Solar Payback worksheet

1. Payback period: 15.8 years

1. Work out the energy to make each year: your monthly use × 12 months × the share you want solar to cover

   $800\text{\hspace{0.17em}kWh}\times 12\times \mathrm{110\%}$$=\mathrm{10,560}\text{\hspace{0.17em}kWh}$

2. Size the system: divide that by what 1 kW of panels makes in a year (365 days × sun hours × efficiency)

   $\frac{\mathrm{10,560}\text{\hspace{0.17em}kWh}}{365\times 5\text{\hspace{0.17em}h}\times 0.62}$$=9.3327\text{\hspace{0.17em}kW}$

3. Price it: size in watts × the installed cost per watt

   $\mathrm{9,332.74}\text{\hspace{0.17em}W}\times \mathrm{\$2.00}$$=\mathrm{\$18,665.49}$

4. Take off rebates and incentives to get what you really pay

   $\mathrm{\$18,665.49}-\mathrm{\$0.00}$$=\mathrm{\$18,665.49}$

5. First-year savings: the power you make × its price × how much of that your utility credits, minus upkeep

   $\mathrm{10,560}\text{\hspace{0.17em}kWh}\times \mathrm{\$0.11}\times \mathrm{90\%}-\mathrm{\$0.00}$$=\mathrm{\$1,045.44}$

6. Payback: savings pass the net cost during year 16. By the start of that year you've saved $17,555.68, and the rest takes part of the year

   $15+\frac{\mathrm{\$18,665.49}-\mathrm{\$17,555.68}}{\mathrm{\$1,324.93}}$$=15.8376\text{\hspace{0.17em}years}$

7. Net gain over 28 years: total savings minus net cost

   $\mathrm{\$36,524.94}-\mathrm{\$18,665.49}$$=\mathrm{\$17,859.45}$

2. Payback period: 9.1 years

1. Work out the energy to make each year: your monthly use × 12 months × the share you want solar to cover

   $900\text{\hspace{0.17em}kWh}\times 12\times \mathrm{140\%}$$=\mathrm{15,120}\text{\hspace{0.17em}kWh}$

2. Size the system: divide that by what 1 kW of panels makes in a year (365 days × sun hours × efficiency)

   $\frac{\mathrm{15,120}\text{\hspace{0.17em}kWh}}{365\times 5.2\text{\hspace{0.17em}h}\times 1}$$=7.9663\text{\hspace{0.17em}kW}$

3. Price it: size in watts × the installed cost per watt

   $\mathrm{7,966.28}\text{\hspace{0.17em}W}\times \mathrm{\$3.00}$$=\mathrm{\$23,898.84}$

4. Take off rebates and incentives to get what you really pay

   $\mathrm{\$23,898.84}-\mathrm{\$0.00}$$=\mathrm{\$23,898.84}$

5. First-year savings: the power you make × its price × how much of that your utility credits, minus upkeep

   $\mathrm{15,120}\text{\hspace{0.17em}kWh}\times \mathrm{\$0.20}\times \mathrm{80\%}-\mathrm{\$0.00}$$=\mathrm{\$2,419.20}$

6. Payback: savings pass the net cost during year 10. By the start of that year you've saved $23,678.66, and the rest takes part of the year

   $9+\frac{\mathrm{\$23,898.84}-\mathrm{\$23,678.66}}{\mathrm{\$2,912.62}}$$=9.0756\text{\hspace{0.17em}years}$

7. Net gain over 25 years: total savings minus net cost

   $\mathrm{\$78,322.39}-\mathrm{\$23,898.84}$$=\mathrm{\$54,423.55}$

3. Payback period: 16.7 years

1. Work out the energy to make each year: your monthly use × 12 months × the share you want solar to cover

   $900\text{\hspace{0.17em}kWh}\times 12\times \mathrm{65\%}$$=\mathrm{7,020}\text{\hspace{0.17em}kWh}$

2. Size the system: divide that by what 1 kW of panels makes in a year (365 days × sun hours × efficiency)

   $\frac{\mathrm{7,020}\text{\hspace{0.17em}kWh}}{365\times 4\text{\hspace{0.17em}h}\times 0.75}$$=6.411\text{\hspace{0.17em}kW}$

3. Price it: size in watts × the installed cost per watt

   $\mathrm{6,410.96}\text{\hspace{0.17em}W}\times \mathrm{\$3.00}$$=\mathrm{\$19,232.88}$

