4. INVESTMENT IN SALES-TYPE LEASES, NET

Under sales-type leases, Xi’an TCH leases the following systems: (i) BMPG systems to Pucheng Phase I and II (15 and 11 year terms, respectively); (ii) BMPG systems to Shenqiu Phase I (11-year term); and (iii) BMPG systems to Shenqiu Phase II (9.5-year term). In addition, as of September 30, 2018, Erdos TCH leased power and steam generating systems from waste heat from metal refining to Erdos (five systems) for a term of twenty years. The components of the net investment in sales-type leases as of September 30, 2018 and December 31, 2017 are as follows:

	2018			2017
Total future minimum lease payments receivable	$	203,269,139		$	222,132,929
Less: executory cost		(62,014,131	)		(67,212,769	)
Less: unearned interest		(24,873,815	)		(29,542,876	)
Less: realized interest income but not yet received		(9,315,463	)		(9,869,358	)
Less: allowance for net investment receivable		(4,839,392	)		(1,802,822	)
Investment in sales-type leases, net		102,226,338			113,705,104
Current portion		12,689,105			13,076,516
Noncurrent portion	$	89,537,233		$	100,628,588

As of September 30, 2018, the future minimum rentals to be received on non-cancelable sales-type leases by year are as follows:

2019	$	44,364,506
2020		19,929,270
2021		20,098,242
2022		22,129,636
2023		16,522,245
Thereafter		80,225,240
Total	$	203,269,139