On 7/18/19 12:01 AM, Mark Abramowitz via EV wrote:
Is solar thermal water heating *still* more efficient?
With a perfect system, solar thermal is probably still more efficient
from a "space on your roof" perspective. [a "square feet of solar
collectors needed to heat the water".] (I'm talking about the vacuum
insulated solar tubes, with a properly sized and insulated system, which
can get 80% of the solar energy that hits it into the water.)
However, from a cost perspective, assuming you are going to be
installing a grid tie solar system anyways, it is probably most cost
effective to add a few more panels (say 4-8) and buy a heat pump water
heater. It certainly makes the installation easier when compared to a
solar thermal hot water system, which also reduces costs.
With 20% efficient solar panels, a grid tie inverter (90% efficient),
and a heat pump hot water heater (400% efficient - gives .20 * 0.90 * 4
= 72% solar energy conversion to heat in the water*). So, you can get
around the same heating performance for a very similar price just by
purchasing a few more solar panels and the heat pump water heater.
This makes special sense if you have excess heat in your house or garage
you'd prefer to be in the hot water (i.e. you live in Florida, and
having a mini AC unit on top of your hot water heater is a good thing
for your house's total energy usage.)
Jay
*-Because a heat pump system is using energy to "move" existing heat, it
gives you 400% (or more!) efficiencies. [i.e. you use 800 watts to drive
a compressor and fans, but get 3,200 watts of heat into the tank, while
cooling the area around the water heater.]
_______________________________________________
UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
http://lists.evdl.org/listinfo.cgi/ev-evdl.org
Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
