Calculator Inputs
Example Data Table
Use these sample entries to understand typical ranges.
| Device | Watts | Hours/Day | Days/Month | Qty | Duty |
|---|---|---|---|---|---|
| LED Grow Light | 200 | 10 | 30 | 1 | Constant |
| Irrigation Pump | 750 | 0.5 | 20 | 1 | Cycling |
| Greenhouse Fan | 90 | 8 | 30 | 2 | Constant |
| Heat Mat | 60 | 6 | 30 | 3 | Seasonal |
Formula Used
For each device, monthly energy use is calculated from power and runtime:
- kWh = (Watts ÷ 1000) × Hours/Day × Days/Month × Quantity × Duty Multiplier
- Effective Rate = Rate × (1 − Off‑peak Discount × Off‑peak Share)
- Energy Cost = Σ(kWh × Effective Rate)
- Solar Credit = min(Total kWh, Solar Offset kWh) × Solar Credit Rate
- Subtotal = Energy Cost + Fixed Charges − Solar Credit
- Tax Amount = Subtotal × (Tax% ÷ 100)
- Grand Total = Subtotal + Tax Amount
Duty multipliers are simple estimates: Constant = 1.00, Cycling = 0.75, Seasonal = 0.60.
How to Use This Calculator
- Enter your electricity rate, fixed charge, and any taxes or surcharges.
- Set off‑peak discount and the share of usage you schedule off‑peak.
- Add each device with watts, hours per day, days per month, and quantity.
- Choose a duty setting to reflect cycling or seasonal operation.
- Press Calculate Monthly Cost to see totals above the form.
- Download a CSV or PDF report using the buttons in Results.
Why monthly energy tracking matters in gardens
Garden power loads often feel small, yet they run many hours. Grow lights, fans, heaters, pumps, and timers can quietly add up across a 30‑day cycle. This calculator converts watts and schedules into kWh, then applies your rate, discounts, and credits to estimate a real monthly bill more accurately. When you know the cost per device, you can prioritize changes that deliver measurable savings without reducing plant health.
Device inputs that drive accurate results
Power (watts) and runtime (hours per day) create the base load. Days per month lets you model seasonal use, such as irrigation that runs only during dry weeks. Quantity matters for multiple fans or mats. Duty settings provide a practical adjustment for cycling motors or intermittent heat. If you are unsure, start with constant duty, then refine after observing actual run patterns.
Understanding rates, off‑peak savings, and credits
Many utilities offer time‑of‑use pricing. If you schedule pumps or lights at cheaper times, the tool applies a discount to the share you mark as off‑peak. Fixed charges represent service fees that do not change with kWh. Solar offset and a credit rate represent the bill value of the energy you produce or export, helping you estimate net monthly cost more realistically.
Interpreting the breakdown and taking action
The results table sorts devices by energy use, making top contributors obvious. A high‑watt light running long hours usually dominates, followed by heaters and pumps. Try reducing runtime, improving insulation, or swapping to efficient equipment. Small changes like optimized timers, cleaned filters, and properly sized pumps can reduce kWh while maintaining airflow and irrigation performance.
Using exports for budgeting and maintenance
The CSV report supports spreadsheets for month‑to‑month comparisons and cost targets. The PDF summary is useful for sharing with partners, clients, or greenhouse staff. Save a baseline in one season, then run a second estimate after upgrades. Consistent reporting helps justify purchases, validate savings, and plan peak‑season electricity needs with fewer surprises.
FAQs
1) What should I enter if my bill shows cents per kWh?
Convert cents to dollars (or your currency) by dividing by 100. For example, 18 cents per kWh becomes 0.18. Then keep the same unit for credits and fixed charges.
2) How do I estimate watts if only amps are listed?
Use watts ≈ volts × amps. Many small devices are 120V or 230V, but check the label. If the device is motor driven, real usage may vary with load.
3) Why does the calculator use duty multipliers?
Cycling and seasonal settings approximate intermittent operation without complex logging. They help model pumps that run in bursts and heaters that turn on and off, improving planning accuracy.
4) What if a device runs only a few days each month?
Set its days per month to the expected run days. If you leave it blank, the calculator uses the default month length. This keeps other entries consistent and faster to manage.
5) Can I use this for battery or generator power?
Yes for estimating energy use (kWh). For cost, enter your effective price per kWh based on fuel or battery recharge cost. Generator efficiency and maintenance can change true costs.
6) How can I validate results against my meter?
Run one device at a time and record kWh from a plug meter or smart outlet for a day. Compare measured kWh to the estimate, then adjust hours, duty, or watts for best fit.