[penteract]

To check I understand you: the smaller tank with heatpump would consume less energy outside the time window in which energy is free than the large tank with resistive heating, but has a higher capital cost which would outweigh the amount saved on energy?

If that's right, it's not obvious to me that building a suitably sized solar panel is environmentally worse than building a heat pump.

[stubish]

The smaller tank with heatpump will consume a lot less energy than the larger tank with resistive heat.

Economically to me, the larger tank is cheaper, because the appliance is cheaper, and I never pay for the power it uses.

Environmentally, yes, it is not obvious. The large tank requires many more solar panels to power it but no battery. The small tank and heatpump needs much less solar but battery for nighttime use.

But it is weird, because for decades heat pump tech has been pushed as the environmental choice and there are still a number of government subsidies to invest in heat pump hot water systems. And maybe that no longer makes sense, with the money saved buying cheaper and less efficient devices spent on more solar deployments.

[hnaccount_rng]

But it’s also environmentally better for you to take the resistive heating thing. As long as you never need to heat it up outside of the noon-window that’s strictly positive. Because the “additional” solar panels will be necessary anyways to cover the night/late evening usage. The optimal buildout will always have superfluous energy at noon. That’s fine. We just need to get over the whole “energy costs anything” thing. That’s only true if you need to spend fuel to generate it

[stubish]

But it not entirely true. While renewables can cover well over 100% of daytime usage on most days in summer in my region, we are down to about 40% during winter. We need lots more solar panels and wind turbines and enough battery to get us through energy droughts, and installation and maintenance has economic and environmental costs. Much less than other forms of generation, but costs nonetheless. If everyone stops caring how much power they draw because it is 'free', the problem of supplying enough sustainable generation becomes harder and takes longer. The extra generation capacity needed is paid for by consumers in the form of connection fees and/or tax payers.

[hnaccount_rng]

You are of course somewhat correct. But - I think - only technically. In practice what happens is that the “maintenance”[1] costs on solar production is extremely limited and should (that’s not yet possible to reliably say) be much lower than the rest of the grid.

If that’s the case, then we really don’t have to care about usage amounts _during the surplus time_. That in turn will enable completely different patterns. I think the correct analogy is the movement from candles/gas lights to electric lights. Before electricity was widely available nearly everything in life had to be done during daylight hours. Today we don’t even think twice about whether a meal can be cooked “after dark” or to move to a different location or ...

And yes that means I say: We will provide electric power for free [2], just like we do with street lighting

[1] let’s just call all replacements of cells and inverters maintenance for this discussion here [2] at the point of consumption. But that happens if the cost is smaller than the implementation of the sales system

[Panzer04]

The magic of market pricing means people will figure out the best solution and optimise towards that.

Hot water heater tanks are easily one of the most obviously good applications of noon excess energy, and resistive heating elements might as well be free.

[stubish]

I agree about market pricing. The new pricing model however distorts this, turning electricity into a subscription service for people with a large enough battery. This distorted market can create bad incentives. But switching to actual market pricing won't work for most customers who don't want or can't afford surprises in their energy bills (it is already available for those that want it). Short term, it seems a good policy to shave or remove peaks. Long term, in a world where every household has a suitably sized battery, it means several times more generation capacity than necessary because consumers have no incentive to reduce consumption (beyond ethics and peer pressure). I don't think this pricing model is a permanent solution. And I have no idea how many years it will remain viable and a good policy, or what sort of hot water system I should buy given 10-20 year warranty periods.