I'm not sure how did you calculate
let me clear billing mechanism in net metering connection
(assuming your case, credit, sharing random figures just to clear your concept)
in monthly bill, in peak, you import, in off peak, you import and export.
then your monthly bill is calculated
as in assumption, exported > imported, bill for off peak hours = 0
and for all rest net exported units, calculated with base tariff, like assume 10 rs/kwh, it will be credited, that amount is going to used for peak hour calculation later on
then come peak hours, and we have to pay for peak hours every month, in form of credit rupees from previous months and price of excess production in current month
(an important point, as you mentioned that you had 1570 units in credit, those units don't count, the credit amount in rupees do, that's why credit amount is mentioned on bill, will share reason behind this later on)
so now in your case, as you have imported 217 units, you have to pay for that
then lesco calculates your bill by using current nepra tariff, FPA, FPA ED, FPA GST, Quarterly tariff, E duty, TV Fee, FC Surcharge and GST
whatever that amount is, assume 5000
you have to pay for it
How? (assuming your case, you had credit from previous months)
you will pay with credit from previous months (check from old bills) +net export in current month (which I assumed above as 10rs/kwh, the amount is calculated accoulated accordingly )
again assuming figures
if credit from all previous bills was combined 10k, and in this month 2.5k rs (from export) total credit now you have is 12.5k
you have to pay 5000 for this month peak hour useage
then what lesco will do, 12.5k-5= -7.5k total credit in your bill
they didn't
your net bill for off peak hours is 0
you only paid for peak hours
now addressing other points
1. why DISCOs don't use units in credit billing but amount for credit, meanwhile units can be calculated easily?
answer is, overall variable electricity generation, distribution costs
like if you had exported 500 units for rs 10/kwh in January, you will get 5000 credit in January
now assume in june, I have 500 units, but now tariff is 15rs/kwh ,bill should be 0? no
because when i exported, back then overall generation cost was 10 rs
but I imported from then, cost increased due to any reason, fuel cost or tarrif etc, they sold me same 500 units for revised generation cost, which will be 7500 now rather than 5k
hence they use amounts rather than units
I had 5000 credit, consumed kwh worth=7500, will get net bill pkr 2500,
net units exported will be of no use now because the amount matters
2.(only for those who import more off peak units than exported)
query is, why discos buy for 10 rs and sell us same for 18-20 rs, isn't that unethical?
answer is, when you pay, other than base nepra tariff, you pay FPA, FPA ED, FPA GST, Quarterly tariff, E duty, TV Fee, FC Surcharge and GST
but when you export, you are only credited for base nepra tariff not fpa or all other taxes I mentioned above, because reason is, lesco will not gonna pay you tax/Fpa amounts which would have been due if you had consumed from grid, only amount payable to you is nepra base tariff
