. ▁ ▁Saf ety ▁Light ning , ▁aircraft ▁traffic , ▁emer gency ▁procedures , ▁system ▁ins pe ctions , ▁visibility ▁mark ing ▁of ▁system ▁parts ▁and ▁its ▁t eth ers , ▁elect rical ▁safety , ▁run away - wing ▁procedures , ▁over - power ing ▁controls , ▁appropriate ▁mo oring , ▁and ▁more ▁form ▁the ▁safety ▁environment ▁for ▁H A WP ▁systems . ▁ ▁Ch alleng es ▁as ▁an ▁emer ging ▁industry ▁ ▁There ▁have ▁been ▁several ▁periods ▁of ▁high ▁interest ▁in ▁H A WP ▁before ▁the ▁contemporary ▁activity . ▁The ▁first ▁period ▁had ▁a ▁high ▁focus ▁on ▁pulling ▁carri ages ▁over ▁the ▁lands ▁and ▁capt uring ▁atmos pher ic ▁electric ity ▁and ▁light ning ▁for ▁human ▁use . ▁The ▁second ▁period ▁was ▁in ▁the ▁ 1 9 7 0 s ▁and ▁ 1 9 8 0 s ▁when ▁research ▁and ▁invest ment ▁fl our ished ; ▁a ▁drop ▁in ▁oil ▁price ▁resulted ▁in ▁no ▁significant ▁install ations ▁of ▁H A WP . ▁Return ▁on ▁invest ment ▁( RO I ) ▁has ▁been ▁the ▁key ▁parameter ; ▁that ▁RO I ▁remains ▁in ▁focus ▁in ▁the ▁current ▁development ▁activity ▁while ▁in ▁the ▁background ▁is ▁the ▁renew able ▁and ▁sust ain able ▁energy ▁movement ▁supporting ▁wind ▁power ▁of ▁any ▁kind ; ▁but ▁H A WP ▁must ▁comp ete ▁on ▁RO I ▁with ▁conventional ▁tower ed ▁solutions . ▁A ▁test ▁center ▁at ▁Lista , ▁Norway ▁provides ▁independent ▁ver ification ▁of ▁research . ▁ ▁Early ▁references ▁to ▁H A WP ▁Early ▁centuries ▁of ▁k iting ▁demonstrated ▁that