What Difference Panel & Roof Angles Make

The question of angle of solar panels comes up in about every serious discussion of PV installations.

We recently had a chance to photograph two different arrays on the same day at the same time. It gives a great comparison:

Snow Covered Solar Array At 40 Degree Angle
Snow Covered Solar Array At 40 Degree Angle
Snow Covered Array At 23 Degree Angle
Snow Covered Array At 23 Degree Angle

The top array is basically at full power, the bottom is at zero.

But as with any design question, there is more to consider:

1. What additional cost might be involved to increase a tilt angle from 23 degrees, (a typical 5/12 pitch roof) to 40 degrees?

2. How often does this condition actually exist in use?

3. What is the optimum angle for yearly power generation?

When I designed our system I looked at the cost of fancy racking to lift the panels to 40 degrees, It was quite significant. Additionally there are maintenance costs that come with a more sophisticated arrangement.

Our Michigan weather conditions don’t produce this condition very often so in terms of actual power lost I probably estimated less than $100 worth of energy a year.

Finally the 23 degree angle of our roof is somewhat short of the optimum yearly location, so I would be generating less power by about 10%.

However, with the above in mind I determined I would be better off using the money I would have spent for a fancier racking system to buy and install more solar panels at the 23 degrees. That way I would receive benefit from that investment on the vast majority of the days the system is in use, even if i sacrificed generation when the system is snow covered.

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Three Years With a Zero Net Utility Bill

This month marks three years since we’ve had our solar array turned on.

And even though we spend five to eight hundred dollars a year on our firewood we are still coming out with a net of zero on our utility bills.

Some background:

With the contract we have with DTE they pay us about ten cents a killowatt hour for generating power, then they allow us to use what we generated. The net result is a negative electric bill for the last three years.

However, we do use some natural gas, primarily for the dryer, but also for the cooktop and for some space heating and some hot water heating. So we have a gas bill, it is just far less than the electric credit.

The balance comes to us every year or so in the form of a check. This money has basically paid our bill for hardwood delivery. (We really enjoy wood heat, I’m not convinced that it actually saves us money.)

Our total power generation for 3 years is 31 Mega Watt Hours, or roughly $3,100 of electricity at our current rates.

Not bad!

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