Monday, July 5, 2010

Gettin' Thermal, Solar Style

We talked about the fundamental challenge of the net-zero energy in another post, but we wanted to update you with our loads, and show you how solar thermal panels will contribute to lowering our carbon footprint.

The table shows a month by month estimate of the thermal loads for the One Planet Reno for space heating and domestic hot water (DHW).  We've been able to keep the loads for space heating pretty teensy. Using the  modeling Malcolm did with the Passive House software we're figuring roughly 29kwh/square meter.  The DHW loads are estimated based on our families current consumption habits and improving the flow rates in some key fixtures.  Together you can see the total thermal load we need to meet.

We are working with Chris Weissflog of Ecogen Energy Inc (check out
for the solar themal system.  Chris ran some modeling for us to see what contribution could be made with a solar thermal system and storage tanks, given our roof orientation and space limitations.   He ran several scenarios and costed a 3 panel and a 4 panel system.   Here's the shakedown (for those keeners check out the spreadsheet below)  with a 4 panel system we can meet a significant portion (63.4%) of our thermal energy needs - but we do have a lot of excess heat in the summer.  (We will post more about how to deal with this “waste heat” in another post - sneak peek - it's not a hot tub.)

To keep our heads firmly planted in economic reality – the 4 panel solar thermal system (120 evacuated tubes) will cost around $22,000 installed, complete with storage, and maintained for 20 years.  This does not include a means to distribute that heat to the house or the DHW system.  Assuming 20 years of energy production, the cost per kwh of heat is 17.7 cents for a 4 panel system versus 19.3 cents for a 3 panel system.  The added panel gives us around 900kwh of useful energy per year for only 9.1 cents per kwh.

So – we are going to pay about 18 cents per kwh of carbon neutral thermal energy, vs. Ontario’s grid energy at 8 cents per kwh for dirty power.  It is certainly a high premium, but it appears to be our best path to meeting the zero carbon principle.


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