What an 8 kW Rooftop Can Produce in a Year

Important: this is an illustrative model, not a real customer

This article walks through a hypothetical 8 kW rooftop system on a south-facing home in central Iran (modeled for a high-insolation plateau city such as Isfahan). No real household, installer quote, or utility account is described here. Every kWh figure comes from a transparent spreadsheet-style model for education only. Do not treat the tables as a promise of savings or payback for your roof. Apply the same structure with your own bills, production estimate, and tariff rules using solar ROI payback method Iran.

Direct answer: what this model shows

An 8 kW DC array on an unshaded south-facing roof in a sunny central-Iran climate can plausibly produce on the order of 12,400 kWh per year in this illustration, while a household using about 5,400 kWh per year with modest summer cooling load might self-consume the full annual usage on an energy basis during solar hours and export roughly 7,000 kWh of surplus under a grid-tied arrangement. The gap between production and annual usage is normal: midday surplus does not automatically equal bill elimination unless export rules and your consumption timing align. This case study makes those splits visible month by month so you can see why payback math depends on self-consumption share, not nameplate kW alone.

Model assumptions (check these against your site)

Production totals use a simple monthly shape (strong spring and summer, weaker winter) consistent with a PVWatts-style annual yield near 1,550 kWh per kW per year for this class of site. Consumption uses a mild summer peak for cooling. Neither curve is copied from a specific meter; both are round-number teaching inputs.

Monthly modeled production (kWh)

Monthly bill offset: production vs consumption (kWh)

In this simplified illustration, daytime solar covers all modeled annual consumption on an energy basis, with 7,000 kWh exported as surplus. Real homes import grid power at night and on cloudy days, so import is rarely zero across every month unless storage or very high self-consumption shifts load into solar hours. The table is deliberately optimistic on timing to show the upper bound of energy matching; your actual import line will be higher. That is why self-consumption explained and your utility's export rules matter more than the annual kWh total alone.

Illustrative annual benefit index (no currency quoted)

To connect production to payback without inventing toman prices, use a benefit index where each self-consumed kWh counts as 1.0 unit of retail value and each exported kWh counts as 0.6 units (standing in for an export credit worth 60% of retail, a common teaching assumption only).

If your distribution company credits exports at full retail, the index rises. If exports are worth less, it falls. Replace 0.6 with the ratio you confirm in writing.

Simple payback illustration (apply your own cost)

Payback years ≈ installed cost ÷ annual money benefit. Using the index above as a stand-in for benefit when each index point equals one currency unit of value (for example, if each point represented the retail value of one kWh in your tariff):

The cost row is not a market price. It exists only to show how the formula moves when you plug in numbers from your quotes. Add an inverter replacement reserve and any fixed grid fees as described in solar ROI payback method Iran before treating any payback as final.

What to do with this model

Export the monthly table structure into a spreadsheet. Replace production with your installer's month-by-month estimate for your address. Replace consumption with your billed kWh. Swap the 0.6 export weight for your utility's actual rule. Run the sensitivity rows. Then compare complete proposals with solar proposal checklist. The value of this case study is the workflow, not the headline payback year.

Closing

A modeled 8 kW system in a sunny Iranian plateau city can produce far more kWh than a typical home consumes annually, yet bill impact still depends on when you use power and how exports are credited. Use this illustration to practice the math, then rebuild every input from your own roof and bills before you decide.