Parker.wiki.spring.2011


 * [[image:pic11.jpg]]﻿ **
 * Shown above are 2 4’x8’ solar collectors and a small 2’x2’ PV panel **

I recently installed a solar hot water heating system on my home in Cape Cod Massachusetts. The following is a evaluation of the performance of the system, based on its geographical location and the orientation of the solar collectors. Other areas of concern were an evaluation of GHG emission savings and a thorough financial analysis of the system. The tool I will be using for this analysis is RETScreen Clean Energy Project Analysis Software. This free software is provided by Natural Resources Canada to evaluate renewable energy projects. Before looking at this tool let’s first examine the solar domestic hot water (SDHW) system he installed. The system I chose is an active, closed loop, pressurized glycol system sold by Thermo-dynamics, Ltd –a Canadian company. I personally visted the factory in Dartmouth Nova Scotia and observed the manufacturing process of the solar boiler along with the collectors. The system consists of two solar collectors, a heat exchanger, a solar storage tank, a pump (powered by its own PV panel), a temperature-mixing valve, and an oil-fired back-up hot water tank. An active system uses pumps and valves. A closed loop system uses a separate heat transfer fluid (propylene glycol and water) and heat is added to the domestic hot water via a heat exchanger. This is how the system works:



1. Solar collectors absorb sunlight and convert it to heat. 2. When there is sufficient sunlight, the photovoltaic module produces electricity and turns the pump. 3. The pump circulates heat transfer fluid, (HTF), through the solar collectors. 4. Heat is transferred to the HTF in the solar collector. 5. The HTF is returned to the heat exchanger in the Solar Boiler™ module. 6. The heat is transferred to the water which circulates naturally to the top of the solar storage tank. 7. Solar heated water is stored in the solar storage tank until water is drawn from the auxiliary tank (in this case an oil-fired water heater). 8. As hot water is drawn from the oil-fired water heater it is replaced with solar heated water. 9. The oil-fired water heater increases the temperature of the solar heated water, if necessary. The Solar Boiler™ is designed to shut off when a temperature of 180°F is attained in the solar storage tank. The HTF is a 40/60 % by volume mixture of Propylene Glycol USP and distilled water, and will provide freeze protection to - 10°F (-24°C)

From left to right, here is a picture of the Solar Boiler (heat exchanger), the hot water storage tank (Sears Power-miser 80 gallon tank with heating element disconnected), and the auxiliary hot water heater (a 32 gallon Brock oil-fired unit). These components are located in the basement of my home. The green valve shown in the photo is the temperature-mixing valve that is connected between the cold water in and the hot water out of the solar storage tank. This valve keeps the maximum water temperature to 120 degrees F. This mixed water feeds the auxiliary oil-fired water heater. The temperature set point for this heater is also set to 120 degrees F. Here is another picture that better shows the components:

The valve in the middle (green color) is the temperature-mixing valve. It is located between the two heat loop traps.

Since a PV module supplies power to the pump there are no parasitic electrical losses with this system. To insure that the pump starts with relatively low solar insolation levels (as low as ~200 W/m^2), the PV module is fed by a Linear Current Booster (LCB) that raises the current from about 0.2A to 1.1A. The output of the LCB feeds the pump. The pump is a positive displacement unit that supplies a nominal 1.2 L/m at about 800 RPM, at full sun conditions. Before evaluating this system, lets do a component inventory and look at some installation details.

Here is the system description:

Solar Boiler by Thermo Dynamics Model SB64-9PV System consists of, 2- 4' x 8' collectors 1- solar boiler module (heat exchanger 3 1/2" copper pipe with 3/8" copper tubing inside 1- 2' x 2' PV module powers the solar pump 1 - mixing valve 75' 3/8” supply and return copper tubing with insulation 1- Sears 80 gal storage tank model 32184 (electric element not connected). 1- existing aux 32 gal oil Bock water heater Boiler, collectors, PV module, mixing valve copper tubing installed $6300. Water storage tank $485. Pump and materials $785. total cost $7570.

Tax rebates: Federal $2000 State MA $1000 Warranty 10 years A note on installation: The 3/8” copper pipe supply and return lines as well as the PV electrical wires were routed through a 2 ½” diameter PVC pipe that runs between the basement of the home and the attic. This pipe was installed when the home was built in 1988.

