It's always the same problem: You save energy but the electricity bills
are still getting more expensive. Luckily, there is a solution: Solar
power can be generated in Germany for 12 cents per kilowatt hour. In
contrast, utilities currently charge an average of 25 cents for domestic
electricity. What better reason to invest into your own photovoltaic
system? Solar storage systems can increase on-site consumption by up to
70 percent. They absorb surplus solar power and pass on the energy as
required — expensive grid power is hardly necessary. This makes the
systems very attractive for consumers: According to an EuPD Research
survey, almost 90 percent of solar operators are already thinking about
buying an additional storage system.
Storage system providers are promising economical solutions that
customers can’t refuse. Many companies are advertizing that their
photovoltaic systems will remain economical despite rising electricity
prices during the first twenty years of operation. Scientists, however,
are skeptical as to whether these promises can be kept. Battery expert
Uwe Sauer from the Institute for Power Electronics and Electrical Drives
at RWTH Aachen has developed a model to calculate just how economical
battery-based storage units are. It takes into consideration the
efficiency of the system, the number of full cycles per year, capital
costs and costs for storing power. This has rendered domestic storage
systems as downright useless.
Sauer’s approach: First of all, the amount of energy the battery can
absorb during its cycle life and pass on again needs to be calculated.
For example, the company Deutsche Energieversorgung’s conventional
lead-acid battery system may have 3,000 cycles for a capacity of 24
kilowatt hours, equaling 72,000 kilowatt hours in total. A 50 percent
depth of discharge at which this cycle life can be achieved must be
deducted. Another 80 percent must be deducted to cover the loss of
efficiency to the whole system. During its cycle life, the battery has a
capacity of around 30,000 kilowatt hours. At €6,300 for the system,
storage costs come to 21 cents per kilowatt hour. If you add the 12
cents it costs to produce power on-site, the total cost comes to 33
cents. This sum is considerably higher than the current domestic
electricity cost of 25 cents — meaning the system is not economical.
Modern lithium-ion batteries offer even less value for money, according
to Sauer’s calculations. Storage costs alone come to at least 35 cents
for current systems.
According to battery expert Margarete Wohlfahrt-Mehrens from the Centre
for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW) the
situation is not quite as dramatic as that. She currently calculates the
storage costs of classic lead batteries at around 10 cents and those of
lithium ion batteries at 25 cents. These costs could soon drop, as she
reckons that lithium technology could also become considerably cheaper.
“We estimate that storage costs will be cut by half in the next few
years,” says Wohlfahrt-Mehrens. Her reasons include the development of
mass production and new innovations, which are helping the industry to
develop more efficient production methods and higher-performance lithium
The cathodes and anodes of lithium ion batteries are produced by
applying suspensions containing carbon and lithium as liquid
electrolytes over a cylinder. It is now the manufacturer’s aim to use
larger sheets to speed up the production process. In addition, companies
are developing more robust and higher-performance electrode materials.
Today’s batteries use graphite for the anode and lithium metal for the
cathode. It serves as a chemical reactant for graphite. Manufacturers
want to use new anodes made from lithium titanate in the future, which
recharge faster and can withstand more load cycles than graphite.
Until economies of scale begin to take effect with more production and
innovations, the German Federal Government intends to support the
technology. For example, the government is considering granting
low-interest loans from state bank KfW to solar installations with
storage systems. Paying a subsidy of 30 percent of the costs for the
battery is also under consideration. This would significantly reduce the
payback period. Will solar batteries soon pay off or do they still have
a long way to go?