So I'm looking at these:
Now, let's look at these systems.
- The 150L system would generate about 2.9SREC; the 300L might generate over 5 (maximum)
- Federal 30% rebate, state 20% rebate, taxable, gives about a 35% total savings on these systems.
- I'd spend around $500/year normally on water heating (I spend $40/mo on gas and that's basically all I use it for)
SREC in MD float around $190-$280 on the market. Without a SREC, businesses have to pay 40 cents per kWh for energy in certain conditions, so the value of a SREC is less than $400. Basically the hot water system generates about 2.9MWh per year, and I can sell that offset. A bigger system generates more, but the state caps residential installations at 5SREC from solar hot water.
If I did put in a big system, I'd also put in radiator heating. I'd run a plate exchanger to the radiator boiler tank, supplementing gas. I'd put an expansion tank on the boiler, but also have an extra thermal switch to shut off the loop going to the boiler (there's already one on the solar hot water system, it's required or it overheats the tank). A bigger system has additional tubes for more collection; in the winter there is less sun, but I would offset some of my house heating costs (I usually space heat, but this would give me an incentive to switch).
Finally, a $1000 tankless heater driven by natural gas could be used. Solar hot water tank has a gas backup; disable that. Run the solar hot water output to a thermostatic mixing valve--this is standard, it mixes cold water in to regulate temperature, so if your hot water is over 140F it brings it down. Set the valve to 140F or lower; set the tankless heater to that value as well (they max at 140F generally). Run the hot water output from the thermostatic mixing valve into the cold water input of the tankless heater. You'll never burn gas when you run the tank down, never burn gas when the sun isn't out and the tank cools, EXCEPT if you actually turn on the hot tap while the tank's cool. The cooler the tank, the more gas you burn; if the tank's 120F and your hot water is 140F, you only have to raise it 20 degrees rather than (say) 88 or so.
All in all, the ROI on a solar water heating system would basically be 1 year? Then I'd make about $700/year just for having it. It'd be about 2 years if I tacked on a tankless heater, but I'd have absolute hot water stability (the tank losing temperature isn't going to cool my hot water) and wouldn't burn gas just to idle the tank if there's not enough sunlight.
On top of that, photovoltaic 3kW array is like $10,000? SRECs aren't capped for PV in MD. You only get SREC if you have a synchronous inverter: any extra capacity you don't use goes back on the grid. MD credits you for raising the available solar energy, which you can consume yourself in lieu of grid energy OR put back on the grid for others to consume.
a 3kW array at 10 hours of sunlight per day (16 in the summer down to like 8 in the winter, it's a crude guess) would generate some 10-11 megawatt hours per year, 10-11 SREC. You'd get like $2000-$3000 based on market forces. So like, 4 years to pay off a solar array?
In the end you'd be making over $5000/year and saving nearly as much in utility costs.
Seriously? When the hell did this happen?