Home solar update after seven years

The rooftop PV system we installed seven years ago has just passed another good round number – 16 000 KWh – having produced 4 000 KWh since my last update, in September 2016.

The daily average in that period is therefore 5.9 KWh/day, a little lower than the average of the first five years.  The drop in output is so small that it’s not really worth worrying about but three explanations come to mind, and all may have contributed to it:

  • We don’t bother cleaning the panels, so full-sun output may have dropped;
  • Our trees have kept on growing, so the panels may be shaded for longer, especially in winter;
  • The period we are considering includes two full Wet seasons but not quite two full Dry seasons (the month-by-month variation is shown here).

How much money are we saving now?

Continue reading “Home solar update after seven years”

Put Solar On It!

putsolaronitFor a while now I’ve been collecting snippets of news about innovative – or just plain smart  – uses for solar photovoltaic power (PV) with the intention of posting them to Green Path. When I read about an American day of action coming soon, #Put Solar On It!, I decided I should assemble my finds now rather than later.

#PutSolarOnIt brings together the strength of Organizing for Action, Mosaic, The Solar Foundation, Solar Energy Industries Association, SolarChat, Vote Solar, NRDC, Interfaith Power & Light, Sierra Club, Environment America, World Wildlife Fund, REVERB, The Climate Reality Project, Alliance for Climate Education, League of Conservation Voters  and The Solutions Project.

This June 21st, the longest day of the year, a coalition of groups will come together in a National Day of Action to show support for switching to clean energy, fighting climate change, and the power of bringing solar power to communities all across the country. …

All across America there are opportunities to #PutSolarOnIt – to turn our homes, our churches, our schools our lands and our neighborhood rooftops into solutions to climate change. June 21st is a National Day of Action for us all to find a way to #PutSolarOnIt by identifying, supporting, and rallying our social networks to support solar energy, or joining a local event to support a community based solar installation.

Their press release also notes that …

2014 has been a breakout year for solar. Solar equipment costs continue to come down and installations continue to grow. More solar energy generation has been installed in the U.S. in the last 18 months than in the 30 years prior, and solar energy is the leading source of new electric generation capacity so far this year.

– and this is in spite of a sustained Republican campaign to block any and all renewable energy initiatives.

Anyway, back to the good stuff, the ingenuity and innovations. As in previous collections here, I’ve linked images to sources where I can. After collecting items for a while I realised that a lot of them involve transport. That’s a Good Thing, to my mind, since transport has always looked liked being one of the hardest areas to decarbonise because it requires compact portable power, and I will start with them.


PV trees make shade sails and a recharging station for electric cars. Townsville airport has had a smaller, simpler instance of the same idea since 2011 – see it on YouTube here. Or there’s the no-frills (but still really useful) version here.
Of course, if you know you won’t be near a facility like any of these, you can take your own gorgeous solar umbrella with you and erect it as you leave your car.

Solar roads, which in practice may begin as driveways, bikeways and car-parks.

Solar cars (and don’t forget the World Solar Challenge).

There’s probably a partially solar powered car in your future, but I wouldn’t bet on a solar powered plane – however pretty this one is.

Good places to put lots of solar panels

solar-airport• Airports – whether closed down, as at left, or fully functional as here – are wide open spaces near urban areas, already kept clear of trees and tall buildings which might shade any panels.


• Canals (above) and dams – reducing evaporative water loss as well as making electricity.

• Football stadium – one good outcome of the World Cup building programme in Brazil.

The price of solar cells has dropped to a point where unsubsidised solar power is cheaper to install than coal-fired power and the reliability and longevity of solar power installations is beyond doubt. Solar power now seems unstoppable and stories like this one on Think Progress drive home that point. Its last line, “shifting economics has increased interest in Texas’ long-untapped solar power potential,” is code for, “coal is no longer a profitable investment,” something for which the environment should be profoundly thankful.

Going Solar: Malcolm, one year on

We installed a 1.5kW solar power system on our roof in the middle of last year. As I said at the time, it took a little while to get it all connected and working the way it should. However, we now have a whole year of data on its performance, so we can assess the annual output and see the seasonal effects.

solar power output chart

The blue curve shows how much power the sytem has produced and, as expected, generally follows day length but with bumps created by specific weather conditions. The amount exported tracks it fairly well, but is reduced by air-con use during the hotter part of the year (the gap betweeen the two curves is widest from Dec-Feb). The spike in exports last September-October, incidentally, is explained by the fact that family members were away from home for several weeks: less consumed => more exported.

Annual numbers are:

  • Total produced = 2220 kWh (6.1 kWh/day)
  • Total exported to grid = 960 kWh, for $425 income
  • Total PV power used at home = 1260 kWh, for $270 savings
  • Total benefit = $700

In the coming year/s we can expect a slightly higher net benefit, since the electricity tariff has recently increased from 20.7 to 23.07 c/kWh. On the same output and consumption figures, the panels should save us an extra $20 per year because of that price rise. However, cutting our daytime power consumption would be even better. If we had used half as much power during the day this year, for instance, our net benefit would have been $130 higher. That is something we will now look at more carefully.

I will keep tracking monthly figures but won’t keep posting them to Green Path so my updates will be less frequent.