Originally posted by: JonathanHill
I like your thinking - I offer comments as follow (some coming from investigations I've been involved with) :
- 1MWh storage - probable cost ~£3M for either Li-Ion or Vanadium Redox (power converters extra)
- "Round trip" efficiences likely to be in the range 75 - 90% dependant on battery technology) and charging regimes
- it is overly optimistic to assume the nameplate rating of the battery can be fully utilised. Different regimes may be necessary to optimise the lifetime "work" that can be reasonably achieved for any battery technology type. Eg it can be very inefficient to get the last 20% of charge into the battery, and life expectancy can be severely compromised if discharged to the extent of the nameplate capacity . Would suggest 60% of nameplate as a budget operating window.
- Placing of Batteries & power converters - I think transmission losses will be minimised if these are sited close to (and probably in approx proportion to) the generating plant that is anticipated to provide the charge, or possibly close to load centres
This has all the hallmarks of a good topic for a Masters or Post Grad research study, though I fear the utility-scale storage technology is not yet adequately developed for serious roll-out.
Keep up the left-field thinking - we're ready for a paradign shift with attendant challenges for our engineers (though personally I currently favour demand side management applied to thermal "storage" as a cheaper-cost option).
So a 6.5 MWh rating for grid use would require a 10 MWh rated battery module operated normally between 90% charge and 25% charge.
The costs structure is slightly better than I originally because the existing power converter is being swapped out for a new power converter with battery storage.
The maximum export power to the grid is 4.5MW, and the maximum import power from the grid is 2.0 MW.
The questions I have are:
1. are there any ways that the battery banks can be used to de-stress, de-rate and cheapen the power electronics and extend their design lifetimes.
Perhaps by splitting the battery into two separate modules the turbine can charge one set of batteries, while another set is charging from the grid or discharging to the grid. The design would specify that the two battery modules can be swapped around every so often using some sort of automated switching mechanism.
2. In power electronics is it generally cheaper and more reliable to specify a high voltage, low current DC-AC Converter to supply directly to an AC Isolation or low voltage gain transformer (for example) or a low voltage high current DC-AC Converter and AC transform up?
3. In this respect would it help to remap the cells of the battery when switching battery modules between turbine interface mode and grid interface mode?
I think placing battery storage close to the wind turbines is better from an investor point of view, especially if capital cost savings and reliability improvements made on the existing power converter.
A 2V 3000Ah lead acid battery stores 6kWh of energy (1667 of them are needed to construct a 10 MWh battery - that de-rated gives a 6.5 MWh capacity) that's probably £75,000 in lead acid batteries per 2.5 MW wind turbine - without haggling for extra bulk discount. Well designed, the recycle value of the batteries, could be improved by design, so the net battery cost figure (allowing for the recycle value) can be reduced as much as possible.
Lets say that the batteries have a 10 year life, that gives 3 changes over a lifetime of 40 years. Lets make the batteries a consumable cost and charge them to the wind turbine at £7,500 per year. Lets triple that cost to reflect other costs i.e. £22,500 in battery costs per year.
According to the DECC onshore wind energy is worth £95 per MWh.
The income from a 2.5 MWh wind turbine in theory will be (assuming capacity factor 0.21)
£95 * 24 * 365 * 2.5 * 0.21 = £436,905
Lets multiply this by the battery cycle efficiency (75%)
So net income now is £436,905 x 0.75 = £327,679 per year
The other element of the income involves buying electricity during the night cheaply and selling it at profit during the day.
The money that can be made from this depends on the percentage of the overnight battery charge that is due to imports from the grid. If 25% of the energy on average is due to the grid and the day night cost differential is £25 per MWh then
£25 * 365 * 6.25 * 0.25 = £14,257 (very little, spinning and standing reserve payments will be worth much more)
(The battery energy capacity may have to be increased slightly to realise this income)
£327,679 + £14,257 gives a combined income of £341,936
The rest of the income in this simplistic view has to come from grid services, such as providing backup to the grid, spinning reserve and standing reserve.
National Grid Standing Reserve Market
We could tender part of our storage to maintain the spinning and standing reserve. See page 7 in above National grid document.
An availability price is set, along with an exercise price. It will be rare that the full availability from the battery storage system will ever be called upon, so some of the availability sold can be assigned to the de-rated specification of the battery system. Deep cycling the batteries once in a while will be fine and will raise revenues suitable to pay for the battery replacement and maintenance costs.
There is a 1 MWh capacity between 15% minimum charge and a 25% minimum charge.
Over the year this brings in an income of
Availability price * 365 * 24 = £4 x 365 * 24 = £35,040 per year (on 2002/2003 prices)
If this exercised 5 times a year say the extra income is
£200 * 5 * 1 = £1000 (on 2002/2003 prices)
A standing reserve income of £36,040 per year (from part of the de-rated capacity of the battery). I suspect this is a large underestimate on what can be earned at todays prices.
Other availability income can be generated on the active part of the storage but the cost/benefit of bidding will depend on some detailed statistical analysis, which is beyond me at this stage.
These are just quick and dirty calculations, just to get a feel for whether this can work from an economic perspective.
As I have said before do this we will save considerable amounts of capital outlay require to buy extra assets in the capacity market.