in peak demand billing, they will benefit from matching their usage to their system’s output. “You’re importing less from the grid, so your bill will be cheaper.”
Rowe senses that the solar installation industry already knows panels should be oriented north-east and north-west to match load, but they probably don’t know to what degree it makes a difference. The university’s research could offer valuable guidance. Anyway, it’s very hard to make generalisations in the world of PV because different roofs have different slopes and not all street grids are laid out in neat north, east, south, west orientation. “Often installers will just have to use whatever they’ve got,” she says.
The model tested results for panels placed at 45-degree increments – west, north-west, north, north-east and east – but another version of the model where orientation was “unconstrained”, so arrays could be aimed in any direction, improved the result by up to 4% in reduced import, she says.
In an update to the research the authors found with a 20% decrease in PV area, the import required for a community with 700 square metres of optimally placed panels is still less than 900 square metres of panels facing north.
A lot on their plates
Installers are pushed for time as it is, scrambling between jobs in an effort to stay ahead of competitors. They may not have the time to work out a mix of panel orientations that best matches a client’s energy usage. If a customer is an energy nerd, as some are, and asks what layout would best help them minimise reliance on the grid, an installer in all likelihood would not be able to answer the question.
With research like this out in the open, installers stand a better chance at delivering systems that suit clients’ requirements.
Rowe’s motivation is to be part of a movement that will make communal life far more efficient and meaningful, she tells EcoGeneration. “If we were to change that structure of living into more a community-based living and restructure the way houses are set up, there are a lot of benefits to that,” she says, such as alleviating loneliness, stirring the social spirit and enabling simple but important communication.
“I chose energy as the one essential resource necessary in a community to help communities form and be structured in a better way. That’s my intention: to help them achieve cheaper energy bills and maximise the use of their own energy.”
She hopes the work will be useful to developers, energy businesses, embedded network operators and communities.
The results of the research reflect outcomes at a “precinct” level, where the load profile reflects average consumption. A solar system that is designed to match its generation with an individual household’s load profile might not be well aligned with the researchers’ results. “But if you are averaging a lot of houses, you will get that curve,” she says. “It’s typical of the state-wide curve as well.”
The data used for the apartments in the initial paper didn’t include energy for common usage, such as lifts and lighting, but apartments still use significantly less energy than separate dwellings, she says. Lochiel Park is an “eco village” in Adelaide, developed with government and university funding. Allowing communities such as this to form an embedded network, with shared energy resources and a single connection to the outside grid, can result in cost savings and encourage the uptake of renewables, she says.
Rowe has also worked on a yet-to-released paper that shows how to fairly share energy costs among residents connected to embedded networks.
Another study that’s in the works includes storage and looks at the payoff threshold between adding a battery and increasing the number of PV modules. “There is a point where it is better to add a battery than just add more solar panels,” she says.