4. Take off rebates and incentives to get what you really pay

   $\mathrm{\$19,232.88}-\mathrm{\$0.00}$$=\mathrm{\$19,232.88}$

5. First-year savings: the power you make × its price × how much of that your utility credits, minus upkeep

   $\mathrm{7,020}\text{\hspace{0.17em}kWh}\times \mathrm{\$0.15}\times \mathrm{90\%}-\mathrm{\$0.00}$$=\mathrm{\$947.70}$

6. Payback: savings pass the net cost during year 17. By the start of that year you've saved $18,207.60, and the rest takes part of the year

   $16+\frac{\mathrm{\$19,232.88}-\mathrm{\$18,207.60}}{\mathrm{\$1,382.64}}$$=16.7415\text{\hspace{0.17em}years}$

7. Net gain over 32 years: total savings minus net cost

   $\mathrm{\$44,771.51}-\mathrm{\$19,232.88}$$=\mathrm{\$25,538.64}$

4. Payback period: 14.5 years

1. Work out the energy to make each year: your monthly use × 12 months × the share you want solar to cover

   $900\text{\hspace{0.17em}kWh}\times 12\times \mathrm{75\%}$$=\mathrm{8,100}\text{\hspace{0.17em}kWh}$

2. Size the system: divide that by what 1 kW of panels makes in a year (365 days × sun hours × efficiency)

   $\frac{\mathrm{8,100}\text{\hspace{0.17em}kWh}}{365\times 4.4\text{\hspace{0.17em}h}\times 0.72}$$=7.005\text{\hspace{0.17em}kW}$

3. Price it: size in watts × the installed cost per watt

   $\mathrm{7,004.98}\text{\hspace{0.17em}W}\times \mathrm{\$3.00}$$=\mathrm{\$21,014.94}$

4. Take off rebates and incentives to get what you really pay

   $\mathrm{\$21,014.94}-\mathrm{\$0.00}$$=\mathrm{\$21,014.94}$

5. First-year savings: the power you make × its price × how much of that your utility credits, minus upkeep

   $\mathrm{8,100}\text{\hspace{0.17em}kWh}\times \mathrm{\$0.16}\times \mathrm{100\%}-\mathrm{\$0.00}$$=\mathrm{\$1,296.00}$

6. Payback: savings pass the net cost during year 15. By the start of that year you've saved $20,146.51, and the rest takes part of the year

   $14+\frac{\mathrm{\$21,014.94}-\mathrm{\$20,146.51}}{\mathrm{\$1,616.73}}$$=14.5372\text{\hspace{0.17em}years}$

7. Net gain over 24 years: total savings minus net cost

   $\mathrm{\$37,522.63}-\mathrm{\$21,014.94}$$=\mathrm{\$16,507.68}$

5. Payback period: 8.1 years

1. Work out the energy to make each year: your monthly use × 12 months × the share you want solar to cover

   $900\text{\hspace{0.17em}kWh}\times 12\times \mathrm{80\%}$$=\mathrm{8,640}\text{\hspace{0.17em}kWh}$

2. Size the system: divide that by what 1 kW of panels makes in a year (365 days × sun hours × efficiency)

   $\frac{\mathrm{8,640}\text{\hspace{0.17em}kWh}}{365\times 4\text{\hspace{0.17em}h}\times 0.88}$$=6.7248\text{\hspace{0.17em}kW}$

3. Price it: size in watts × the installed cost per watt

   $\mathrm{6,724.78}\text{\hspace{0.17em}W}\times \mathrm{\$2.00}$$=\mathrm{\$13,449.56}$

4. Take off rebates and incentives to get what you really pay

   $\mathrm{\$13,449.56}-\mathrm{\$0.00}$$=\mathrm{\$13,449.56}$

5. First-year savings: the power you make × its price × how much of that your utility credits, minus upkeep

   $\mathrm{8,640}\text{\hspace{0.17em}kWh}\times \mathrm{\$0.18}\times \mathrm{100\%}-\mathrm{\$0.00}$$=\mathrm{\$1,555.20}$

6. Payback: savings pass the net cost during year 9. By the start of that year you've saved $13,340.88, and the rest takes part of the year

   $8+\frac{\mathrm{\$13,449.56}-\mathrm{\$13,340.88}}{\mathrm{\$1,819.94}}$$=8.0597\text{\hspace{0.17em}years}$

