System Design

design1The main components of a domestic hot water solar system are the solar collectors, water storage tank, solar controller and solar pumping station. The diagram on the right shows a basic concept layout of a solar hot water heating system. When designing a solar system it is imperative that the system is sized correctly; otherwise inadequate performance or overheating may occur. The following is the generally accepted best practice for sizing a solar system for the Irish and the U.K. climate.

Step 1: Calculate the household hot water usage

Generally speaking the average daily hot water usage is between 40 -50 litres per person When sizing solar systems 50 litres is normally taken as an average.

Step 2: Determine location of collectors

Ideally, collectors should be orientated due south if possible and at a pitch of between 40° and 50°. Variations to the optimum positions are permissible and the chart on the right shows the % reduction in solar energy captured. For example collectors facing due east at a 30° inclination will capture 80% of the maximum potential energy.

Step 3: Calculate number of collectors required

design2A solar system should be designed to cover the hot water requirement almost completely during summer months. As a rule of thumb approximately 1 m2 of collector aperture area is required per person.

Note if the collectors can’t be installed to optimum conditions the correction factors in the chart above should be applied. i.e. if the collectors are facing due east at a 30° inclination, then 1 m2 is multiplied by 100/80 = 1.2 m2.

Step 4: Determine storage tank size

A general recommendation is to have 50 litres of water storage capacity for every m2 of collector aperture area.

Recommended tank sizes for Firebird solar collectors are shown in the table below:

No. of Persons No. of collectors Tank Size (I)
2-4 2 x CPK-7210 Flat panels
2 x CVSKC - 10 Vacuum tubes
30 or 40 TZ58 Heat Pipes
5-6 3 x CPK-7210 Flat panels
3 x CVSKC - 10 Vacuum tubes
50 or 60 TZ58 Heat Pipes