Solar or fixed-term deposit? Interest account and real asset in an honest comparison

Private households in Germany hold around €9.5 trillion in financial assets, and a large share of it sits where it feels safest: in current accounts, instant-access savings and fixed-term deposits. For a while, that was decently paid again. In August 2026, the best two-year fixed-term deposits pay around 2.8 % per year; in July, the inflation rate stood at 2.8 %. Those two figures are not a coincidence engineered for a headline; they describe the normal state of interest-based saving: the interest roughly offsets the loss of purchasing power, and tax then tips the calculation into the red. This article puts the energy direct investment next to the fixed-term deposit; not as a replacement for the liquidity reserve, but as a question for the part of your wealth that will not be touched for years anyway.

What do fixed-term deposits really deliver in 2026?

Nominally, depending on term and bank, between a good 2 % and just under 3 % per year; in real terms, after taxes and inflation, currently a result around or below zero. The ECB's deposit rate stands at 2.25 %, and conditions track it: instant-access accounts usually pay somewhat less, the best two-year deposits around 2.8 to 2.9 %. Offers well above that almost always come from banks in other EU countries or are tied to conditions. At the same time, inflation is back above the two-percent mark: 2.8 % in July 2026, driven above all by energy prices, which were 8.3 % higher than a year earlier.

Worked through concretely: €100,000 at 2.8 % yields €2,800 in interest per year. After deducting the saver's allowance of €1,000, €1,800 remains taxable; on that, 26.375 % flat-rate capital gains tax including the solidarity surcharge falls due, around €475. Roughly €2,325 remains net, a return of 2.33 % after taxes. At 2.8 % inflation, the balance thus loses around 0.5 % per year in real terms, even though the number on the account statement grows. This is not the slip of a single year: across long stretches of recent decades, deposit rates sat below the inflation rate. Why monetary assets have this problem structurally and which asset classes help against it is set out in Real assets as inflation protection: what actually protects and where energy assets fit in.

How safe are fixed-term deposits, and how safe is a direct investment?

In nominal euros, a fixed-term deposit within the statutory deposit guarantee is as safe as an investment can be: €100,000 per customer and bank is protected by law across the EU, and at many German institutions voluntary deposit protection funds cover amounts beyond that. Anyone investing larger sums spreads them across several banks and, with high-interest offers from abroad, checks which national protection scheme would pay in an emergency. This safety is real and is not to be talked down here.

It applies, however, only to the number on the account, not to its purchasing power. The real risk of the fixed-term deposit appears in no prospectus: it is the combination of tax and inflation calculated above, plus the reinvestment risk at maturity; nobody guarantees that the same conditions will still be available in two years. An energy direct investment sits at the other end of the scale: it is an entrepreneurial investment in a single project, with electricity price, technology and regulatory risks, a corresponding risk of loss, and without a regulated secondary market. What that means concretely for storage projects and how these risks can be addressed structurally is covered in Risks in BESS direct investments, and how they are structurally addressed. Anyone who labels both investments flatly as “safe” or “risky” misses the point: the deposit guarantees the nominal amount and surrenders purchasing power in exchange; the participation aims at real returns and accepts entrepreneurial risk in exchange.

How are interest and participation income taxed?

Interest is fiscally simple and inflexible at the same time: it is subject to the flat-rate capital gains tax of 25 % plus the solidarity surcharge, 26.375 % in total, plus church tax where applicable. The solidarity surcharge still applies to investment income in full and from the first euro, even though it has largely been withdrawn for income tax. Only the saver's allowance of €1,000 per person and €2,000 for jointly assessed couples remains untaxed; at 2.8 % interest, it is already used up at around €36,000 of deposits. And there is no tax effect at entry: neither opening a fixed-term deposit nor a contribution to a securities portfolio reduces taxable income by a single euro.

