{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"solar-payback"},"result":{"entity_type":"calculator","id":"solar-payback","calculator_id":"solar-payback","canonical_url":"https://tttkmbb.com/energy/solar-payback","name":"Solar Payback Calculator","title":"Solar Payback Calculator – Payback Period, Lifetime Savings and LCOE of a Rooftop PV System","category":"energy","category_name":"Home Energy & Electrical","tool_name":"estimate_solar_payback","featured_mcp_tool":false,"description":"Estimates the annual generation of a photovoltaic system from its size and specific yield, the first-year savings from self-consumed electricity and exported energy, the simple payback period, and a year-by-year table with panel degradation and electricity price escalation over the analysis period, including the levelised cost of the solar electricity.","use_when":"You want to judge a solar quote: how many years until the system has paid for itself, what it saves over its life, and what its electricity costs per kWh.","do_not_use_when":"You need the daily output of a panel array from irradiance (use solar-panel-output), a financed system with loan interest, or discounted cash-flow measures; results are estimates, not financial advice.","inputs":[{"name":"system_size_kw","label":"System size","type":"number","unit":"kWp","required":true,"max":100000,"exclusive_min":0,"description":"Rated DC capacity of the array in kilowatts-peak.","example":6},{"name":"system_cost","label":"System cost","type":"number","required":true,"max":1000000000,"exclusive_min":0,"description":"Installed cost after rebates and tax credits, in your currency.","example":12000},{"name":"annual_yield_kwh_per_kw","label":"Specific yield","type":"number","unit":"kWh/kWp/year","required":false,"default":1400,"min":300,"max":2500,"description":"Annual generation per kWp: about 900–1,100 in northern Europe, 1,300–1,600 in the southern US and southern Europe, up to 1,900 in deserts (PVWatts gives a site value).","example":1400},{"name":"electricity_price_per_kwh","label":"Electricity price","type":"number","unit":"per kWh","required":true,"min":0,"max":100,"description":"Retail price per kWh that self-consumed solar electricity displaces.","example":0.3},{"name":"self_consumption_percent","label":"Self-consumption","type":"number","unit":"%","required":false,"default":100,"min":0,"max":100,"description":"Share of generation used on site (100 with net metering; 30–50 without a battery; higher with one). The rest is exported at the feed-in tariff.","example":100},{"name":"feed_in_tariff_per_kwh","label":"Feed-in tariff","type":"number","unit":"per kWh","required":false,"default":0,"min":0,"max":100,"description":"Payment per exported kWh.","example":0},{"name":"annual_degradation_percent","label":"Panel degradation","type":"number","unit":"%/year","required":false,"default":0.5,"min":0,"max":5,"description":"Yearly loss of output; 0.5 % per year is the NREL median for crystalline silicon.","example":0.5},{"name":"price_escalation_percent","label":"Electricity price escalation","type":"number","unit":"%/year","required":false,"default":0,"min":-10,"max":20,"description":"Yearly increase of the retail electricity price (the feed-in tariff is held constant).","example":0},{"name":"analysis_years","label":"Analysis period","type":"integer","unit":"years","required":false,"default":25,"min":1,"max":25,"description":"Years in the savings table (25 matches typical panel performance warranties).","example":25}],"outputs":[{"name":"annual_generation_kwh","label":"First-year generation","type":"number","unit":"kWh","decimals":0,"description":"system_size_kw × annual_yield_kwh_per_kw."},{"name":"first_year_savings","label":"First-year savings","type":"number","decimals":2,"description":"Generation × (self-consumed share × price + exported share × feed-in tariff)."},{"name":"simple_payback_years","label":"Simple payback","type":"number","unit":"years","decimals":2,"description":"system_cost / first_year_savings."},{"name":"cumulative_payback_years","label":"Payback with degradation and escalation","type":"number","unit":"years","decimals":2,"description":"Year (interpolated) in which cumulative savings reach the system cost; absent when not reached within analysis_years."