In many parts of the world there are significant financial incentives for homeowners to install roof-top solar panels. This can include capital grants for the equipment, tax write-offs and/or Feed-In-Tariffs that guarantee that electricity produced by the solar panel will be purchased by the local utility at above-market prices. In Hawaii the annual cost of these incentives is at least $200 million. In Germany it is now in the $billions.
As I pointed out in an earlier blog posting there is inherent unfairness in these subsidies which are only available to relatively wealthy single-family home owners. People living in multi-family dwellings, renters, and those on low or fixed incomes that cannot afford the capital costs of the installation cannot share in these programs. They can, however, contribute through taxes and electricity bill payments to the cost of the subsidies. They can also disproportionately help pay for the added complexities of a grid that can incorporate distributed power generation.
The incentive programs in many areas are also vulnerable to abuse. One couple in Ohio have installed over $180,000 worth of solar panels in order to provide year-round heating for their large indoor swimming pool and indoor tennis court. I'm sure they are most grateful to the taxpayers of Ohio and in fact the entire U.S. for the more than $55,000 they will receive in various tax breaks. And by the way, their solar panels do not help anyone become independent of Middle Eastern Oil. Electricity in Ohio is generated primarily by coal-fired plants with a small amount from natural gas-fired and nuclear plants.
Putting aside the fairness issue there is also a very strong argument against residential roof-top solar panels based upon basic economics.
If you live in the suburbs your street probably has dozens of single family homes of different sizes and shapes with various configurations of roofs covered by a variety of materials. Imagine if you will a veritable army of roofers crawling over these houses, attaching frames and mounting solar panels. If you think about that for a moment you will have to come to the conclusion that it is not an overly efficient operation. Lots of up and down ladders time and safety setup time and not so much install solar panel time. Now imagine that same scenario when it is raining or snowing - more than a little scary for everyone involved.
Compare that to utility-scale solar where uniform racks can be laid out and solar panels mounted from the ground in a matter of minutes. The two scenarios are illustrated by the photographs.
Recognizing that the public and electrical utility customers are footing a large part of this installation bill which configuration would seem to provide the best return on investment? It would be hard to argue against the utility-scale solar panels.
What about efficiency in terms of making the best use of the solar resource?
In the case of residential roof-top solar there are likely to be plenty of other buildings, trees, and hills nearby so that the solar panels are often in the shade. Almost all of these solar panels will also be mounted rigidly, most commonly at the angle that is the roof pitch. This will not be the optimal angle for most sites and latitudes.
Utility-scale solar panels can easily be equipped with single or dual-axis tracking which very significantly increases the power generated under all circumstances. They will also be located in large open areas where they will be in direct sunlight for most of the day.
Having small, deep-cycle batteries as backup for the solar panels might be an expensive necessity at Possum Lodge but in suburban North America that type of installation doesn't make a lot of sense - which is probably why almost nobody does it. Instead, through the magic of net metering, the surplus solar at mid-day is pushed out onto the grid whether it is needed or not. The home-owner effectively gets to use this mid-day electricity as a credit against the much more expensive evening and night electricity that would otherwise have to be purchased from the local utility at peak demand prices.
For the local utility the end result is a significant reduction in revenues from the owners of the roof-top solar panels even though they are making the grid more expensive to build and maintain. Who picks up the slack? Everyone that does not have roof-top solar panels.
The home owner that installs the roof-top solar panels will probably be pretty excited about them and will maintain them to some degree. But as houses change hands that commitment could fade; as leaves, moss, and dirt accumulate through the years who is going up on the roof-top to polish up those solar panels. Nobody is my guess. So the overall efficiency of the panels is bound to decline over time. The same with local battery storage if it has been installed.
Finally, the presence of roof-top solar panels has been identified as a significant danger to fire fighters.
All in all, looking at roof-top solar panels perfectly objectively they just don't make sense. There are better ways to spend those dollars as we transition away from a hydro-carbon economy. Some other ideas are described in my Sustainable Energy Manifesto.