# Solar Utilization Rate

Registered Users Posts: 6 ✭✭
Can someone please explain what "Solar Utilization Rate" means?   There is a solar website that claims that without their special home energy management system you get a 50% solar utilization rate but you get 95% utilization rate if you install their energy management system (no batteries).

It seems to me that it would be very, very difficult to achieve 95% utilization rate even with batteries let alone without batteries.

With batteries:
My argument is (maybe too) simple-  A) Your solar array produces more energy on average than your house uses, then the battery will eventually charge to 100% and you will end up sending energy into the grid.    Your solar array produces less energy on average than what your house uses and you will be drawing from the grid.  C)  Your batteries and charger are never going to be 100% efficient, there will be losses when charging and when discharging.   That's with batteries....

Now without batteries:
If your array is creating less energy than your lowest draw circuit (i.e. pool pump uses 1Kw when the array is producing only 500 watts) then you either send the 500 watts into the grid or turn on the pool pump and draw 500 watts from the grid.   With higher draw circuits such as an electric water heater drawing 3Kw, the waste is worse.   So unless your array is creating exactly what you need to run a circuit you lose, one way or another.

Please tell me how you could get a 95% utilization rate without batteries.

Regards,

Bert

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• Solar Expert Posts: 5,876 ✭✭✭✭✭
So with a grid tied system, you should be near 95% without any real difficulty. The energy you generate is available for home utilzation or is forced back to the grid. There's no waste. If you are generating 1500 watts and using 1000watts you are sending 500 watts back to the grid. If you are using 2000 watts you are using 1500 watts you generate and pulling 500watts from the grid. The grid acts as a battery. In the US with Net Metering, the 500 watthours you send into the grid each hour you are producing more than you are using can be drawn from the grid without penalty or cost.

With a battery based system without grid tie, you must be VERY wasteful having enough energy t full charge the batteries regularly and once full, you can use the energy fr opportunity loads or it just gets wasted with no storage available.

With batteries and grid tie, you still have to charge the batteries and you will have some penalty in the energy you store and use later. So grid tied will always be the best. I have no clue what 'optimizer' you are speaking off, but you are welcome to leave a link to it.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Registered Users Posts: 6 ✭✭
Hi Photowit,

I think that the company marketing the home energy management system is talking about self use of the solar energy by switching various loads on and off during the day when solar power is available.

Here we only get paid NZ\$0.07 per Kwh for power we send to the grid and have to pay NZ\$0.25 per Kwh for power we draw from the grid.

• Solar Expert Posts: 5,876 ✭✭✭✭✭
edited September 2020 #4
That makes more sense...

I live off grid (No connection to the grid at all) and use simple timers and weather reports to optimize my energy use. I have charge controllers which will turn on items based on the state of charge on my battery as well.

So sunny days, I'll turn on my water heater...

Since you likely have a single unit which charges batteries or sends energy back to the grid, I would guess it works in a similar fashion. Turning on heavy loads when there is an abundance of  power from the sun.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.