Solar part 2

Today I took a shower in the morning (lately I've been showering at night), and after a full night, the water was plenty hot. The tanks are insulated (and the collector tubes tend to be vacuum insulated). M says they stay warm for 3 days. So after 3 days of no sun, you might need another source of heat. Or take a shower Lao style (aka, cold).

So we're inputting energy use data on the Ecolodge into the Green Globe database, which is quite slick. A question comes up: do we need to count solar energy?

Can't believe I still remember thermo: a calorie is the energy needed to raise 1 g of water from 14.5C to 15.5C. From cal we can get joules.

Okay. Suppose it takes 30 L for a typical shower. And we heat it 50C, from 15C to 65C: it really is hot- boiling, M says- maybe closer to 100C. Let's stick with a difference of 50C for now- easier to calculate. That means we need 1500 kcal per shower. Or 6.25MJ. Hm. This is not insignificant, for the average guest in Dec used about 11 MJ of energy per night (mainly electricity). If we count this, that'll increase their per night use by 50%.

Thing is, do we really need to count solar? The sun will shine whether someone showers or not. For that matter, do we need to count all the solar energy that makes it so pleasant these days, not too hot, not too cold?

And, importantly: we don't have a record of the ambient temp of the water from which it must be heated, we're not sure of how hot it really is, and we don't know how much water guests are using. In the low season when it's uber humid and hot, people probably take many showers. But cold. In the high season, when it's more temperate, probably fewer showers, but hotter. How to know? Install temp and flow sensors on the solar hot water heaters?

We'll wait for an answer from the folks in Sydney, where Green Globe is based out of.

In the meantime, I'm still dreaming of a solar hot water system for my own home.