10ECEN2060

Economics of battery storage

Example: the deep dischargebatteries in our lab

Retail cost: $150

Assumptions:50% depth of discharge

20 hour uniform discharge

Average voltage 12.4 V

1000 cycles

Energy of each dischargecycle:

I = (Cp/t)1/k = (63/20)1/1.15 = 2.7A

ED = (2.7A)(12.4V)(20hrs) = 0.67 kWh

Battery capital cost per kWh:

($150)/[(0.67 kWh)(1000 cycles)] = $0.22/kWh

Typically $0.10/kWh for large optimized installations

Battery costs more than the energy it stores!

11ECEN2060

Backup gas generation

Cost of gasoline

Estimated 5 kWh/gallon, $3/gal

$0.60/kWh

Capital cost

$0.50 to $1.00 per Watt

Adds another $0.05 to $0.10 per Watt if amortized over 19 years

12ECEN2060

The value of grid energy

Power supplied by the utility is available

Estimated cost $0.10/kWh in Colorado

Available on demand, very high reliability

To reproduce this in a standalone PV system:

1. Must generate the power with PV; est. cost $0.21/kWh

2. Must store in batteries, est $0.10 to $0.41 / kWh

3. May additionally need other backup power sources, with additionalcosts but substantially improves reliability

Utility bill has a charge for kWh consumed only

Reliability is worth at least as much per kWh as theenergy itself, but is not included in current pricingschemes approved by PUC