Example 1: the lower headline price can hide a different scope
The following amounts are invented teaching inputs. They are not current or historical Summit National Energy prices, installed-cost estimates or financing offers.
Suppose Example A includes the required work at $24,000. Example B shows $22,500 but excludes work for which you set a $2,000 comparison allowance. The adjusted arithmetic becomes A: $24,000 and B: $24,500. B is $500 higher on those assumptions.
An allowance is still an estimate. Confirm the actual scope and written price before treating the offers as equivalent. Price alone does not resolve equipment quality, responsibilities or contract terms.
A monthly number needs its contract beside it
For a simple illustration with no down payment, fees, escalation or payment changes, $150 each month for 240 months totals $36,000. It is not a financing quote or a cost-of-credit analysis. A different term, fee, escalation schedule or balloon payment changes the calculation.
Ask for the cash price, amount financed where relevant, term, rate, fees, payment schedule and total obligations. For a lease or power purchase agreement, identify its own pricing, escalation, transfer and end-of-term terms. Compare the actual agreements rather than treating unlike contracts as the same purchase.
Example 2: watts × hours becomes an energy budget
These assumed wattages teach arithmetic. They are not measured loads, manufacturer ratings or a backup design. Real cycling, startup and simultaneous demand need separate assessment.
| Example load | Assumed average W | Hours | Energy |
|---|---|---|---|
| Refrigerator average | 150 | 8 | 1.20 kWh |
| Selected lights | 60 | 5 | 0.30 kWh |
| Router | 15 | 8 | 0.12 kWh |
| Office equipment | 120 | 4 | 0.48 kWh |
| Combined example demand | 2.10 kWh | ||
Energy in kWh = average watts × operating hours ÷ 1,000. If the chosen teaching budget is 10 kWh and you set aside 20% as a combined reserve/loss allowance, the remaining arithmetic budget is 8 kWh. Subtracting the example demand leaves 5.90 kWh. The 20% allowance is an invented input, not a Tesla specification or recommended design setting.
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Energy arithmetic is only one part of a backup decision
A positive energy balance does not establish that a battery can start a motor, support the simultaneous power draw or energize the desired circuits. Starting charge, operating settings, system configuration and actual usage also affect performance. No solar recharge is modeled in this worksheet.
Tesla’s backup guidance explains why the appliances and system configuration matter. A project-specific design must identify supported loads and required electrical equipment.
Bring a list of the equipment you want supported to your quote review. We can identify what still needs confirmation. This worksheet does not recommend an installable system, a battery count or an outage duration.
Sources and further reading
Source links checked October 30, 2026. Utility terms and offers can change; confirm the terms applicable to your project.