Hot water heat pumps can slash energy bills and carbon emissions due to their sheer efficiency, but take things to another level when timed to draw on cheap solar instead of expensive grid energy. Here’s what your heat pump needs to make this possible.
How Do You Time Hot Water Heat Pumps To Use Solar?
There are three basic options to consider when choosing a hot water heat pump that works hand-in-glove with rooftop solar: internal timers, external timers, and daytime controlled load circuits. Each offer their own benefits, and can also assist non-solar owners too by ensuring a heat pump runs when electricity is cheapest.
Option 1: A Heat Pump With An Internal Timer
The first option is a timer that can control when the hot water heat pump is on and off. Some heat pumps will have internal timer controls which can offer different time windows for heat pumps to be programmed and operated. Some options include a solar time window during the day to make use of excess solar (i.e. between 9am-3pm) or an off-peak electricity time window to make use of cheaper electricity rates (i.e. between 10pm-7am, this may be preferable for households that don’t have a solar system).
The programmable internal timer of an Aquatech heat pump.
Changing With The Seasons
Certain heat pumps can also give more customized timing options for the users which includes choosing a more specific time window (or different windows) depending on user preference. Moreover, some options can automatically change the timer window based on season, which can be very useful as a household’s hot water requirements, heat pump’s efficiency (often known as Coefficient of Performance – COP), daily energy consumption and the available excess solar generation window can significantly change across seasons. Regardless of these options, you should consider a heat pump manufacturer’s recommendations on the minimum required number of hours per day for heat pumps to run.
I’ve compiled information on heat pump models with and without timers for this piece, drawing on reviews and heat pump manufacturers’ data from manuals and sheets. The first table below is for brands with simple internal timers.
| Heat Pumps With Simple Internal Timers | ||||
|---|---|---|---|---|
| Brand & Model | Programming Ease | Performance | Timer Type | Notes |
| Aquatech X6 | Simple interface | Rated as reliable and straightforward to program. | Basic: Simple digital, multiple periods | Easily adjusts for day vs night loads. |
| Enviroheat 200EH1-14 / 250EH1-15 | Basic onboard | Good for set-and-forget, some DIY confusion reported. | Basic: Single or dual period on/off | Suitable for set-and-forget, less granular. |
| Rinnai Enviroflo | Basic controller menu | Consistent reviews on energy savings. | Basic: Single or dual block | May need installer to help program. |
| Solahart Atmos Eco 280HER | Onboard digital, once learned | Good customer satisfaction. | Basic: Single or dual period | Often set with “solar” default by plumber. |
| Thermann Split | Simple digital, usually set at install | Reliable performance, often “plug & play.” | Basic: Single or dual block | Controller often mounted near tank. |
How To Program An Internal Timer
Internal timers can be programmed by the installers during the installation, left at the default program set by the heat pump manufacturer, or be programmed/changed later by the owners if desired, as some of these timers can easily be controlled by manufacturer apps or LED screens provided on the heat pumps.
Internal Timers Know What The Heat Pump Needs
The advantage of having an internal timer is that you don’t have to buy an external timer to make the most of your solar generation. Furthermore, the internal timer is aware of heat pump operational cycles and wouldn’t turn the unit off during critical operations and cause potential damage or shorten its lifecycle (such as de-frost cycles in colder climates, refrigerant cycles and compressor operation).
| Heat Pumps With Complex Internal Timers | ||||
|---|---|---|---|---|
| Brand & Model | Programming Ease | Performance | Timer Type | Notes |
| Apricus APHP-R290-260 | Easy Wi-Fi app scheduling | Positive user reviews on energy savings & app. | Advanced: Multi-period + Wi-Fi | Digital controller supports multiple time slots, ideal for solar self-use. |
| Emerald All-In-One | Intuitive digital + Wi-Fi | Positive reviews on smart scheduling & quiet operation. | Advanced: Wi-Fi app, multiple schedules | Great for daily or seasonal tweaks. |
| Evoheat EVO150-1 / EVO270-1 / EVO315-C | Advanced touchscreen | Top reviews for energy + solar optimization. | Advanced: Multi-period + optional Wi-Fi module | Allows day split (e.g. 10-3) to maximize solar. |
| Haier Monoblock HP200M1-U1 / HP250M1-U1 | Clear settings | Well-liked for quiet, reliable operation. | Mid: Multi-period digital | Good for daily adjustments. |
| iStore PASHW015-270LD-FL02 | Very clear digital | Excellent ratings on energy bills. | Mid: Digital, supports daily blocks | Easy to tweak to PV export windows. |
| Reclaim CO2 | Often programmed by installer | Widely praised for efficiency & minimal grid use. | Advanced: Multi-period via wall controller | Controller may be tricky DIY, needs plumber to program. |
| Rheem Ambiheat | Digital interface, often set by tradie | Known for reliability & brand trust. | Mid: Multi-period controller | Settings often hidden in installer menu. |
| Sanden SAN-160SAQA / SAN-250SAQA etc | External controller, usually installer set | Leading COP, best for cold climates. | Advanced: Multi-period external | Ideal for complex schedules, but often dealer-only set. |
Option 2: An External Timer
If the heat pump model doesn’t have an internal timer, you can buy an external timer which can control the electrical circuit of the heat pump based on programmed timing windows. The external timer can be a plug-and-play solution, or the timer can also be installed in your switchboard.
