Alternative energy

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Across
  1. 3. has a limit
  2. 5. relates to movement
  3. 8. relates to money
  4. 9. can be replaced
  5. 11. a particle of light
  6. 13. capable of working
  7. 16. able to be maintained
  8. 17. relates to sun
  9. 18. A unit of voltage
Down
  1. 1. has no limit
  2. 2. internal heat of earth
  3. 4. relates to light and energy
  4. 6. geological period
  5. 7. relates to heat
  6. 10. A measurement of current
  7. 12. Moral
  8. 14. particles involved in electricity
  9. 15. He discovered photovoltaic