☀ SolarCalculatorHQ

About SolarCalculatorHQ

What this site is

SolarCalculatorHQ is an independent publisher of free residential solar photovoltaic calculators. Each tool answers a single, well-defined question that a homeowner, DIY installer, or small commercial buyer needs to resolve before signing a contract or ordering equipment. The questions cover system sizing, panel tilt and azimuth, conductor sizing and voltage drop, battery autonomy, payback period, and the levelised cost of energy from a household array compared with the local utility tariff.

The site exists in ten language and country variants. Each variant uses the local currency, the local units of measurement, the relevant electrical and building code references, and authority sources native to that market. A user in Munich does not see dollar costs converted from a US calculator. A user in Brisbane sees STC zone data and the AER Default Market Offer rather than NREL irradiance and a US state rebate.

Editorial methodology

Every calculator on the site is derived from a primary source. We do not paraphrase competitor sites. We do not accept manufacturer or installer talking points as inputs. The chain of reasoning behind each tool is published on the same page as the calculator, with citations to the underlying authority, code clause, or dataset. When a result depends on a rule of thumb rather than first-principles math, we say so explicitly.

Photovoltaic yield models follow the NREL PVWatts methodology. The annual energy output of an array is the product of nameplate DC capacity, plane-of-array irradiance derived from a Typical Meteorological Year dataset for the user's location, total system losses (soiling, wiring, inverter efficiency, mismatch, snow, age, and shading), and the array's geometric exposure to the sun across the year. We expose every loss factor as an editable input rather than hiding them behind a single derate.

Conductor sizing and voltage drop calculations follow NEC Article 690 for US deployments. The voltage-drop equation Vdrop = 2 x I x R x L uses ampacity values from NEC Chapter 9 Table 8 with corrections for temperature and conduit fill from Table 310.16. We surface every multiplier so an installer can verify the calculation against the same code reference an electrical inspector will use. For deployments outside the United States we substitute the relevant national wiring regulation: BS 7671 in the UK, AS/NZS 3000 in Australia and New Zealand, CSA C22.1 in Canada, VDE-AR-N 4105 in Germany, NF C 15-100 in France, REBT in Spain, NBR 5410 in Brazil, CEI 64-8 in Italy, and NEN 1010 in the Netherlands.

Tilt-angle optimisation uses the latitude rule for fixed-tilt arrays with seasonal-bias adjustment when a user selects a winter or summer production weighting. Tracking arrays use single-axis backtrack geometry. Roof azimuth is a continuous input, not a cardinal picker, because real roofs face every angle.

Financial calculations use the actual incentive schedules in force at the time of computation. We re-derive numbers when the underlying authority changes a rate. We do not roll a year of changes into a single annual update.

How we adapt to each market

Ten locales are supported: English (United States, United Kingdom, Australia, Canada), German, French, Spanish, Portuguese (Brazil), Italian, and Dutch. The adaptation goes deeper than translation. Each locale uses its native currency, units, terminology, electrical code, and tariff or incentive framework.

Currency is USD for the United States, GBP for the United Kingdom, AUD for Australia, CAD for Canada, EUR for Germany, France, Spain, Italy, and the Netherlands, and BRL for Brazil. We do not blindly convert a US dollar figure to euros. Instead, we source local installed-cost data from the relevant trade body or installer marketplace.

Units follow the local convention. The United States uses imperial throughout (kW for capacity, kWh for energy, square feet for area, AWG for conductors). Canada uses a mixed convention common in the trades: AWG for wire, square feet for residential roof area, and degrees Celsius for temperature. Every other locale uses metric.

Code references map to the relevant national wiring regulation: NEC for the United States, BS 7671 for the United Kingdom, AS/NZS 3000 for Australia and New Zealand, CSA C22.1 for Canada, VDE-AR-N 4105 for Germany, NF C 15-100 for France, REBT for Spain, NBR 5410 for Brazil, CEI 64-8 for Italy, and NEN 1010 for the Netherlands.

Terminology adapts to local industry usage. We use string inverter and microinverter rather than translated equivalents. We use the German Wechselrichter, the French onduleur, the Spanish inversor, the Portuguese inversor, the Italian inverter (loanword), and the Dutch omvormer where the local industry expects them. We retain industry-standard acronyms (MPPT, IGBT, SOC, AWG) in every locale.

Tariff and incentive structures are locale-specific. United States pages model the federal Residential Clean Energy Credit, state rebates from the DSIRE database, net-metering rules by utility, and MACRS five-year accelerated depreciation for commercial systems. United Kingdom pages model the Smart Export Guarantee, the Ofgem energy price cap, and Microgeneration Certification Scheme installer requirements. Australian pages model Small-scale Technology Certificates by zone, state feed-in tariffs, and the AER Default Market Offer. German pages model the EEG paragraph 48 monthly degression schedule and KfW loan terms. French pages use EDF Obligation d'Achat tariffs and ADEME guidance. Spanish pages model Real Decreto 244/2019 self-consumption rules and the IDAE Next Generation funds. Brazilian pages model Lei 14.300/2022 Fio B compensation. Italian pages use GSE incentive schemes and Bonus Casa fiscal mechanisms. Dutch pages model the Salderingsregeling net-metering phase-out timeline and Energie Investeringsaftrek deductions.

Update commitment

We update the relevant pages within seven days of any official rate change. Specific recurring update windows include:

Funding and conflicts of interest

The site is funded by display advertising served through Google AdSense. We do not run affiliate links to installers, equipment manufacturers, or financing providers. We do not sell or share user data. We do not accept paid placements, sponsored guides, or installer-network referral arrangements. If we ever add affiliate links to a piece of content, that content will be marked clearly at the top of the page.

Corrections policy

If you find a math error, a stale tariff, an outdated code reference, or a citation that no longer resolves, please email contact@solarcalculatorhq.com. We acknowledge corrections within one business day, fix the page within 48 hours of confirmation, and log the change in the page-level changelog. We do not silently rewrite history. The changelog records the prior value, the corrected value, the date of change, and a one-line reason.

Common questions about our methodology

We are sometimes asked why our results differ from a quote a homeowner received from an installer. The most common reasons are: the installer modelled a different array tilt or azimuth than the user entered, the installer used a different irradiance source (often a postcode-level average rather than a TMY3 dataset for the specific location), the installer applied a different system loss assumption (commonly a single 14 percent derate rather than the per-component breakdown we publish), or the installer's quote includes financing costs we treat as a separate calculation.

We are also asked why the federal tax credit shown on a US calculation can change between sessions. The credit applies only to qualifying expenditures and only for the tax year the system was placed in service. Pages that compute payback with the credit show the relevant Internal Revenue Service Form 5695 line items so a user can verify the treatment with a tax professional.

Battery autonomy calculations are sometimes questioned for being conservative. We use a 50 percent depth of discharge (DoD) for lead-acid chemistries by default and 80 percent for lithium iron phosphate, both as recommended by the chemistry's typical manufacturer warranty terms. Users who own a battery rated for a higher DoD can adjust the input. We will not push a higher default because it shortens the warrantied service life of the battery.

Limits

A calculator returns an estimate, not a quote. Site-specific factors including shading, roof condition, electrical service capacity, local permitting, and utility interconnection rules affect every real installation. Always confirm with a licensed installer before ordering equipment or signing a contract. The estimates on this site are not a substitute for engineering judgment, are not legally binding, and should not be used to support a building permit application without independent review.

Contact

Questions, corrections, or suggestions for new calculators? Email contact@solarcalculatorhq.com or use the contact page. The single address handles general enquiries, editorial questions, privacy requests, and partnership messages.