},{"name":"lifetime_generation_kwh","label":"Lifetime generation","type":"number","unit":"kWh","decimals":0,"description":"Sum of yearly generation over analysis_years with degradation."},{"name":"lifetime_savings","label":"Lifetime savings","type":"number","decimals":2,"description":"Sum of yearly savings over analysis_years."},{"name":"net_benefit","label":"Net benefit","type":"number","decimals":2,"description":"lifetime_savings − system_cost."},{"name":"lcoe_per_kwh","label":"Levelised cost of solar electricity","type":"number","unit":"per kWh","decimals":4,"description":"system_cost / lifetime_generation_kwh (undiscounted, no maintenance costs)."},{"name":"yearly","label":"Year-by-year table","type":"list","decimals":2,"description":"Per year: year, generation_kwh, savings, cumulative savings."}],"input_schema":{"type":"object","properties":{"system_size_kw":{"description":"Rated DC capacity of the array in kilowatts-peak. Unit: kWp.","type":"number","maximum":100000,"exclusiveMinimum":0,"examples":[6],"x-unit":"kWp"},"system_cost":{"description":"Installed cost after rebates and tax credits, in your currency.","type":"number","maximum":1000000000,"exclusiveMinimum":0,"examples":[12000]},"annual_yield_kwh_per_kw":{"description":"Annual generation per kWp: about 900–1,100 in northern Europe, 1,300–1,600 in the southern US and southern Europe, up to 1,900 in deserts (PVWatts gives a site value). Unit: kWh/kWp/year.","type":"number","minimum":300,"maximum":2500,"default":1400,"examples":[1400],"x-unit":"kWh/kWp/year"},"electricity_price_per_kwh":{"description":"Retail price per kWh that self-consumed solar electricity displaces. Unit: per kWh.","type":"number","minimum":0,"maximum":100,"examples":[0.3],"x-unit":"per kWh"},"self_consumption_percent":{"description":"Share of generation used on site (100 with net metering; 30–50 without a battery; higher with one). The rest is exported at the feed-in tariff. Unit: %.","type":"number","minimum":0,"maximum":100,"default":100,"examples":[100],"x-unit":"%"},"feed_in_tariff_per_kwh":{"description":"Payment per exported kWh. Unit: per kWh.","type":"number","minimum":0,"maximum":100,"default":0,"examples":[0],"x-unit":"per kWh"},"annual_degradation_percent":{"description":"Yearly loss of output; 0.5 % per year is the NREL median for crystalline silicon. Unit: %/year.","type":"number","minimum":0,"maximum":5,"default":0.5,"examples":[0.5],"x-unit":"%/year"},"price_escalation_percent":{"description":"Yearly increase of the retail electricity price (the feed-in tariff is held constant). Unit: %/year.","type":"number","minimum":-10,"maximum":20,"default":0,"examples":[0],"x-unit":"%/year"},"analysis_years":{"description":"Years in the savings table (25 matches typical panel performance warranties). Unit: years.","type":"integer","minimum":1,"maximum":25,"default":25,"examples":[25],"x-unit":"years"}},"additionalProperties":false,"required":["system_size_kw","system_cost","electricity_price_per_kwh"]},"output_schema":{"type":"object","properties":{"annual_generation_kwh":{"description":"system_size_kw × annual_yield_kwh_per_kw. Unit: kWh.","type":"number","x-unit":"kWh"},"first_year_savings":{"description":"Generation × (self-consumed share × price + exported share × feed-in tariff).","type":"number"},"simple_payback_years":{"description":"system_cost / first_year_savings. Unit: years.","type":"number","x-unit":"years"},"cumulative_payback_years":{"description":"Year (interpolated) in which cumulative savings reach the system cost; absent when not reached within analysis_years. Unit: years.","type":"number","x-unit":"years"},"lifetime_generation_kwh":{"description":"Sum of yearly generation over analysis_years with degradation. Unit: kWh.","type":"number","x-unit":"kWh"},"lifetime_savings":{"description":"Sum of yearly savings over analysis_years.","type":"number"},"net_benefit":{"description":"lifetime_savings − system_cost.","type":"number"},"lcoe_per_kwh":{"description":"system_cost / lifetime_generation_kwh (undiscounted, no maintenance costs). Unit: per kWh.","type":"number","x-unit":"per kWh"},"yearly":{"description":"Per year: year, generation_kwh, savings, cumulative