[Retric]

More like 4.5:1 solar is 20% or so efficient and solar thermal is only like 90% when including losses.

Anyway, the real question here costs both in equipment and labor. Solar hot water panels involve plumbing and need radiators etc they quickly pay for themselves when heating a large home but don’t scale down very well.

Running the numbers I was surprised how cost competitive the sand bucket is for something like a chicken coop. Sure the panel(s) are wasted most of the year, but you don’t exactly need an electrician to set this up either. Probably also worth considering for redundancy in some situations.

[slow_typist]

The monetary case of PV does not account for the damage that is done to the environment over the entire lifecycle. Solar hot water panels are ecologically superior. Not only are they more efficient in W/sqm. Their production is not as energy intensive (plumbing included), the recycling process is less complex, poisonous materials can mostly be avoided. If heat is the desired product, they probably beat PV by an order of magnitude in the energetic dimension.

[Retric]

PV’s falling prices have also been associated with falling environmental harm. When you’re talking multiple orders of magnitude you just cannot require as much in production.

IE: You can’t burn 500 gallons of gas if the end product costs 500$. That applies not just to transportation but also how much material and thus mining the raw materials you need, including refining them, the amount of chemicals you can use per panel, how much electricity you can use in production of the device including precursors etc.

[slow_typist]

The argument is valid, if energy is not subsidised. However, burning pv for resistance heating is still wasteful and should be avoided. It is only acceptable for peak production that cannot be put to better use.

[Retric]

It’s wasteful of electricity not necessarily resources.

One of the numbers I was looking at compared air sourced heat pump at night when it’s coldest vs this kind of resistive heat battery. Solar panels are far cheaper and better for the environment on a kWh/day basis so even if the COP is 3 (or less it gets colder at night) * 90%(losses from battery) = fewer panels you more than offset it by needing far more batteries.

Obviously solar thermal setups have advantages if you need lots of heat, but they are also wasted most of the year. If 8-10 months a year you’re only using them for hot water then annual efficiency is closer to 25% than 90%.

[adrianN]

You can run a heat pump with the electricity. That changed the calculation a bit.

[slow_typist]

Sure but a heat pump was not the scenario in the parent post.