Heat accumulators / heat storage tanks
A heat accumulator does what it's name suggests - it accumulates heat. Often a heat accumulator will be a well insulated tank of 1000 litres or more, with many tapping points built in, and possibly with multiple coils inside the tank.
Electrical heating elements
Some can come with electric heating elements to provide an electric backup. Please bear in mind that non renewable electricity has the highest kg CO2 / kWh figure of any fuel (wood, gas,oil,coal).
Stratification is important
A good heat accumulator will stratify well. The hot water at the top of the tank is separated from the cold water at the bottom of the tank by a stratification layer. The thinner this layer the better and the bigger the difference between the hot and cold water. That is because the hotter the water at the top of the tank, the more useful it is for providing domestic hot water. Reducing mixing in the tank means that the top of the tank comes up to temperature much faster giving you access to useful hot water.
Sometimes a charger is used to keep the flow rate into the tank to a minimum. Two examples are the H2 Panel and the Laddomat, both of which promote stratification and reduce mixing in the tank.
Letting you use the stove in an efficient way
The most efficient way to use a wood boiler stove is to burn it relatively fast, allowing for complete combustion of the wood. This can make a lot of hot water which you do not always want to use at the time. The heat accumulator tank lets you store it up for later when you do want it. With a larger boiler stove and biomass boilers a decent heat accumulator tank can let you fire up the wood boiler once every 3 days and then use the water from the tank in between (in the depths of winter you would may to fire up more often than this).
Heat Accumulators are ideal for use with solar panels
Similarly with solar panels a heat accumulator lets you store heat generated during the daytime for use later - you may well find that you use more hot water during the night time - when solar panels are not that useful....
Boiler stove installation using a heat accumulator
Our Installation Type 4 covers the idea behind using a heat accumulator to link-up a boiler stove with colar panels and a conventional boiler.