On residential solar PV systems

I find solar electricity production a fascinating topic. One of the curiosities of Australia is that the country is among the best in the world for solar electricity production, yet the vast majority of electricity production is based on coal power plants. The coal lobby is likely to be partially blamed for this, but things are slowly starting to change – the nation is about to introduce a carbon tax and one of the dirtiest coal power plants face a shutdown, so one would think there is still hope that solar will take off in the not-too-distant future. With the operational start of Gemasolar’s 24/7 CSP plant in Spain the argument of solar being unable to produce baseload power should also begin to lose traction.

While the industrial-scale production is lacking in Australia, the residential production is doing a bit better. About a year ago, Australia had about 200,000 households using solar PV panels for electricity production, and that figure is increasing rapidly. Many, many more households have solar hot water systems in place. Both systems enjoy significant government incentives which unfortunately are being slowly scaled back.

Anyhow, to satisfy my curiosity and desire to understand in detail how the residential-scale systems work, I read the Solar Electricity Handbook – 2011 Edition by Michael Boxwell. This is a book that covers residential solar deployments in quite some detail, but focuses purely on residential PV panels. Now, one can be forgiven to think solar is easy – after all, how complicated can it be slap a panel on a roof and plug it in? Turns out it can be surprisingly complicated and the Solar Electricity Handbook is there the show you how.

The book basically covers pretty close to everything you need to know when planning, dimensioning, selecting, installing and operating a solar PV system for residential use. Some of the more interesting things to note for me were the various inefficiencies introduced by a number of the system components and features (batteris, MPPT, inverters, temperature etc), the numerous complexities introduced by systems with battery storage and the inherent dangers in solar panels.

Even such basic things as making sure the roof can handle the panel loads – and remembering that there can be a significant upwards lifting loads on the panels in windy conditions – easily slip the minds of a “layperson” such as myself, so it was interesting to learn about such details. Other news to me was the somewhat disappointing revelation that the vast majority of grid tie-in systems will shut down if the grid shuts down – grid fallback systems, on the other hand, continue to operate if grid power is lost. Also, it’s essentially impossible to switch a solar panel off – hence the connections and circuit breakdown conditions need to be managed carefully or they can easily lead to overheating or even fire. On a positive surprise-side, some people have occasionally complained of poor carbon payback times of the panels due to high production emissions; turns out the panels, depending on the method of manufacture, have carbon payback times of only 3-5 years – considering the panels have a lifetime of 20-30 years or even more, that’s a pretty good figure I think.

Solar in Australia is a no-brainer. Finland, however, seems like a pretty useless place for solar electricity when you first think about it. I was, however, surprised to find out that where the irradiance levels of Melbourne in December is 6.24 kWh/m2/day, it reaches 5.74 kWh/m2/day in Helsinki in July; so the output during the best times of the year do not radically differ between Melbourne and Finland. The story is obviously quite different in the winters, with Melbourne having irradiance levels of 4.07 kWh/m2/day even during the worst month (May), whereas the Helsinki winter level in December is a downright pathetic 0.66 kWh/m2/day. An additional complication to having any significant solar electricity generation take place in Finland is that the peak power usage occurs in exactly the opposite time of the year than peak production, whereas the peak production & consumption times align much better over here.

What comes to the Solar Electricity Handbook, it’s a great resource for planning and installing residential solar PV systems. It covers all the basics and the quirks introduced by different systems, and the online resources at http://solarelectricityhandbook.com/ are very useful. It does not, however, cover the most recent developments in any great depth, such as Solar Edge‘s technology of distributed maximum power point tracking, but the handbook definitely provides a good, solid foundation for anything thinking of installing PV solar systems.

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