Comparing solar installation companies is most useful when each quote is based on the same household needs and a clearly explained system design. A lower price may reflect a smaller system, different equipment, less site assessment or work excluded from the quote—not necessarily better value. Ask each installer to show how roof orientation and shading, electricity use, inverter choice and any battery plans shaped its proposal. Then compare what is included, what savings assumptions depend on, and what happens if your plans change. A good quote should make its reasoning clear enough for you to weigh the trade-offs, not just compare a headline price.
Two proposals can look similar at a glance while being based on different assumptions. One might use more of your roof, another might avoid a shaded section; one might aim to cover more of your annual electricity use, while another prioritises using solar power during the day. Before comparing totals, ask each company to explain how it reached its design.
Look for a site assessment that considers the roof’s available area, orientation, pitch, shading and condition. The proposal should identify any constraints that affect panel placement or installation. If an estimate was prepared without a site visit, ask what information the company used and whether the design or price could change after a closer inspection.
Use the same household information when requesting quotes. Provide recent electricity bills, explain when people are usually home, and mention major appliances or planned changes such as an electric vehicle, heat pump or renovation. If you share different information with each company, their system sizes and savings estimates may not be directly comparable.
Rather than relying on a salesperson’s overall recommendation, compare the proposal’s evidence and scope item by item. The table below can help you identify what to clarify before deciding.
| What to compare | What a useful proposal explains | Question to ask |
|---|---|---|
| Roof assessment | Panel locations, shading, usable roof area and any visible installation constraints | What site information could change the layout or final price? |
| System size | How the proposed capacity relates to your electricity use and daily patterns | What consumption assumptions did you use, and why? |
| Solar production | The assumptions behind the estimate, including roof orientation and shading | Does the estimate account for the conditions on my roof? |
| Inverter | Equipment type, location, monitoring and how the design handles shading or future changes | What are the advantages and limitations of this option for my home? |
| Battery | Whether storage is included, optional or designed for possible future addition | Does the system provide backup during a power cut, or only store energy for later use? |
| Installation scope | Included electrical and roof work, equipment, commissioning and handover | Which likely extra costs are excluded from this price? |
A larger system is not automatically the right choice. The useful size depends on how much electricity your household uses, when you use it, how much suitable roof space is available, and what you expect to do with surplus generation. A proposal that focuses only on annual consumption can miss the difference between using electricity during sunny hours and using it in the evening.
Ask each solar installation company to show the electricity-use information behind its recommendation. Bills can help establish overall consumption, while interval data, if available from your retailer or meter information, can give a clearer picture of when demand occurs. The installer should explain whether the design is intended to serve daytime loads, increase overall solar generation, or leave room for a battery or future appliances.
Look closely at the production estimate, too. It should reflect your actual roof layout rather than an idealised, unshaded roof. Ask how shading, panel direction and the proposed arrangement affect the estimate. A projection is not a promise of a particular bill reduction; actual results also depend on household use, equipment performance, electricity tariffs and how much power is exported rather than used at home.
Tell the installer about credible plans that could change your electricity use, such as adding an electric vehicle or replacing a heating system. These plans may affect whether a different system size, inverter or battery arrangement is worth considering. If the change is uncertain or several years away, ask for the cost and practical implications of designing for it now versus adding equipment later.
Do not pay for extra capacity simply because future use might rise. Ask the company to separate the current-home recommendation from any future-ready option, and to explain what each additional component would enable. That makes it easier to judge whether the added cost matches a real plan.
The inverter converts the electricity produced by the panels into a form used by household appliances or supplied to the grid. Proposals may use different inverter arrangements, and there is no single type that suits every roof. Shading, roof layout, system size, equipment compatibility and plans for expansion can all matter. Ask why the recommended inverter suits your specific design rather than accepting the model name as proof of quality.
Check where the inverter will be installed, how its performance can be monitored and what the warranty covers. Ask whether the proposed design allows the system to be expanded and what equipment or changes that might require. If two quotes specify different inverter arrangements, ask both companies to explain the practical consequence for your roof and future options.
