Pressurized Solar Thermal Storage Tanks

Pressurized Solar Thermal Storage Tanks

How do I properly size my storage tank for the collector area?

The rule of thumb of 1-3 gallons of storage per ft2 of collector will only get you so far, so it is best to try being creative with your storage. As your load increases in the winter and production decreases, you should adjust your storage capacity accordingly. Even slight changes from day to day in your production vs. consumption, can dramatically affect total system performance. Tank prioritization allows you to maintain a target temperature in one tank while still charging another. Better yet, you may be able to run directly from your solar field to your heat load and bypass the tank altogether. With the use of aquastats and 3-way solenoid valves this can easily be accomplished for the greatest solar return

How do I know which type of storage tank that I need?

Well, there are really two main options here; pressurized tank or non-pressure tank. The pressure tank will come with heat exchange coils on the inside (2 or 3 depending on style) that will be tied into a closed solar loop and open DHW loop. The additional coil (s) can be used for space heating or auxiliary heating. The drwaback to large pressurized tanks is that they require larger doors when you exceed 200 gallons or so. The Non-pressure tanks are basically custom built, insulated tubs that can be brought in through the smallest of doors and assembled on location to a volume of up to 4000 gallons. With these tanks, the heat exchangers are submersible copper coils typically and designed to specification for each application. Usually, this type of tank is used for home space heating system or for large DHW systems as a pre-heat buffer tank.

How do I know which size of storage tank I need?

There are many answers to this question but it really boils down to this...you need the one that best suits your application, your solar collector field, your budget and your available space. If you use a Heliomaxx kits from Sunmaxx, we have sized the storage vessels relative to the size of the collector field. For sizing, we generally consider first the temperature requirement of the tank. For instance, if you need your solar tank to be a cetain temperature before it ties into your home heating sytem then we would likely reduce the storage capacity but if you are using your tank as a pre-heat system only then we try and maximize the storage. And also we need to consider your budget, because even though a bigger tank give us more solar gain annually, there may not be the payback on that larger tank that justifies the expense. Here are the ratios we typically use for storage relative to solar collector area: 1 gallon per Ft2- high temp loads or in northern climates with flat plates 1.5 gallon per ft2- medium temp loads and typical with most Flat plate installs 2 gallons per Ft2- high temp loads for Evacuated tubes or Low temp for flat plates 2.5 gallons per Ft2- medium temp loads for EVT 3 gallons per ft2- low temp loads 4+ gallons per ft2- sometimes it does make sense but would need to be analyzed based on payback.

How do I determine the most appropriate solar thermal storage size?

Q: How to determine the best solar thermal storage size. A: Choosing your storage tank size is dependent on three things. 1- the number of ft2 of collector- for example we typically recommend any where from 1-3 gallons of storage per ft2 of collector,   2- the daily load profile (usage pattern) for example if most of your usage occurs in the early morning or in the evening, then you would not adjust your storage ratio. However, if your usage occurs more in the mid-day then you would reduce your storage ratio because you will be consuming that which you are producing, therefore saving energy can be a moot point  3- the required temperature. For example the colder the required temperature, the more storage you can have per area of collector. If you need some really high temps for baseboard heating then your storage ratio will be 1:1 or less. But if your required temperature is 100 degrees F then you can maximize your storage capacity with, say, a 3:1 ratio.