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Considering that hot water does not need to be heated right away, solar water heating (Direct or via photo-electric) with an electric hot water cylinder as a ba

Considering that hot water does not need to be heated right away, solar water heating (Direct or via photo-electric) with an electric hot water cylinder as a backup for overcast days would result in more reliable and more long lasting system.

teruakohatu 6y ago
Some people have them here, but it is not that popular. Most of the country has a mild climate and so you would still need an electric heater to keep the tempreture constantly high enough to kill legionnaires bacteria (over 60 degrees celcius). I think over the lifetime of the system money saved in electricity would not be offset much due to installation. Most of the country is run off hydro so not much environmental benefits either.
- robocat 6y ago
  > Most of the country is run off hydro so not much environmental benefits either. Actually, the majority of marginal units of electricity come from gas. That means that every extra kWh you use comes from gas, and every kWh you save reduces gas usage. There are few times when the lakes are full and your marginal unit would come from hydro. The easy way to think of it is that all the hydro is already used up by other people, so your electricity usage comes from gas. Hopefully NZ gets some large solar generation, since NZ can “store“ it in lakes by reducing lake outflows during the day (I think).
  - teruakohatu 6y ago
    I get what you are saying but that is not quite how it works. The marginal price may be determined by gas, but my electricity in the south island is mostly hydro. Right now as I write this comment, the grid in the south island is being powered by hydro and wind. Less power is currently being exported north than is being generated right now by gas up North. So if I turn on a heater, it does not mean that an extra couple of kw of gas is being turned on in Auckland. Right now the total power accross the country is 84% renewable. So worst case if I use a heater it is 16% not renewable. In any case, electric water heaters in nz are ripple controlled and only heat at the lowest demand. So any electric water is using as much hydro as possible.
    - robocat 6y ago
      > So worst case if I use a heater it is 16% not renewable. As a choice as an individual: The heater is off. You turn it on. The extra demand you added usually comes 100% from gas generation. > In any case, electric water heaters in nz are ripple controlled and only heat at the lowest demand. So any electric water is using as much hydro as possible. Our lakes are like batteries. If you choose to take an extra long hot shower powered by hydro at the moment, but 3 months later the lakes get low (because there is not enough rainfall) then extra gas generation is used 3 months later which matches 100% of your extra power usage due to your hot shower choice. Reducing your power usage works similarly, in that you save gas generation. As an individual, your choices 100% affect how much gas is used, because we are assuming others make no change. This is the key to thinking about marginal usage. Marginal economics are critical to understand when running a business too, since it is similarly confusing (and we all naturally make simple mistakes when thinking about it). There are times when your extra usage comes only from hydro, but it is usually not simple to know at the point when you are adding power usage. Reducing power usage can only ever help, so different.
gwicks56 6y ago
I have heard too many horror stories about direct solar hot water. Sure it might work well, and can save a lot of money, but if it breaks it can get VERY expensive. I am looking at electic hot water that only heats with excess solar power though, not mains. Saves sending power to the grid and getting paid very little for it.

teruakohatu 6y ago

Some people have them here, but it is not that popular. Most of the country has a mild climate and so you would still need an electric heater to keep the tempreture constantly high enough to kill legionnaires bacteria (over 60 degrees celcius). I think over the lifetime of the system money saved in electricity would not be offset much due to installation. Most of the country is run off hydro so not much environmental benefits either.

robocat 6y ago
> Most of the country is run off hydro so not much environmental benefits either. Actually, the majority of marginal units of electricity come from gas. That means that every extra kWh you use comes from gas, and every kWh you save reduces gas usage. There are few times when the lakes are full and your marginal unit would come from hydro. The easy way to think of it is that all the hydro is already used up by other people, so your electricity usage comes from gas. Hopefully NZ gets some large solar generation, since NZ can “store“ it in lakes by reducing lake outflows during the day (I think).
- teruakohatu 6y ago
  I get what you are saying but that is not quite how it works. The marginal price may be determined by gas, but my electricity in the south island is mostly hydro. Right now as I write this comment, the grid in the south island is being powered by hydro and wind. Less power is currently being exported north than is being generated right now by gas up North. So if I turn on a heater, it does not mean that an extra couple of kw of gas is being turned on in Auckland. Right now the total power accross the country is 84% renewable. So worst case if I use a heater it is 16% not renewable. In any case, electric water heaters in nz are ripple controlled and only heat at the lowest demand. So any electric water is using as much hydro as possible.
  - robocat 6y ago
    > So worst case if I use a heater it is 16% not renewable. As a choice as an individual: The heater is off. You turn it on. The extra demand you added usually comes 100% from gas generation. > In any case, electric water heaters in nz are ripple controlled and only heat at the lowest demand. So any electric water is using as much hydro as possible. Our lakes are like batteries. If you choose to take an extra long hot shower powered by hydro at the moment, but 3 months later the lakes get low (because there is not enough rainfall) then extra gas generation is used 3 months later which matches 100% of your extra power usage due to your hot shower choice. Reducing your power usage works similarly, in that you save gas generation. As an individual, your choices 100% affect how much gas is used, because we are assuming others make no change. This is the key to thinking about marginal usage. Marginal economics are critical to understand when running a business too, since it is similarly confusing (and we all naturally make simple mistakes when thinking about it). There are times when your extra usage comes only from hydro, but it is usually not simple to know at the point when you are adding power usage. Reducing power usage can only ever help, so different.

gwicks56 6y ago

I have heard too many horror stories about direct solar hot water. Sure it might work well, and can save a lot of money, but if it breaks it can get VERY expensive. I am looking at electic hot water that only heats with excess solar power though, not mains. Saves sending power to the grid and getting paid very little for it.