I have had a flat plate solar hot water heater for 15 years. It heats what looks to be standard Rheem hot water heater with a copper coil wrapped around the tank and incorporated in the tank insulation. It has an upper resistance element that I never hooked up. The SHW system provides all the hot water for about 7 months a year but in the shoulder season it starts to run low on outlet temp. Flat plate exchangers are very robust but they are limited to about 80 degrees over day time temps while the sun is out. Add in some heat transfer loss in the piping and the tank coil and its closer to 70 degrees. Therefore when the temps go below 50 deg F things start to get cool in the shower. I normally swap a few valves and use the solar water water as preheat to an external hot water tank fed off a coil from the wood boiler which is also tied into the oil boiler. It used to work out as I would usually start running the wood boiler about this time and would charge up the hot water tank after I had run my storage up to temp. Since my incoming water is preheated with solar and I set the external hot water temp control to 180, I don't need much hot water to boost the solar heated water. I do have antiscald in the mixing valve and overall it seems to work well.
About three years ago I installed a nominal 12,000Btu mini split. I have a small house and with some planning I have been running the unit in shoulder seasons to heat the house. I run it off surplus net metered PV so its effectively free heat. The output drops as its gets colder so I generally look to fire the boiler when outdoor temps hit 30 F. Last winter was the first year I ran the mini split full time and I ran it until early December as the sole source of heat. In this mode I have no waste heat to boost the solar so on occasion I would run the oil boiler which was distinctly wasteful. I am going into this winter with 2500 kwh surplus and expect about 2000 kwh is going to the heat pump with the rest to compensate for lower solar electric performance. Obviously last winter was a warm winter so I have decided to hook up the electric coil on my solar tank, set it to 120 F and put it on timer for use during the shoulder seasons. In theory this will reduce the need for running the oil boiler as a backup during shoulder season. I realize that a HPHW heater would be less costly to run but as my system is already overly complex and power is effectively "free" it would be hard to justify unless one fell into my lap.
Getting hard to justify spending money on any heating system component as the payback isn't there when wood is effectively free and I haven't filled my oil tanks for three years.
About three years ago I installed a nominal 12,000Btu mini split. I have a small house and with some planning I have been running the unit in shoulder seasons to heat the house. I run it off surplus net metered PV so its effectively free heat. The output drops as its gets colder so I generally look to fire the boiler when outdoor temps hit 30 F. Last winter was the first year I ran the mini split full time and I ran it until early December as the sole source of heat. In this mode I have no waste heat to boost the solar so on occasion I would run the oil boiler which was distinctly wasteful. I am going into this winter with 2500 kwh surplus and expect about 2000 kwh is going to the heat pump with the rest to compensate for lower solar electric performance. Obviously last winter was a warm winter so I have decided to hook up the electric coil on my solar tank, set it to 120 F and put it on timer for use during the shoulder seasons. In theory this will reduce the need for running the oil boiler as a backup during shoulder season. I realize that a HPHW heater would be less costly to run but as my system is already overly complex and power is effectively "free" it would be hard to justify unless one fell into my lap.
Getting hard to justify spending money on any heating system component as the payback isn't there when wood is effectively free and I haven't filled my oil tanks for three years.
Most folks just cant seem to wrap their heads around that with some planning that they don't have to burn fossil fuels to heat their home, their hot water and supply all their power. I don't have an expensive custom built net zero home, I have just gradually upgraded a standard home over the years making improvements where it makes sense. My hot water maker was a leaky unit that someone was going to throw away so I repaired it and have been using it for 15 years. My boiler is not a superefficient gasifier, rather its was an improperly installed boiler that I got for free if I removed it. The majority of my PV system is made from surplus panels from companies that got out of the business and most of the racking systems are home assembled. Its all legal I just do it myself if possible
