Solar Panel Efficiency (Wellington)

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tchart

1534 posts

Uber Geek

Trusted

# 257172 19-Sep-2019 10:29

Hi,

I'm looking into an off grid power supply for a shed.

The battery setup I'm looking at can take a max input of 120W, 10A etc

Given a solar panel is not 100% efficient I'm trying to figure out if I should run a 200W panel. I mean is a 200W panel realistically ever going to reach 120W?

Does anyone have any experience in NZ or preferably Wellington with DIY solar?

Failing that is there a way to regulate the input I to a device? The controllers I've seen seem to only limit volts

wellygary

4074 posts

Uber Geek

# 2320176 19-Sep-2019 10:45

A 200W Panel will produce well over 120W with full sunshine on the panel.... it should do 200W

Panels wattage are based on output, so efficiency is already factored out,

kotuku4

278 posts

Ultimate Geek

Lifetime subscriber

# 2320196 19-Sep-2019 11:26

One person supports this post

I have a DIY solar shed system in Blenheim, and a 4.9kw grid tied house system.

The panels if certified should be rated on a nominal output under standard test conditions.

In ideal conditions the output can exceed the rating. Can be over or under depending on the batch of panels or individual panel.

Peak output will only occur a few hours per day. The panels will degrade slightly over time.

There are programmable controllers, if required. eg Epever Tracer MPPT, I changed to one of these mainly for efficiency, flexibility to change panel or battery in future.

The old controller was very basic but worked well.

Niwa has solar view calculator for solar radiance at your location.

Solar shed

80 watt B Grade panel (Cause it was cheap) on self made aluminium brackets

6 amp Steca PWM solar charge controller, upraded to Epever Tracer MPPT 10 amp AN series

12v 120 ah deep cycle battery, second hand

DC Fuse, circuit breaker

Xuyuan 2000w Cheap inverter 12 v dc to 220-240 v ac (rubbish), Changed to Epever 500w pure sine wave inverter. This powers Ryobi tool charger, bike charger, lawnmower, some LED lights, (12v shed radio/stereo is powered off charge controller).

Hobby charger off battery, There is usb and cigarette lighter socket, power small compressor etc.

tchart

1534 posts

Uber Geek

Trusted

# 2320346 19-Sep-2019 14:02

wellygary:
A 200W Panel will produce well over 120W with full sunshine on the panel.... it should do 200W

Panels wattage are based on output, so efficiency is already factored out,

So two things

1. The wattage is based on lab standard conditions with a fixed input and I quote;

as Standard Test Conditions (STC). The STC measure the solar panel’s energy output using common conditions of light exposure, orientation, and panel temperature. Under STC, a 250-watt panel produces 250 watts of electricity when the sunlight (or “solar irradiance”) on the panel is 1000 watts per square meter and the panel is operating at 25°C

So no it won't ever do 200W unless in ideal conditions and there will always be something - dust, clouds, angle etc

2. I've seen figures of 20% efficiency which suggests out of the gate you are missing out on 20% of 200W. So my unders6is that even under ideal conditions you'll be getting the 160W range on a 200W panel.

Bear in mind this is my first foray into solar so I probably do t know what I'm talking about.

I just don't want to get a 120W panel and then get ~90W in perfect conditions.

I guess I'll just have to bite the bullet and go for a 120W to start and then scale if required.

Thanks

tchart

1534 posts

Uber Geek

Trusted

# 2320349 19-Sep-2019 14:04

kotuku4:
I have a DIY solar shed system in Blenheim, and a 4.9kw grid tied house system.

The panels if certified should be rated on a nominal output under standard test conditions.

In ideal conditions the output can exceed the rating. Can be over or under depending on the batch of panels or individual panel.

Peak output will only occur a few hours per day. The panels will degrade slightly over time.

There are programmable controllers, if required. eg Epever Tracer MPPT, I changed to one of these mainly for efficiency, flexibility to change panel or battery in future.

The old controller was very basic but worked well.

Niwa has solar view calculator for solar radiance at your location.

Solar shed

80 watt B Grade panel (Cause it was cheap) on self made aluminium brackets

6 amp Steca PWM solar charge controller, upraded to Epever Tracer MPPT 10 amp AN series

12v 120 ah deep cycle battery, second hand

DC Fuse, circuit breaker

Xuyuan 2000w Cheap inverter 12 v dc to 220-240 v ac (rubbish), Changed to Epever 500w pure sine wave inverter. This powers Ryobi tool charger, bike charger, lawnmower, some LED lights, (12v shed radio/stereo is powered off charge controller).

Hobby charger off battery, There is usb and cigarette lighter socket, power small compressor etc.

Thanks I'll check the NIWA calculator out.

So I know Blenheim is super sunny but does your install ever exceed the ratings?

wellygary

4074 posts

Uber Geek

# 2320366 19-Sep-2019 14:32

One person supports this post

tchart:
wellygary:

A 200W Panel will produce well over 120W with full sunshine on the panel.... it should do 200W

Panels wattage are based on output, so efficiency is already factored out,

So two things

1. The wattage is based on lab standard conditions with a fixed input and I quote;

as Standard Test Conditions (STC). The STC measure the solar panel’s energy output using common conditions of light exposure, orientation, and panel temperature. Under STC, a 250-watt panel produces 250 watts of electricity when the sunlight (or “solar irradiance”) on the panel is 1000 watts per square meter and the panel is operating at 25°C

So no it won't ever do 200W unless in ideal conditions and there will always be something - dust, clouds, angle etc

The assumption of 1000w/m or radiant energy is not applicable to NZ.. its higher, so you should manage to hit the specced output reasonably easily....

The accumulated, average, yearly, solar energy gain for New Zealand is about 1400 kilo-Watt-hours per square metre (kWh/m² per year). Although this is not as high as in the desert areas of Northern Australia, the United States of America, North Africa and the Middle East (2,100-2,400 kWh/m² per year), it is higher than many European countries where solar installations have a much higher market penetration. In Europe, sites with accumulated, average, yearly, solar energy gains as low as 1000 kWh/m² per year are seen as potential candidates for solar technologies.

https://www.niwa.co.nz/sites/niwa.co.nz/files/imported/__data/assets/pdf_file/0006/95523/EnergyScape-Basis-Review-Section-2-_Renewables__E.pdf