“Be kind, for everyone you meet is fighting a hard battle” - Often attributed to Plato but likely from Ian McLaren (pseudonym of Reverend John Watson)

Tuesday, December 25, 2007

Going renewable (part 1)

My last couple of posts have dealt with my family's overall use of energy. I've calculated it in terms of equivalent continuous power and included transportation, food, durable and consumer goods, and household energy use. For those unclear on the distinction between power and energy, an analogy would be that power in watts (and kilowatts, etc.) is to speed in miles per hour as energy in kilowatt hours (or, equivalently, 3,600,000 joules) is to distance in miles. Or, alternatively, power is to energy as speed is to distance. You can go a long way by going fast for a little while or going slowly for a long time. Equivalently, you can use a lot of energy by using a lot of power (watts) for a short time or a little power for a long time. So my calculation of our family's use of energy at the rate of around 40 kilowatts is the average "speed" of constant rate energy use that would use the same amount of energy at the end of, say, a month that our actual sporadic use totals.

In thinking about what it would take to go completely renewable, several factors must be considered. First is that I don't really need to be able to supply power at the rate of 40 kilowatts. A lot of the energy conversion in that number is from the consumption of food and consumer goods. However, if I'm really intending to be entirely sustainable, I should put energy into the grid to compensate for that used in those types of consumption. The same rationale applies to transportation fuel. For this reason, I'll proceed as if that's what I'm going to do.

Next, what renewable sources are available to me? Such exotics as geothermal and tidal are not scaleable to my needs, even if they were geographically and geologically available. Wind is not practical because wind of sufficient velocity is infrequent and the (%$#&*&^%) homeowners' association would never let me put in a tower. (Note to self: NEVER buy a house where there's a homeowners' association). So solar seems to be my only "realistic" option. The reason for the quotation marks will become clear later.

So, should it be photovoltaics? How about a concentrator heating a liquid to boil water and run a turbine? Passive solar for water and home heating? All of the above? Well, what can the sun deliver to me? I'm in Southern California at a latitude of about 33 degrees 50 minutes. Using the U.S. Solar Radiation Resource Map from the National Renewable Energy Laboratory I find that with a two-axis tracking flat plate collector during the worst months of the year I should be able to collect, on average, about 5.5 kilowatt hours/square meter/day of solar energy.

Suppose that I can use, in some fashion, this insolation with 20% efficiency (difficult on my scale but certainly possible on an industrial scale). I'd have 1.1 kilowatt hour/square meter/day available to me. Now our 40 kilowatt rate of consumption is equivalent to 960 kilowatt hours/day, so I'll need to collect solar radiation at 20% efficiency over an area of 960/1.1=873 square meters. Hmmm... That's about 9400 square feet, or an area 94 feet wide by 100 feet long. Our south-facing roof is not that big. Our whole two story house's floor area is only 2480 square feet. I do think that our lot is big enough to encompass such an area of 0.22 acres, but not by much. OK, so I'll erect a structure that spans corner to corner both ways on our lot and top it with some as yet to be determined type of collector.

Now that my needs are defined, what about the type of system and the cost? This is a complex area in which I am by no means an expert. But that has never stopped me before, so let's give it a go. I speculate that setting up a solar to steam turbine system in my suburban neighborhood that can deliver the kind of power I'm discussing here won't be permitted so it appears that photovoltaics is my only option (note that I've dropped the "realistic"). It's impossible that I could cover my lot with photovoltaic panels, so I'd have to use the strategy of concentrating the energy. Maybe mylar sun-tracking reflectors to concentrate the incoming solar energy onto a much smaller set of panels.

Now in June at local noon, I might expect something like 1,300 watts/meter^2 over my 873 meter^2 or a capacity for output of about 227 kilowatts at 20% efficiency. So at an installed rate on the order of $8,000 per kilowatt, I'm looking at spending about $1,800,000. This overstates the requirement by a little bit, since I've sized my system to supply the energy we use in the short, low-sun days of December and January. So I'll cut this in half, to $900,000. I wonder if they take VISA?

Obviously, before getting out the plastic or taking out a second on the house, etc. the most economical thing by far is to reduce consumption. This is easy to say and, in my experience, difficult to do. Compact fluorescent bulbs, turning off lights in rooms not being used, reducing the amount of time the pool filter runs, etc., only nibble at the margins. The biggest consumer is my wife's use of automobile fuel, the next two largest are her and the children's "stuff" consumption and my automobile fuel. Dramatically reducing these would be a huge lifestyle change. But it's going to have to be done.

As discouraging as this is, there's a positive element to it. My family is a fairly hefty consumer of energy, and yet the sun provides enough energy to supply us with our needs over the area of the property we own. If we extrapolate that nationwide, the possibility exists that we could actually become self-sufficient and sustainable. There are many, MANY, MANY hurdles to be overcome but there's reason to think it just might not be impossible. It's now up to us to figure out how to make it happen.


Mark said...

I don't see how you get your solar electricity calculations. What are you trying to offset with solar photovoltaics? Your entire carbon footprint? You want to use solar photovoltaics to offset your household direct electricity use; to try to exceed that would be useless, since the power company buys the excess energy at "bulk" rate, but the amount you produce up to 100% of your use is credited at "Retail/Consumer" rate. A $1,800,000 solar system would be a large solar system, indeed, for a residential application.

Go to a website like gaim.com to do a realistic solar assessment instead of doing some kind of foolish projection like the one in your blog. It is misdirecting, meaningless and insulting to the intelligence of someone who knows the facts and value of solar photovoltaic generation.

King of the Road said...

Thanks for the reply. In another post, I calculated the amount of energy my family uses in its entirety, including transportation, food, embedded energy in "stuff," etc.

The post relates to what it would take to harvest enough "renewable" energy to entirely offset my family's use. I've been to gaim.com and other such sites, in fact, I've subscribed to "Homepower" for years.

The post was emphatically NOT presented to be a practical application of photovoltaics, in fact, the opposite. The point is that putting some panels on the roof to supply a portion of household electricity will have little effect for two SUV , McMansion w/ spa and swimming pool, central air conditioning owners.

Anonymous said...

Saw your comment about mylar tracking
panels. Have you seen this?

King of the Road said...

It looks like the concentrator I saw on Discover Channel's "Invention Nation" show. Is that the case?