Estimated Energy Usage & PV Offset

JimmysLimeade

JimmysLimeade

EE Student & PV Design
Location
Utah
Occupation
PV Design
Hi, I was asked by my boss if we could make something similar to this form for our own internal use. The form is used for new homes that don't have enough utility history to verify that the PV offset is less than 120% (or something like that, idk the exact number the utility requires).
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I know how to get to the monthly kWh when I know how many hours/day each load is used, but here there seems to be pre-filled/static values for different types of loads. I am curious if there is a table somewhere that has an average hours per day for typical loads, and if so where can I find it. We do a lot of third party work so obtaining the hours per day for these appliances on all the jobs we need this form on isn't ideal, so I am hoping there is a general list I can pull from.

Thanks!
 
JimmysLimeade said:
Hi, I was asked by my boss if we could make something similar to this form for our own internal use. The form is used for new homes that don't have enough utility history to verify that the PV offset is less than 120% (or something like that, idk the exact number the utility requires).

I know how to get to the monthly kWh when I know how many hours/day each load is used, but here there seems to be pre-filled/static values for different types of loads. I am curious if there is a table somewhere that has an average hours per day for typical loads, and if so where can I find it. We do a lot of third party work so obtaining the hours per day for these appliances on all the jobs we need this form on isn't ideal, so I am hoping there is a general list I can pull from.

Thanks!
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You may be able to get data from energystar.gov for certain appliances, but there is not really a great typical average available online that I have found, and there are certain loads that would have a great deal of variability based on the building or the habits of the residents. You will probably just need to start collecting and verifying usage numbers as you go. Get a kil-a-watt meter or similar and measure a few appliances you have access to, trying to capture average usage over time for loads that cycle on and off or are variable. This is always somewhat of a challenge and you should not expect to be able to precisely predict the load usage, it will be an estimate.
 
What does 'for internal use' mean?

I second solarken's suggestion to sample energystar estimates appliances similar to what's likely to be installed. But understand that individual household use with the same appliances will vary by a *lot*, like possibly 100% on the higher side.

There are also some glaring errors in that sample form. Like, who runs their microwave for 10-12 hours each month? Or their garbage disposal for 6? And the brand of an EV makes no real difference compared to miles driven (and charged at home).
 
solarken said:
You may be able to get data from energystar.gov for certain appliances, but there is not really a great typical average available online that I have found, and there are certain loads that would have a great deal of variability based on the building or the habits of the residents. You will probably just need to start collecting and verifying usage numbers as you go. Get a kil-a-watt meter or similar and measure a few appliances you have access to, trying to capture average usage over time for loads that cycle on and off or are variable. This is always somewhat of a challenge and you should not expect to be able to precisely predict the load usage, it will be an estimate.
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Thanks for the suggestions, Ill look into that!

jaggedben said:
What does 'for internal use' mean?
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Probably a bad choice of words on my bosses end, I think this is something that we could provide in addition to our plans for utilities that requires it, but Im not too sure if that's the case.

jaggedben said:
There are also some glaring errors in that sample form. Like, who runs their microwave for 10-12 hours each month? Or their garbage disposal for 6? And the brand of an EV makes no real difference compared to miles driven (and charged at home).
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This was my thinking too, it looks like a bunch of BS to justify basically any size of PV system. Our client sent us this, and I think they have gotten this type of document past review so idk how important it is to the utility that it is accurate.
 
It's all a guessing game. Doing off-grid systems this kind of analysis has to be done and if not accurate the system will not support the customer's load. So a lot bigger problem than doing this for grid-tied. Still involved sitting with the client and asking, so how much do you use the microwave every week? And them saying, I don't know. I did something similar to this for a new commercial site for a company that was moving. I basically took the data from their old site and tweaked it based on the change in the loads at the new site.
Personally if I were doing this for residential system I would try to find a similar home in the area and ask if I can get their annual energy usage, maybe discount it by 20%, and use that. If you mess up and go over the export limit know what the utility will do. At best they will just not pay for the overage and the customer ends up with an oversized PV system they spent too much money on. If there is a penalty though you might be having an uncomfortable talk with the owner about who pays that.
 
pv_n00b said:
Still involved sitting with the client and asking, so how much do you use the microwave every week? And them saying, I don't know.
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Even this would be better than the scenario I have, we dont have direct contact with any homeowners. We do third party design and engineering for the sales/install companies.

pv_n00b said:
Personally if I were doing this for residential system I would try to find a similar home in the area and ask if I can get their annual energy usage, maybe discount it by 20%, and use that.
Click to expand...
This is probably the best option for us, thanks for the suggetions!
 
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