Calculator Inputs
Use this to estimate how much of your garden electricity use can be covered by a solar system over a chosen period.
Example Data Table
These examples show how changing sun hours, system size, and loads affects offset.
| System (kW) | Sun hours | PR (%) | Days | Garden use (kWh) | Solar (kWh) | Offset (%) |
|---|---|---|---|---|---|---|
| 3.00 | 4.5 | 80 | 30 | 260 | 324 | 100 |
| 2.00 | 3.8 | 78 | 30 | 220 | 178 | 81 |
| 5.00 | 5.2 | 82 | 30 | 420 | 639 | 100 |
Formula Used
- Offset_kWh = min(Solar_kWh, GardenLoad_kWh)
- Export_kWh = max(0, Solar_kWh − GardenLoad_kWh)
- Offset_% = (Solar_kWh ÷ GardenLoad_kWh) × 100 (optionally capped)
- Savings = Offset_kWh × ElectricityRate
- CO₂ avoided = Offset_kWh × EmissionsFactor
How to Use This Calculator
- Enter your solar system size in kW from the equipment label or design.
- Add your location’s average peak sun hours per day.
- Choose a performance ratio to reflect typical system losses.
- Set the period days (30 for month, 365 for year).
- Enter garden electricity use in kWh for the same period.
- Optionally add your electricity rate and grid emissions factor.
- Click Calculate to view results and download reports.
Sizing Solar for Garden Loads
Garden power needs often concentrate around irrigation pumps, grow lighting, ventilation fans, and seasonal heaters. This calculator converts a solar system’s rated capacity into expected energy for your chosen period, then compares it to the garden’s kWh consumption to estimate practical offset.
Understanding Peak Sun Hours and Seasonality
Peak sun hours represent the daily solar resource equivalent to full sunlight. A location might average 4.5 hours in mild seasons but drop during winter or monsoon periods. For planning, run the calculator with different sun-hour values to see best-case and conservative outcomes.
Using Performance Ratio for Real-World Output
Performance ratio (PR) captures losses from temperature, shading, wiring, inverter efficiency, and panel soiling. Typical small systems often fall between 75% and 85% depending on maintenance and heat. Adjust PR to match your site: higher for clean, cool conditions; lower for dusty or shaded areas.
Interpreting Offset, Export, and Storage Options
Offset kWh is limited to energy your garden actually uses during the period; any remaining solar becomes excess. If excess is frequent, consider shifting loads to daylight, adding a timer, or sizing storage for critical irrigation cycles. Export value depends on net metering or battery strategy, so treat it as an operational note.
Turning Results into Budget and Carbon Metrics
Savings are estimated from onsite offset multiplied by your electricity rate, while avoided emissions use your selected grid factor. Example data: a 3.0 kW system, 4.5 sun hours, 80% PR, over 30 days produces about 324 kWh. If the garden uses 260 kWh, the calculator shows 100% offset and roughly 64 kWh excess, helping you plan upgrades or load shifting.
FAQs
1) What garden devices should I include in kWh use?
Include irrigation pumps, grow lights, fans, heaters, controllers, and tool charging. If you have only a bill amount, estimate kWh by dividing the bill by your rate per kWh for the same period.
2) What performance ratio should I choose?
Use 75–85% for most systems. Choose the lower end for dusty areas, shading, or high heat. Choose the higher end for clean panels, good ventilation, and efficient inverters.
3) Why does my offset cap at 100%?
Capping helps show how fully solar can cover your garden use. If you want to see oversupply, enable the option to allow offset above 100%, and review the excess energy value.
4) Does excess energy always reduce my bill?
Not always. Benefits depend on net metering rules, export tariffs, and whether you have batteries. Treat excess as a sizing signal: shift loads to daytime, export, or store energy if supported.
5) How do I pick peak sun hours?
Use a local solar resource estimate or historical averages. For better planning, run the calculator twice: once with a conservative seasonal value and once with a typical annual average.
6) How accurate are savings and CO₂ avoided?
They are directional estimates. Savings depend on your rate structure, and emissions depend on grid mix. The calculator bases both on onsite offset energy, which is usually the most reliable portion to value.
7) Can I use this for off-grid garden systems?
Yes. Enter solar size, sun hours, and PR to estimate energy. Compare against your planned loads, then use the export figure as a proxy for storage needs or additional daytime loads.