But, the talk of powering water heater, heating, AC, etc. from a little DIY solar system is extremely optimistic. I've done the math, and I couldn't run my AC from the number of solar panels that I could fit on my roof. I can fit 900 watts worth, an additional couple hundred watts on the truck, if I really wanted to get extreme and was willing to connect/disconnect them every time I drove the truck away from the RV. That's just not enough. It could power a small window unit as long as the sun is up, but overnights would kill a small battery bank dead (like dead dead, not just discharged, as repeatedly discharging below about 50% reduces the life of lead acid batteries by a huge amount) in short order.
With a big enough inverter and a bigger battery bank, you can run microwave or toaster oven for short periods of time (I do). But any big amperage device that runs for extended periods of time (like heating, AC, and water heater) is not in the cards for small solar systems.
Battery replacement also needs to be taken into account. In my experience, you get about 3 good years, and another year of limping along, from this kind of workload on this kind of battery. He's being more kind to his batteries than I am to my batteries (I usually end up running down to about 60% each day when off grid), so he might get another good year. But they probably won't even be limping along after five years.
But, the good news is that solar panels are extremely durable. They're often warrantied for 25+ years! And, the expected output after that length of time is still pretty good. So, if batteries get better, our systems today will get better just by replacing one component, because everything else is gonna keep working forever (well, cheap charge controllers die sometimes, but the panels are practically forever parts).