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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 installation, Council building consents, and Unison’s DG connection fees. If you have not had a quote yet, you can use our indicative prices from the table below, or use one of the NZ-based online quoting tools available.

Tell me about the cost of solar equipment.

Size of Solar Generator
1.5kW 2kW 3kW 4kW 5kW
$6,500 $7,000 $9,600 $11,100 $13,000

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%


From 1 April, Unison is introducing a new price category for Distributed Generation (DG) customers. This price category will be comprised of a fixed component, and a variable component, with a ‘Low User’ option for those using less than 8,000kWh/year. As with all distribution pricing, these costs are included within the retailers’ charges.

The DG price category is mandatory for all new DG consumers after 1 April 2016. For existing DG customers, they will remain on their existing price category through until 31 March 2019, after which the DG price category will also be mandatory.

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

Tell me about electricity costs and savings.

Tell me about the DG price category.

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 $0.3450 $0.3450 $0.3450 $0.3795
Standard User
  Fixed ($/day) Variable ($/kWh)
Year No Solar With Solar No Solar With Solar
1 $2.1850 $2.9383 $0.2610 $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)