Why the common rule of thumb 'from €200,000 equity' is misleading, and how tax refunds and project debt push the effective equity outlay into the single-digit-percent range.
Jakob HubertPublished 11 June 2026~5 min read
'You need at least €200,000 in equity': This rule of thumb circulates in the market; it is a rough simplification and it is wrong in practice. For a €300,000 direct investment in a battery storage system the equity actually required, after bank financing and IAB tax refund, typically sits in the low single-digit percent of the nominal volume. An investor in the top tax bracket with access to project-typical bank financing funds the bulk from sources that do not touch their own bank account.
This article walks through the calculation line by line, and identifies the taxable-income threshold above which the structure unfolds its full leverage.
The misleading rule of thumb
The rule of thumb runs like this: investment volume €300,000, so €200,000 or more must sit in the account. That calculation equates the nominal investment amount with the equity required, and ignores the two largest funding sources of the structure. First, the asset largely carries itself: battery storage projects are typically financed with 60–75 % bank debt, secured against the system. Second, the IAB tax refund, 22.15 % of the investment volume at a 44.3 % marginal rate, arrives before or with closing and is available for the acquisition. What actually leaves your own account is the remainder after both positions, far below the nominal amount.
IAB tax refund (44.3 % × 50 % = 22.15 % of investment), arrives before or with closing.
Equity, the remainder.
Example: €300,000, what's left as equity?
Source
Share
Amount
Investment volume
100 %
€300,000
Bank financing (70 %)
70 %
€210,000
IAB tax refund (year 0)
22.15 %
€66,450
Effective equity
7.85 %
€23,550
Example calculation at a 70 % debt ratio, the default value of the calculator on the homepage.
The debt ratio is the biggest lever in this calculation. The same investment at three market-typical ratios:
60 % debt: €53,550 effective equity (17.85 % of volume).
70 % debt: €23,550 (7.85 %).
75 % debt: €8,550 (2.85 %).
Deliberately not included: Sonder-AfA and regular depreciation reduce the effective outlay further in the following years; in the example the Sonder-AfA alone adds another €26,580 in tax effect. They still do not appear in the year-0 calculation because they only become cash-effective from the acquisition year onwards. The table therefore shows the conservative case: what actually has to leave your own account on the day of closing. What this comparatively small outlay can earn in ongoing return is a question of its own; it is placed in order by Battery storage returns: where the revenue comes from, and what is realistic.
Why the top tax rate is the lever
The IAB is not a subsidy but a profit reduction: 50 % of the planned acquisition cost, €150,000 in the example, is deducted from taxable income. The cash effect is therefore simple: €150,000 × marginal tax rate. At 42 % that is €63,000, with the solidarity surcharge (44.3 %) €66,450, and in the 45 % top bracket including the surcharge (47.5 %) €71,250. Between the lower and the upper end lie €8,250, for an identical investment, identical project, identical risk. That is exactly why the structure is aimed at top-bracket incomes: every percentage point of marginal rate adds €1,500 to the refund. If a GmbH subscribes instead of you personally, the same loss works against only around 30 % tax; when that still pays off is compared in Invest through your GmbH or privately? The honest tax comparison.
From which income threshold it works
The structure becomes worthwhile from a taxable annual income of roughly €120,000–150,000: at that level your income sits reliably in the top tax bracket, so the IAB's profit reduction works at a consistently high marginal rate. The 44.3 % top-rate leverage is reached from roughly €68,000 in taxable income; from the Reichensteuer threshold of around €278,000 it rises to 47.5 %. The opposite applies downwards: once the deduction pushes income below the 42 % threshold, every further euro loses value; how much deduction a year can carry and what happens to an excess loss is shown in The loss created by an investment deduction (IAB): offsetting it against salary, carrying it back and carrying it forward. Repeatability matters too: anyone earning income of this order year after year can form a new IAB annually; how that builds an investment portfolio over several years is shown in Using the investment deduction every year: building a portfolio over multiple years.
How much equity do I need for a direct investment of €300,000?
Typically far less than the nominal amount: with 70% bank financing and a 44.3% marginal tax rate, around €23,550 of effective equity remains, i.e. 7.85% of the investment volume. The rest comes from two sources that do not draw on your own account: the bank financing secured against the asset and the IAB tax refund of 22.15% of the volume.
Why is the rule of thumb 'from €200,000 equity' misleading?
Because it equates the nominal investment amount with the equity requirement and ignores the two largest sources of financing: battery storage projects are typically financed with 60-75% debt, and the IAB tax refund arrives before or with the closing. What actually leaves your own account is the remainder after both positions, and that is far below the nominal amount.
How much does the equity requirement depend on the debt ratio?
It is the biggest lever in the calculation: for a €300,000 investment, 60% debt leaves €53,550 of effective equity, 70% leaves €23,550, and 75% only €8,550.
Why is the structure aimed at incomes in the top tax bracket?
Because the cash effect of the IAB depends directly on the marginal tax rate: 50% of the planned acquisition cost reduces taxable income, €150,000 in the example. At 44.3% that is a €66,450 refund; at the 47.5% wealth surtax rate it is €71,250. Every percentage point of marginal tax rate adds €1,500 to the refund.
Do the special depreciation and regular depreciation reduce the equity requirement further?
Yes, but only in the following years: the special depreciation alone adds another €26,580 of tax effect in the example. Both are deliberately left out of the year-0 calculation because they only become cash-effective from the acquisition year onwards; the table therefore shows the conservative case of what actually has to come from your own account on closing day.
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