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Tank Placement

4 min read

Mount the solar storage tank at least 30 cm above the top of the collector, as close to it as the pipework allows, insulated and vented, and treat its weight as a structural load: a 200 L tank of water plus about 30 kg of steel is 230 kg, which is 2,256 newtons of downward force on a footprint of under a square metre. Put the draw-off tap where a person can reach it without climbing, and temper the hot outlet before it reaches the user.

Part of Thermosiphon Systems

Tank placement is the choice of where, how high and on what to mount a solar storage tank, so that it circulates, stays warm and is held up safely.

Height, Distance And Insulation

The bottom of the tank must be above the top of the collector by at least 30 cm (parent page). Keep the pipe runs between collector and tank as short as possible and well insulated, and wrap the tank itself heavily (parent page: blankets, foam or straw in a box). The parent page’s household tank is 100-200 L (How Thermosiphon Works explains why height drives the circulation).

A Tank Is A Heavy Point Load

A kilogram is a mass; a roof feels force in newtons, and force = mass × 9.81 m/s². Inputs, assumed: 200 L of water (200 kg), tank and fittings 30 kg, a footprint of 0.6 m × 1.2 m.

  1. Mass = 200 + 30 = 230 kg.
  2. Force = 230 × 9.81 = 2,256 N, about 2.3 kN.
  3. Footprint = 0.6 × 1.2 = 0.72 m², so average pressure = 2,256 ÷ 0.72 = 3,133 Pa, about 3.1 kPa.
  4. If the tank rests on two rafters, each carries about 2,256 ÷ 2 = 1,128 N.

That is what 2.9 adults standing in one spot would load (an 80 kg adult is 785 N, and 2,256 ÷ 785 = 2.9). Concentrated on two beams, it can exceed what a roof designed for spread loads carries, so have the supporting timbers checked or build a platform that carries the tank to the walls or the ground, not just the roof covering. Wind adds a lift and a sideways push on the tank and the collector (Wind Loads).

Pressure At The Collector

Water pressure rises with depth by 9.81 kPa per metre. A tank with its bottom 1 m above the collector inlet pushes 9.81 kPa onto the collector; with the tank surface 2 m above a ground-level tap, the tap sees 19.6 kPa (about 0.2 bar), a weak flow. That is enough for a shower rose only at low flow (Tank Sizing & Placement covers the cold-feed head).

What You Need

  • A platform or rafters sized for the load above
  • Insulation around the tank, kept dry
  • Pipe short and rising, with a vent at the top
  • A tempering mixer at the outlet

Method: Place It

Step 1: Choose the position: bottom of tank above collector top by 30 cm or more, close to the collector, shaded from nothing, and sheltered from cold wind.

Step 2: Check the support: compute the force as above and assure yourself the structure holds it with margin, especially when the tank is full and wet.

Step 3: Insulate the tank and the hot pipe.

Step 4: Plumb the vent and the outlet. Fit the tempering mixer before any tap.

Common Mistakes

  • Tank in an attic with the bottom below the collector top. The loop will not circulate or will run backwards.
  • Thinking in kilograms. A roof carries newtons; 230 kg is 2,256 N, not 230 N.
  • Long uninsulated pipes. Heat is lost before it reaches the tank.

Safety

Falling load, scalding outlet, hot vent

A tank full of water that falls through a roof can kill; support it properly and secure it against wind and earthquake. Water from a solar tank can leave at 60°C or hotter, hot enough to scald badly in seconds and far hotter than a person expects from a tap: temper it with a mixing valve or by blending cold water, because tempering is a safety feature, not a comfort one. Children and the elderly are injured at lower temperatures and shorter exposures than adults. The vent and relief must discharge away from people (Plumbing Connections).

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