## Welcome to my Adventures

The pupose of this Blog is to keep in contact with many good

friends spread out all over the world.

friends spread out all over the world.

## Sunday, December 2, 2012

### Effect of adding the last 3 panels

Since we added the last 3 250W PV panels a few months ago we now

are producing up to 40kWh a day on clear sunny days which are the norm

in Johannesburg. We must have at least 300 of such days per year.

One of the very best climates on the planet. Beautiful days and cool nights.

But even on cloudy days we produce up to 30kWh. The sunlight is more

diffused then and the ambient temperature is lower which is a major factor when it comes to the efficiency with which the panels convert sunlight into electricity.

The limiting factor as this point in time is the MPPT (Maximum Power

Point Tracker) which limits at 80 Amperes. The panels can supply more.

I have ordered a new 8kW Grid tied inverter with two 100 A MPPT's

build in but there were some delays with the design of the MPPT's I was told. Then the bottleneck of the 80A limit is gone and we should be

able to harvest the maximum power.

Since I am running the entire property on solar, including the pool pump,

2 air cons, a electronic design lab with a staff of 8, half a dozen computers

and last but not least a 3 kW kettle which is probably most heavily used item, working overtime daily I could use the extra power.

A calculation showed that we could expect 50kWh a day.

Looking at some data which gives the level of insolation at our latitudes

it says we are receiving over 6kWh per square meter. If you multiply this

with the area of a panel and its efficiency then one comes very close to the

250W the panel can deliver. This is a very effective way to calculate the

number of panels required for a particular installation. I will do some

measurements to see how much a panel can actually deliver on a perfect

day. I am sure it will be more then 250 Watts. The 250 Watt figure is

the factory spec when the panel is tested in the factory with the industry

standard 1000W/m2 light source. Not sure what is the spectral distribution of that light source, (does it approximate sun light?)

since a PV panel is sensitive to spectral variations.

are producing up to 40kWh a day on clear sunny days which are the norm

in Johannesburg. We must have at least 300 of such days per year.

One of the very best climates on the planet. Beautiful days and cool nights.

But even on cloudy days we produce up to 30kWh. The sunlight is more

diffused then and the ambient temperature is lower which is a major factor when it comes to the efficiency with which the panels convert sunlight into electricity.

The limiting factor as this point in time is the MPPT (Maximum Power

Point Tracker) which limits at 80 Amperes. The panels can supply more.

I have ordered a new 8kW Grid tied inverter with two 100 A MPPT's

build in but there were some delays with the design of the MPPT's I was told. Then the bottleneck of the 80A limit is gone and we should be

able to harvest the maximum power.

Since I am running the entire property on solar, including the pool pump,

2 air cons, a electronic design lab with a staff of 8, half a dozen computers

and last but not least a 3 kW kettle which is probably most heavily used item, working overtime daily I could use the extra power.

A calculation showed that we could expect 50kWh a day.

Looking at some data which gives the level of insolation at our latitudes

it says we are receiving over 6kWh per square meter. If you multiply this

with the area of a panel and its efficiency then one comes very close to the

250W the panel can deliver. This is a very effective way to calculate the

number of panels required for a particular installation. I will do some

measurements to see how much a panel can actually deliver on a perfect

day. I am sure it will be more then 250 Watts. The 250 Watt figure is

the factory spec when the panel is tested in the factory with the industry

standard 1000W/m2 light source. Not sure what is the spectral distribution of that light source, (does it approximate sun light?)

since a PV panel is sensitive to spectral variations.

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