Evacuated Tube vs Solartwin

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

Indirect

   The water in the panel stays in the panel / loop. It generally contains antifreeze which needs to be changed every year.

Direct

   The water in the panel is the same fresh water that's come from the tank. Popular in warmer countries where freezing is not a problem.  Some systems are freeze tolerant E.g. Solartwin

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 Solartwin
   I have been personally using this type for 13 years and found it excellent. 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)
   Solartwin was 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.
Pros
  • Off grid
  • Freeze tolerant
  • Self powered with its own  PV
  • Fits regular 120L tank
  • No antifreeze
  • No annual antifreeze renewal
  • DIY kits available​
Cons
  • May not comply with regs
  • Pump valves degrade
The solar controller (middle unit) included with the panel has 3 sensors showing temperatures in the -
  • Solar panel
  • Top of tank
  • Bottom of tank

   I have added an immersion heater timer (bottom unit), during winter set to come on for 1 hour during the cheap night time rate.
   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.
For DIY solar check out solarfriend.co.uk

Evacuated Tube (Indirect)

   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.
Pros
  • Solar hot water​
Cons
  • More expensive
  • Requires mains electricity 
  • No suitable for off grid
  • Susceptible to hail stones
  • May not work with existing regular 120L tank if using coil already
  • Annual antifreeze renewal

​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

Cheapest hot water

   I have and EV which gets me the cheapest night rate, and a solar thermal panel that I service my self. I'm paying only £48 a year for all hot water, where most are paying £569 for instant hot water / showers.
   Generally the more green tech you add the cheaper your bills get, but you have more initial out lay and higher servicing costs.
Down load the spreadsheet for Openoffice -
solar_and_ev_hot_water.ods
File Size: 37 kb
File Type: ods
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