Solar thermal, solar hot water, solar hot air, solar heating, solar cooling
California Solar Thermal (CST) is a San Diego-based solar installation business on pace to do 42 solar thermal projects this year. According to California Solar Statistics data they are the #1 solar thermal company in southern California, and are currently in the middle of installing the biggest non-utility system in the state. Who are these […]
Last week, I spent a day repairing a solar thermal system that has been operating for more then 30 years in NYC. I just wanted to share a few pictures and points because it’s super cool.
The system was installed in installed in 1980, expected “payback” (don’t ever use that term again) was just around 3 years
The client paid $3,200 for the system, which is about $8,900 in todays dollars.
The system was providing 70-80% of the hot water for 2 families
It was offsetting natural gas, which was expensive for a long time, and current prices are going back up, to the tune of 70%.
DAS Solar Systems was the name of the EPC contractor in NYC. They’re aren’t around anymore.
The name of the module manufacture was SunWorks, the spec sheet said New Haven, CT but I’m assuming they were imported from Israel.
The system is in the heart of NYC
You can even see the module from google earth! There were 6 existing modules, but we replaced them with 4.
Front of the house. Getting equipment on roofs in NYC can be an issue.
The old modules. They held up pretty well, and managed to work 12 years after their “warranty” expired.
Again, the help up remarkably well well. There was a small amount of rust on the back sheets.
The rack was pretty simple and standard using unistrut. In fact, I’ve built a system that was 6 modules in Medford and were used the exact same parts as this! Though the roof flashing was a little different.
Vermont has long been on the cutting edge of renewable energy and energy efficiency. They like to get stuff done, from solar permitting to efficiency and biomass. Two weeks ago, I spoke with executive director of Renewable Energy Vermont, Gabrielle Stebbins to learn a little more about the current state of the industry, and where […]
Over the past month, I’ve seen a pick up in the amount of companies that are offering ‘bridge financing’ to small and middle size solar PV contractors. So, I thought I would put together a short post and a free downloadable guide based on my research that outlines what bridge financing is, the best markets […]
I’m doing some sales consulting work in NYC, and there’s one question I’m getting a lot from property owners: “What is the most efficient renewable energy technology?”
In the city, they are mainly speaking of solar PV vs solar thermal, because generally there’s not enough room for geothermal in the city. However, for fun, I’ll expand it and include geothermal.
The answer is, of course, it depends on how you’re defining efficient.
Which technology produces the most energy in the least amount of area
Which technology produces the most valuable energy
Which technology has the best financial return. Again, however you’re defining return.
There are two ways that I’m going to frame the discussion to search for an answer, or a methodology for finding an answer:
Efficiency of the technology (is this a good design for this specific application)
Efficiency of cash, which takes into consideration the site characteristics and policy (is this a good investment?)
As always, it’s easiest to see this when we look at a few examples, being clear to highlight when and where the examples might be different in the real world and how said sensitivity might impact our results.
1. Technology Efficiency. Right now, let’s just look at GROSS INSTALLED Costs and raw energy production.
Here’s what I’m going to calculate: Gross Installed cost / Net energy produced in year 1 (energy produced / energy used)
Again, I’ll keep it in residential for simplicity. And I’ll focus on Boston because I’m most familiar with the solar resource available and the average heating degree days needed when understanding geothermal production.
Our example home will be:
1500 square feet
Average home shell construction.
South Facing roof, no shading, 10 pitch, that is 60 feet by 12 feet.
Solar PV: $25,000 / 6,843 kWH produced per year = 3.65, which means that you must invest 3.65 dollars in year 1 to get 1 kWh of production
5kw DC Installed @ $5.00/watt = $25,000
Avg Insolution = 5 hours of full sunlight per day.
We’ll derate from DC to AC is .75, which is extremely conservative.
AC Production = 3.75 AC output
3.75 X 5 hours per day = 18.75 kWh production per day on average.
18.75 X 365 = 6,843 kWH produced per year
$25,000 / 6,843 kWH produced per year = 3.65, which means that you must invest 3.65 dollars in year 1 to get 1 kWh of production
Solar Thermal: $8,000 / 4,982kWh = 1.6. For every $1.6 dollars invested you get 1kWh of production.
3 to 4 family home
Gross Installed Costs for a simple drawback system by a well trained crew is ~$8k
Each Module will likely produce around 85 therms per year, totally 170 therms per year
170 therms is 17,000,000 BTUs / 3,412 = 4,982 kWH equivalent.
$8,000 / 4,982kWh = 1.6
For every $1.6 dollars invested you get 1kWh of production.
Note: For solar thermal, unlike solar PV, production of solar energy and usage of that energy doesn’t necessarily match. For this example, I’ll assume it does.
Geothermal: $27,000 / 13,478 kWh equivalent = 2. You must invest $2 in year 1 to get 1kWh of energy production.
We’ll assume the heat pump is only heating, to make the calculation more simple and keeping in mind that our ratio of dollars invested to energy produced will be a little larger, if we considered cooling.
63 MBTU average heating load
Avg COP of 3.75 (this is important, because lower efficiency will increase the tonnage needed for the same btu’s delivered, all else equal)
3 Ton system
9k ton X 3 tons = 27k
Energy Produced = 63 M BTU –> Let’s convert BTU to kWh equivalant
63 M BTU = 18,463 kWH (Remember that 1kWh = 3,412 BTUs. Thus long calc is 63MBTU = 630 Therms (10 therms = 1MMBTU) 630 therms = 63,000,000 BTUS divide by 3,412 = 18,464)
Many will point out that geothermal uses energy (in pumps and fans) to produce more energy, which is true. However, we want to find out what EXTRA energy that was created by the system, this is the renewable part. With an average COP of 3.75 it means that 3.75 units of energy was created for every equivalivent energy put into the system.
3.75 means we need to reduce the energy produced by 26.66% (1 / 3.75) to find the amount that was produced by the system.
18,464 X 73% = 13,478 kWh equivalent produced
27k installed costs gross / 13,478 kWh = 2 in equivalent energy produced. Which means, that for you must invest $2 in year 1 to get 1kWh of energy
Here is our conclusion about gross installed costs and energy produced:
Solar PV: $25,000 / 6,843 kWH
Solar Thermal: 8,000k / 4,982 kWh
Geothermal: 27k installed costs gross / 13,478 kWh
A few things to note about the sample examples
PV: $5 a watt is average and there are much higher installed costs.
Thermal – Production of modules and usage don’t necessarily match. Also, assumptions around water usage are not accurate. ~8k is also for a great site and a well trained crew. It’s common to see $10k+ projects.
Geothermal – Only assumed it was heating. Assuming 72 set point and 62MMBTU needed to heat the home. 3.75 COP also impact the energy produced from that invested cash. Higher COP = greater output, all else equal, per dollar invested.
As we’ll discuss in section 3, site characteristics can change the analysis of any one of these by making some technologies, cheaper or non-available in certain areas.