A battery should also be treated as a separate design and financial decision, not simply an add-on that makes any solar system better. Ask what capacity is usable, what power the battery can supply, how it will be controlled and which household loads it is intended to serve. The proposal should make clear whether stored electricity is intended for use after solar generation falls, for backup, or for another stated purpose.
Do not assume that a battery will keep the house running during a power cut. Backup operation depends on the system design and may require particular equipment or a selected-circuit arrangement. Ask the installer to identify exactly what would remain powered, for how long the system is designed to support those loads, and what happens when demand exceeds its capability.
If you are unsure whether to buy a battery now, request two comparable designs: one without storage and one with it. Ask the company to state the assumptions used for estimated savings, including electricity use, export arrangements and any tariff assumptions. Compare the added cost and expected benefit with your priorities, rather than relying on a general claim that storage will pay for itself.
Quotes can differ because they include different work. Check whether each price covers the panels, inverter, mounting equipment, wiring, monitoring setup, installation labour, commissioning and handover. Ask how the installer has allowed for access to the roof, cable routes, the switchboard and any work needed to prepare the site.
Have the company identify exclusions and possible additional charges in writing. Roof repairs, switchboard work, unusual access requirements or changes requested after the site assessment may affect the final cost, but you should not have to guess which items are included. If an installer cannot confirm an item before inspection, ask when that uncertainty will be resolved and how any change will be approved.
For a New Zealand home, ask who will manage any required connection steps with the local network company and your electricity retailer, and what information or documents you will receive. The process can depend on the location and system setup, so get responsibilities and timing expectations explained for your project rather than assuming every installer handles them in the same way.
Compare warranties by component and by responsibility. Find out what is covered for the panels, inverter, battery if included, installation workmanship and any roof-related work. Ask who you contact if a problem occurs, whether labour or removal and reinstallation are included in relevant warranty terms, and what maintenance or monitoring the homeowner is expected to handle.
Once the designs and scopes are clear, compare the total price and the differences that explain it. A cheaper quote may be a sensible choice if it meets your needs and includes the work you require. It deserves closer scrutiny if the lower price depends on a smaller system, less suitable equipment, missing installation items or an optimistic estimate that is not explained.
Be cautious with savings and payback figures that appear precise but do not show their assumptions. Ask what electricity prices, solar-use patterns, export payments, system performance and maintenance expectations the estimate relies on. If you are considering finance, compare the total amount payable and any fees or conditions, not only the advertised repayment.
Incentives and financing options can change, and eligibility may depend on the offer and your circumstances. Ask the company to identify any incentive included in its calculation and verify the conditions before treating it as a guaranteed reduction in your project cost. Keep the decision grounded in the written quote and the assumptions you can confirm.
There is no fixed number that guarantees a good decision. Comparing more than one proposal can reveal differences in design and scope, but the important point is to give each company the same information and ask consistent questions. A few detailed, comparable quotes are more useful than a larger collection of headline prices.
Not without understanding why that size was recommended. A larger system may suit higher daytime use or a well-supported plan to add electrical loads, but it may not be the best fit for every roof or household. Ask how the extra capacity affects expected generation, use at home, exports and total project cost.
It depends on your goals, electricity-use pattern, system design and the cost of adding storage. Ask for a clear comparison between installing a battery now and leaving it out, including what would need to change if you add one later. Treat backup power as a separate requirement and confirm what the proposed system can actually supply during an outage.
Only after checking that the estimates use comparable assumptions. Ask each installer how it accounted for roof conditions, household consumption, electricity tariffs, exports and system performance. If the methods differ or are unclear, the estimates are not a reliable like-for-like comparison.
Keep the final design, equipment list, price, inclusions, exclusions, expected project responsibilities and warranty terms with the agreement. Ask for any stated savings or production estimates to include their assumptions, and clarify how design or price changes will be handled after further inspection.
The strongest proposal is one that connects your roof, electricity use and future plans to a clearly scoped system. Compare solar installation companies on the reasoning behind their designs, the work included and the limits of their savings estimates. If a company can answer those questions plainly and put the agreed details in writing, you can judge its price on a more meaningful basis.
