Very good read that discusses a lot of options & strategies for using solar power cost-effectively.
1 thing I found lacking: discussion of optimal power point tracking. If ignored (PV panel -> load directly) then depending on the load's characteristics, it can pull the solar panel into very sub-optimal power generation.
That is an advantage of heaving batteries in the system: they can serve as a predictable / constant load, which a charge controller uses to have the solar panel operate at near-maximum output.
But as the article notes: any power that goes through a battery rather than used directly, is relatively expensive. So it makes sense to minimize battery size & throw money at more solar panels instead.
I think there's something to be said for time-shifting predictable large energy consumption events to points at which you're producing more solar energy than can be stored.
Scheduling an electric water heater to run at noon until 2pm for instance, depending on the insulation and size of the tank might be enough to provide all the hot water you might need for 24 hrs. Likewise, for electric car charging.
But there is definitely a minimum battery bank size requirement for maximum efficiency, especially if this is an off-the-grid setup where you can't rely on the grid to act as infinite excess storage.
Without batteries, you're either overproducing (and therefore throwing that power away by backing off the MPPT point), or you're underproducing (and therefore browning out). Therefore, you have to size your solar array for the worst case spike. AC locked rotor might be 30A for instance -- better make sure you're producing at least 7.2kW (~9.5kW of solar+) at any time the AC might flick on.
The higher the peak-to-average of your daily load, the more inefficient your setup will be. In our 9.5kW array example, this means any time you're consuming less than that, you're paying for panels that are effectively offline.
I think it's an interesting problem to solve, with a lot of variables. If the limiting factor is $ vs. roof space vs. ROI vs. 99.9% uptime, you might get different "optimal" answers.
Funny thing — heating a hot water tank is still storing energy in a battery.
Charging your car is still putting energy in a battery.
And the article mentions that devices sometimes have a built in battery.
The article is talks about getting rid of batteries but really is talking about maximizing energy usage during times of cheaper energy… which is the “smart grid” stuff OP is throwing shade at.
I don’t disagree with the idea of maximizing your energy usage during times of cheap energy availability but obviously most people don’t do it because the trade off is higher scheduling complexity. What if you set a timer for your washing machine but the sun doesn’t come out — now you just have no fresh clothes..
And plus some batteries are only possible at scale — like pumped water storage. Setting up that complex distribution infrastructure allows society to invest in more efficient forms of energy storage and distribute its costs.
If you have an electric car then the whole article gets thrown out the window. An electric car battery is significantly larger than what you would need for an average house, so just have a battery that can also feed back into the house and you're done.
Yes but. It turns out that PV solar wins on maintenance by a lot; since you don't have to run hot water pipes and keep the solar heater from leaking. With a reasonable system design you can pretty much just connect the wires to your heater element.
I think I read it ends up being close with solar heat still winning. The panels have a range of effectiveness and the heat pump isn't always 400%. The solar thermal is cheap too so even if efficiency were superior with PV panels it would still only be useful if you just had a massive excess of wattage.
> 1 thing I found lacking: discussion of optimal power point tracking. If ignored (PV panel -> load directly) then depending on the load's characteristics, it can pull the solar panel into very sub-optimal power generation.
The discussion: Buy MPPT controller
End of discussion
> That is an advantage of heaving batteries in the system: they can serve as a predictable / constant load, which a charge controller uses to have the solar panel operate at near-maximum output.
Well the single disadvantage of batteries is cost, everything else is an advantage so there is not much else to discuss here too.
1 thing I found lacking: discussion of optimal power point tracking. If ignored (PV panel -> load directly) then depending on the load's characteristics, it can pull the solar panel into very sub-optimal power generation.
That is an advantage of heaving batteries in the system: they can serve as a predictable / constant load, which a charge controller uses to have the solar panel operate at near-maximum output.
But as the article notes: any power that goes through a battery rather than used directly, is relatively expensive. So it makes sense to minimize battery size & throw money at more solar panels instead.