{"id":12453,"date":"2026-08-24T17:48:10","date_gmt":"2026-08-24T17:48:10","guid":{"rendered":"https:\/\/eauchauffage.com\/solar-water-heater-payback\/"},"modified":"2026-08-24T17:48:10","modified_gmt":"2026-08-24T17:48:10","slug":"solar-water-heater-payback","status":"publish","type":"post","link":"https:\/\/eauchauffage.com\/ar\/solar-water-heater-payback\/","title":{"rendered":"Solar Water Heater Payback: What It Actually Saves"},"content":{"rendered":"

Ask three suppliers how long a solar water heater takes to pay for itself and you will get three confident answers, all different, and none of them calculated from your building. That is because payback is not a property of the equipment<\/strong>. It is a ratio between what you pay to install a system and what it saves you every year, and both halves of that ratio belong to you, not to the product.<\/p>\n

This guide gives you the arithmetic. Four steps, real numbers, and two worked examples. By the end you will be able to take any quotation you are handed and work out its payback yourself, including the mistakes that make most published figures far too optimistic.<\/p>\n\n

The Only Formula That Matters<\/h2>\n

Payback in years = installed cost ÷ annual saving.<\/strong><\/p>\n

That is the whole calculation. Everything below exists to fill in those two numbers honestly, because a wrong input on either side produces an answer that is not merely imprecise but misleading. The annual saving in particular is built from three separate quantities that people routinely confuse: how much energy your hot water consumes, how much of that energy solar will actually carry, and what one displaced kilowatt-hour is genuinely worth on your bill.<\/p>\n\n

Step 1: How Much Energy Your Hot Water Actually Uses<\/h2>\n

Start with physics rather than with a brochure. Raising one litre of water by one degree Celsius takes about 0.00116 kWh<\/strong>. That constant does not change with brand, technology or marketing claim, which makes it the most reliable number in this entire calculation.<\/p>\n

Daily kWh = litres per day × temperature rise in °C × 0.00116<\/strong><\/p>\n

The temperature rise is the gap between the water arriving at your building and the temperature you store at. In the Gulf, incoming mains water is warm by international standards, often near 30 °C in high summer and falling to roughly 20 °C in winter. Storing at 55 °C therefore means a rise of about 25 °C in summer and 35 °C in winter, so 30 °C is a fair annual average<\/strong> for this region. That regional warmth is quietly in your favour, because you are paying to close a smaller gap than a building in a cold climate.<\/p>\n

\n
Hot water used per day<\/th>Energy per day (30 °C rise)<\/th>Energy per year<\/th><\/tr><\/thead>
100 litres<\/td>3.5 kWh<\/td>1,274 kWh<\/td><\/tr>\n
150 litres<\/td>5.2 kWh<\/td>1,910 kWh<\/td><\/tr>\n
200 litres<\/td>7.0 kWh<\/td>2,547 kWh<\/td><\/tr>\n
300 litres<\/td>10.5 kWh<\/td>3,821 kWh<\/td><\/tr>\n
500 litres<\/td>17.4 kWh<\/td>6,367 kWh<\/td><\/tr>\n<\/tbody><\/table><\/figure>\n

Two honest caveats. First, this is the energy that ends up in the water<\/em>; a real installation also loses heat from the tank and the pipe runs, so your actual consumption is somewhat higher. Treat the table as a floor, which makes every payback figure derived from it conservative. Second, if you do not know your daily litres, do not guess wildly. Our guide to working out what size water heater you need<\/a> converts occupants, bathrooms and fixtures into a defensible daily figure.<\/p>\n\n

Step 2: How Much of It Solar Will Actually Carry<\/h2>\n

The proportion of your annual hot water energy that solar supplies is called the solar fraction<\/strong>, and it is the number most sales conversations quietly round up to 100 per cent.<\/p>\n

It is never 100 per cent, and chasing that last stretch is bad economics. Sizing collectors to cover your worst winter week means that for most of the year you generate more heat than the tank can absorb, and the surplus simply has nowhere to go. That is why every properly designed system includes backup, and why our solar sizing guide<\/a> treats solar fraction as a deliberate design choice rather than a target to maximise.<\/p>\n

Crucially, solar fraction is an output of a simulation for your specific roof<\/strong>, not a specification you can read off a product. It depends on your latitude, orientation, tilt, shading, collector area and how your demand is distributed across the day. Ask any supplier quoting you a payback figure which annual solar fraction they assumed. If they cannot answer, their payback number was not calculated.<\/p>\n

Here is what different assumptions do to the 300-litre household above, which uses 3,821 kWh a year:<\/p>\n

\n
Assumed annual solar fraction<\/th>Energy solar displaces per year<\/th><\/tr><\/thead>
50 per cent<\/td>1,910 kWh<\/td><\/tr>\n
60 per cent<\/td>2,293 kWh<\/td><\/tr>\n
70 per cent<\/td>2,675 kWh<\/td><\/tr>\n
80 per cent<\/td>3,057 kWh<\/td><\/tr>\n<\/tbody><\/table><\/figure>\n

The gap between the top and bottom row is 60 per cent more saving, which means roughly 60 per cent less payback time. A supplier can make a system look excellent or ordinary purely by choosing this one assumption, which is exactly why you should insist on seeing it.<\/p>\n\n

Step 3: What One Displaced Kilowatt-Hour Is Really Worth<\/h2>\n

This is the step most often done wrong, and getting it right can change your answer by half.<\/p>\n

People divide their monthly bill by their monthly kWh and use that average rate. That is the wrong number.<\/strong> Solar removes consumption from the top<\/em> of your bill, not from the middle, so what matters is your marginal rate<\/strong>: the price of the last kilowatt-hour you buy. Where tariffs rise in bands, the marginal rate is higher than the average, and using the average understates your saving.<\/p>\n

The second omission is tax. Saudi Arabia applies 15 per cent VAT to the electricity bill, so a kilowatt-hour you avoid buying saves you the tariff plus<\/em> the VAT on it. Using the published Saudi Electricity Company tariff bands, the real value of one displaced kWh works out as follows:<\/p>\n

\n
Tariff category<\/th>Published rate<\/th>Value including 15 per cent VAT<\/th><\/tr><\/thead>
Residential, up to 6,000 kWh per month<\/td>SAR 0.18 \/ kWh<\/td>SAR 0.207<\/strong><\/td><\/tr>\n
Residential, above 6,000 kWh per month<\/td>SAR 0.30 \/ kWh<\/td>SAR 0.345<\/strong><\/td><\/tr>\n
\u0633\u062e\u0627\u0646 \u062a\u062c\u0627\u0631\u064a<\/td>SAR 0.32 \/ kWh<\/td>SAR 0.368<\/strong><\/td><\/tr>\n<\/tbody><\/table><\/figure>\n

Tariffs are revised from time to time, so take your own current rate from your latest bill rather than from any article, including this one. But note the structural point: a villa that regularly crosses 6,000 kWh a month saves two-thirds more per displaced kWh than one that stays below it<\/strong>, and a commercial building saves more still, because commercial consumption is charged at a flat rate from the first unit. The same array, on the same roof, pays back at very different speeds depending on which line of the tariff table you sit on.<\/p>\n

If you are displacing diesel or LPG rather than grid electricity, the value per unit of heat is usually higher again, and the payback correspondingly shorter.<\/p>\n\n

Step 4: Installed Cost, Not Equipment Cost<\/h2>\n

The other half of the ratio is the number people underestimate. Payback must be calculated on what the system costs working on your roof<\/em>, not on the price of hardware on a pallet.<\/p>\n

A complete installed cost includes:<\/p>\n