Measuring payoff for installation of the system simply involves collecting annual data on propane use. Consider that there is always a base use of propane used for the drying of clothes, and we do operate a wood stove during cold periods. This year has provided a lot of sunny days, which has helped in propane savings.
Domestic hot water use has remained constant, as our home has three full-time residents. One factor in savings on DHW use is that clothes washing and dishwasher running is generally done in the early afternoon, when the DHW tank is fully heated and has time to recover with solar collection. Showering is generally done during the early morning, but the well insulated tank is still hot from the day before.
Propane usage for the year (Jan 1 - Dec 31) is somewhat dependent on when the tank is filled. I have tried to be consistent on fill times not only to avoid skewing the data, but to take advantage of filling at lower pricer periods. I just did my annual October "top off" of the tank to take advantage of the lower pre-winter prices.
All that being said, here are the figures:
2007 propane usage - 1390 gallons, average price was $1.81, total cost $2728
2008 propane usage - 1180 gallons, average price was $2.11, total cost $2763
2009 propane usage - 892 gallons, average price was $1.69, total cost $1578
The system as installed in the summer of 2008. So, thoerectically savings for that year should have only been half of that this year. The numbers bear that out.
Gallons usage is the main factor in calculating gain. Cost ($) savings is kind of a mixed blessing. Lower propane cost does save me real dollars, but lengthens how long it takes to achieve a payback.
Saturday, October 10, 2009
Saturday, February 21, 2009
Exploring Possibilities for Savings
The boiler system is presently configured to start at 6AM, and heat up the DHW tank and provide heat to the floors. It shuts down at 7PM
On sunny days, the collectors begin heating water at 9AM, and by 10:30, the DHW tank is usually up to temp. On week days, I shower at 4:30 AM, and there is still ample hot water in the 80 gallon tank. My wife showers at 6:30, so I have the boiler start at 6AM to make sure she does not run out of hot water. There is still a lot of residual heat left in the tank, even after my shower, all resulting in less propane usage needed. So, there is probably not much savings available (let alone the risk of having my wife running out of hot water) with changes to the DHW system.
What may help with propane savings, is to not let the boiler bring the in-floor heating system up to temp until 10:30, so that the solar collection system has a chance to heat up the capacity tank.
On sunny days, the collectors begin heating water at 9AM, and by 10:30, the DHW tank is usually up to temp. On week days, I shower at 4:30 AM, and there is still ample hot water in the 80 gallon tank. My wife showers at 6:30, so I have the boiler start at 6AM to make sure she does not run out of hot water. There is still a lot of residual heat left in the tank, even after my shower, all resulting in less propane usage needed. So, there is probably not much savings available (let alone the risk of having my wife running out of hot water) with changes to the DHW system.
What may help with propane savings, is to not let the boiler bring the in-floor heating system up to temp until 10:30, so that the solar collection system has a chance to heat up the capacity tank.
System Saving Money and Pay-Off Projections
The $2000 Federal tax credit this year is the first obvious benefit, and I look forward to future tax credits (30% up to $2000) when I install additional vacuum tube arrays.
But, in the long term, saving on the cost of propane was the goal. My average usage for propane 2005 to 2007 was 1150 gallons. I installed the collection system last summer. My usage for 2008 dropped to 1180 gallons, and the system only began saving me propane the last half of the year. Winter temps have not been exceptional.
More accurate data will take time to produce, but it is not overly optimistic to expect my propane usage to drop to 700 gallons per year. A savings of 450 at $2 a gallon is $900. After tax credit cost of the system was $10,000 dollars, so I am still over a 10 year pay-off.
Installation of an additional 30 tube array should only cost (after tax credit) about $2400, and should further reduce propane usage by at least 200 gallons, shortening the pay-off to below the 10 year mark.
But, in the long term, saving on the cost of propane was the goal. My average usage for propane 2005 to 2007 was 1150 gallons. I installed the collection system last summer. My usage for 2008 dropped to 1180 gallons, and the system only began saving me propane the last half of the year. Winter temps have not been exceptional.
More accurate data will take time to produce, but it is not overly optimistic to expect my propane usage to drop to 700 gallons per year. A savings of 450 at $2 a gallon is $900. After tax credit cost of the system was $10,000 dollars, so I am still over a 10 year pay-off.
Installation of an additional 30 tube array should only cost (after tax credit) about $2400, and should further reduce propane usage by at least 200 gallons, shortening the pay-off to below the 10 year mark.
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