Packing Heat

BTUser

https://forum.heatinghelp.com/discussion/comment/1847096#Comment_1847096

Thank you for this, I will be doing those tutorials and running our numbers through when time permits.

https://forum.heatinghelp.com/discussion/comment/1847150#Comment_1847150

38 cents and 8416 sound reasonable. I gathered the numbers on my existing 6.48kw:

9760 Average annual production over 5 years of monitoring data. It was knocked out of production for around one month summer, so SunPower's predicted production from the original paperwork (10,122) is quite close. Assuming their prediction is spot on, I calc I'd need to add 5.39kw to go the A2AHP route. That'd be 15 more panels if I somehow found the exact same type. And, 15 more panels happen to be exactly the amount that could fit on the remaining prime territory remaining on the roof. Panels are 3.5x5 so that's about 262.50sqft of additional paneling. When I bought the first ones in 2018, the panels ran $1000 each installed which makes for some easy math.

There is a problem, though. My understanding is that adding additional PV panels would knock us out of the NEM 2.0 we're grandfathered into until 2038. California's NEM 3.0 appears to be significantly worse for people like us who have optimized our energy consumption patterns around avoiding Peak pricing. I think it would worsen the math not just for the 15 new panels, but also the 18 existing ones. Workarounds: Apparently one can add up to 1 kW or 10% of existing system size w/o triggering the switch. Any more than that would have to be in the form of a separate Zero-Export system, but that's going to be problematic, given that the concept is to generate production credits during summer and shoulder seasons.

Kaos

Perfect is the enemy of good enough. The goal isn't to use zero grid but minimize it since it is expensive. With your costly power, even an oversized zero export setup where you waste some solar has a good ROI. With a bit of home automation, you can set the heat pump to run when you have extra PV and try to coast through peaks.

You can also install an oversized resistance tank with a diversion controller to capture the excess PV. These are very common item overseas but are now some available here as well.

Some car chargers also have the option to monitor load and can throttle back if the sun is not shining.

BTUser

Agreed, zero grid isn't the objective. Objective is to minimize TCO. Point of the exercise here is to come up with the PV+A2AHP based option that does so, which would include some of the optimizations you're talking about.

I'm assuming the resistance tank application would be limited to short term (a day, maybe a couple days) usage, so it could help some in the winter. Nevertheless, the NEM 3.0 issue appears to be a pretty significant consideration here. Apparently NEM 3.0 exports credits are only worth about 25% of import costs. Under utility agreements where import costs = export credits with annual true-ups, in effect with PV you have access to an unlimited amount of 100% efficient annual storage for your exports. That's huge and it's going to change what the optimization looks like.

I suspect that gravy train is on its way out elsewhere too, at least in locations that continue to head toward electrification. As it does, it will lessen a key benefit that PV has had in the past, one that would play a non-trivial role in a PV+A2AHP+Forced Air vs Thermal+W2WHP+Radiant Hydronic comparison.

hot_rod

I'd like to see Resol offer these in the US and Canada.

DCContrarian

The next step would be to look at your gas bills and find the month with the highest therm usage. Then look up insolation for your location for that month, and average high temperature for your location for your month. Figure out what kind of thermal collector you would like to use, and calculate its efficiency at that outdoor temperature, and figure out how many panels you'll need to produce the heat equivalent of that number of therms, at that insolation and efficiency.

That gives a lower limit on the size of a thermal system, you'd still need some sort of storage. But you can compare that to the PV size estimated above to get a ballpark of how competitive it will be.