Building High Performance Solar Collectors

Oil embargoes and hour-long lines to purchase gas in the 1970s started me developing high performance solar collectors that harness todays energy, reducing need for ancient fuels. The primary design challenge was making solar equipment affordable, with efficiency a secondary goal. The reason: fossil fuels were becoming ever more difficult to procure. These relics inherited two hundred million years of chemically processing ancient plants to become highly concentrated stored energy, readily available for power. Digging and selling coal, oil and gas have been very profitable. Those profits helped grow government, build highways and airports, manage world trade markets, and provide food, jobs, education, and healthcare. And we’ve burned a lot more of these resources since the 1970s.

Each US person currently consumes about 50 pounds of fossil fuels every day. Remaining fossil fuel supplies cannot sustain this demand and highly profitable fossil fuel reserves are almost gone. The oil price needed to extract a barrel of oil is double today’s $60 price. Yet low cost renewable solutions are not available for heating homes, driving industrial thermal processes, or simply harvesting solar energy to minimize burning fossil fuels.

    

Forty years ago, we had to build every solar collector module from scratch. There still are no “off-the-shelf”, affordable solar concentrating modules to work with. After building a few prototypes that used flat mirrors to direct sunlight to a receiving area, intensifying it up to 500 times, I learned that it was better to slightly warp flat mirrors so that each image intensified sunlight around 10 times. An array of hundreds of mirrors then readily magnified the sun’s radiant energy 1,000 times or more, without adding cost. The concentrator with its array of mirrors follows the sun so its reflections enter the opening in a receiver that converts sunlight into other energy forms such as heat and/or electricity. A low cost, high performance concentrator, like a “Swiss Army Knife”, should become a primary tool for using solar energy cost effectively today.

Why not just use solar panels mounted on roofs?

Rooftop solar collectors are expensive and typically deliver less than 20% of what’s available. Those that convert sunlight into electricity cover the area with semiconductor material. Heat collectors use insulated metal and fluid lines for transferring heat that have to be protected from weather. Both types deliver rated outputs only when the sun shines directly on them. Solar collectors that are fixed to a roof miss sunlight that does not directly shine on the front. When covered with snow, they collect nothing at all.

Won’t high performance solar collectors that track the sun be too expensive?

High performance solar concentrators do not have to cost much. Mirrors for a solar collector that can supply half the energy for a typical home can cost $300 to $500. The structure, controls, tracking, foundation and heat transfer equipment collectively cost about the same amount. A module that converts intensified sunlight into six kilowatts of power along with 12 kilowatts of heat in the area the size of a typical frying pan should become available for less than $3,000. But it will take a few teams tending engineering prototypes to prove simple equipment that runs itself and can be maintained by anyone handy.

Can high performance solar collectors diminish our consumption of fossil fuels?

High performance solar collectors can certainly reduce our fossil fuel use and one with three hundred square feet of mirrors can deliver the energy required for a typical home. However, the timing of sunshine does not exactly match a home’s heating need. Night, bad weather, and winter diminish how much sun we get. Much comes during long summer days, not long and cold winter nights. A logical goal when adopting solar energy might be to displace half the electric power and conventional heat (gas, propane, fuel oil) of a home, cutting in half the carbon footprint.  High performance solar collectors should be able to do almost anything fossil fuels do now but it will take time to commercialize technologies and prove energy storage strategies. Oil, gas and coal burning power plants have more than a century of development and we all expect that level of performance and cost. Many do not realize the potential nor support research into alternatives that enable living without altering climate. It’s easier to kick the oilcan down the road until it’s empty rather than develop equipment that allows living well without transferring underground energy resources into the atmosphere.

Processes that utilize intense solar power are shown below along with an option of substituting conventional photovoltaic panels for mirrors until modules that deliver both heat and power become available. Tracking these aims them directly at the sun enabling them to collect over 40% more energy and turning them away from the sky when the sun is not out keeps them clean and frost/snow free.

Point-focus Solar Concentrators Can Power a Variety of Processes

What is the current program for making the next solar collector?

Now that the maple-sugaring season is over, seven cords of firewood for heating my home are drying, and an acre of garden mulched and growing; I’ll be building our next solar collector. Over the next weeks I’ll present short histories of each module: mirror assembly, tracking structure, drives, foundation, receiver/pump module and controls before detailing the latest design. Over the years I’ve made lots of missteps while trying to develop cost effective solar collectors and these histories may enable others to pursue more promising possibilities. My next effort will be to build a solar collector that provides our hot water year-round and to significantly diminish how much wood we burn to keep our home comfortable. I’ll also use it to preserve food, dehydrate fruit and vegetables, sterilize soil, dehumidify our basement, transform sap into maple syrup and other heat intensive tasks.

This next solar collector should:
1.    Intensify sunlight 1,000 times so it can power tiny receivers that deliver both heat and power;
2.    Harvest more than 80% of available sunlight;
3.    Require home shop tools (no welding or costly equipment) to build it;
4.    Utilize only materials that can be readily reused or recycled;
5.    Go up using only hand tools and follow the sun by itself;
6.    Provide year-round hot water, air conditioning and space heating when integrated with backup systems;
7.    Power itself and connected systems that work in any weather;
8.    Return the energy invested in materials used in fewer than six months;
9.    Operate for 30 years: with any part easily repaired or replaced; and
10. Pay back money invested in fewer than ten years, without subsidies.

My wife and I are bootstrapping this effort. To minimize cost, I’ll primarily use materiel left over from past projects. The mirrors and aluminum extrusions will prove function but an optimized design will require new extrusions that incorporate features that reduce labor and minimize material.