A simple effective solar water heater with minimal install.

[Dave]

This is a four layer solar water heater.

Main component - readily available black grow bag tray - UV stabilised
plastic.

You insulate the bottom of the tray, and put it on the ground in the
sun. You put about 15mm of water in the tray and cover it with an
acrylic sheet.

When the water is heated you pour it out into a basin and use it. It
will easier to have the tray up on blocks so you can tip it.

High temp. cheap 12v pumps are a possibility, since there is not
continuous use.

Additionally you can put a reflective film behind the tray.

Sums:

Internal area : 0.97m x 0.37m = 0.35m^2

Heating power = 800W/ m^2 = 800x 0.35 = 200W

Volume of water = 0.35x0.015 = 5l (enough for a bowl). 5 litres is 1
1/3 US gallons.

Time to heat water to 45 Celsius
Assume 5 degree incoming.

Water has latent heat = 4200J/Kg K.

Energy needed is 4200x40x5 = 840000 J

200W is 0.2kWh which is 0.2 x3600000 J = 720000J

So in 70 minutes should get water warm and safe enough for human washing.

OK for work from home people, not people rushing out the door.

There is this web site:
https://power.larc.nasa.gov/data-access-viewer/
Where I can check the figures - hopefully better than a wet finger in
the air.

[Dave]

Post by Dave
This is a four layer solar water heater.
Main component - readily available black grow bag tray - UV stabilised
plastic.
You insulate the bottom of the tray, and put it on the ground in the
sun.  You put about 15mm of water in the tray and cover it with an
acrylic sheet.
When the water is heated you pour it out into a basin and use it.  It
will easier to have the tray up on blocks so you can tip it.
High temp. cheap 12v pumps are a possibility, since there is not
continuous use.
Additionally you can put a reflective film behind the tray.
Internal area : 0.97m x 0.37m  = 0.35m^2
Heating power = 800W/ m^2 = 800x 0.35 = 200W
Volume of water  = 0.35x0.015 = 5l  (enough for a bowl). 5 litres is 1
1/3 US gallons.
Time to heat water to 45 Celsius
Assume 5 degree incoming.
Water has latent heat = 4200J/Kg K.
Energy needed is 4200x40x5 = 840000 J
200W is 0.2kWh which  is 0.2 x3600000 J = 720000J
So in 70 minutes  should get water warm and safe enough for human washing.
OK for work from home people, not people rushing out the door.
https://power.larc.nasa.gov/data-access-viewer/
Where I can check the figures - hopefully better than a wet finger in
the air.

As someone said, open water isn't the best for heating up with solar
because a lot of energy is wasted on evaporation. Need to float
something matt black on top. Plus if floating, the water heating would
be at the top, so need fins going down. Full size grow bag trays weigh
about 1.5 Kg, but conduction through the plastic wouldn't be enough?

Currently trying floating a matt black aluminium roasting tray in 1.5l
of water in a seed tray which is a good fit. Need a better cover than
bubble wrap, but you get the idea. Also no fins, but be easy enough to
sit the roasting tray on top of metal stands to help conduction.

In a couple of hours, 750ml of water heated up successfully in a cast
iron frying pan with a lid (black inside), and I could see the
condensation on the inside of the lid. One piece pan with cast handle,
and weighing about 2Kg, so yes, this was all wasted. and conducting heat
away.

[Dave]

Post by Dave

Post by Dave
This is a four layer solar water heater.
Main component - readily available black grow bag tray - UV stabilised
plastic.
You insulate the bottom of the tray, and put it on the ground in the
sun.  You put about 15mm of water in the tray and cover it with an
acrylic sheet.
When the water is heated you pour it out into a basin and use it.  It
will easier to have the tray up on blocks so you can tip it.
High temp. cheap 12v pumps are a possibility, since there is not
continuous use.
Additionally you can put a reflective film behind the tray.
Internal area : 0.97m x 0.37m  = 0.35m^2
Heating power = 800W/ m^2 = 800x 0.35 = 200W
Volume of water  = 0.35x0.015 = 5l  (enough for a bowl). 5 litres is 1
1/3 US gallons.
Time to heat water to 45 Celsius
Assume 5 degree incoming.
Water has latent heat = 4200J/Kg K.
Energy needed is 4200x40x5 = 840000 J
200W is 0.2kWh which  is 0.2 x3600000 J = 720000J
So in 70 minutes  should get water warm and safe enough for human washing.
OK for work from home people, not people rushing out the door.
https://power.larc.nasa.gov/data-access-viewer/
Where I can check the figures - hopefully better than a wet finger in
the air.

As someone said, open water isn't the best for heating up with solar
because a lot of energy is wasted on evaporation.  Need to float
something matt black on top.  Plus if floating, the water heating would
be at the top, so need fins going down.  Full size grow bag trays weigh
about 1.5 Kg, but conduction through the plastic wouldn't be enough?
Currently trying floating a matt black aluminium roasting tray in 1.5l
of water in a seed tray which is a good fit.  Need a better cover than
bubble wrap, but you get the idea. Also no fins, but be easy enough to
sit the roasting tray on top of metal stands to help conduction.
In a couple of hours, 750ml of water heated up successfully in a cast
iron frying pan with a lid (black inside), and I could see the
condensation on the inside of the lid.  One piece pan with cast handle,
and weighing about 2Kg, so yes, this was all wasted. and conducting heat
away.

Since this post, used thin framing glass and the water got to 54
Celsius. Too hot for bare hands. There wasn't much insulation
underneath, just a folded towel. Was in the conservatory which was cut
wind cooling.

Tipping the 1.5l from the small seed tray into a basin was easy-peasy.
Size of the seed tray is 0.24m x 0.375m. There is stress in moving
framing glass though, need some polycarbonate of acrylic. Will get a
10L production facility going on my table with an expected BOM under GBP
120. If outside, needs weighting down, and checked for snails etc
crawling in.

Others may remember that an eco-way to heat your swimming pool is to
float many black aluminium roasting trays. My roasting dish was free
from the shop at Christmas.

Posted to uk.politics.misc to show that there are quick wins for going
eco. Doesn't need billions to get the basics right. e.g. My yearly gas
use went from 9000kWh to 5000kWh in 21/22 with sensible heat management
(SE England). e.g. Get as much sun in through the windows as you can.
Put door curtains up.