Detailed AC/DC system design

Physical evaluation

Location: Puerto Arturo, Madre de Dios, Peru
GPS coordinates: -12.48694444, -69.21305556
Altitude: 3378m
Description: A community building with lighting and AC power needs. The system is used all year long, but it is typically only used three to four times a week by community members for meetings, parties, or training sessions. Load usage is typically during the day. The community does not intend on adding any major appliances in the near future.

The system will use DC for lighting and AC for powering loads. DC is used for lighting so that the system continually provides light regardless of whether the inverter is turned on. As the building is used intermittently, the inverter can be turned off to reduce wear and to lessen the liklihood of an accident or damage from lightning.

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  Photo of the building.

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  Location of the building.

Load evaluation

Although the system is used only one day a week, inputting 1 day a week of usage for the loads will lead to an undersized array and a poor system design. We will input 4 days a week to ensure that the PV source is still of a reasonable size.

DC load evaluation

Step 1: Fill out DC load chart

						April - September			October - March
#	Load	Quantity	Watts	Total watts	Duty cycle	Hours per day	Days per week	Average daily DC watt-hours	Hours per day	Days per week	Average daily DC watt-hours
1	LED light	8	5 W	40 W	1	3 hours	4 days	69 Wh	3 hours	4 days	69 Wh
2	Inverter	1	7 W	7 W	1	3 hours	4 days	12 Wh	5 hours	4 days	12 Wh

• Load: The make and model or type of load.
• Quantity: The number of the particular load.
• Watts: The power rating in watts of the load.
• Total watts = Quantity × Watts
• Duty cycle = Rated or estimated duty cycle for the load. If the load has no duty cycle a value of 1 should be used. A load with a duty cycle of 20% would be inputted as .2
• Hours per day: The maximum number of hours the load(s) will be operated per day. If the load has a duty cycle 24 hours should be used.
• Days per week: The maximum number of days the load(s) will be operated per week.
• Average daily DC watt-hours = Total watts × Duty cycle × Hours per day × Days per week ÷ 7 days

Step 2: Determine DC energy demand

Total average daily DC watt-hours (April - September)	= sum of Average daily DC watt-hours for all loads for April - September
	= 81 Wh

Total average daily DC watt-hours (October - March)	= sum of Average daily DC watt-hours for all loads for October - March
	= 81 Wh

AC load evaluation

Step 1: Determine inverter efficiency

A conservative inverter efficiency value of .85 is going to be used.

Inverter efficiency	.85

Step 2: Fill out AC load chart

										April - October			March - September
#	Load	Quantity	Watts	Total watts	Duty cycle	Surge factor	Surge watts	Power factor	Volt-amperes (VA)	Hours per day	Days per week	Average daily AC watt-hours	Hours per day	Days per week	Average daily AC watt-hours
1	Projector	1	300 W	300 W	1	0	0	.9	333 VA	3 hours	4 days	605 Wh	3 hours	4 days	605 Wh
2	Stereo	1	30 W	30 W	1	0	0	.9	33 VA	3 hours	4 days	61 Wh	3 hours	4 days	61 Wh
3	Cell phone	5	5 W	25 W	1	0	0	.9	28 VA	1 hour	4 days	17 Wh	1 hour	4 days	17 Wh

• Load: The make and model or type of load.
• Quantity: The number of the particular load.
• Watts: The power rating in watts for the load.
• Total watts = Quantity × Watts
• Duty cycle = Rated or estimated duty cycle for the load. If the load has no duty cycle a value of 1 should be used. A load with a duty cycle of 20% would be inputted as .2
• Surge factor = Rated or estimated duty cycle for the load. Common values are between 3-5. If the load does not have a surge requirement a value of 0 should be used.
• Power factor = Rated or estimated power factor for the load.
• Volt-amperes (VA) = Total watts ÷ Power factor
• Hours per day: The maximum number of hours the load(s) will be operated per day. If the load has a duty cycle 24 hours should be used.
• Days per week: The maximum number of days the load(s) will be operated per week.
• Average daily AC Watt-hours = Total watts × Duty cycle ÷ Inverter efficiency (Step 1) × Hours per day × Days per week ÷ 7 days

Step 3: Deteremine AC energy demand

Total average daily AC watt-hours (April - September)	= sum of Average daily AC watt-hours for all loads for April - September
	682 Wh

Total average daily AC watt-hours (October - March)	= sum of Average daily AC watt-hours for all loads for October - March
	682 Wh

Step 4: Determine AC power demand

Total VA	= sum of volt-amperes (VA)
	394 VA

Total VA with surge watts	= sum of Surge watts for all loads + Total VA
	394 VA

Weather and solar resource evaluation

Maximum ambient temperature = 35°C
Minimum ambient temperature = 15°C
Maximum indoor temperature = 30°C
Minimum indoor temperature = 20°C

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  Retrieving PVGIS monthly insolation data.

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  Retrieving PVGIS monthly insolation data.

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  Retrieving PVGIS weather data.

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  Retrieving PVGIS weather data.

Load and solar resource comparison

Step 1: Determine monthly ratio of energy demand to solar resource

Month	Average monthly insolation	Total average daily energy demand	Ratio
January	131.2 kWh/m²	763 Wh	.722
February	162.2 kWh/m²	140 Wh	.86
March	179.81 kWh/m²	140 Wh	.78
April	174.98 kWh/m²	140 Wh	.8
May	214.31 kWh/m²	140 Wh	.65
June	200.05 kWh/m²	140 Wh	.7
July	210.35 kWh/m²	140 Wh	.67
August	229.96 kWh/m²	140 Wh	.61
September	126.87 kWh/m²	140 Wh	1.1
October	214.82 kWh/m²	140 Wh	.65
November	212.91 kWh/m²	140 Wh	.66
December	176.98 kWh/m²	140 Wh	.79

• Month: The month of the year.
• Average monthly insolation: Solar resource data obtained for the location from Weather and solar resource evaluation.
• Total average daily energy demand for the month from the load evaluation.
• Ratio = Total average daily energy demand ÷ Average monthly insolation

Step 2: Determine design values

Design daily insolation	= Average monthly insolation from month with the highest ratio ÷ 30
	= 126.87 kWh/m² ÷ 30 = 4.23 kWh/m²

Design daily watt-hours required	= Total average daily energy demand from month with the highest ratio
	= 140 Wh