7. Net gain over 19 years: total savings minus net cost

   $\mathrm{\$35,469.57}-\mathrm{\$13,449.56}$$=\mathrm{\$22,020.00}$

6. Payback period: 15.6 years

1. Work out the energy to make each year: your monthly use × 12 months × the share you want solar to cover

   $880\text{\hspace{0.17em}kWh}\times 12\times \mathrm{65\%}$$=\mathrm{6,864}\text{\hspace{0.17em}kWh}$

2. Size the system: divide that by what 1 kW of panels makes in a year (365 days × sun hours × efficiency)

   $\frac{\mathrm{6,864}\text{\hspace{0.17em}kWh}}{365\times 5.5\text{\hspace{0.17em}h}\times 0.9}$$=3.7991\text{\hspace{0.17em}kW}$

3. Price it: size in watts × the installed cost per watt

   $\mathrm{3,799.09}\text{\hspace{0.17em}W}\times \mathrm{\$3.00}$$=\mathrm{\$11,397.26}$

4. Take off rebates and incentives to get what you really pay

   $\mathrm{\$11,397.26}-\mathrm{\$0.00}$$=\mathrm{\$11,397.26}$

5. First-year savings: the power you make × its price × how much of that your utility credits, minus upkeep

   $\mathrm{6,864}\text{\hspace{0.17em}kWh}\times \mathrm{\$0.11}\times \mathrm{80\%}-\mathrm{\$0.00}$$=\mathrm{\$604.03}$

6. Payback: savings pass the net cost during year 16. By the start of that year you've saved $10,901.10, and the rest takes part of the year

   $15+\frac{\mathrm{\$11,397.26}-\mathrm{\$10,901.10}}{\mathrm{\$886.15}}$$=15.5599\text{\hspace{0.17em}years}$

7. Net gain over 28 years: total savings minus net cost

   $\mathrm{\$24,391.16}-\mathrm{\$11,397.26}$$=\mathrm{\$12,993.90}$

7. Payback period: 16.2 years

1. Work out the energy to make each year: your monthly use × 12 months × the share you want solar to cover

   $900\text{\hspace{0.17em}kWh}\times 12\times \mathrm{120\%}$$=\mathrm{12,960}\text{\hspace{0.17em}kWh}$

2. Size the system: divide that by what 1 kW of panels makes in a year (365 days × sun hours × efficiency)

   $\frac{\mathrm{12,960}\text{\hspace{0.17em}kWh}}{365\times 4.6\text{\hspace{0.17em}h}\times 0.88}$$=8.7715\text{\hspace{0.17em}kW}$

3. Price it: size in watts × the installed cost per watt

   $\mathrm{8,771.45}\text{\hspace{0.17em}W}\times \mathrm{\$3.00}$$=\mathrm{\$26,314.36}$

4. Take off rebates and incentives to get what you really pay

   $\mathrm{\$26,314.36}-\mathrm{\$0.00}$$=\mathrm{\$26,314.36}$

5. First-year savings: the power you make × its price × how much of that your utility credits, minus upkeep

   $\mathrm{12,960}\text{\hspace{0.17em}kWh}\times \mathrm{\$0.15}\times \mathrm{70\%}-\mathrm{\$0.00}$$=\mathrm{\$1,360.80}$

6. Payback: savings pass the net cost during year 17. By the start of that year you've saved $25,935.26, and the rest takes part of the year

   $16+\frac{\mathrm{\$26,314.36}-\mathrm{\$25,935.26}}{\mathrm{\$1,953.68}}$$=16.194\text{\hspace{0.17em}years}$

7. Net gain over 32 years: total savings minus net cost

   $\mathrm{\$63,170.11}-\mathrm{\$26,314.36}$$=\mathrm{\$36,855.75}$

8. Payback period: 16.9 years

1. Work out the energy to make each year: your monthly use × 12 months × the share you want solar to cover

   $975\text{\hspace{0.17em}kWh}\times 12\times \mathrm{130\%}$$=\mathrm{15,210}\text{\hspace{0.17em}kWh}$

2. Size the system: divide that by what 1 kW of panels makes in a year (365 days × sun hours × efficiency)

   $\frac{\mathrm{15,210}\text{\hspace{0.17em}kWh}}{365\times 4\text{\hspace{0.17em}h}\times 0.8}$$=13.0223\text{\hspace{0.17em}kW}$

3. Price it: size in watts × the installed cost per watt

   $\mathrm{13,022.26}\text{\hspace{0.17em}W}\times \mathrm{\$3.00}$$=\mathrm{\$39,066.78}$

