Kenneth Elwell wrote:Sean, the article is about solar thermal collection, not PV. It would work with PV, perhaps in an off-grid scenario, but there’s lots of reasons to maybe do it differently.
The top one for me is lesser efficiency of PV vs. thermal when heat is the goal.
Next would be net-metered grid-tie PV, where over production (summer in Northern hemisphere) could be “saved” as credit with utility company or stored as cash payments (and used for anything you wish , even heating).
Then there’s the time scale... these systems are generally for balancing production and loads for electric utility plants in the scale of hours and days, not months. And they’re working with steam.
There are underground Annualized Thermal Inertia systems that use a heat pump for storage and delivery. If you have surplus PV it could power the heat pump, and you’d get cooling in the summertime as well. (Not just a stack of hot bricks)
William Bronson wrote:OK, I just realized I had shared my reaction but failed to offer any useful advice.
To avoid the problem of water in a coil running through a mass that's hotter than the 100c, you can set an tank of water into the mass and run a coil through that.
Leave that tank unpressurized and open to the atmosphere and add a fill valve to keep it topped up.
You will lose water and energy to the atmosphere through evaporation, but a tall enough column (pipe for steam exhaust) would give the steam time to condense and return to the tank.
Alternatively keep an empty tank in the heated mass and add water when you need it.
It will flash into steam, which is very dangerous.
Don't close in the tank, leave it open to the atmosphere.
Instead run a large (huge!) diameter pipe from the tank through cooler space to a second(header) tank, set as high as possible where the condensed water can gather.
This set up will reduce the amount of energy lost on an ongoing basis.
Kenneth Elwell wrote:Sean, I get the idea of the "no moving parts", and that wires don't freeze. I also understand that the cost of PV panels has dropped quite a lot over the years.
Here's what I'm not quite getting: Solar PV is something like 15% efficient, and Solar Thermal is something like 85% efficient, so why use PV to make heat?
Do you have another need for that much electric that is a factor? Like a workshop or car charging? And then, why not store the electricity in batteries? That way you have the option to use electricity for anything: lighting, electronics/appliances, even for heat/hot water.
Have you looked at what has been done at Tamera in Portugal? They are using hot vegetable oil as a working fluid in a solar thermal system, with an insulated storage tank. That allows for >100C temps. (200C I think) and can be used on demand in a jacketed kettle to boil water for cooking, and for steaming.