Introduction
This calculator estimates how a rooftop solar project in Dubai may perform once it is connected under DEWA’s Shams Dubai net-metering program. The purpose is practical rather than abstract: before a villa owner, landlord, facilities manager, or small business signs an installer quote, they usually want to know how much electricity the system could generate, how much of that energy will likely be used on site, how much surplus will be exported to the grid for credit, and how many years it may take before the cash flow becomes attractive. The form below turns those questions into a set of annual inputs so you can compare scenarios without building a spreadsheet from scratch.
That distinction between self-consumption and export is the heart of the model. A solar array creates value in two ways. First, any kilowatt-hour used immediately inside the building avoids buying that energy at the retail tariff. Second, any excess generation can be exported and credited through net metering. In Dubai, both parts matter, but they do not always matter equally for every building profile. A family that uses a lot of daytime cooling, pool pumping, or EV charging may capture a larger share of its production directly on site. A holiday home with low daytime occupancy may export more of its solar output. The calculator separates those streams so the economics are easier to read.
It also adds the longer-term assumptions that often get skipped in sales conversations. Panels slowly degrade, tariffs may escalate, annual cleaning and maintenance costs do not disappear, and future cash flows are worth less than cash received today. That is why the tool shows not only year-one savings, but also simple payback, a cash-flow payback year within the chosen horizon, and net present value. Used together, those outputs help you compare a conservative system design against a more aggressive one with transparent trade-offs rather than guesswork.
How to use
Start with the installer or site facts you know, then layer in the assumptions you want to test. System size is the nameplate DC capacity of the array. Specific yield is the expected annual production per installed kilowatt, which is where roof orientation, shading, module quality, dust, and cleaning frequency quietly enter the picture. Self-consumption share is your estimate of how much generated electricity is used behind the meter instead of exported. If that number feels uncertain, run at least two scenarios: one conservative and one optimistic. That single sensitivity check often tells you more than a single headline payback figure.
- Enter the proposed system size and a realistic specific yield for Dubai conditions.
- Choose the self-consumption share that matches your daytime load pattern rather than your total annual bill.
- Enter the retail tariff you expect solar energy to offset and the export credit rate you want to assume for exported power.
- Add installed cost, annual operations and maintenance, panel degradation, tariff escalation, discount rate, and the analysis horizon.
- Click calculate, then compare the result against one or two alternative scenarios before drawing a conclusion.
Use annual values consistently. If your quote gives monthly cleaning costs, convert them to an annual amount before entering them. If a consultant provides a yield range rather than a single value, use the lower end first. In early-stage screening, conservative inputs usually produce the most useful conversation because they tell you whether the project still looks sensible when the easy optimism is removed.
Formula
The first step is straightforward: year-one generation equals system size multiplied by specific yield. If a 25 kW system is expected to deliver 1,650 kWh per kW-year, the first-year output is 41,250 kWh. The calculator then splits that generation into the share used on site and the share exported. Self-consumed energy is multiplied by the avoided retail tariff. Exported energy is multiplied by the export credit rate. Annual maintenance is then subtracted to reach year-one net savings.
Here, P is the installed DC capacity and Y is the specific yield in kilowatt-hours per kilowatt-year. The calculator then treats the result as a function of several connected assumptions, which is why a full cash-flow estimate is better thought of as one output built from many inputs rather than a single shortcut number.
For readers who like to visualize the structure, the calculator behaves like a weighted sum of energy and money flows. Some inputs scale output directly, while others act as weights, discounts, or conversion factors. That is why a change in self-consumption can shift value almost as much as a change in system size: it changes which tariff applies to each kilowatt-hour.
After year one, the model repeats the same logic across the analysis horizon. Generation declines each year according to the degradation assumption. Tariffs and export credit rates rise according to the escalation assumption. Every annual savings figure is added to cumulative cash flow, and each one is also discounted back to present value. The annual savings relationship used in the page is preserved below in MathML.
In plain language, G(0) is the starting generation, d is the annual degradation rate, c is the self-consumption share, T(t) is the retail tariff in year t, and E(t) is the export credit in year t. If you want a quick reality check after changing one input, ask yourself a simple question: did the result move in the direction you expected? If not, it usually means a unit or assumption needs another look.
Example
Using the default values in the form gives a clear worked example. A 25 kW rooftop system with a specific yield of 1,650 kWh per kW-year produces 41,250 kWh in year one. If 55% of that production is used directly on site, self-consumed energy equals 22,687.5 kWh and exported energy equals 18,562.5 kWh. At an avoided retail tariff of 0.40 AED per kWh, the self-consumed portion creates 9,075 AED of savings. At an export credit of 0.32 AED per kWh, exported energy creates 5,940 AED of credits. After subtracting 4,500 AED of annual maintenance, year-one net savings are 10,515 AED.
That does not mean the project has a ten-year life or that every year will look identical. It means the first-year savings imply a simple payback of roughly ten years on a 105,000 AED installation cost before any deeper discounting. The longer model can still look stronger or weaker depending on the mix of degradation, tariff escalation, and discount rate that you enter. If you raise self-consumption to 70%, the same generation becomes more valuable because more kilowatt-hours avoid the full retail tariff. If you lower specific yield because the roof is dusty or shaded, the output falls immediately and the economics soften. That is exactly why scenario testing matters.
A practical way to use the example is to keep every input fixed except one. Try a lower specific yield if the roof is not ideal. Try a higher maintenance number if the site needs frequent cleaning. Try a lower self-consumption share if the property is often empty during the day. When a project still makes sense across those less favorable cases, the decision is usually more robust than a sales-sheet headline might suggest.
Limitations
This is a planning calculator, not a permit document or a financing agreement. It intentionally works with annual averages so the page stays fast and understandable. That means it does not simulate every month separately, it does not model battery storage dispatch, and it does not track temporary inverter outages, module mismatch losses, roof repairs, or a detailed debt schedule. Those factors can matter in real projects, but adding all of them to a simple public calculator would make the model harder to use and easier to misuse.
- Program details can change: DEWA rules, export treatment, or bill structures may evolve over time.
- Annual averages hide timing: a building with the same yearly load can behave very differently depending on when energy is consumed.
- Maintenance can be uneven: inverter replacement and occasional repairs rarely arrive as a perfectly smooth annual cost.
- Site conditions matter: shade, soiling, tilt, temperature, and curtailment risk are simplified into the specific-yield assumption.
- Financing is not modeled directly: if the system is funded with debt, compare the output here with your loan schedule before making a final investment decision.
Use the calculator for screening, comparison, and clearer conversations. Then verify the final design with installer production estimates, roof constraints, interconnection requirements, and your actual tariff structure. That workflow gets the best of both worlds: quick scenario testing here, then project-specific detail when the numbers justify going further.