Does a heat pump change the case for solar?

A heat pump changes the solar decision because it changes when the house uses electricity, and how much. Heating demand in New Zealand rises in winter, which is when a rooftop array produces less. Cooling demand, where people use it, rises on the hot afternoons when the array is strong. The same machine can make solar look better in January and leave a large import bill in July.

Solar power for your house does not run a heat pump for free all winter. It can cover a useful share of daytime heating and cooling if someone is home, or if the unit is allowed to run while generation is high. Night setback and evening use still come from the grid unless you have storage.

Winter is the awkward season

Day length is shorter, the sun is lower, and cloud is more common. A north-facing array still produces, but a clear January day is a poor picture of July. EECA's savings examples are annual figures for a reason. A heat pump that is asked to hold 21 degrees from 6am to 11pm in July will import heavily in the hours the panels are weak or off.

That does not make the combination pointless. It means you judge it on the year. If the heat pump replaces resistance heaters or a large plug-in load, the house may use fewer kilowatt-hours overall, and solar covers the daytime slice of what remains. If you are adding heat to a house that used to rely on a wood burner during the day, you are adding electrical load in the weak season. Tell the designer which change you are making.

Insulation and curtains still cut the kilowatt-hours the heat pump has to supply. Solar on a cold, leaky house is the slower comfort upgrade. Many households do both. The worth-it guide compares solar with other energy work: https://homesolarinstallation.co.nz/blog/is-solar-worth-it-nz/

Summer cooling lines up better

Afternoon cooling sits closer to generation, especially on a west or north-west face. A house in a warmer pocket that actually runs cooling will self-consume more in summer than a house that only heats at night in winter. Say whether you use the heat pump for cooling. A design that ignores it will understate summer self-consumption. A design that assumes cooling you never switch on will overstate it.

Coastal and elevated sites do not all want cooling. A Devonport or Takapuna house and an inland Coatesville or Kumeu house can have different afternoon patterns. The installer should use your bill, not a national persona.

Efficiency and what to hand the designer

Heat pumps deliver more heat per kilowatt-hour than an electric element or a fan heater. Replacing those with a heat pump can shrink the annual total even before solar. Size the array on the bill you expect after that replacement, not on last year's fan heaters if the fan heaters are leaving.

Give the designer the heat pump size if you know it, the rooms it serves, and the hours you run it. Work-from-home days and empty weekdays produce different solar results. A timer or a preheat that starts late morning can move some of the load under the array. Comfort limits are real: preheating a house you do not arrive at until 6pm only helps if the building holds the heat.

EECA's planning examples start from annual use and daytime presence: https://www.eeca.govt.nz/for-homes/solar-for-homes/plan-your-solar-system/ A rough national context they cite is around 7,000 kWh a year for an average household. A heat pump house can sit well above or below that. Use your figures.

Export limits and a heat pump that is off at noon

If everyone is out and the heat pump is off, midday generation goes to export or gets clipped if the street has an export cap. A heat pump you refuse to run while you are out will not soak up that surplus. Decide that on purpose.

A battery can shift noon generation to the evening heating peak. EECA notes that solar without a battery generally returns better financially. Buy storage because the evening peak is large and you accept a longer payback, not because a brochure put a heat pump and a battery in the same picture. The battery guide is here: https://homesolarinstallation.co.nz/blog/solar-battery-storage-nz/

The export cap, if there is one, belongs in the same model: https://homesolarinstallation.co.nz/blog/solar-export-limits-nz/

Electrical capacity

A new heat pump circuit and a solar inverter both land on the switchboard. If the board is full, price that once. An EV charger on top of both is a third circuit and may need load management so the main supply is not overloaded. Say what is coming in the next few years.

The electrical work is licensed. A solar quote that excludes the heat pump circuit is fine if it says so. It is not a complete price for the house you are planning. Board checks are covered here: https://homesolarinstallation.co.nz/blog/solar-switchboard-upgrade-nz/ and Tromar Electrical can look at the board: https://tromarelectrical.co.nz/

How to judge the quote

Ask for two self-consumption pictures if the heat pump is part of the reason you are buying solar: winter weekday, and summer weekday. A single annual kilowatt-hour number hides the season you actually care about.

Then put the installed price next to a cautious annual saving. EECA's medium-system band is around $11,500 and their Auckland 5 kW savings example is $1,246 a year. Your heat pump pattern can move you off both numbers. The cost bands are here: https://homesolarinstallation.co.nz/blog/solar-panel-cost-nz/

Home Solar Installation NZ can introduce a local partner. The form is free and there is no obligation. Tell them the heat pump is part of the design brief.

Across these suburbs the climate is not one number

Heat pump and solar designs for Algies Bay, Arkles Bay, Army Bay, Big Omaha, Coatesville, Dairy Flat, Dome Forest, Dome Valley, Glorit, Gulf Harbour, Hatfields Beach, Helensville, Huapai, Kaukapakapa, Kawau Island, Kumeu, Leigh, Matakana, Muriwai, Omaha, Orewa, Puhoi, Riverhead, Snells Beach, South Head, Waimauku, Warkworth, Wellsford, Bayswater, Belmont, Campbells Bay, Castor Bay, Devonport, Forrest Hill, Hauraki, Milford, Narrow Neck, Stanley Point, Sunnynook and Takapuna still use the house, not the suburb slogan. Exposed coastal sites at Muriwai, South Head, Leigh, Hatfields Beach and on Kawau Island lose heat faster in a wind than a sheltered Belmont or Hauraki section. Inland mornings around Coatesville, Dairy Flat, Kumeu and Huapai can be colder than a Takapuna afternoon. Those differences belong in how you run the heat pump, and in the yield model for that roof.

EECA's regional savings table is a briefing tool, not a room-by-room result: https://www.eeca.govt.nz/for-homes/solar-for-homes/solar-costs-and-savings/