PV vs Solar Thermal…one of our readers asks why

by schmidt on April 1, 2009 · 3 comments

in Miscellaneous Schmidt

One of the slew of emails that came in over the weekend was from Stacey, a local architect.  Stacey asks:

I just read the SF Chronicle article about your Sunset neighborhood house. Thank you very much for your efforts in going sustainable. I think this is a very important thing to be doing.

However, I have a question for you. Since your house’s main energy consumption component is heating, why did you spend $20,000 on a PV system when you could have spent half that on a solar thermal system to heat your hot water instead of using natural gas (a non-renewable, carbon emitting fuel)? You would save much more energy doing that than those PV panels will ever produce. In the total energy/polution equation, this would have greatly reduced your house’s energy consumption and carbon emmisson. The solar thermal would have had a much faster payback as well, despite the incentives being less than PV, particularly considering how you are utilizing hot water to heat the house.

Stacey Stemach
Architect

An outstaning question, my response below.  But I ask you, gentel reader,wWhat do you think about PV vs Solar Thermal systems?

{ 3 comments… read them below or add one }

1 schmidt 04.01.09 at 12:54 pm

One of the first questions I thought of is if in fact the houses main energy using component is heating. It is a major component, but I have no metric for determining total energy use and then breaking it down to specific and accurate sub categories for comparison. Wouldn’t it be cool if there was some sort of device, like a household dashboard, that could give you that sort of feedback on your own energy and water consumption? I would buy one.

But to Stacey’s point as to why PV panels over Solar Thermal, it is because I wanted to generate electricity. The aggregate consumption of power, when you add up the lights, the appliances, everything, is pretty high. I wanted to address that and it was either a wind turbine or PV panels, and panels made more sense; wind turbines are so new the city department of building inspection seems confused on how to permit them. Also, I do not anticipate huge heating costs for this house because it is so well insulated – most days there really is no need to have it on at all.

Solar Thermal is cool, but my understanding is that it gives the water coming from the street a “boost” in temperature, but still not hot enough to use for, lets say, a shower. Am I wrong?

2 Stacey 04.01.09 at 2:34 pm

Hi Helmut,
2 part response:
I actually went through the whole energy use question in a recent renovation of our 1920’s house here in Bend, OR.

Before the flood we had in Dec of 2005, our 1920s house was a poorly insulated 1,700 sq ft house that was heated with an average natural gas furnace, hot water came from an average 50 gallon natural gas furnace. Our cooking stove is also natural gas. Prior to the flood, our typical electrical bill (lights and appliances) was about $35 a month. Our highest gas bill (Dec, Jan, Feb) was about $200.

We decided to convert the house almost exclusively to electricity for 3 reasons: Natural gas is a carbon emitting non-renewable resource, and pretty dangerous to transport, we wrongly believed we did not have the solar access to do anything significant with solar thermal (trees), and our power company offers an “all renewable” electricity program, which basically means they have to purchase our amount of energy usage solely from renewable resources (solar, wind, biomass). To that end, we replaced our gas furnace with an extremely efficient all temperature heat pump, and we replaced our hot water heater with a 50 gallon electric. The stove is the only thing gas. We insulated as best we could given the existing walls, and in fixing the flood damage, we fully excavated the basement and finished it entirely, adding about 1,000 sq ft to the house’s heated area.

Now, our gas bill is about $4 per month. Our highest electric bill (Dec, Jan, Feb) is between $180 and $200. Our lights and appliance use really hasn’t changed, so the component of energy use for heating is pretty clearly demonstrated. We spend about $35 a month in lights and appliances, and between $145 and $165 for heat in the winter (in Bend, OR).

As to solar thermal’s potential:
Current solar thermal technology still includes flat plate collectors, and although their efficiency has improved, they clearly work best on clear sunny days. The best, latest tech is now evacuated tube collectors, which has been available and in use for many years now. These collectors are exceptionally efficient at heating water, producing almost industrial strength hot water. I often work with a local solar contractor here in Bend, and one winter day in January he told me he had just gotten off a client’s roof after checking over a newly installed system. He told me that on that particular day, with outside temps running about 18 degrees F, overcast with slow snow flurries, the evacuated tube collector array was delivering 110 degree F water to the storage tank! That has completely changed my perceptions of solar thermal.

The best part of your situation is that you can still add it if you want. The evacuated tubes take up less space than PV, would integrate very easily into your water-based heating system, and given your climate in the sunset district (I’m an SF Bay area native), it really wouldn’t take much to satisfy all of your hot water heating demands.

If you have questions about this or other projects, I’d be happy to discuss. Just drop me a line.

3 Fernanda 10.23.15 at 10:39 pm

You know, there has to be SOME difference, or else etriyvheng would be the same including thermal energy.The obvious difference to pick upon is temperature, if the amount of water is the same.

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