savings.","type":"array"}}},"formula":"annual_generation_kwh = system_size_kw × annual_yield_kwh_per_kw; generation_y = annual_generation_kwh × (1 − annual_degradation_percent/100)^(y−1); savings_y = generation_y × (self_consumption_percent/100 × electricity_price_per_kwh × (1 + price_escalation_percent/100)^(y−1) + (1 − self_consumption_percent/100) × feed_in_tariff_per_kwh); simple_payback_years = system_cost / savings_1; lifetime_savings = Σ savings_y; net_benefit = lifetime_savings − system_cost; lcoe_per_kwh = system_cost / Σ generation_y","method":"Undiscounted cash-flow model with linear-geometric degradation (NREL median 0.5 %/year) and no inverter replacement, maintenance or financing costs; the specific yield should come from a site tool such as NREL PVWatts. Informational estimate, not financial advice.","sources":[{"name":"NREL PVWatts Calculator","url":"https://pvwatts.nrel.gov/","type":"government","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Levelized cost of electricity","url":"https://en.wikipedia.org/wiki/Levelized_cost_of_electricity","type":"reference","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Solar panel","url":"https://en.wikipedia.org/wiki/Solar_panel","type":"reference","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"6 kW for 12,000 at 1,400 kWh/kWp, 0.30 per kWh, 100 % self-use","inputs":{"system_size_kw":6,"system_cost":12000,"annual_yield_kwh_per_kw":1400,"electricity_price_per_kwh":0.3,"self_consumption_percent":100},"expected":{"annual_generation_kwh":8400,"first_year_savings":2520,"simple_payback_years":4.76,"lifetime_savings":59361,"net_benefit":47361,"lcoe_per_kwh":0.0606},"url":"https://tttkmbb.com/api/v1/calculate/solar-payback?system_size_kw=6&system_cost=12000&annual_yield_kwh_per_kw=1400&electricity_price_per_kwh=0.3&self_consumption_percent=100"},{"name":"10 kW, 40 % self-use, 0.08 feed-in, 3 % escalation, 20 years","inputs":{"system_size_kw":10,"system_cost":18000,"annual_yield_kwh_per_kw":1100,"electricity_price_per_kwh":0.25,"self_consumption_percent":40,"feed_in_tariff_per_kwh":0.08,"price_escalation_percent":3,"analysis_years":20},"expected":{"annual_generation_kwh":11000,"first_year_savings":1628,"simple_payback_years":11.06,"lifetime_savings":38129.87,"net_benefit":20129.87,"lcoe_per_kwh":0.0858},"url":"https://tttkmbb.com/api/v1/calculate/solar-payback?system_size_kw=10&system_cost=18000&annual_yield_kwh_per_kw=1100&electricity_price_per_kwh=0.25&self_consumption_percent=40&feed_in_tariff_per_kwh=0.08&price_escalation_percent=3&analysis_years=20"}],"faq":[{"q":"Where do I get the specific yield?","a":"Run NREL PVWatts (or PVGIS in Europe) for your address, tilt and orientation; it returns annual kWh per kW of installed capacity."},{"q":"What is self-consumption and why does it matter?","a":"It is the share of solar output used in the house instead of exported. Self-consumed energy is worth the retail price; exported energy only earns the feed-in tariff, often a third of it."},{"q":"Why does the payback with degradation differ from the simple payback?","a":"Simple payback assumes first-year savings repeat forever; the cumulative version applies yearly panel degradation and price escalation, so it is longer without escalation and can be shorter with it."}],"tags":["solar payback","solar panel roi","pv payback period","solar savings","lcoe solar","feed-in tariff"],"related":[{"calculator_id":"solar-panel-output","reason":"Daily energy of the array from irradiance and panel rating."},{"calculator_id":"electricity-cost","reason":"What the displaced consumption costs at your tariff."},{"calculator_id":"carbon-footprint-electricity","reason":"CO₂ avoided by the generated kWh."}],"links":{"html":"https://tttkmbb.com/energy/solar-payback","markdown":"https://tttkmbb.com/energy/solar-payback.md","json":"https://tttkmbb.com/energy/solar-payback.json","api":"https://tttkmbb.com/api/v1/calculate/solar-payback","schema":"https://tttkmbb.com/api/v1/calculators/solar-payback","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T03:45:46Z","next_actions":[{"tool":"run_calculator","calculator_id":"solar-payback","reason":"Run Solar Payback Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/energy/solar-payback.md"}}