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Solar Calculator


Annual Household Electricity Consumption

This is the current amount of electricity your household consumes annually. This information can generally be found on the monthly account you receive from your electricity retailer.

System Size (kW)

This is the size of the solar energy system you are planning to install. For the average household, a 3kW system is the most common choice.

Tell me about selecting the right system size.

Solar System Installed Cost (inc. GST)

This is your total investment cost to install solar energy. In addition to the price of the system itself, you should also include any additional costs such as installationand Council building consents. If you have not had a quote yet you can use one of the NZ-based online quoting tools available.

Tell me about the cost of solar equipment.

Solar Generation Consumed (%)

This is the percentage of energy you are actually able to use, from the solar energy your system generates. Based on our research of residential homes in Hastings, we have developed the following guidelines, based on system size in the table below.

Tell me about using solar energy.

Size of Solar Generator 1.5kW 2kW 3kW 4kW 5kW
Generation consumed (kWh) 95% 85% 67% 55% 46%
Generation exported (kWh) 5% 15% 33% 45% 54%


Unison distribution charges for residential properties will typically be calculated on our Time of Use plans. This means there are different prices for different times of the day. The lowest rates, off-peak, occur during the late night-early morning from 11pm to 7am. The highest rates, peak, occur from 7am to 11am and from 5pm to 9pm. In between these times the shoulder rates apply. These rates apply to all residential connections whether you have solar generation or not, battery storage or not.

There is an option of selecting the low-user plan if you expect to source less than 8,000kWh of energy per year from the grid, this offers a reduced level of fixed daily rate and will be a lower overall cost at these levels of grid use.

For the purposes of the solar calculator, it has been assumed that electricity retailers will directly pass-through the Unison line charges to the customer. To keep the calculator as simple as possible, we have applied Hawke’s Bay residential pricing, however it should be noted that pricing levels are slightly different for customers in Rotorua or Taupo.

Tell me about electricity costs and savings.

Interest Rate

We recommend using the standard market rate for your chosen finance plan. We have used a typical home mortgage rate.

Tell me about financing my purchase.

Calculating the Benefits

To calculate the financial benefits, we have used the following current market rates:

Low User

  Fixed ($/day) Variable ($/kWh)
Year No Solar With Solar No Solar With Solar
1 $0.69 $0.3450 $0.29 $0.3795

Standard User

  Fixed ($/day) Variable ($/kWh)
Year No Solar With Solar No Solar With Solar
1 $2.1850 $2.9383 $0.22 $0.2610

Note: Assumed market rates are GST inclusive and 1.4% annual pricing increases have been applied.

The benefits of solar are driven by both surplus generation exported to the grid, and avoided purchases of electricity from your retailer, as a result of directly consuming solar generation. The calculator includes a market buy-back tariff of $0.08.

Internal Rate of Return (IRR)

If the IRR is equal to, or greater than, the interest rate used in the calculation, this would indicate positive long-term benefits from your investment.

The Internal Rate of Return is a calculation used to evaluate the attractiveness of an investment. If the IRR of the investment exceeds the required rate of return, that project is desirable. If IRR falls below the required rate of return, the investment should not be considered.

Investment Net Present Value (NPV)

If the NPV is positive, this indicates support for investing in solar.

Net Present Value is a calculation that estimates the ‘present’ value of an investment's expected cashflows, less the costs of acquiring the investment.

Outputs from this assessment tool are indicative only. The "Payback Years", "Internal Rate of Return" and "Net Present Value" all include an allowance for gradual panel degradation (from 97% of nominal capacity in year 1 to 82% in year 25.