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) Shenqiu Phase II (9.5-year term). In addition, as of March 31, 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 March 31, 2018 and December 31, 2017 are as follows:

	2018			2017
Total future minimum lease payments receivable	$	227,863,380		$	218,176,104
Less: executory cost		(69,291,742	)		(66,443,813	)
Less: unearned interest		(28,842,316	)		(33,638,086	)
Less: realized interest income but not yet received		(10,871,828	)		(6,450,202	)
Less: allowance for net investment receivable		(1,976,750	)
Investment in sales-type leases, net		116,880,744			111,644,003
Current portion		14,462,637			11,034,452
Noncurrent portion	$	102,418,107		$	100,609,551

As of March 31, 2018, the future minimum rentals to be received on non-cancelable sales-type leases by years are as follows:

2019	$	43,576,604
2020		20,889,274
2021		22,603,270
2022		22,680,747
2023		21,224,190
Thereafter		96,889,295
Total	$	227,863,380