Solar Water Heating Payback
Calculator
Results
- Break-even (years)
- 18.510865 yr
- Net position at the horizon
- $469.40
- Total savings
- $4,469.40
- First-year saving
- $143.32
- Energy saved per year (kWh)
- 2,133.333333 kwh
Cumulative cash flow crossing zero at break-even
- Cumulative cash flow
- Cumulative cost of doing nothing
- Cumulative cost with the upgrade
Year-by-year cash flow until break-even
| 1 | 143.32 | 143.32 | -3,856.68 | 426.67 | 4,283.35 |
| 2 | 150.32 | 293.64 | -3,706.36 | 866.13 | 4,572.49 |
| 3 | 157.53 | 451.17 | -3,548.83 | 1,318.78 | 4,867.62 |
| 4 | 164.96 | 616.12 | -3,383.88 | 1,785.01 | 5,168.89 |
| 5 | 172.60 | 788.73 | -3,211.27 | 2,265.23 | 5,476.50 |
| 6 | 180.48 | 969.21 | -3,030.79 | 2,759.85 | 5,790.65 |
| 7 | 188.60 | 1,157.81 | -2,842.19 | 3,269.32 | 6,111.51 |
| 8 | 196.95 | 1,354.76 | -2,645.24 | 3,794.06 | 6,439.30 |
| 9 | 205.56 | 1,560.32 | -2,439.68 | 4,334.55 | 6,774.23 |
| 10 | 214.43 | 1,774.75 | -2,225.25 | 4,891.26 | 7,116.50 |
| 11 | 223.56 | 1,998.31 | -2,001.69 | 5,464.66 | 7,466.34 |
| 12 | 232.97 | 2,231.28 | -1,768.72 | 6,055.27 | 7,823.98 |
| 13 | 242.66 | 2,473.94 | -1,526.06 | 6,663.59 | 8,189.65 |
| 14 | 252.64 | 2,726.58 | -1,273.42 | 7,290.16 | 8,563.58 |
| 15 | 262.92 | 2,989.50 | -1,010.50 | 7,935.54 | 8,946.04 |
| 16 | 273.50 | 3,263.00 | -737.00 | 8,600.27 | 9,337.27 |
| 17 | 284.41 | 3,547.41 | -452.59 | 9,284.94 | 9,737.53 |
| 18 | 295.64 | 3,843.06 | -156.94 | 9,990.16 | 10,147.10 |
| 19 | 307.21 | 4,150.27 | 150.27 | 10,716.53 | 10,566.26 |
| 20 | 319.13 | 4,469.40 | 469.40 | 11,464.69 | 10,995.30 |
Comparison
| Scenario | Total cost over the horizon | Cumulative energy cost | Net position at the horizon |
|---|---|---|---|
| Do nothing | 11,464.69 | 11,464.69 | 0.00 |
| With the upgrade | 10,995.30 | 10,995.30 | 469.40 |
Formula
saving(n) = (Q·f/η × price − pump kWh × p_elec) × (1+g)^(n−1) − maintenance= 18.51
Note
This is a simplified cash-flow model. It projects the prices, escalation rate and equipment costs you entered with a single geometric escalation and no discounting, no inflation adjustment, no financing costs and no tax treatment; savings are assumed to accrue evenly within each year, which is what the fractional break-even interpolates. Real energy prices, tariff structures, grants, weather, occupancy and equipment performance vary widely and change over time. A break-even of zero means the cumulative cash flow never crosses into positive territory within the horizon you chose. Get a professional energy assessment and a written quotation before committing to any of these measures.
More in Energy payback
See all →Frequently asked questions
What's actually being offset by the solar water heater — all my hot water energy, or just part of it?+
A solar thermal system typically covers 50-80% of annual hot water energy needs, since it can't fully meet demand on cloudy days or during winter in most climates, and a backup electric or gas element still handles the shortfall. The calculator should apply that solar fraction to your hot water energy cost, not eliminate the whole hot water bill.
Why does my current water heating fuel type change the payback so much?+
The savings are the difference between what you currently pay per unit of hot water energy and zero (since the sun is free), so replacing an expensive fuel like resistance electric heating yields a much bigger dollar saving than replacing an already-cheap natural gas water heater. The same solar collector array can have a payback that's two or three times faster depending purely on what it's displacing.
Does the calculator account for the backup system's electricity use?+
It should, because the backup heating element or boiler still runs during low-sun periods, and a complete payback model nets that residual energy cost against the full previous water heating cost rather than assuming 100% of the old bill disappears. Overlooking this is a common way solar thermal payback estimates come out too optimistic.
How much does household hot water usage affect the result?+
Payback scales with how many gallons or liters of hot water you actually use, since a system sized for a family of four sitting mostly idle in a two-person household won't generate proportionally more savings just because it has capacity. Enter your actual usage pattern rather than the system's rated capacity for an accurate estimate.
Why is solar water heating payback usually longer than solar electric (PV) payback?+
Solar thermal systems have higher installation complexity per unit of energy delivered (plumbing, tank integration, freeze protection) and displace a cheaper commodity (hot water fuel) compared to PV displacing retail electricity, which is usually priced higher per kWh. This is why many households now find PV plus a heat pump water heater more cost-effective than dedicated solar thermal, depending on local rebates and climate.