To evaluate this solar thermal system, I chose to use RETscreen as my primary tool. I wanted to be able to look at the system performance, the financial benefits/costs, and also get an idea on what greenhouse gas (GHG) emission reductions were possible. This tool does all this. One of the nice things about this program is that it has geographical data for over 4700 locations around the world so one does not have to manually enter solar insolation data, for example. Another benefit in using this tool is that it has an extensive product database built-in. The Thermo-dynamics solar thermal system specifications are already known so the tool is very easy to use. Before looking at the Retscreen data for this installation we need to consider the computer system requirements. Retscreen runs under Windows XP or Vista and uses Microsoft Excel for its output. Excel 2003 or 2007 will work. I am using Retscreen on a MacBook running XP with Excel 2007. Let’s take a quick look at the Retscreen data screens (Appendix A).

Figure 1 shows the Start TAB for Retscreen. Here one enters the project name, project type, project location, etc… Figure 2 shows the specific climate data for the chosen location. Figure 3 gives the load characteristics and assumptions made for the energy calculations that follow. Figure 4 give the average daily solar radiation on a monthly basis. Figure 5 gives the specific vendor data for the Solar thermal system chosen as well as basic energy output. Figure 6 gives you GHG emissions offset analysis and a financial analysis including payback information. Let’s look at each figure now in detail.

For Figure 1, the key information entered here is the project type (Heating) and the technology (solar water heater). For the climate location, I chose Otis Air National Guard Base. This location is within 4 miles of my home. The database contained about a dozen locations in the state of Massachusetts.

Figure 2 shows the climate data. As you can see, the data contains all the information needed in terms of the resources available (solar insolation, in our case) to make valid performance estimates of the solar hot water system.

Figure 3 shows the load assumptions for the system. In our case, the home has three occupants and we assume an estimate of hot water use of 240 liters/day ( ~60 gallons/day). Although you can change the units for some of the calculations, Retscreen uses the SI system (metric units) for it’s output. Figure 4 may shows how the expected solar radiation changes month by month during the year. It also shows the annual solar radiation (tilted) of 1.62 MWh/m^2. We can use this value, along with data from Figure 5, to calculate the overall efficiency of the system.

Figure 5 contains a wealth of information. For instance, the storage capacity (423 liters) is based on the capacity of the Sears 80 gallon tank & the Brock 32 gallon back-up water heater/tank. The system rated capacity is given as 3.9 kW. Based on the solar collector area (5.96 m^2) and peak solar irradiance of 1000 W/m^2 we can calculate the system’s peak efficiency as. The overall annual efficiency can be calculated based on annual solar radiation (tilted) of 1.62 MWh/m^2 times the collector area of 5.96 m^2 and the heating delivered value of 3.0 MWh. This value is ~31%. You may consider this low but, compared to the typical photovoltaic system efficiency of <20%, this is pretty good. The annual oil consumption goes from over 136 gallons to less than 38 gallons. This still reduces that annual fuel use by 60%! That is a significant savings.

Figure 6 shows that GHG emissions are reduced by 1.2 tons annually. The financial analysis shows the equity payback period of 10.4 years. This was based on a fuel cost of $3.53/gallon for fuel oil. This was the price at the time the system was installed in August of 2008. The fuel costs at initial installation where about $2.25 a gallon however fuel costs have risen greatly since the installation in 2008. Plugging these new fuel costs into the scenario would make the payback period significantly longer but who knows how long the price of fuel oil will remain at these historic low prices?

I am very pleased with his solar hot water system. With this software I now have some information on the relative performance of his system, the GHG emissions reduction, and a rough idea on the financial payback period. By the use of a new (free!) energy project analysis tool I have been able to have this this information. I believe that anyone, with a minimum period of familiarization, can use this tool to examine what makes sense economically in terms of home improvement projects aimed at reducing your energy use and/or offsetting your use with various renewable energy generation technologies.

= = Daniel Parker, student Massachusetts Maritime Academy 101 Academy Drive Buzzards Bay, Ma 02532 Main Number: 503-830-5000
 * Access **

Thermo Dynamics Ltd. 101 Frazee Avenue Dartmouth, Nova Scotia Canada, B3B-1Z4 tel: +1 (902) 468-1001 fax: +1 (902) 468-1002 email: solarinfo@thermo-dynamics.com []

RETscreen International RETScreen Clean Energy Project Analysis Software <span style="font-family: 'Helvetica','sans-serif';">A product of Natural Resources Canada <span style="font-family: 'Helvetica','sans-serif';">[]

= Appendix A – RETScreen Data =

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6