4. Take off rebates and incentives to get what you really pay

   $\mathrm{\$39,066.78}-\mathrm{\$0.00}$$=\mathrm{\$39,066.78}$

5. First-year savings: the power you make × its price × how much of that your utility credits, minus upkeep

   $\mathrm{15,210}\text{\hspace{0.17em}kWh}\times \mathrm{\$0.13}\times \mathrm{100\%}-\mathrm{\$0.00}$$=\mathrm{\$1,977.30}$

6. Payback: savings pass the net cost during year 17. By the start of that year you've saved $36,536.62, and the rest takes part of the year

   $16+\frac{\mathrm{\$39,066.78}-\mathrm{\$36,536.62}}{\mathrm{\$2,667.11}}$$=16.9487\text{\hspace{0.17em}years}$

7. Net gain over 32 years: total savings minus net cost

   $\mathrm{\$85,819.61}-\mathrm{\$39,066.78}$$=\mathrm{\$46,752.83}$

9. Payback period: 20.6 years

1. Work out the energy to make each year: your monthly use × 12 months × the share you want solar to cover

   $900\text{\hspace{0.17em}kWh}\times 12\times \mathrm{110\%}$$=\mathrm{11,880}\text{\hspace{0.17em}kWh}$

2. Size the system: divide that by what 1 kW of panels makes in a year (365 days × sun hours × efficiency)

   $\frac{\mathrm{11,880}\text{\hspace{0.17em}kWh}}{365\times 3.4\text{\hspace{0.17em}h}\times 0.9}$$=10.6366\text{\hspace{0.17em}kW}$

3. Price it: size in watts × the installed cost per watt

   $\mathrm{10,636.58}\text{\hspace{0.17em}W}\times \mathrm{\$4.00}$$=\mathrm{\$42,546.33}$

4. Take off rebates and incentives to get what you really pay

   $\mathrm{\$42,546.33}-\mathrm{\$0.00}$$=\mathrm{\$42,546.33}$

5. First-year savings: the power you make × its price × how much of that your utility credits, minus upkeep

   $\mathrm{11,880}\text{\hspace{0.17em}kWh}\times \mathrm{\$0.16}\times \mathrm{88\%}-\mathrm{\$0.00}$$=\mathrm{\$1,672.70}$

6. Payback: savings pass the net cost during year 21. By the start of that year you've saved $41,008.54, and the rest takes part of the year

   $20+\frac{\mathrm{\$42,546.33}-\mathrm{\$41,008.54}}{\mathrm{\$2,529.78}}$$=20.6079\text{\hspace{0.17em}years}$

7. Net gain over 24 years: total savings minus net cost

   $\mathrm{\$51,449.34}-\mathrm{\$42,546.33}$$=\mathrm{\$8,903.01}$

10. Payback period: 14.5 years

1. Work out the energy to make each year: your monthly use × 12 months × the share you want solar to cover

   $900\text{\hspace{0.17em}kWh}\times 12\times \mathrm{72\%}$$=\mathrm{7,776}\text{\hspace{0.17em}kWh}$

2. Size the system: divide that by what 1 kW of panels makes in a year (365 days × sun hours × efficiency)

   $\frac{\mathrm{7,776}\text{\hspace{0.17em}kWh}}{365\times 5.5\text{\hspace{0.17em}h}\times 0.75}$$=5.1646\text{\hspace{0.17em}kW}$

3. Price it: size in watts × the installed cost per watt

   $\mathrm{5,164.63}\text{\hspace{0.17em}W}\times \mathrm{\$3.00}$$=\mathrm{\$15,493.90}$

4. Take off rebates and incentives to get what you really pay

   $\mathrm{\$15,493.90}-\mathrm{\$0.00}$$=\mathrm{\$15,493.90}$

5. First-year savings: the power you make × its price × how much of that your utility credits, minus upkeep

   $\mathrm{7,776}\text{\hspace{0.17em}kWh}\times \mathrm{\$0.13}\times \mathrm{90\%}-\mathrm{\$0.00}$$=\mathrm{\$909.79}$

6. Payback: savings pass the net cost during year 15. By the start of that year you've saved $14,909.99, and the rest takes part of the year

   $14+\frac{\mathrm{\$15,493.90}-\mathrm{\$14,909.99}}{\mathrm{\$1,264.95}}$$=14.4616\text{\hspace{0.17em}years}$

7. Net gain over 20 years: total savings minus net cost

   $\mathrm{\$22,966.25}-\mathrm{\$15,493.90}$$=\mathrm{\$7,472.36}$