Design PV off grid solar station

BillK-AZ

Senior Member
Location
Mesa Arizona
The distance between modules and the tilt angle are not items covered by the USA NEC. This is a complex subject, but not a safety issue.

The more general question is "How to design a PV system". Some basic consideration, using Cairo with a latitude of 30 degrees as an example:

If you are designing a PV system that needs to supply a continuous load all year, such as a microwave repeater with a constant load, the optimum tilt is 55°.

If you have a utility connected system that can accept all the energy you produce, a tilt of 35° will maximize the annual output.

If you have high summer loads, such as air conditioning, you can use a lower tilt such as 5° or 10°. Do not use a tilt less than 5° or there will be problems due to dirt build up that will not wash off with rain.

Assuming "distance between modules" is row-to-row spacing in an array field, the spacing varies with the tilt angle. This varies with site latitude and how much output you can afford to lose due to shading at low sun elevations. A good reference is https://azsolarcenter.org/pv-row-to-row-spacing

PV manufacturers generally have installation instructions that specify spacing between side-by-side modules. These instructions are required by any IEC or UL Listing for the modules.

In some cases in hot climates row-to-row spacing may have to be increased, as well as clearance under the modules for air circulation. Some studies of 30+ year old PV array fields in the Phoenix area (where the wind is generally from the same SW direction during periods of peak temperatures) have shown PV module degradation is much higher on the northern most areas of the array field. Additional spacing is needed, but this subject has not been studied in detail.

Determining how many PV of a specific rating are required for the system is another question that is beyond the scope of this posting.
 
The distance between modules and the tilt angle are not items covered by the USA NEC. This is a complex subject, but not a safety issue.

The more general question is "How to design a PV system". Some basic consideration, using Cairo with a latitude of 30 degrees as an example:

If you are designing a PV system that needs to supply a continuous load all year, such as a microwave repeater with a constant load, the optimum tilt is 55°.

If you have a utility connected system that can accept all the energy you produce, a tilt of 35° will maximize the annual output.

If you have high summer loads, such as air conditioning, you can use a lower tilt such as 5° or 10°. Do not use a tilt less than 5° or there will be problems due to dirt build up that will not wash off with rain.

Assuming "distance between modules" is row-to-row spacing in an array field, the spacing varies with the tilt angle. This varies with site latitude and how much output you can afford to lose due to shading at low sun elevations. A good reference is https://azsolarcenter.org/pv-row-to-row-spacing

PV manufacturers generally have installation instructions that specify spacing between side-by-side modules. These instructions are required by any IEC or UL Listing for the modules.

In some cases in hot climates row-to-row spacing may have to be increased, as well as clearance under the modules for air circulation. Some studies of 30+ year old PV array fields in the Phoenix area (where the wind is generally from the same SW direction during periods of peak temperatures) have shown PV module degradation is much higher on the northern most areas of the array field. Additional spacing is needed, but this subject has not been studied in detail.

Determining how many PV of a specific rating are required for the system is another question that is beyond the scope of this posting.
Thanks for all this clarification.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
FWIW, off grid PV system design is generally much more involved than designing grid tied systems. You need to have a detailed analysis of your loads both in time and magnitude and of course you will need batteries. It is critically important to get the battery component of the system done right, and that can be very challenging to a designer.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
FWIW, off grid PV system design is generally much more involved than designing grid tied systems. You need to have a detailed analysis of your loads both in time and magnitude and of course you will need batteries. It is critically important to get the battery component of the system done right, and that can be very challenging to a designer.
Design starts with a load analysis and battery system design; it's only after that when you can determine the size of the PV part of the system you will need. Most of the time, especially with larger systems, you will need separate inverters of a different design to power the loads from the batteries. Are you going with AC or DC coupling?
 
Design starts with a load analysis and battery system design; it's only after that when you can determine the size of the PV part of the system you will need. Most of the time, especially with larger systems, you will need separate inverters of a different design to power the loads from the batteries. Are you going with AC or DC coupling?
I have AC and DC loads.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I have AC and DC loads.
That's not what I mean. Are you going to couple your PV via AC or DC with your batteries?

You should get a handle on the requirements of your loads and what sort of battery capacity you'll need to service them before you even start thinking about sizing your PV.
 
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