Solar thermal System - Marathon water heater?
I am looking to upgrade my home with an active closed loop solar thermal water heating system. I live in Portland, Oregon. Given the information that I can get from my local utility, PGE, and Energy Trust of Oregon this should save roughly 2,800kWh or roughly $280 per year on my utility bill.
The solar thermal system is made by Rheem USA. They have two systems that I am considering:
Rheem RS80-48BP - this is an 80 gallon tank with heat exchanger. Refrigerant is circulated through the pipes and solar panels. The system has 48 square feet of panel surface. The heat is transferred to the water via heat exchanger that comes with the Rheem Solaraide tank.
Rheem RS120-64BP - it is the same system as above, but has a larger 120 gallon tank and 64 square feet of panels.
I am wondering - what size should the system be for a household of 4 people?
The smaller system would force me to have a booster tank installed. I am thinking about using a 50 gallon Marathon water heater, since it would easily match the life of the solar equipment. Marathons have a lifetime guarantee and can be used in standard stand-alone installations. If I went without the a second tank like the Marathon water heater I'd run the risk of running out of hot water.
The larger system can go as a stand-alone, but the guaranteed hot water amount in the Rheem Solaraide tank is roughly 40 gallon....the amount of water above the upper heating element. This risk of running out of water still seems real to me.
What are your thoughts? Go smaller? Go bigger? Would you use a Marathon water heater as booster tank in both systems just to make sure?
The second portion of my consideration revolves around whether to execute the project as a DIY project or to go with a specialized contractor?
While the equipment is somewhat specialized I was able to find either one of the solar thermal systems for purchase online:
I think that I can probably get the system installed on my own for roughly $5-$6k. I have seen contractor quotes for more than $10k. This seems way too high for me.
Last but not least - Rheem Marathon water heaters cost between $800 - $1,000 retail. If I used a regular electric water heater I could save between $400 - $700. With that said I do like the durability and high temperature resistance on the tanks. Marathon water heaters can be heated up to 180 degrees without voiding the manufacturer's warranty. This should be beneficial if the pre-heated water from the Rheem Solaraide tank comes in too hot.
Here is more information on Marathons I was able to find:
I appreciate your input on the system configuration and choices. I don't want to end up spending the money just to set up a system that falls short.