A free tool has been developed specifically for New Zealand’s covered crop industry – so why aren’t more growers using it?

At the recent TomatoesNZ and Covered Cropping NZ Conference, Helen Barnes from GNS Science gave an excellent presentation on geothermal energy and the new Geothermal for Glasshouses Calculator. What surprised me most wasn’t what the calculator could do. It was how few growers in the room had actually used it.

If you are a greenhouse grower looking at your future heating options, I would strongly encourage you to have a look.

👉 TRY THE GEOTHERMAL FOR GLASSHOUSES CALCULATOR HERE

It is free, it has been developed specifically for covered cropping in New Zealand, and you can enter your own greenhouse information to start getting an idea of whether geothermal could potentially work for your business.

Why haven’t we used it?

Perhaps the answer is simply that growers haven’t realised the calculator is now available. I have written about the geothermal project previously on Grower2Grower. In 2025, we reported on the development of the tool and the work being undertaken by GNS Science, GeoExchange NZ, TomatoesNZ and Vegetables NZ. At that stage, it was still under development.

It isn’t anymore.

The Geothermal for Glasshouses Calculator has now been launched and is available for growers to use. And I think we should be using it.

What does it actually do?

This isn’t simply a map showing where geothermal resources might exist. The calculator allows you to select your location and combines available information about the geology, known underground temperatures, groundwater flow and aquifer characteristics with information about your greenhouse.

You can enter things such as:

• Greenhouse size
• Internal temperature
• Humidity control
• Thermal screens
• Electricity cost
• Gas cost

The calculator then estimates the heating requirement and provides an initial comparison of different heating options, including geothermal, ground-source heat pumps, air-source heat pumps and gas boilers. It also estimates capital and operating costs and compares the different options over a 25-year period. That doesn’t mean the calculator is going to tell you, “Drill here and install a geothermal system.” It isn’t a feasibility study. What it does is much more useful at the beginning of the decision-making process: it helps you establish whether geothermal is worth investigating further.

Don’t assume geothermal isn’t available

I think this is another reason growers may overlook it. When we hear “geothermal”, most of us immediately think of Rotorua, Taupō and the high-temperature geothermal fields. But greenhouse heating doesn’t necessarily require those sorts of temperatures.

Low-temperature geothermal resources can potentially provide useful heat for covered crops, either directly or through heat-pump technology. The calculator is currently focused on the greater Auckland, Waikato and Bay of Plenty regions, where the project has brought together available subsurface information. And that is what makes the tool particularly interesting. You don’t have to know whether you have a geothermal resource before using it. That is what the calculator is helping you find out.

Energy is becoming too important to ignore

I have written extensively about the energy situation facing New Zealand’s greenhouse industry. For many growers, heating is one of the biggest costs of production, and the uncertainty around future gas availability and pricing makes long-term planning increasingly difficult. We are looking at biomass, waste oil, heat pumps, electricity, solar and geothermal. There is no single answer. Some options will work brilliantly for one grower and make no economic sense for another. That is precisely why I think the geothermal calculator deserves a closer look. It costs nothing to investigate. If you put your information into the calculator and the result tells you geothermal doesn’t stack up, that’s useful information. But what if it shows that there is potentially a viable resource underneath your property? Then you may have something worth investigating further.

Don’t wait until you need the answer

One of the biggest mistakes a grower can make with energy is waiting until the existing heating system or fuel supply becomes a problem before investigating alternatives. Changing a greenhouse heating system is not a decision you make overnight. It can involve millions of dollars, infrastructure, consents, engineering, electricity supply, drilling and significant planning. So why not start investigating now?

The calculator is still being developed and Earth Sciences New Zealand is actively encouraging growers to use it and provide feedback. The organisation also stresses that geothermal resources are site-specific and that further investigation and testing would be required before making any investment decision. That’s fair. Nobody should be making a multi-million-dollar investment decision based solely on an online calculator.

But nobody should be making that decision without first knowing what options are available either.

So, why aren’t you using it?

Perhaps the answer is that you didn’t know it was available. Perhaps you assumed geothermal wasn’t an option for your property. Perhaps you are happy with your current heating system. Or perhaps, like many growers, you simply haven’t got around to it. Whatever the reason, I would encourage you to spend 15 minutes having a look.

You may find nothing.

But you might also find that there is an energy opportunity sitting underneath your greenhouse that you hadn’t even considered. And with energy becoming an increasingly important part of the future of New Zealand’s covered cropping industry, I think that is worth finding out.

👉 Click here and try the Geothermal for Glasshouses Calculator

You might be surprised by what is underneath you.