3. Calculations

Definitions

• 1Wh = 1W generated over 1 hour
• 1 toe = 1 tonne of oil equivalent energy = 11.63 megawatt-hours (MWh)
• 1 tonne of oil = approx $440

Calcs

• How much does 1kWh of energy from oil cost?
  1kWh from oil = 440 / 11630 = $0.038 (not accounting for efficiency loss of fossil fuel to electricity conversion)

• How much energy is generated from 1sqm of solar array in 1 year?
  Assuming 244W/sqm of solar energy on average
  Assuming 15% efficiency of solar to electricity
  1 year of electricity generated by 1sqm = 244 * 0.15 * 24 * 365 = 321kWh / year on 1sqm

• How much money does 1sqm of solar electricity create?
  Assuming tariff of £0.05/kWh
  Assuming 1sqm of solar array generates 321kWh/year
  Revenue = 0.05 * 321 = £16.05
  So 1% of solar to electricity efficiency is worth 16.05 / 15 = £1.07

• How much does it cost to build 1sqm of solar array, and how long will it last?

  Example 1

  Taking South Africa supplier of 300W, pallet of 26, 1.96m x 0.99m, 15.48% efficiency at cost of R56,794 = £3039
  Excluding cost of installation and other electrical components, shipping, taxes
  1sqm cost = 3039 / (1.96 * 0.99 * 26) = £60.24
  Initial annual return at 15% efficiency, before depreciation = 16.05 / 60.24 = 26.6%

  Example 2

  Taking UK supplier of 300W, 1.64m x 0.99, 18.9% efficiency at cost of £145
  Excluding cost of installation and other electrical components, shipping, taxes
  1 year of electricity generated by 1sqm = 244 * 0.189 * 24 * 365 = 404kWh = £20.20
  1sqm cost = 145 / (1.64 * 0.99) = £89.31
  Initial annual return, before depreciation = 20.2 / 89.31 = 22.6%

• What area of solar array would be needed to cover Malawi's current energy use?
  Assuming 430MW average use in 2015
  Assuming 15% solar efficiency
  Solar array sqm required = 430,000,000 / (244 * 0.15) = 11,748,634 sqm = 11.7sqkm = 3.4km by 3.4km
  Approximate cost would be = 11,748,634 * 60.24 = £708 million
  (For comparison, in 2015 India built a 648MW solar farm for £545 million)

• How much does 1kWh of energy from solar cost?
  Assuming 25 year lifespan
  Assuming 1sqm costs £60.24 and generates 321kWh / year
  Ignoring costs of land, etc...
  1kWh from solar = 60.42 / (25 * 321) = £0.008 = $0.01