An external heat pump timer.
Give The Heat Pump Enough Time To Do Its Job
Like internal timers, external timers give users a programmable time window which can be set to run during solar generation windows, while some units may give options to choose multiple time windows during the day as well. One of the important considerations when using the external timer is to give enough of a time window for the heat pump to complete the operation when heating water, so you are not left without sufficient hot water. Similarly, longer time windows may also reduce the risk of cutting power to a heat pump in the middle of operation. Some installers program external timers on a longer time window to minimize these risks (this can be an easy set & forget solution for some users). On the other hand, longer time windows may potentially reduce utilization of excess solar especially if these time windows cover periods with no or minimal solar.
Less Customisation
Most external timers may not allow detailed customization or seasonal adjustments, and users may manually need to change timer settings if they would like to get more out of their solar across different seasons, depending on their water heating consumption.
External timers will incur additional capital and installation costs however; these are generally not significant. You may get your timer installed during the heat pump installation which can save some money.
| Heat Pumps Without Internal Timers | |||
|---|---|---|---|
| Brand & Model | Performance | External Timer Recommendation | Notes |
| Ecogenica R-series | Highly efficient but lacks internal scheduling, so solar optimization depends on external timer. | Hager EG203E or ABB DBT digital timer. | Needs DIN rail timer to align to solar. |
| Quantum | Reliable heating but always on unless externally controlled. | Clipsal 56 series or ABB DBT recommended. | External Clipsal or Hager timer recommended for solar self-use. |
| Stiebel Eltron WWK 222 / WWK 302 | Quiet operation, efficient but requires external timer for solar. | Clipsal or Hager timer recommended. | Often paired with Hager timer on switchboard. |
Option 3: Controlled Load
Another option to run your heat pump during solar generation window is through controlled load circuits which are managed by the distribution network service providers (DNSPs) or more recently by the retailers (especially in South Australia and New South Wales). Controlled load was traditionally used to run the water heaters in the middle of the night where there wasn’t much demand in the network to keep coal power plants operational. With increasing solar installations and excess generation during the day, controlled load now includes a solar generation window as well, offering cheaper network rates for water heating. This option currently doesn’t allow a household to make use of their own rooftop solar behind their meter but running your heat pump in the middle of the day will indirectly make use of the abundant excess generation in the network.
Putting a heat pump on a controlled load can help save money on your energy bill.
Discounts For The Solar Window
Depending on the retailer, users may get discounted prices for running their appliances during the peak solar generation window. It is a good idea to check with your retailer and ensure their general electricity and controlled load tariffs offer cheaper daytime rates for running their heat pumps.
Potential Damage To Hot Water Heat Pumps
A potential downside with this solution is that heat pump operations may get interrupted in the middle of operations, which may cause potential damage and shorten the life cycle of certain units (not all heat pump manufacturers raise this as a concern however, some do). Also, this solution may not be as financially attractive as the timer solutions, especially if you have your own rooftop solar system.
No Matter What, Understand Your Heat Pump First
No matter which control option you choose, it is extremely helpful to monitor the daily energy operations of your heat pump to understand its operational cycle and power requirements. You may refer to your heat pump manufacturer’s apps or third-party monitoring solutions to do this. This can help you in choosing the optimal solution to make the most of your solar and ensure your heat pump is operating smoothly. It is also important to consider heat pump manufacturer’s recommendations when running your heat pumps on external timers and controlled load to ensure longevity.
Beyond these three options, there are more advanced alternatives to consider, such as configuring your solar inverter to only activate the heat pump when there’s enough solar available, although take care that this doesn’t lead to intermittent turning on and off of the appliance.
For more on hot water heat pumps, browse SolarQuotes’ comparison chart which covers not only whether brands have internal timers, but all the other key specs.
This article was produced in collaboration with Dr. Arastoo Teymouri.
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I dont make enough solar for 3 months in winter to guarantee enough power for a heat pump, I get my battery charged most days, but not much else.
It would be great if power companies allowed your system to be connected to both your own solar, and the controlled load for when the solar wasn’t enough, but that would make to much sense…
For myself I still believe my solar HWS with a timer which I can over ride and set its boosting function is the most effective system. I set my boost function between 11AM and 3PM daily. It simply allows my heating elements power should the temperature be below the systems hot water settings. So in reality that equates to only drawing power if it needs to and even in winter it often only draws power for less than an hour. Worse scenario is cold weather and no sun for my pvc battery system.
The costs of scrapping a performing solar HWS for a new efficient one together with consideration for impressed pollution ie manufacturing, and disposal etc doesn’t add up no matter how I cut it.
Sure it may be a consideration when the time comes for replacement.
I believe Im getting more solar energy ie from the infared spectrum as an addition to visual light spectrum with both types of collection methods
There are a LOT of links to methods to control Heat Pumps from Home Assistant. Ideal for the tech savvy or geeks.
Home Assistant can read data from PV equipment (Inverters, batteries, EVs, etc) then can be programmed to control loads such as EV chargers, Heat pumps, A/C´s etc. HA as a total home management solution can monitor &
control the home (even AV equipment), depending on the level one wishes. Many options are already enabled now HA is becoming a more fully featured Open Source solution. Even Bi-directional EV charging management is already included even tho not yet fully available in Australia.