Evacuated Tube vs Solartwin

   Its important to understand the difference between Direct and Indirect when deciding on solar hot water

Indirect

Direct
   The water in the panel stays in the panel / loop. It generally contains antifreeze which needs to be changed every year.
   The water in the panel is the same fresh water that's come from the tank. This will freeze in winter but some systems are freeze tolerant such as this one from Genfit.

Evacuated Tube (Direct)

   In these evacuated Tube type, the water circulating the panel is separate to the water in the tank and contains antifreeze. The antifreeze needs to be changed every year, so they are quite high maintenance. They also require a thermal coil in the hot water tank. So you may need a dual coil tank if you are already using the coil. Also the pump is generally mains powered, so although the tubes are very efficient the mains pump continuously draws power.
  1. Pros
  • Solar hot water

Cons
  • More expensive
  • No suitable for of grid
  • Requires mains electricity
  • May not work with regular 120L tank if using coil already
  • Anual antifreeze renewal

Direct

   The water in the panel is the same fresh water that's come from the tank. This will freeze in winter but some systems are freeze tolerant such as this one from Genfit.
   I have been personally using this type for 13 years and found it excellent. Main maintenance wise it is very easy to repair if there are problems such as
  • Pump valves degrading (tiny rubber flaps replaced with hand made ones out of cycle inner tube)
Pros
  • Off grid
  • Freeze tolerant
  • Self powered with its own  PV
  • Fits regular 120L tank
  • No antifreeze
  • No anual antifreeze renewal
  • DIY kits available

Cons
  • May not comply with regs
  • Pump valves degrade (tiny rubber flaps replaced with hand made ones out of cycle inner tube)
   Solartwin is a great Solar Thermal Panel system.
It can be installed in a day. Cost £3500 inc installation or £2500 DIY.

   Solar Thermal AKA solar hot water, can reduce the energy required to heat your hot water for washing and bathing by as much as 70% providing free hot water for 1-4 people for most of the year.
   Controls shown >

Top - Heat Recovery Ventilation switch (nothing to do with solar)

Middle - Solar controller showing temperatures of -
  • Solar panel
  • Top of tank
  • Bottom of tank

Bottom - Immersion heater timer.
   During winter set to come on for 1 hour during the night time rate 12:30 - 4:30
7.5p/kWh

   If the water temp is a bit low for a shower <37c just push the 15min booster & by the time it takes to get in the shower, the water will be warm enough.

​Solar PV vs Thermal

Solar Thermal

Pros
  • 80-95% efficient
  • Low cost install
  • Does not require and expensive bank of batteries such as Tesla Power wall
  • Low installation costs
  • Can top up hot water with cheap rate night time electricity
  • ​Small roof area required​
Cons
  • Requires hot water tank
  • Can't charge a power wall

PV's

Pros
  • Convert sunlight directly into electricity
  • Can charge an Electric Vehicle directly
  • Can heat water in a tank directly
Cons
  • More expensive than thermal
  • Only 16-23% efficient
  • Larger roof area required
  • Storing the energy can be expensive as you may need something like a £7000 Tesla power wall
  • Can't charge the car if you've gone to work in it
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