This is a general ramble about heating fuels and different systems. Feel free to ignore if it doesn't apply but the situation described in the opening post touches a lot of variables. Some of these will touch all of us in one form or another.......
I don't anticipate anything but continued volatility in the traditional fuel markets. Electricity included.
Right now Saudi Arabia is basically fighting for it's life and trying to hang on to market share by cutting the price of crude. Many of the oil producing countries in the Mideast need oil well above $100/bbl to support their economies and crude selling for 20% less than that is killing them. I'll make a prediction that this will not end well if it continues......
Global energy demand to soar 60% by 2040, says OPEC
In a super efficient home like you are describing you can easily see design heat loss come in under 10 / sq ft., even in Maine.
So in your case heating 1500 sq ft., it presents a special challenge for cord wood burning boilers. (A forced air wood furnace is nearly out of the question)
Given that the full heating load will likely be far below the output of any cord wood boiler, storage will be mandatory and this of course adds cost and complexity.
Can be done but the design and layout of the system need to be addressed correctly or you will buy yourself problems. A well insulated Garn Jr would probably have to be fired only 3-4 times per week in a home like that.......
There are pellet boilers that are designed for houses with very small heating loads (common in Europe) and they can also modulate between 30-100% output. In the case of a Windhager 10KW Bio Win, you would have actual output capability between 10,000 to about 30,000 btu. This would give you a boiler that needs very little thermal storage and would still have enough ooomph to do domestic hot water production if given priority. Another way to accomplish thermal storage and virtually instant hot water production is through the use of an indirect hot water heater. The volume of the tank is used as thermal storage, maybe 40-64 gallon capacity and the domestic hot water is piped through the coil in the indirect before going into a normal hot water heater and directly to faucets. It goes without saying that a tempering valve has to be used on the outlet of the tank to prevent scalding.
There are some interesting pellet products on the market and more coming. Look at some of the models on Marc Caluwe's website for instance. Heat for the house, domestic hot water production + the ability to have a nice fire to watch in your living room. All in one unit.
Heat pumps: Two types, air to air and water to air. ..... I have heard mixed reviews on the air to air types especially after last winters temperatures. Claims by manufacturers of good heat output near 0* outdoor temps were shown to be rather "optimistic" from what I heard and observed. Even if they did heat the space, the COP became so low at those outdoor conditions that the owners may as well have run regular resistance type heating. I was told, but haven't personally confirmed, that the largest Mitsubishi distributor in our state dumped the product line because actual performance was far less than advertised and Mits would not stand behind their advertising.
If you have the right soil type a vertical loop water to air or water to water ground source heat pump can be very efficient. In a well designed and installed water to air type system you can get around 4 watts of energy out for every watt of input making the system in effect 400% efficient. This would be with a vertical loop system pulling heat from 100' down. For any ground source heat pump, you will find if it is used in water to water situations the COP will drop significantly. Many times real performance will be in the 2-2.5 range rather than 4+ like a water to air. This becomes even more pronounced as you try to drive water temperatures produced by the unit much above 115*. Heat transfer efficiency really falls off after about 110*. You will also have to have an electric or other type backup for DHW as the heat pump will not supply 100% of your needs in most cases.
In a high efficiency house there is much to be said for the ultimate simplicity of a wood burning stove if you can deal with the mess and multiple loadings per day. This too would have to sized pretty tight in order to avoid creosote formation..... I don't care how dry the wood is, it will make creosote if idling constantly. The downside is no hot water production, poor room temperature control, temperature variation throughout the house. But the initial cost is very low compared to a wood or pellet boiler.
All that being said...........you are on the right track designing your house to be as energy efficient as possible. All forms of energy will only index upward in price as the world demands more and more of any type you can imagine.
As far as pellet supply is concerned I wouldn't be too concerned. As demand increases the supply will also. One of the local mills here just added a complete second line to keep up with demand and the more popular and accepted pellets become, the more comfortable the mills are in making additional investments in equipment.
Soap box is now open......