The direct investment works the other way round fiscally. It creates trade income under §15 EStG, so it is taxed at your personal rate and knows no flat 26.375 %. In exchange, it pulls its effect to the front: through the investment deduction (IAB) under §7g EStG, up to 50 % of the planned investment can be deducted from profits in advance, and in the year of acquisition the special depreciation of 40 % and regular depreciation are added. These amounts work against the marginal tax rate, at 42 % plus solidarity surcharge against 44.31 %. What the calculation looks like for an investment of €300,000 is shown in IAB under §7g EStG: example calculation for battery storage; how strongly the tax effect reduces the equity actually tied up is worked through in How much equity is actually required?. The honest counter-entry: ongoing income and the later sale are taxed in full at your personal rate; the advantage comes from timing and the difference in tax rates, not from permanent tax exemption. The details are covered in After the IAB: How the ongoing returns and the sale of a direct investment are taxed.

What does an energy direct investment deliver instead?

Revenues from the electricity market instead of an interest promise. A photovoltaic plant sells electricity via the feed-in tariff and direct marketing, a battery storage facility earns on price spreads and system services; both revenue sources hang on generation, consumption and the grid situation, not on the ECB's next rate decision. Which orders of magnitude are realistic and which assumptions sit behind them is broken down in Battery storage returns: where the revenue comes from, and what is realistic; the entry routes into both asset classes are shown in Investing in solar parks: revenues, costs and tax leverage at a glance and Investing in battery storage: the options at a glance.

Two differences from the fixed-term deposit are decisive. First, the nature of the income: interest is a nominal claim against a bank; electricity revenues are the turnover of a real economic asset whose prices are linked to the general price level over the long run. That is not a guarantee of inflation compensation either, but it is a structural difference from a fixed euro claim. Second, the order of magnitude: while the fixed-term deposit currently returns around zero in real terms after taxes, energy projects are calculated with returns well above deposit rates; as compensation for illiquidity, project due diligence and entrepreneurial risk. That premium is earned only by those who can genuinely carry the multi-year commitment and the risk.

Fixed-term deposit or direct investment: where do the differences lie?

In the tax effect, in the origin of the income, in availability and in the risk profile. The following overview puts the typical characteristics side by side:

When is a fixed-term deposit still the right choice?

Whenever an amount has to be available in full nominal terms at a fixed point in time. That is the task the product is built for, and in that role it is unbeatable. Three typical cases:

• The liquidity reserve: three to six months of expenses, rather more for business owners, belong in instant-access or short-term deposits, not in a real asset. This reserve is not an investment; it is insurance.
• Amounts with a due date: next year's tax payment, the down payment on a house, an investment already planned. Anyone who knows when they have to pay must not take valuation risk with that money; that explicitly includes capital standing ready for the capital call of a participation already subscribed.
• The wish for nominal predictability: anyone who knows the real loss of purchasing power and accepts it deliberately, because the fixed number matters more to them, is making a legitimate decision. It just should not be confused with return-oriented investing.

Fixed-term deposits only become a problem in a different role: as a permanent parking spot for six-figure amounts that will not be needed for the foreseeable future. That is exactly where the combination of tax and inflation costs substance year after year; quietly, and without the loss ever appearing on an account statement.

How do you combine interest account and real asset sensibly?

By task, not by gut feeling. In practice, a simple layer model has proven itself: the first layer is liquidity in an instant-access account, available at any time. The second layer covers plannable expenses of the coming years, for instance via staggered deposit maturities. Only the third layer is long-term investment capital that can be tied up for years; here, securities portfolio, property and energy direct investment compete for their place, and only here does the question of returns belong. The comparison with the equity portfolio is drawn in Solar or ETF? Real asset and portfolio in an honest comparison, the one with the rented flat in Solar or property as an investment: an honest comparison of two real assets. How firmly the capital in that third layer is actually tied up, and on what terms an early exit remains possible, is set out in Selling a direct investment early: how liquid an energy direct investment really is.

For that third layer: the higher your personal tax rate, the more strongly the §7g lever shifts the calculation in favour of the participation, and the more expensive it becomes to park six-figure capital permanently at 2.33 % after taxes. We make no return promises: in a no-obligation initial conversation we work through your situation with disclosed assumptions instead, explicitly including the comparison with the simple alternative of leaving the money in the fixed-term deposit.